3+$1(52=2,& 675$7,*5$3+< 2) 6$8', $5$%,$ 3$57 … · Berwath Formation ... Siq Formation is exposed...

PHANEROZOIC STRATIGRAPHY OF SAUDI ARABIAPART 1–PALEOZOIC SUCCESSIONS OF THE ARABIAN SHELF

(COVER ROCKS)

SAUDI STRATIGRAPHIC COMMITTEESPECIAL PUBLICATION

SGS-SP-2012-1FIRST EDITIONA.H. 1434 - A.D. 2013

www.sgs.org.sa

من إصدارات هيئة املساحة اجليولوجية السعودية

i

PHANEROZOIC STRATIGRAPHY OF SAUDI ARABIA

PART 1 -PAleozoic SucceSSionS of The ARAbiAn Shelf (coveR RockS)

SAudi STRATigRAPhic commiTTee membeRS

SAudi geologicAl SuRvey

Mohammed A. Halawani

SAudi ARAmco

Abdulaziz A. Al-Duaiji

Bassam H. Bahabri

king AbdulAziz univeRSiTy

Prof. Mohammed H. Basyoni

king SAud univeRSiTy

Dr. Mohammad E. Al Dabbagh

king fAhd univeRSiTy of PeTRoleum And mineRAlS

Dr. Khalid Al Ramadan

miniSTRy of WATeR And elecTRiciTy

Hussain F. Al Ajmi

king AbdulAziz ciTy foR Science And Technology

Dr. Abdullah K. Al Mahri

Sub-commiTTee membeRS

king SAud univeRSiTy

Prof. Abdulaziz A. Ibn Laboun

king fAhd univeRSiTy foR PeTRoleum And mineRAlS

Dr. Osman Abdullatif

SAudi geologicAl SuRvey

Mohammed A. Ali

Adel H. Matari

ii

PRefAce

Phanerozoic successions in Saudi Arabia have received much attention from many generations of geologists working in petroleum companies, Saudi Geological Survey (SGS), universities, and other communities. This is largely due to their oil potential since they host vast economic mineral deposits and the largest oil fields in the world besides the rich aquifers.

The existence of many lithostratigraphic classifications and nomenclatures have resulted into many controversies. For this reason, there is a need to establish a unified, acceptable and reasonable classification as well as nomenclature for the Phanerozoic successions.

In compliance with the initiative of the Deputy Ministry of Mineral Resources (DMMR) to create the Saudi Stratigraphic Committee (SSC), the Saudi Ministry of Petroleum and Mineral Resources of the Kingdom of Saudi Arabia appointed its first members in1977.

In 2001, the SSC was reactivated by the Saudi Geological Survey (SGS) and chaired by its president. SSC members are the representatives of Saudi Aramco, King Abdulaziz University, King Saud University, King Fahd University of Petroleum and Minerals, King Abdulaziz City for Sciences and Technology, and the Ministry of Water and Electricity as members. One of its tasks is to establish and maintain a unified, acceptable and reasonable scheme of names for the different Phanerozoic rock units in Saudi Arabia. With the Saudi Geological Survey as the base for all the activities of the committee, representatives from interested communities have worked together to achieve this target. Since mid-2008, the members of the committee have collected and discussed numerous publications, technical reports, and geological maps on the different stratigraphic aspects of the Phanerozoic successions in the Kingdom. The members have also visited some of the important exposures of these successions.

The Phanerozoic is subdivided into three eras: Paleozoic, Mesozoic and Cenozoic. This publication is concerned with the Paleozoic era; the other two eras will follow in subsequent editions.

This publication would not have been possible without the support of H.E.Engineer Ali Bin Ibrahim Al-Naimi, the Minister of Petroleum and Mineral Resources and Chairman of SGS Board of Directors.

Dr. Zohair bin Abdul Hafeez Nawab Chairman, Saudi Stratigraphic Committee

President, Saudi Geological Survey

iv

CONTENTSIntroduction ......................................................................................................................... 1Tayma Group ....................................................................................................................... 2

Siq Formation ................................................................................................................. 3 Quweira Formation ......................................................................................................... 7Saq Formation................................................................................................................. 9

Risha Member ........................................................................................................ 10Sajir Member .......................................................................................................... 12

Qasim Formation .......................................................................................................... 13Hanadir Member .................................................................................................... 14Kahfah Member ...................................................................................................... 17Ra‘an Member ........................................................................................................ 18Quwarah Member................................................................................................... 19

Tabuk Group...................................................................................................................... 21Zarqa Formation ........................................................................................................... 23Sarah Formation............................................................................................................ 25Hawban Formation ....................................................................................................... 28

Qalibah Group ................................................................................................................... 30Uqlah Formation .......................................................................................................... 31Qusaiba Formation ....................................................................................................... 34Sharawra Formation ...................................................................................................... 39

Jarish Member ........................................................................................................ 41Khanafriyah Member .............................................................................................. 42Nayyal Member ...................................................................................................... 42Zubliyat Member .................................................................................................... 42

Huj Group ......................................................................................................................... 43Tawil Formation ............................................................................................................ 44

Samra Member ....................................................................................................... 47Ghuwar Member .................................................................................................... 47Tufayhah Member ................................................................................................... 47Juraniyat Member ................................................................................................... 47

Jauf Formation .............................................................................................................. 48Sha’iba Member ...................................................................................................... 50Qasr Member .......................................................................................................... 50Subbat Member ...................................................................................................... 50Hammamiyat Member ........................................................................................... 50Murayr Member ..................................................................................................... 51

Jubah Formation ........................................................................................................... 51Buraydah Group................................................................................................................. 53

Berwath Formation ....................................................................................................... 54Unayzah Formation ....................................................................................................... 55Khuff Formation ........................................................................................................... 58

Ash Shiqqah Member.............................................................................................. 60Huqayl Member ..................................................................................................... 60Duhaysan Member ................................................................................................. 61Midhnab Member ................................................................................................... 61Khartam Member ................................................................................................... 61

References .......................................................................................................................... 62

Phanerozoic Stratigraphy of Saudi Arabia

1Saudi Stratigraphic Committee

INTRODUCTIONThe Phanerozoic successions or cover rocks of the greater Arabian basin host enormous amounts of groundwater, oil, gas, and mineral deposits. The potential reservoir rocks of the Arabian Peninsula in general, and of Saudi Arabia in particular, are primary exploration targets. These rocks are composed mainly of siliciclastics and shallow marine carbonates.

Orientalists started geological studies in the Arabian Peninsula in the beginning of the 20th century. Oil companies have been granted oil concessions since the beginning of the last century. Systematic geological survey of Saudi Arabia began in 1933. However, detailed study on Phanerozoic successions was not started until 1935, when geologists of the Standard Oil Company of California began oil exploration in Saudi Arabia, and worked out the stratigraphy of the Al Qasim region. Although most of the Phanerozoic units defined by the Saudi American Oil Company (Saudi Aramco) geologists were included in “Geology of the Arabian Peninsula: Sedimentary Geology of Saudi Arabia” by Powers and others (1966) and “Lexique Stratigraphique International” of Powers (1968), an enormous amount of geologic work has been done since then. As a result, a substantial amount of data has been disseminated in the form of published articles, reports, theses, books, and geologic maps.

At present, almost every geological organization in Saudi Arabia has its own terminology and definition of the lithostratigraphic units of the geologic column. This practice has resulted in confusion with regard to the stratigraphy of Arabia and controversies among geologists.

The main objective of this volume is to establish a unified, generalized column to be used as reference or guide to stratigraphers of the Phanerozoic. One of the requirements for establishing a formal lithostratigraphic unit is to publish its definition in a recognized scientific medium in conformance with a recognized stratigraphic code. Accordingly, all adopted lithostratigraphic units in this work are formally defined. The formal names of the lithostratigraphic units are used, taking into consideration the rules of the stratigraphic classification and nomenclature in the International Stratigraphic Guide (ISSC, 2004) and the Saudi Arabian Code of Lithostratigraphic Classification and Nomenclature (1984).

In general, time-stratigraphic assignments of the Arabian rock units are based on paleontological dating and stratigraphic position. Several pronounced stratigraphic breaks, caused by regional tectonic movements or sea level fluctuations, are identified in the succession. The effect of such breaks is clearly recognized as they divide the succession into well-defined groups.

Detailed information about each lithostratigraphic unit is arranged in the following order: rock unit, author(s), year of publication, origin of name, definition, type locality, reference section, thickness, contacts, lithology, fossil content, age, depositional environments, remarks, etc.

2 Saudi Stratigraphic Committee


TAYMA GROUP

مجموعة تيماء

Figure 1. Lithostratigraphic classification of Tayma Group in Saudi Arabia. The geological time scale is from the International Stratigraphic Chart (2004).

Rock uniT

Tayma Group

AuThoR

Vaslet and othersyeAR

1987

oRigin of nAme

The name “Tayma Group” (fig. 1) was derived from Tayma town, 450 km northeast of Al Madinah Al Munawwarah, along the highway between Madinah and Tabuk (fig. 2).

definiTion

Vaslet and others (1987) and Vaslet (1990) proposed Tayma Group to encompass all lower Paleozoic deposits that predate the first glacial episode of Late Ordovician age. The group underlies the periglacial unconformity at the base of Zarqa Formation of Tabuk Group. From base to top (fig. 1), it comprises the formations Siq, Quweira, Saq, and Qasim.

TyPe locAliTy

The reference section and the type locality for each formation are defined in their respective sections.

ThickneSS

Approximately 1,268 meters thick.

conTAcTS

Upper

Disconformable with the overlying glacial sediments of Tabuk Group.

Lower

Nonconformable with the underlying basement rocks.



liThology

Siq, Quweira, and Saq formations are composed mainly of sandstones. Conglomerates lie at the base of some formation. Quartz pebbles are scattered throughout the succession. Red shales and silt beds are found towards the top of each formation.

foSSilS

Mainly trace fossils occur in the rocks of this group. Graptolites and trilobites are found in Hanadir Member of Qasim Formation.

Age

This group is considered to be of late Early Cambrian to early Late Ordovician age.

dePoSiTionAl enviRonmenT

Depositional environments of the formations are described in their respective sections.

Figure 2. Location map of type and reference sections of formations and members of the Tayma Group.

Siq foRmATion

Rock uniT

Siq Formation

AuThoR

Bramkamp and others

yeAR

1963

oRigin of nAme

The formation was named after Shaib as Siq, about 65 km southwest of Tabuk City.

definiTion

Siq Sandstone was first described and assigned formational status by Bramkamp and others (1963). Later studies in northwestern Saudi Arabia (Vaslet and others, 1994; Halawani and others, 1996, 1997; Janjou and others, 1998) showed the regional extent of Siq Formation and its relationships with overlying formations. The Saudi Stratigraphic Committee members made a field trip to Tabuk and Jabal al Misma quadrangles in

)سيق(متكون سق



2009 and modified the reference section for this unit to include two informal members: lower and upper.

TyPe locAliTy

Siq Formation is exposed and defined at lat 28°00’00”N., long 36°00’00”E. (coordinates from Bramkamp and others, 1963; fig. 2). The Saudi Stratigraphic Committee assigned the section exposed at Bayda’ Nathil area (Jibal al Misma quadrangle) as the type locality, with base at lat 27°01’31”N., long 40°19’47”E., and top at lat 27°04’33”N., long 40°19’23”E.

RefeRence SecTion

Located east of Al Muwaylih quadrangle.

ThickneSS

It is 20 to 25 meters thick in Tabuk region (Al Bad’ quadrangle), 79 meters thick in Bayda’ Nathil area (Jibal al Misma quadrangle). It is 200 meters thick at the reference section east of Al Muwaylih quadrangle

conTAcTS

Upper

Unconformable with Quweira or Saq formations.

Lower

A major nonconformity with basement rocks (fig. 3).

liThology

The formation is subdivided into two informal lower and upper members.

Lower member

The lower member has base with up to 12 meters of red, well bedded, fine- to medium-grained, arkosic sandstone with a quartz pebble conglomerate (fig. 4). Quartz pebbles are also scattered throughout the unit. The maximum thickness of this member is 25 meters in Al Bad’ quadrangle and 26 meters at Bayda’ Nathil. It is assumed that this member may thicken to the southeast of Al Bad’ quadrangle.

Upper member

From the base upwards, the succession consists of:

1. Red to violet, horizontally bedded, silty claystone. Near the top, thin beds of fine-grained sandstone with small-scale trough cross-bedding are intercalated. The unit is 7 meters thick.

2. Dark-red to brown microconglomeratic sandstone in meter-thick lenticular beds; sigmoidal and planar

Figure 3. Thin polymictic conglomerate at the base of Siq Formation nonconformably overlying basement rocks (Al Bad’ quadrangle).



cross-bedding. The unit is 11 meters thick.

3. Violet, yellow to white, clayey siltstone, which has horizontal bedding with bioturbation and Tigillites (fig. 5). This unit is 15 meters thick.

4. Dark-brown to red, fine-grained sandstone in decimeter-to-meter-thick beds have horizontal to wavy bedding and are intercalated with centimeter-thick layers of silty claystone, where Tigillites are abundant. The thickest beds have trough (wedge) and sigmoidal cross-stratification and wave ripples, where Tigillites are rare. This unit is 12 meters thick.

5. Red, pink to beige, fine-grained homogeneous sandstone with giant trough cross-bedding. This unit is 8 meters thick (fig. 6).

foSSilS

Tigillites were found.

Figure 4. Lithostratigraphic section and paleo-environments of Siq Formation in Bayda’ Nathil area (modified from Janjou and others, 1998).



Age

No diagnostic fossils have been found in Siq Formation. Its age is usually deduced from its stratigraphic position as late Early to early Middle Cambrian (Powers, 1968). In Bayda’ Nathil area, the sandstone of the upper member contains only bioturbation (Tigillites?) and fossil trails, which occur in the sand-flat deposits. Bramkamp and others (1963) and Powers (1968) proposed an Early Cambrian age based on its position below the Quweira Formation. Possible correlation between Siq Formation and the transgressive Middle Cambrian Burj Limestone in Jordan (Bender, 1975) justifies extension of its age to Middle Cambrian. As a result of this tentative correlation, the upper member of the formation is assumed to be of late Early to Middle Cambrian age.


Filling depressions on top of basement rocks, Siq Formation was probably deposited in a braided-stream environment. Clayey siltstones with Tigillites and fine-grained sandstones with parallel to wavy bedding and sigmoidal cross-stratification indicate coastal and tidal flat environments, with maximum flooding indicated

Figure 5. Clayey siltstone with horizontal bedding and Tigillites at the base of the upper member of Siq Formation in Bayda’ Nathil area.

Figure 6. Eolian sandstone at the uppermost part of the upper member of Siq Formation in Bayda’ Nathil area.



by fine-grained sandstone with current ripples. The uppermost part of the upper member is represented by coastal eolian sandstone that becomes thicker to the north and to the south of Jibal al Misma (Halawani and others, 1996, 1997; Janjou and others, 1998). In Bayda’ Nathil area, the deposits of the upper member record the first transgressive event of the Paleozoic succession onto northeast Arabia.

RemARkS

The Saudi Stratigraphic Committee recommends additional detailed work on this formation to properly define its vertical and lateral extent and to determine its relationship to overlying sandstone units in different areas of the Kingdom. The detailed study should take into consideration the previous studies that correlated the Early Paleozoic formations exposed in the Kingdom with those exposed in Jordan (Al-Husseini, 2010, 2011) and which suggest that they may have been deposited in two different basins.

In Ha’il quagrangle, the 21-m-thick “Yatib formation” was mapped by Ekren and others (1987). This very localized unit nonconformably overlies basement rocks and unconformably underlies Saq Formation. It consists of a basal conglomerate overlain by poorly sorted, cross-bedded sandstone. The whole unit is channeled by the Risha Member of Saq Formation. In view of its extremely restricted occurrence and stratigraphic position, it is now considered as a lateral equivalent of the lowermost Siq Formation.

quWeiRA foRmATion

Rock uniT

Quweira Formation

AuThoR

Quennell, A.M.

yeAR

1951

oRigin of nAme

The name was derived from Jabal Quwayrah in Jordan.

definiTion

Quweira Sandstone was originally defined by Quennell (1951) in Jordan. Bramkamp and others (1963) and Brown and others (1963a, 1963b) traced and described the formation from the Saudi-Jordan border to Al Ula town along the old Hijaz Railway.

TyPe locAliTy

No type locality has been measured in Saudi Arabia.

ThickneSS

West of Tabuk town, Quweira Formation is 266 meters thick. Near Al Ula town, it was measured by Vaslet and others (1994) to be 191 meters thick.

conTAcTS

Upper

Unconformable with the overlying Saq Formation.

Lower

Unconformable with the underlying Siq Formation and nonconformable at places with basement rocks (figs. 7 and 8).

liThology

West-northwest of Tabuk town, the formation consists mainly of massive, reddish to brown, cross-bedded, medium- to coarse-grained sandstone. With local intercalations of siltstone, the basal conglomerate is made up of quartz and feldspar pebbles. Near Al Ula town, it consists of yellow or buff, medium-grained sandstone with varicolored milky-quartz pebbles of various sizes scattered throughout the formation.

foSSilS

No diagnostic fossils were found in this formation in Saudi Arabia.

Age

Using the lithologic correlation proposed by Bender (1968) for the succession in south Jordan, Powers (1968) suggested a Cambrian age for the Quweira Formation. Bender (1968) suggested a Lower to Middle Cambrian age based on trace fossils and stratigraphic position.

متكون قويرة



Fiure 7. Basal conglomerate of Quweira Formation overlying basement rocks (Al Bad’ quadrangle).

Figure 8. Landscape showing Quweira Formation overlying the basement rocks (Al Bad’ quadrangle).


Quweira Formation may have been deposited in fluvial to intertidal systems.

RemARkS

1) This unit requires detailed studies in order to verify its lithologic character in Saudi Arabia after which, a new name and type section must be suggested.

2) The attribution of Quweira Formation in the Kingdom to the Middle Cambrian based on its correlation with the Middle Cambrian Burj or Abu Khashiba formations in Jordan needs more detailed studies in the future.



SAq foRmATion

Rock uniT

Saq Formation

AuThoR

Burchfiel and Hoover

yeAR

1935

oRigin of nAme

The name was derived after Jabal Saq in Al Qasim region (fig. 9).

متكون ساق

Figure 9. Jabal Saq in Al Qasim region, where the name of the formation was derived.

definiTion

“Saq” was originally used as the lower member of the obsolete “Uyun formation” Bramkamp (1952) raised the Saq to formation status. Steineke and others (1958) and Powers and others (1966) published detailed studies on the type locality. Powers (1968) described the formation from Jabal Saq. Helal (1964, 1965) excluded the rocks containing traces of Cruziana from the upper part of the “Saq Sandstone.” Delfour and others (1982) divided the “Saq Sandstone” into lower and upper members which Vaslet and others (1985) named as Risha Member and Sajir Member respectively. In the northwest of the Kingdom, Vaslet and others (1994) identified three informal litho-sedimentologic units in the Sajir Member: lower, middle, and upper units.

TyPe locAliTy

The type locality at Jabal Saq does not represent the whole Saq Formation. This section is derived from a very long traverse extending from the base of Jabal al Hanadir (lat 26°27’24”N., long. 43°30’11”E.) to Jabal Saq (lat 26°16’02”N., long 43°18’37”E.) and from there, to the top of basement rocks at lat 26°15’14”N., long 43°06’21”E. in Al Qasim region of central Arabia.

RefeRence SecTion

The reference section, about 710 meters thick, was measured in Jibal al Misma quadrangle in northwest Saudi Arabia.

ThickneSS

Williams and others (1986) remeasured it to be 663 meters thick. At the type locality, Powers (1968) calculated a thickness of more than 600 meters.

conTAcT

Upper

Conformable with the overlying graptolite shale of the Hanadir Member of Qasim Formation. In some



places, there is a hiatus between Saq and Qasim in Jabal Habashi quadrangle, as indicated by the presence of placoderm fish debris, brachiopods, orthoceratids, and lingulids.

Lower

Nonconformable with basement rocks or unconformable with the underlying Siq or Quweira formations (fig. 10).

Figure 10. General view showing the Saq Formation (light colored) unconformably overlying the Quweira Formation (dark) nonconformably overlying basement rocks (Al Bad’ quadrangle).

Risha MemberRock uniT

Risha Member

AuThoR

Vaslet and others

yeAR

1985

oRigin of nAme

“Risha” was derived from Wadi ar Risha (Al Faydah quadrangle).

TyPe locAliTy

The type section was measured between lat 25°04’19”N., long 44°12’37”E., and lat 25°05’24”N., long 44°17’40”E., in Al Qasim region of central Saudi Arabia (Al Faydah quadrangle).

RefeRence SecTionS

At latitude 26°16’N of Jabal Saq

ThickneSS

Risha Member is 190 meters thick at the type locality (Wadi ar Risha), but it is 308 meters thick at the reference section in Jabal Saq.

conTAcTS

Upper

Conformable contact with the overlying Sajir Member.

Lower

The member nonconformably overlies a peneplaned surface of basement rocks.

شاءعضو الر



liThology

Risha Member consists of the following (fig. 11):

• In most places, the base of the formation consists of coarse-grained, poorly sorted, pebbly sandstone, but locally a basal conglomerate less than a meter thick.

• Ochrous sandstone, 80 to 120 meters thick, overlies the basal pebbly sandstone and consists of mostly of coarse to medium-grained quartz and lesser amounts of lithic grains.

• In the overlying 20 to 25 meters,the sandstone is also very coarse grained and microconglomeratic, but appears to be more sorted and bedded than the underlying sandstone. Cross-bedding and inclined cross-bedding are present. Brown, medium-grained, laminated sandstone.

• The overlying 100 meters are composed of brown and white, medium to coarse-grained sandstone, which is well sorted and bedded.

• The uppermost consists of beige to brown, medium-grained, well-bedded sandstone containing numerous inclined-bedding and rarer cross-bedding. This sandstone is more homogenous and better sorted than the underlying part.

Figure 11. Lithostratigraphic section and paleoenvironment of Saq Formation in Jabal Habashi quadrangle (Williams and others, 1986).



foSSilS

No fossils

Age

Upper Middle to Late Cambrian


Braided alluvial fan or braided stream system.

Sajir MemberRock uniT

Sajir Member

AuThoR

Vaslet and others

yeAR

1985

oRigin of nAme

The name “Sajir” was derived from Wadi Sajir (Al Faydah quadrangle).

TyPe locAliTy

The type section was measured between lat 25°05’24”N., long 44°17’40”E. and lat 25°06’21”N., long 44°23’36”E., in Al Qasim region of central Saudi Arabia (Al Faydah quadrangle).

RefeRence SecTion

Sajir Member was measured at lat 26°25’00”N. of Wadi al Wasi‘ah (Jabal Habashi quadrangle).

ThickneSS

147 meters thick at the type locality in Wadi Sajir. It is 355 meters thick at lat 26°25’00”N. of Wadi al Wasi‘ah.

conTAcT

Upper

It is conformable with the overlying graptolite shale of Hanadir Member of Qasim Formation. In Jabal Habashi quadrangle, there is a hiatus between Sajir Member of Saq Formation and Hanadir Member of Qasim Formation, as indicated by the presence of placoderm fish debris, brachiopods, orthoceratids, and lingulids.

Lower

Nonconformable with basement rocks or unconformable with Siq Formation, and possibly disconformable with the underlying Quweira Formation.

liThology

Sajir Member consists of the following, from base to top: fine to medium-grained, dark red to white, cross-bedded silty sandstone and stone.

• Dark-red, fine-grained, silty and micaceous sandstone (3.5 meters thick).

• Fine to medium-grained, white, cross-bedded sandstone (80 meters thick).

• Alternating sandstone and siltstone. The sandstone is brown and white, medium and fine grained. The siltstone beds are brown or red and very micaceous. Numerous Cruziana traces are present. (204.5 meters thick)

• The uppermost consists of brown to beige, fine-grained sandstone, in inclined and graded beds, intercalated with red and brown, micaceous, bioturbated siltstone. (65 meters thick).

foSSilS

No diagnostic fossils were found in Saq Formation. Although bioturbation (Scolithos) and rare bilobate trails (Cruziana) are present in the uppermost part of the member (figure 12).

Age

After comparing with similar facies in Jordan (Helal, 1965; Powers and others, 1966; Powers, 1968; Vaslet and others, 1994; Al Hajri and Owens, 2000), Vaslet and others (1985) and Willams and others (1985) suggested a Cambrian age for Risha Member and an Early Ordovician (Arenigian) age for Sajir Member.

عضو ساجر




The lower unit of Sajir Member represents a broad, fluviodeltaic, very flat distributary plain traversed by braided streams. Towards the middle part of Saq Formation, an increase in marine influence is indicated by the presence of supratidal and upper intertidal deposits. The top of the formation represents marine depositional environment.

RemARkS

Janjou and others (1998) recognized and described Hilwan Member of the uppermost part of Saq Formation, which was not recognized outside Jibal al Misma quadrangle. For this reason, the Saudi Stratigraphic Committee did not consider this unit as a part of the formation.

Figure 12. Cruziana trace fossils in Sajir Member of Saq Formation

qASim foRmATion

Rock uniT

Qasim Formation

AuThoR

Williams and others

yeAR

1986

oRigin of nAme

The name was derived from the Al Qasim region of central Saudi Arabia.

definiTion

Qasim Formation corresponds to the lower part (units 1 to 3, at least) of the obsolete Tabuk Formation as defined by Powers and others (1966) and as amended by Powers (1968). The Ordovician part of Tabuk Formation was studied by Davis and others (1981) in the Ha’il region, and by Clark-Lowes (1980) and McClure (1988a, b) in the Qasim region. These studies, together with a compilation by Wolfart (1981), defined the lithostratigraphy and sedimentology of the formation. The formation is subdivided into four members, from bottom to top: Hanadir, Kahfah, Ra‘an, and Quwarah.

TyPe locAliTy

See the type localities for each member.

ThickneSS

The combined thickness of Qasim Formation in the type localities of its four members is 261 meters. It is 358 meters thick in reference sections in northwestern Saudi Arabia.

متكون القصيم



conTAcTS

Upper

Unconformable with glacial and periglacial deposits of Zarqa or Sarah formations of Tabuk Group.

Lower

In general, the relation with the underlying Saq Formation is conformable. It is sometimes disconformable as indicated by the presence of conglomerate or a thin, red ferruginous breccia at the base of Qasim Formation.

Age

In northwest Saudi Arabia (Vaslet and others, 1994; Janjou and others, 1996c, 1997), the formation was dated as Early to Late Ordovician based on graptolite and trilobite faunas. Senalp and Al-Duaiji (2001) dated Qasim Formation as Late Llanvirnian to Late Caradocian (possibly Ashgillian). Dating of outcrop samples is based mainly on the identification of graptolites, trilobites, and chitinozoans that are common in shales of Hanadir and Ra‘an members.

Hanadir MemberRock uniT

Hanadir Member

AuThoR

Holm and others

yeAR

1948

oRigin of nAme

The name was derived after Jabal al Hanadir in Al Qasim region of central Saudi Arabia (Jabal Habashi quadrangle).

definiTion

Hanadir Member is the basal member of Qasim Formation. The member corresponds to Powers’ (1968) unit 1 of the obsolete “Tabuk Formation” and to the “Didymograptus shale member” of Helal (1964, 1965).

TyPe locAliTy

The type sequence is located at lat 26°26’58”N., long 43°30’11”E., Jabal al Hanadir, Al Qasim area. It crops out between Al Hanadir and Jal at Tiraq in the form of a cuesta truncated near Jal al Aswad by the Sarah ridge.

RefeRence SecTion

The reference section of Hanadir Member is 48 meters thick in At Tiniyat and Jal as Saqiyah (Baq‘a’ quadrangle).

ThickneSS

Originally 12.2 meters thick as defined by Holms and others (1948); 25 meters thick at the type locality measured later by Williams and others (1986).

conTAcTS

Upper

Conformably overlain by Kahfah Member of Qasim Formation.

Lower

Conformable with the underlying Sajir Member of Saq Formation. In some places, there is a hiatus between Saq and Qasim formations in Jabal Habashi quadrangle, as indicated by the presence of placoderm fish debris, brachiopods, orthoceratids, and lingulids.

liThology

From bottom to top, the member is composed of the following units (fig. 13):

1. Brown, bioclastic conglomerate containing sandstone pebbles and clay pebbles.

2. Brown, medium to coarse-grained sandstone containing graptolites, lingulids; interbedded with bioclastic material rich in fish debris forming phosphatic bone beds.

3. Gray, white or dark-red, silty claystone rich in graptolites and trilobites.

عضو الحناذر



Figure 13. Composite type section of Qasim Formation at Jabal Habashi quadrangle (after Williams and others, 1986; Vaslet and others, 1987).



4. Gray clay cut by channel deposits of laminated, micaceous, calcareous sandstone with fossils fragments of orthoceratids, brachiopods, gastropods, and trilobite.

5. Gray to green claystone with rare silty beds and diagenetic gypsum.

foSSilS

Placoderm fish debris, brachiopods, orthoceratids, and lingulids are common, while gastropods are rare, as yet unidentified (Williams and others, 1986). The fish debris includes bones, bony plates of a pearly appearance, and teeth (Williams and others, 1986). Graptolites (Didymograptus) and trilobites are also present in this member (figs. 14 and 15).

Figure 14. Graptolites (Didymograptus) in an outcrop of Hanadir Member of Qasim Formation (Tayma quadrangle).

Figure 15. Trilobites in Hanadir Member of Qasim Formation (Baq‘a’ quadrangle).



Age

Dated as Late Arenigian (Powers, 1968). The age was revised to Llanvirnian by Helal (1965), McClure (1978), and Clark-Lowes (1980). Williams and others (1986) studied the graptolite fauna and placed this member in the Didymograptus murchisoni Zone. The Llanvirnian age is supported by studies of the trilobite fauna by Thomas (1977), who described Plaesiacomia vacuvertis, and El-Khayal and Romano (1985), who described Ningkianolithus hanadirensis from Al Hanadir locality.


Hanadir Member represents shallow, siliciclastic, marine platform sedimentation ranging from a transitional zone below wave base to the lower shoreface zone. Most deposition occurred in calm, low-energy conditions that allowed fine particles to settle.

Kahfah MemberRock uniT

Kahfah Member

AuThoR

Vaslet and others

yeAR

1987

oRigin of nAme

It was named after Al Kahfah village, Qasim area (Baq‘a’ quadrangle).

definiTion

The member corresponds to “unit 2 Scolithos Sandstone” of Powers (1968), to the lower “Tabuk sandy member” of Helal (1964 and 1965), and to the “Ordovician sandstone” of Al-Laboun (1982).

TyPe locAliTy

The section was measured between lat 27°01’14”N., long 43°05’04”E., and lat 27°05’43”N., long 43°07’02”E. (Baq‘a’ quadrangle).

RefeRence SecTionS

At Wadi al Makhrim at about lat 27°10’N. (Jabal Habashi quadrangle).

ThickneSS

The type section is 104 meters thick while the reference section is 110.5 meters thick.

conTAcTS

Upper

Conformably overlain by Ra‘an Member.

Lower

Conformably overlies Hanadir Member.

liThology

The member is divided into two lithologic assemblages (fig. 13). The lower assemblage at the reference section is 55 meters thick and composed of the following units, from bottom to top:

1. Fine-grained, laminated, micaceous sandstone forming the upper part of the Hanadir and Jal at Tiraq cuestas.

2. Gray to bluish, very silty claystone interspersed with laminated flaser bedded sandstone.

3. Dark-gray, fissile sandstone at Jal at Tiraq, forming the edge of a second cuesta recessed from Hanadir Member cuestas.

4. Alternating well-bedded, micaceous sandstone and gray to green, silty claystones.

5. Alternating gray to blue, micaceous, silty claystone and several layers of fine-grained, laminated, and ripple-marked sandstone and rarer bioclastic beds.

6. Gray sandstone displaying tidal-channel structures and ripple marks, with silt and clay intercalations.

The upper assemblage at the reference section is 54.5 meters thick and mainly composed of Tigillite-bearing sandstone (Scolithos sandstone) (fig.16). It consists of red and gray, uniformly fine-grained, and somewhat silty, micaceous sandstone. The sandstone is perforated by abundant vertical Tigillites over its

عضو آهفة



entire thickness.

foSSilS

Fish, bivalve debris, and Tigillites (Williams and others, 1986).

Age

Vaslet and others (1987) considered Kahfah Member as Llandeilian based on the presence of Glyptograptus sp. and Diplograptidae in the lower part of lower assemblage at At Tiniyat area.


The lower assemblage of Kahfah Member represents a mixed, fine- to coarse-grained sedimentation in the shoreface zone of a shallow-marine, siliciclastic platform. Claystone and siltstone were deposited in calm conditions in the lower shoreface environment, where energy conditions were generally low, except during storms that induced the spreading of thin sand layers or the formation of flat, sandy megaripples or hummocky cross-bedding.

The lower part of the upper assemblage of Kahfah Member represents a shoreface environment with features similar to those described for the lower assemblage. The upper part of the upper assemblage is characterized by a slightly different environment, ranging from lower shoreface to zone that is transitional towards shallower conditions.

Figure 16. Tigillites (Scolithos) in the Kahfah Member of the Qasim Formation, Al Qasim area.

Ra‘an MemberRock uniT

Ra‘an Member

AuThoR

Williams and others

yeAR

1986

oRigin of nAme

It was named after Khashm ar Ra‘an, Al Qasim region.

definiTion

Ra‘an Member corresponds to the middle shale of the “Tabuk Formation” (Pocock and Kobb, 1949). It also corresponds to the informal unit 3 or the obsolete “Ra‘an Shale member” of the “Tabuk Formation” of Powers (1968), to the “Diplograptus shaly member” of Helal (1965), and to the “Ra‘an shale member” of

رعنالعضو



Al-Laboun (1982).

TyPe locAliTy

The succession is best exposed at lat 26°51’27”N., long 43°21”53”E.

RefeRence SecTionS

The base of the member is exposed at lat 27°49’40”N., long 37°48’00”E., and the top is at lat 27°50’42”N., long 37°47’35”E.

ThickneSS

The thickness at the type locality is 30 meters (Jabal Habashi quadrangle). The reference section is 48 meters thick (Tayma quadrangle).

conTAcTS

Upper

Conformably overlain by Quwarah Member.

Lower

Conformably overlies Kahfah Member.

liThology

Ra‘an Member consists of gray and dark-red, finely laminated, silty clay to greenish gypsiferous clay (fig. 13).

The basal 3 meters are composed of gray and dark-red, finely laminated, silty clay interspersed with beds of brown micaceous siltstone containing graptolites. They are overlain by 27 meters of greenish gypsiferous clay. The succession is capped by 9.5 meters of gray silty clay and fine-grained, bioturbated, clayey sandstone in beds about a centimeter thick.

foSSilS

Graptolites, conodonts, and trilobites were identified in the basal layers (Williams and others, 1986).

Age

Early Late Ordovician (Late Caradocian) age has been suggested by several authors (McClure, 1978; Williams and others, 1986).


Ra‘an Member represents sedimentation in a calm setting below wave base—in an environment ranging from outer shelf to lower shoreface.

Quwarah MemberRock uniT

Quwarah Member

AuThoR

Williams and others

yeAR

1986

oRigin of nAme

The name was derived from Al Quwarah town, Al Qasim region in central Saudi Arabia.

definiTion

The name “Quwarah Member” was introduced by Williams and others (1986). It corresponds to the informal upper part of unit 3 of the “Tabuk Formation” of Powers (1968).

TyPe locAliTy

The section was measured between lat 26°49’40”N., long 43°24’38”E. and lat 26°50’38”N., long 43°27’56” E. (Jabal Habashi quadrangle).

RefeRence SecTion

The reference section was measured at Tayma quadrangle where the base of the section lies at lat 27°50’42”N., long 37°47’35”E. and the top is at lat 27º53’42”N., long.37º48’06”E.

ThickneSS

Quwarah Member is 87.5 meters thick at the type section and 128 meters thick at the reference section.

عضو القوارة



conTAcTS

Upper

Unconformable with glacial and periglacial deposits of Zarqa or Sarah formations.

Lower

Conformably overlies Ra‘an Member.

liThology

The member comprises the following seven units from bottom to top (fig. 13):

1. Beige, fine-grained, laminated, micaceous sandstone with ripple marks and trails on the upper surface of beds and containing some layers with rare clay pebbles; 7 meters thick.

2. Blue to green, silty, and micaceous clay, centimeter-thick microconglomeratic and bioclastic layer with lingulids and orthoceratids at the base and interlayered with several gray and brown, psammitic beds; 17.5 meters thick.

3. Gray, laminated, ripple-marked, micaceous sandstone containing bioturbation and trails, interbedded with greenish micaceous siltstone; 15.5 meters thick.

4. Fine-grained sandstone and pink, micaceous siltstone, cross-bedded at the top and including a ripple-marked, bioturbated, ferruginized surface at the top of the uppermost sandstone bed; 17.5 meters thick.

5. Pink, medium-grained, homogeneous sandstone; 4 meters thick.

6. Greenish siltstone capped by decicentimeters-thick beds of black ferruginous sandstone containing Tigillites; 22 meters thick.

7. Micaceous and silty clay, blue to green gypsiferous at the base, and intercalated with sandy laminations in the uppermost part; 22 meters thick.

foSSilS

Apart from monolobate trails and evidence of bioturbation, the fauna are limited to fragments of as yet unidentified orthoceratids and lingulids (Williams and others, 1986).

Age

Late Ordovician (Late Caradocian to possibly Ashgillian; Williams and others, 1986).


Intertidal to deep subtidal to offshore (Williams and others, 1986; McClure, 1988; McGillivray and Husseini, 1991; Powers, 1968; Senalp and Al-Duaiji, 2001).



TABUK GROUP

مجموعة تبوك

Figure 17. Lithostratigraphic classification of Tabuk Group in Saudi Arabia. The geological time scale is from the International Stratigraphic Chart (2004).

Rock uniT

Tabuk Group

AuThoR

Janjou and others

yeAR

1996

oRigin of nAme

Derived from Tabuk town

definiTion

Janjou and others (1996c) defined Tabuk Group in Al Qalibah area of northwestern Saudi Arabia. It comprises all glacial deposits accumulated in Saudi Arabia during the Late Ordovician. Tabuk Group consists of, from oldest to youngest, Zarqa, Sarah, and Hawban formations (fig. 17). These formations include glacial and periglacial sediments that filled paleo-valleys incised into the Qasim and/or older formations. The glacial origin was first suggested by McClure (1978). In part, they correspond to the brown to tan sandstone of the lower and middle parts of the “Tabuk Formation” described by Bramkamp and others (1964), to the “Upper Tabuk sandy member” of Helal (1964), and to the “Ordovician-Silurian Sandstone” described by Al-Laboun (1982, 1986). Lozej (1983) and Smith (1984) identified glacial features in the middle part of the former “Tabuk Formation”.

In central Saudi Arabia, it is easy to differentiate Zarqa Formation from Sarah Formation. In this area, Tabuk Group comprises, from oldest to youngest, Zarqa, Sarah, and Hawban formations (Vaslet and others, 1987; Vaslet, 1990) (fig. 18). In Tabuk, Qalibah, and Jibal al Misma areas, the differentiation between Zarqa and Sarah formations is difficult. TSarah Formation was designated to include the glacial succession there. The Uqlah Formation was introduced by Janjou and others (1996c) for similar facies of the uppermost part Hawban Member of Vaslet and others (1987).



The Saudi Stratigraphic Committee studied the four units of the type section of Uqlah Formation in Al Qalibah quadrangle and decided to assign the lower two glacial units (unit 1 and unit 2) to Hawban Formation, thereby raising them to formation status. The upper two units (3 and 4) were assigned to Uqlah Formation, the lower formation of the overlying Qalibah Group.

Figure 18. Location of the type and reference sections of formations of Tabuk Group.

TyPe locAliTy

In Jabal Habashi and Baq‘a’ quadrangles

ThickneSS

The composite thickness of Tabuk Group is about 254 meters.

conTAcTS

Upper

Disonformably overlain by Uqlah and/or Qusaiba formations of Qalibah Group.

Lower

Disconformable above Qasim Formation and/or formations of Tayma Group.

liThology

The glacial sedimentary deposits are composed of tillite, boulders of clay, and slumped medium- to coarse-grained sandstone. The sandstone changes locally into pebble conglomerates, and homogeneous, cross-bedded, fine- to medium-grained sandstone. It is capped by well-bedded, bioturbated, fine-grained sandstone of Qalibah Group.

foSSilS

Devoid of fossils.

Age

In the northwest of the Kingdom (Tayma, Al Qalibah, and Tabuk areas), glaciation started before Late Caradocian (early Late Ordovician) and ended by Hirnantian (late Late Ordovician). McClure (1987) dated the glacial deposits as Late Caradocian because of their stratigraphic position above the Ra‘an Member of Qasim Formation. Vaslet and others (1994) reported that Sarah Formation is devoid of fossils in Tayma



quadrangle. A Late Ordovician to Early Silurian age is deduced from its position a few meters below the well-dated Early Silurian Qusaiba Formation and by comparison with subsurface data, which include microflora described in central Saudi Arabia by Vaslet (1987b, 1990; Vaslet and others, 1987), who assigned a latest Ordovician (Late Ashgillian) to Early Silurian (Early Llandoverian) age. Thus, a Late Ordovician (Ashgillian to Hirnantian) age is suggested here for the glacial period in Saudi Arabia, including its Zarqa, Sarah, and Hawban formations.


Zarqa, Sarah, and Hawban formations include glacial and periglacial sediments filling paleo-valleys.

RemARkS (TAbuk gRouP)1. The Saudi Stratigraphic Committee acknowledges the fact that the name “Tabuk Group” may cause some

confusion, as it encompasses “Tabuk Formation” used from the 1960s until the end of 1980s. Powers and others (1966) “Tabuk Formation” included all units between Saq Sandstone up to Tawil Sandstone. Powers (1986), subdivided it into seven units. Williams and others (1986) and Vaslet and others (1987) abandoned “Tabuk Formation” and assigned new name to the units. Therefore, it is recommended that an entirely new name be decided in the future

2. In central Arabia, the glacial sediments are clearly and systematically exposed in three easily identified and mapped formations: the Zarqa, Sarah, and Hawban formations. However, in the Al Qalibah and Tabuk quadrangles of northwestern Arabia, it is difficult to distinguish between the Sarah and Zarqa formations. For this reason, Janjou and others (1996a, 1996b, and 1997) combined all glaciation-related sediments into a single formation: Sarah Formation. Sanamah Formation of the Wajid Group in southern Arabia seems to be lithologically equivalent to glacial deposits of Sarah Formation.

3. Detailed lateral studies that include tracing (where possible) the glacial deposits from central Saudi Arabia to the north, northwest, and to the south (into Wajid Sandstone) can help resolve these issues.

zARqA foRmATion

Rock uniT

Zarqa Formation

AuThoR

Vaslet and others

yeAR

1987

oRigin of nAme

From Jal az Zarqa’, east of Wadi U‘aywij, Baq‘a’ quadrangle.definiTion

Vaslet and others (1987) first introduced “Zarqa Formation” for rock units in central Saudi Arabia (Baq‘a’ quadrangle). Vaslet and others (1994) subdivided the formation into lower and upper assemblages in Tayma quadrangle. Janjou and others (1996b, 1997, and 1998) described “Zarqa” as a facies within Sarah Formation in Tabuk, Qalibah, and Jibal al Misma quadrangles.

TyPe locAliTy

East of Wadi U‘aywij near Jal az Zarqa’, located between lat 27º47’40”N., long 42º20’32”E. and lat 27°49’22”N., long 42°22’48”E.

ThickneSS

Zarqa Formation has maximum thickness of 115 meters at the type section.

conTAcTS

Upper

Disconformably overlain by Sarah Formation of Tabuk Group.

Lower

Unconformably overlies the Qasim and/or older formations of the Tayma Group.

liThology

The lithologic succession in the type section shows that the formation is composed of a repetition of three main facies throughout (fig. 19):

متكون زرقاء



1. the first facies is composed of typical, striated, heterogeneous material form gravel- to boulder-size basement rock. Tillite at the bottom of the formation (2-9 meters thick) is channeled into the underlying Qasim Formation. The matrix is coarse- to fine-grained sandstone, or clayey siltstone, commonly brown or blackened by iron oxides. In places, the boulder-clay and substratum show frost cracks filled with coarse tillite (fig. 20).

2. Boulder clay is a very constant dark-green, clayey, micaceous siltstone (“rock flour” of Beuf and others, 1971) with various amounts of pebbles, cobbles, or boulders. The clasts, in places faceted, are derived from basement and older Phanerozoic rocks and represent commonly striated dropstones in a mudstone matrix. Thickness variations are abrupt due to the lateral changes in the paleodepositional relief.

3. Beige, fine-grained micaceous sandstone (1-3 meters thick) filling channels incised into the boulder clay. Some beds have a coarse or conglomeratic base blackened by iron oxides. Slumping is nearly ubiquitous: sandstone beds slumped into boulder-clay, or microslumps within the sandstone itself. Other structures such as frost wedges and polygonal ground typical of glacial environments (Beuf and others, 1971) are present in this sandstone.

Figure 19. Type section of Zarqa Formation at Baq‘a’ quadrangle (after Vaslet and others, 1987).



Figure 20. Basal part of the glacial deposits (tillite) of Zarqa Formation, Al Qasim area.

foSSilS

Barren

Age

In view of the fact that Late Caradocian deposits of Quwarah Member of Qasim Formation are now known to be above Ra‘an Member, it would appear that the glaciation represented by the Zarqa Formation occurred between the Late Caradocian and the Early Llandoverian. Beuf and others (1971) and Spjeldnaes (1981) suggested a Caradocian to Middle Llandoverian glacial episode especially in Saudi Arabia and Gondwana in general. In adopting the results of Senalp and others (2002), the Saudi Stratigraphic Committee restricts the duration of the glacial period to the Ashgillian. Thus, Zarqa Formation is of Ashgillian age.


Glacial environment prevailed during the deposition of Zarqa Formation.

SARAh foRmATion

Rock uniT

Sarah Formation

AuThoR

Williams and others

yeAR

1986

oRigin of nAme

Named after Sarah ridge in Al Qasim region.

definiTion

Clark-Lowes (1980) first defined “Sarah member” to include glacial and periglacial sediments filling paleovalleys in Saudi Arabia (fig. 21). Williams and others (1986) raised its rank to formation status McClure (1978) was the first to demonstrate their glacial origin. These sediments correspond to the “brown to tan sandstone transgressing the lower and middle parts of the Tabuk Formation” as described by Bramkamp and others (1963), the “upper Tabuk sandy member” described by Helal (1965), and the unnamed “Ordovician-Silurian sandstone” described by Al-Laboun (1982). In northwest Saudi Arabia (Qalibah and Tabuk quadrangles), it is difficult to differentiate between Zarqa and Sarah formations. For this reason, Janjou and others (1996a, 1996b, and 1997) put together all glacial-related sediments into a single Sarah Formation) and the name “Zarqa Formation” was used to describe a facies type in Sarah Formation.

ةمتكون صار



Figure 21. Sinuous paleovalley filled by Upper Ordovician glacial sediments in Tabuk area, northwest Saudi Arabia.

TyPe locAliTy

At Sarah ridge lat 26°31’14”N., long 43°11’33”E. (Jabal Habashi quadrangle)

RefeRence SecTion

The measured reference section of Sarah Formation overlies Zarqa Formation on the eastern bank of Wadi U‘aywij near Jal az Zarqa’, located between lat 27º47’40”N., long 42º20’32”E. and lat 27°49’22”N., long 42°22’48”E.(Vaslet and others, 1987).

ThickneSS

26 meters thick at the type locality, and 85 meters thick at the reference section. The thickness of Sarah Formation is difficult to accertain due to preexisting paleotopography that had a considerable relief in places. The thickness also depends on the relative position within the paleovalley. At the axis, it is estimated to be about 150 to 200 meters thick (Vaslet and others, 1987).

conTAcT

Upper

Disconformably overlain by the Hawban Formation of Tabuk Group.

Lower

Disconformably overlies the Zarqa Formation of Tabuk Group or Qasim and Saq formations of Tayma Group.

liThology

Sarah Formation consists of medium- to coarse-grained sandstone that is locally conglomeratic with rounded quartz pebbles, and homogeneous sandstone deposited as cross-bedded channels and graded beds (fig. 22). Microconglomerate occurs at the base of the channels. The sandstone at the top of the formation contains slumps and overturned bedding. Glacial striations formed during late Ordovician glacier advance were recognized at different levels in the section and in different areas (fig. 23).

foSSilS

No in-situ fossils were found in these glacial deposits.

Age

The age of Sarah Formation is deduced from its stratigraphic position below the Early Silurian fossiliferous claystone of the Qusaiba Formation and from subsurface samples containing fossil microflora from central Saudi Arabia (Vaslet and others, 1987; Vaslet, 1990) that are of Late Ordovician (Late Ashgillian) to Early Silurian (Early Llandoverian) age. Al-Hajri and Owen (2000) suggested a Late Ashgillian (Hirnantian) age for Sarah Formation in Al Jalamid area of northern Saudi Arabia. Thus, Sarah Formation is of Late Ordovician (Ashgillian–Hirnantian) age.



Figure 23. Glacial striations and grooves formed during Late Ordovician glaciation, Al Qalibah area.

Figure 22. Reference section of Sarah Formation at Baq‘a’ quadrangle (modified from Vaslet and others, 1987).




Sarah Formation was deposited in a glacio-fluvial to deltaic environment.

hAWbAn foRmATion Rock uniT

Hawban Formation

AuThoR

Saudi Stratigraphic Committee

yeAR

2012

oRigin of nAme

It was derived from Qa‘ Hawban in Ha’il region (Baq‘a’ quadrangle).

definiTion

This unit was initially named as “Hawban Member” of Sarah Formation (Vaslet and others, 1987) to include the glacial deposits overlying Sarah Formation in Al Qalibah quadrangle. Janjou and others (1996c) recognized an unconformity at the base of the section measured from lat 28º03’87”N., long 37º47’17”E. to lat 28º04’38”N., long 37º47’56”E in Wadi al Uqlah (Al Qalibah quadrangle). Accordingly, the Saudi Stratigraphic Committee raised the Hawban to formation status. The overlying marine units “3 and 4” in the type section of the Uqlah Formation were named “Uqlah Formation”. Hawban Formation includes units “1 and 2” that were considered by Vaslet and others (1987) to be a part of the Hawban Member.

TyPe locAliTy

Lies between lat 27º52’20”N., long 42º25’57”E. and lat 27º53’ 44”N., long42º25’32”E.

ThickneSS

Reaches up to 25 meters thick.

conTAcTS

Upper

Disconformably overlain by Uqlah Formation of Qalibah Group.

Lower

Conformably overlies Sarah Formation of Tabuk Group.

liThology

The formation consists of the following from the top to bottom (fig. 24):

4. Alternations of fine-grained, ripple-marked sandstone (2 meters thick) with flat bedding, and white claystone with secondary gypsum; the topmost sandstone bed is blackened by iron oxides, is very bioturbated, bears numerous monolobate traces as well as ripple marks, and is overlain by gray and red claystone of Qusaiba Formation.

3. Beige, fine- to medium-grained sandstone (14 meters thick) with high-energy cross-bedding.

2. Green to bluish, clayey sandstone (15 meters thick) interspersed with beige, fine- to medium-grained sandstone in decimeter-thick beds showing ripples, and small slumps and load casts.

1. Complex, slumped, and mixed, dark-green boulder clay (23 meters thick) containing components of shield and cover rocks, ranging from 1 to 50 m in size, in a clayey silty matrix; fine- to coarse-grained sandstone is slumped and dislocated in the boulder clay.

foSSilS

Pollen (Miller and Al-Ruwaili, 2007)

Age

Late Ordovician (Hirnantian) on the bases of palynological assemblage and stratigraphic position (Miller and Al-Ruwaili, 2007).


It was deposited in glacio-fluvial to deltaic environment.

متكون هوبان



Figure 24. Type section of Hawban Formation at Baq‘a’ quadrangle (modified from Vaslet and others, 1987).



QALIBAH GROUP

مجموعة القليبة

Figure 25. Lithostratigraphic classification of Qalibah Group in Saudi Arabia. The geological time scale is from the International Stratigraphic Chart (2004).

Rock uniT

Qalibah Group

AuThoR

Janjou and others

yeAR

1996

oRigin of nAme

The name was derived from Al Qalibah town.

definiTion

A complete section of all formations of Qalibah Group (fig. 25) is located between the towns of Al Qalibah and Tayma (fig. 26). From bottom to top, Qalibah Group is subdivided into Uqlah, Qusaiba, and Sharawra formations.

TyPe locAliTy

Located in Al Qalibah quadrangle, northwest Saudi Arabia.

RefeRence SecTion

Located in Tabuk quadrangle, northwest Saudi Arabia.

ThickneSS

The thickness reaches about 729 meters in Al Qalibah quadrangle and 992 meters at the reference section in Tabuk quadrangle.

conTAcTS

Upper

Qalibah Group is overlain disconformably by Tawil Formation of Huj Group. The contact is abrupt and marked by erosion of the topmost, well layered Qalibah beds and channel-filling by quartz-pebble conglomerate of Tawil Formation of Huj Group.



Lower

Qalibah Group unconformably overlies Hawban Formation of Tabuk Group.

foSSilS

Brachiopods, graptolites, chitinozoans, and acritarchs have been documented by many authors ( Vaslet and others, 1987; El Khayal 1985; Miller and Al-Ruwaili, 2007).

Age

Silurian


The lower Silurian clastic deposits represent a regionally regressive sequence (Bender, 1975; Ziegler and others, 1977; Bellini and Massa, 1980; Spjeldnaes, 1981; Al-Husseini, 1990, 1991b).

Figure 26. Location map of the type and reference sections for formations and members of Qalibah Group.

uqlAh foRmATion

Rock uniT

Uqlah Formation

AuThoR

Janjou and others

yeAR

1996

oRigin of nAme

It was named after Wadi al Uqlah in Al Qalibah quadrangle.

definiTion

Janjou and others (1996c) first proposed the formation name in northwest Saudi Arabia to include the sandstone that unconconformably overlies the preglacial-glacial deposits of Hawban or Sarah formations. Senalp and others (2002) and Miller and Al-Ruwaili (2007) informally used the name “Baqa member” to

عقلةمتكون



include the upper part of the original succession of the formal Hawban Member (Vaslet and others, 1986b) which represents the first marine deposition below Qusaiba Formation and above the glacially tectonized portion of the upper Hawban Formation. The original definition of Uqla Formation included four lithologic units (1-4). It is modified here to be restricted to only the 6-m-thick upper two units, 3 and 4 of Janjou and others (1996c).

TyPe SecTion

Base of type section (fig. 26) at lat 28°03'09"N., long.37°47'17"E.; top at lat 28°04'38"N., long 37°47'56"E.

RefeRence SecTion

South of Qa‘ Buhan at Tayma quadrangle at lat 27°53'14"N., long38°23'56"E.

ThickneSS

Uqlah Formation is 6 meters thick in Al Qalibah quadrangle and 10 metres thick at the reference section in Tayma quadrangle.

conTAcTS

Upper

Unconformable contact with the overlying Qusaiba Formation (fig. 27).

Lower

Unconformable contact with the underlying Hawban Formation of Tabuk Group.

Figure 27. Topmost part of the type section of Uqlah Formation of Qalibah Group, Al Qalibah quadrangle.

liThology

Uqlah Formation consists of the upper two units (3 and 4), from bottom to top (fig. 28):

1. Off-white or pale-yellow, fine- to medium-grained sandstone beds, having small- to medium-scale cross-stratification or subhorizontal bedding and reworked clayey chips. The upper surfaces of some beds have ripples with parallel crests. The base of the unit is marked by a layer of green, clayey siltstone. I is 5 meters thick.

2. Off-white or pink, fine-grained sandstone beds. The upper surfaces of beds show linguoid ripples, small vertical burrows, and some traces of bioturbation. It is 1 meter thick.

foSSilS

Only trace fossils.



Age

Based on its relationships with the onset of the Silurian transgression and on unconformable contacts with the underlying deposits of Hawban Formation, Uqlah Formation was assigned an Early Silurian (Early Llandoverian) age by Janjou and others (1996c). The sporadic occurrence and diminished number of reworked specimens combined with sedimentology form the bases for its post-glacial deposition. It is suggested to be Hirnantian (Late Ordovician) (Senalp and others, 2002).


The formation was deposited in a clearly shallow marine environment that preceded the abrupt rise in sea level at the beginning of the Silurian sedimentary cycle.

RemARkS (uqlAh foRmATion)

Senalp and others (2002) introduced Baq‘a’ member as a marine deposit, which represents the upper part of Hawban member of Vaslet and others (1987). Miller and Al-Ruwaili (2007) reported that Hawban and Baq‘a’ members of Sarah Formation (Vaslet and others, 1987) were deposited during and following the Late Ordovician (Hirnantian) glaciation of Gondwana. Thus, the Saudi Stratigraphic Committee recommends that more detailed studies will be necessary to determine the lateral facies changes between Baq‘a’ member introduced by Senalp and others (2002) and Uqlah Formation of Janjou and others, 1996c (fig. 29).

Figure 28. The type section of Uqlah Formation in Al Qalibah quadrangle (modified from Janjou and others, 1996c).



Figure 29. General view of the stratigraphic section of Hawban, Uqlah, and Qusaiba formations (Wadi al Uqlah area).

quSAibA foRmATion

Rock uniT

Qusaiba Formation

AuThoR

Pocock and Kopp

yeAR

1949

oRigin of nAme

The name was derived from the village of Qusayba’ in Al Qasim region of central Arabia.

definiTion

Powers (1968) used “Qusaiba shale member” as an informal name in unpublished reports for the upper shale of the “Tabuk Formation” in the vicinity of Qusayba’. It is now discarded for lack of lateral continuity. It probably corresponds to parts of unit 5 of the type section for the “Tabuk Formation.” This unit is equivalent to the earlier described unit named “Climacograptus-Orthoceratid member” by Helal (1964, 1968). Clark-Lowes (1980) called it “Qusaiba member”. Al-Laboun (1982) used the name “Qusaiba shale member” in Al Qasim region of central Saudi Arabia. Manivit and others (1986) used the name “Qusaiba member” but Vaslet and others (1987) considered these rocks as a member of Tayyarat Formation. The name “Tayyarat” is obsolete as it was used in Iraq for a Cretaceous formation. Al-Khayal and Romano (1988) called it “Qusayba formation”, an informal name. Mahmoud and others (1992) described it as a member of Qalibah Formation in Al Qalibah area. Recent detailed studies in northwestern Saudi Arabia (Janjou and others, 1996c) led to raising this member to formation rank in Qalibah Group and its subdivision into five cartographic units.

TyPe SecTion

The original type section was measured by Pocock and Kopp (1949) and later by Manivit and others (1986) at lat 26°51’08”N., long 43°34’48”E. Since then, several other sections, much thicker than the type section and of slightly different lithologies, were mapped and measured. With base at lat 28°02’18”N., long 37°59’26”E., and top at lat 28°11’51”N., long 38°00’00”E., a new type section was measured in Ad Dahkiyah area, where the Qusaiba was understood to be a formation rather than a member (Janjou and others, 1996c).

RefeRence SecTion

In Tabuk area (Janjou and others, 1997), it was measured between Jabal Mukayhil and Tal at Zufayyir with



base at lat 28º14’47”N., long 37º15’55”E., and top at lat 28º24’42”N., long 37º16’42”E.

ThickneSS

The formation increases in thickness northwards. It is 83 meters thick near Qusayb’ village in Al Qasim region, but reaches 290 meters in the new type locality in Al Qalibah quadrangle. It reaches 482 meters at the reference section in Tabuk quadrangle.

conTAcTS

Upper

Marked by a disconformable, erosional surface below the Sharawra Formation. Residual lag deposits, rich in orthocone and brachiopod debris, mark the contact (fig. 30). This surface could be a candidate for the subsurface equivalent to mid-Qusaiba deposits (A- Duaiji, 2010, oral communication).

Figure 30. Lag deposits rich in orthocone and brachiopod debris mark the contact between Qusaiba and Sharawra formations of Qalibah Group.

Lower

Disconformable over Uqlah Formation in the type locality. In Tabuk quadrangle, Qusaiba deposits disconformably overlay Sarah Formation of Tabuk Group.

liThology

Qusaiba Formation is made up of stacked sedimentary sequences that show identical facies successions marked by overall upward increase in sandstone proportion. It is subdivided into five units, from base upwards (fig. 31):

Unit 1. Pale-gray and white to pink clayey siltstone deposited on weathered surfaces, laminated, with wave ripples and cross-bedding; fine-grained micaceous sandstone and interbedded with siltstone; 25 meters thick.

Unit 2. Subdivided into three sub-units:

a. Black, clayey siltstone with beige to green weathering, and discontinuously intercalated with micaceous siltstone. This unit can be correlated with the “hot shale beds” described in central Arabia from subsurface data and now regarded as the main petroleum source rock in the Paleozoic succession; 24 meters thick (fig. 32).

b. Fine-grained sandstone in lenticular beds, with cross-bedding and gray-green interbeds of silty claystone; 18 meters thick.

c. Gray-green to yellow clayey siltstone alternating with fine-grained sandstone in lenticular sets; abundant cross-bedding; 29 meters thick.



Figure 31. Composite section of Qusaiba Formation, Al Qalibah quadrangle (after Janjou and others 1996c).

Unit 3. The lower part consists of homogeneous, dark micaceous/silty claystone and includes some fine-grained, parallel-bedded sandstone 18 meters thick. The upper part is dark-green to dark-gray, fine- to medium-grained sandstone with parallel beds and hummocky cross-bedding. Green or gray clayey siltstone is interbedded; 22 meters thick.

Unit 4. The lower part of this unit is dark, silty claystone with several thin beds of fine-grained sandstone 37 m thick. The upper part shows horizontal burrows and trails. Bioclastic lags, deposited as a reworked level, mark the base of this subunit; 25 meters thick.

Unit 5. This unit is made up of five informal lithologic subunits. The basal subunit consists mainly of green and/or yellow, clayey siltstone. This part is a coarsening- and thickening-upward sequence. The second subunit has yellow-green, clayey siltstone at the base, intercalated with several clayey sandstone beds coarsening and thickening upward. The third subunit contains reworked layers of fossil debris overlain by fine-grained sandstone in lenticular beds with interference and linguoid ripples, and rare, convolute bedding. The fourth subunit is yellow green, bioturbated, clayey siltstone that coarsen upward. The uppermost subunit 5 consists of yellow-green, bioturbated, clayey siltstone and coarsening-upward fine-grained sandstone. Used as a marker bed for the limit between the Qusaiba and Sharawra formations, a reworked layer at the top contains orthocones. 110 meters thick.



Figure 33. Graptolites (Monograptus) in an outcrop of Qusaiba Formation, Qusaiba area.

foSSilS

Trilobites, graptolites (Climacograptus, Monograptus, and Rastrites) (fig. 33), chitinozoans, and acritarchs have been documented by many authors. Figure 34 shows the occurrence and time ranges of several chitinozoan species from the Llandoverian and that were found in Qusaiba Formation in Saudi Arabia.

Age

In central and northwestern Saudi Arabia, Qusaiba Formation was assigned to the Llandoverian (Early Silurian) on the basis of trilobites, graptolites, and chitinozoans (Clark-Lowes, 1980; El-Khayal, 1985, 1987; Vaslet and others, 1986b; Mahmoud and others, 1992; Aoudah and Al Hajri, 1994; Paris and others, 1995; Janjou and others, 1996c; fig. 34).

dePoSiTionAl enviRonmenTS

Janjou and others (1996c) concluded that each of the informal units 1, 2, 3, and 4 of Qusaiba Formation represents a cycle of transgression and regression. The cycles are principally composed of clayey siltstone

Figure 32. General view of Qusaiba Formation in Tabuk area; inset: close up of “hot shale beds”, regarded as the main petroleum source rcok in Saudi Arabia.



deposits in a well-developed, distal, lower- to upper-offshore domain (black shales). Deposits that represent the regressive part of the cycles are present as upper-middle to proximal, offshore sandstone facies. In the four thinner cycles assigned to informal unit 5, the distal, clayey siltstone is less extensively developed and the proximal sandstone is from the middle- to upper-shore face domain.

The evolution toward increasingly proximal, regressive facies and the decrease in cycle thickness demonstrate the generally regressive character of Qusaiba Formation (fig. 35).

Figure 34. Total range biozone and relative abundance of selected chitinozoan species from the Llandovery of Central Saudi Arabia (from Paris and others, 1995).

Figure 35. Environmental factors controlling deposition of Qusaiba and Sharawra formations (from Sherland and others, 2001; Mahmoud and others, 1992)



ShARAWRA foRmATionمتكون شرورا Rock uniT

Sharawra Formation

AuThoR

Roach, S.J.

yeAR

1954

oRigin of nAme

It was named for Jabal Sharawra in Tabuk area (fig. 36).

definiTion

Roach (1954) first assigned the upper 127 meters of sandstones of the “Tabuk Formation” to “Sharawra member”. Recognized in the type locality and published by Steineke and others (1958), it was discarded by Powers and others (1968), used as “Sharawra sandy member” by Helal (1964, 1965), and used as “Sharawra Member” of “Tabuk Formation” by Clark-Lowes (1980), Al-Laboun (1982, 1986) and Bahafzallah and others (1981a). Vaslet and others (1987) called it “Sharawra member” of the Tayyarat formation in central Arabia. Mahmoud and others (1992) replaced the now obsolete Tayyarat formation with “Sharawra” in northwestern Saudi Arabia. Detailed studies by Janjou and others (1996c) led to the raising of this unit to formation rank in the Qalibah Group.

Figure 36. Jabal Sharawra, where the type section of the formation was derived (Tabuk area).

TyPe locAliTy

Unit-d of the obsolete Tabuk Formation is exposed at lat 28°44’54”N., long 36°34’39”E., in Tabuk area (Roach, 1954). As the basis for raising to the rank of formation, a new type section for the Sharawra Formation is located east of Wadi al Qalibah in Az Zubliyat area. Its base is at lat 28°14’00”N., long 37°53’30”E. and its top at lat 28°31’18”N., long 37°56’18”E. in Al Qalibah quadrangle.

RefeRence SecTion

Between Jibal Zufayyir and Jibal al Midafi; base at lat 28°28’00”N., long 37°16’42”E.; top at lat 28°51’18”N., long 37°06’12”E. in Tabuk quadrangle.

ThickneSS

314.3 meters in the type locality; 433 meters in the new type locality in Al Qalibah quadrangle; 510 meters thick in the reference section in Tabuk quadrangle.



conTAcTS

Upper

Disconformably overlain by Tawil Formation of Huj Group. The boundary is an erosional surface.

Lower

Disconformable above Qusaiba Formation. The unconformity is represented by a reworked layer containing lag-deposits of orthocone debris (fig. 30).

liThology

Sharawra Formation was subdivided into four formal members by Janjou and others (1996c), in ascending order: Jarish, Khanafriyah, Nayyal, and Zubliyat (fig. 37).

Figure 37. A composite type section of Sharawra Formation in Al Qalibah quadrangle (after Janjou and others, 1996c).



foSSilS

On the basis of acritarch evidence for at least the uppermost part of “Sharawra Member” in Kahf-1 well drilled in northwest Saudi Arabia, Al-Ruwaili (2000) suggested a Ludlovian (Late Silurian) age for Sharawra Formation. At the top of Jarish Member, Tentaculites qalibahensis (fig. 38), in association with the lamellibranch Modiolopsis sp., the gastropod Plectonotus sp., carapace fragments of the trilobite Brongniartella sp., and brachiopods of the species Hercotrema sp. cf. whiti were recorded. Trilobite fragments of Brongniartella janjoui and Brongniartella benderi were also recorded from several layers in Sharawra Formation (Janjou and others, 1996c).

Figure 38. Tentaculites qalibahensis recorded at the top of Jarish Member of Sharawra Formation (Janjou and others, 1996), Al Qalibah area.


Cruziana ichnofacies contained in Jarish Member is characteristic of a sublittoral domain and facies. Facies changes are generally very limited, indicating an environment that ranged from shallow to deep subtidal on a storm-dominated shelf. The deposits of Khanafriyah Member have the same sedimentary structures as Jarish Member and may have been deposited in middle upper-offshore to proximal upper-offshore. Nayyal Member is characterized by very intense bioturbation (trails and burrows) and its depositional environment ranged from middle to proximal upper-offshore (shallow-subtidal) to lower to middle shoreface, on a wave-dominated shelf. As in Nayyal Member, vertical facies changes in Zubliyat Member define a succession of regression and transgression cycles within a generally regressive trend that changed from middle-to-proximal upper-offshore to offshore/shore face (fig. 35).

Age

Helal (1964, 1968) and Al-Laboun (1982) suggested a Late Llandoverian (Early Silurian) age for “Sharawra member” and a hiatus during Late Silurian before deposition of e Early Devonian Tawil Formation of Huj Group in central and northwestern Arabia. Vaslet and others (1987) suggested a Silurian age for Sharawra member. Aoudah and Al Hajri (1994) reported a Late Wenlockian to Early Ludlovian (Middle to Late Silurian) age for this unit on the basis of subsurface date. Janjou and others (1996c) reported the same age on the basis of tentaculite and brachiopod fossils.

Jarish MemberJarish Member is named after Qian Jarish. The base of the type section is at lat 28°14’00”N., long 37°53’30”E.; the top is at lat 28°16’54”N., long 37°52’36”E. Its basal sandy lag deposit containing orthocone fragment disconformably overlies the topmost sandstone of Qusaiba Formation. It consists of greenish siltstone and sandstone containing fossil debris (trilobites, bivalves, orthocones, and small gastropods). Consisting of bedding-parallel and U-shaped burrows, bioturbation is well developed. The total thickness in the type section is 79 meters.

عضو جريش



Khanafriyah MemberKhanafriyah Member is named after Jibal al Khanafriyah. The base of the measured section is located at lat 28°16’54”N., long 37°52’36”E., and the top is at lat 28°17’24”N., long 37°52’48”E. This member consists of clayey siltstone and fine sandstone with ball and pillow structures, trails and burrows of Cruziana and Diplocraterion. Bivalves, orthocones, and trilobite fragments occur at the base of some beds. The sandstone becomes coarser and thicker near the top, where a sandstone bench forms a tabular surface capped by a hard-ground. The total thickness at the type locality is 110 meters.

Nayyal MemberNayyal Member is named after Wadi Nayyal. The base of the succession is located at lat 28°19’18”N., long 37°54’18”E., and the top is at lat 28°22’30”N., long 37°55’42”E. This member consists of pale sandstone and beige/green siltstone that becomes coarser and thicker upward. Thin beds of fine-grained sandstone have bases that are marked by red micro-conglomeratic clasts and dark-red phosphatic grains. The top is marked by rusty-brown, fine-grained sandstone. At several levels, lenticular sandstone intervals contain ball-and-pillow structures between a meter and several meters in size (fig. 39). The total thickness at the type section is 125 meters.

Figure 39. Ball and pillow stuctures in Nayyal members of Sharawra Formation (Janjou and others, 1996c) in Al Qalibah quadrangle.

Zubliyat Member Zubliyat Member is named after Az Zubliyat. The base is located at lat 28°30’16”N., long 37°56’05”E.; the top is at lat 28°31’13”N., long 37°58’20”E. This member consists of coarsening-upward sequences of pale to violet siltstone and fine-grained sandstone, overlain by fining-upward sequences of yellow/brown sandstone and sandy siltstone. A composite bench at the top is composed of rusty-brown, fine-grained sandstone with an erosional contact at the base marked by a zone of claystone pebbles. It is overlain and slightly channeled by a quartz pebble conglomerate at the base of Tawil Formation of Huj Group. The total thickness at the type locality is 119 meters.

عضو الخنافرية

نيال عضو

بلياتعضو ز



HUJ GROUP

مجموعة الهوج

Figure 40. Lithostratigraphic classification of Huj Group in Saudi Arabia. The geological time scale is from the International Stratigraphic Chart (2004).

Rock uniT

Huj Group

AuThoR

Janjou and others

yeAR

1996

definiTion

First defined by Janjou and others (1996c), Huj Group in northwestern Saudi Arabia includes Upper Silurian to Lower Carboniferous rocks (fig. 40).

TyPe locAliTy

Huj Group is exposed in Al Huj area, northeast of Al Qalibah town in northwestern Saudi Arabia (fig. 41).

ThickneSS

The total thickness is 774 meters in the type locality.

conTAcTS

Upper

The base of Berwath Formation was not penetrated in the type well. But on the basis of regional considerations, Jubah Formation of Huj Group was presumed to have been penetrated (Powers, 1968).

Lower

Disconformable with the underlying Sharawra Formation of Qalibah Group.

liThology

Huj Group comprises three formations, from oldest to youngest: Tawil, Jauf, and Jubah.

Age

The Huj Group is of Late Silurian to Early Carboniferous age.


See respective section for each formation.



Figure 41. Location map of the type and reference sections of formations and members of Huj Group in Saudi Arabia.

TAWil foRmATion

Rock uniT

Tawil Formation

AuThoR

Berg and others

yeAR

1944

oRigin of nAme

The name was derived from At Tawil escarpment in the northern Jabal Tawil escarpment, lat 29°20’N., long 39°30’E.

definiTion

The term “Tawil Formation” was used originally by Berg and others (1944) in an unpublished report, but it was first published as “Tawil sandstone” by Thralls and Hasson (1956). Steineke and others (1958) provided the first lithologic description based on sections measured near Al Jawf area (lat 29°20’N., long 39°30’E.). Bramkamp and others (1963), Powers and others (1966), and Powers (1968) revised the rank of the Tawil Formation to a member of the “Tabuk Formation”—the Tawil Member. Bahafzallah and others (1981a) and Al-Laboun (1982) regarded the Tawil Sandstone member as the lowermost member of the enlarged Jauf Formation. Vaslet and others (1987) suggested that these Early Devonian rocks constitute an entirely separate formation, mainly because of the probable disconformity at the base of Jauf Formation as defined by Powers (1968).

TyPe locAliTy

In the north-facing escarpment of At Tawil (lat 29º29’ N., long 39º30’ E).

RefeRence SecTion

The reference section is represented by two sections measured in Ash Sha’ib area: the lower at lat 28°59’39”N.,

متكون الطويل



long 37°02’36”E. and the upper at lat 28°59’28”N., long 32°06’42”E. A new and more complete type section was measured in Al Huj area, northwestern Saudi Arabia (Janjou and others, 1996c) between lat 28°33’30”N. to lat 28°36’24”N., and long 37°57’06”E. to long 38°03’36”E.

ThickneSS

200 meters in the type section, and 247 meters in Al Huj area.

conTAcTS

Upper

Disconformable; at the change from sandstones of Tawil Formation below to the siltstone, claystone and sandstone intercalated with fossiliferous limestones of the Jauf Formation above.

Lower

A significant unconformity separates Tawil Formation from the underlying Sharawra Formation of Qalibah Group (fig. 42).

Figure 42. Erosional disconformable contact between Qalibah Group (Sharawra Formation) and Huj Group (Tawil Formation) in Wadi Fajr, Qalibah quadrangle.

liThology

Tawil Formation consists of weathered, brown to dark, large-scale cross-bedded, medium- to coarse-grained sandstone with red shale interbeds, especially in the lower part. A coarse-grained to microconglomeratic sandstone containing quartz gravels forming lenticular bands is present at the base. The formation is subdivided into four members, from the base upwards: Samra, Ghuwar, Tufayhah, and Juraniyat members. (Janjou and others, 1996a , b, and c; Halawani, 2001) (fig. 43).

Age

No diagnostic fossils were recorded in the outcrops of Tawil Formation. Steineke and others (1958) suggested a Silurian age for this formation based on its position relative to the underlying Silurian rocks. Powers and others (1966) and Powers (1968) suggested an Early Devonian age for the Tawil member of the “Tabuk formation” based on its stratigraphic position. Helal (1964, 1968) assigned to it a Silurian age, due to the presence of traces of Cruziana. Bahafzallah and others (1981a) and Al-Laboun (1982) suggested an Early Devonian (Gedinnian) age based on microflora from drill-hole samples and on the Middle Devonian age of the overlying Jauf Formation. Janjou and others (1994) suggested a Late Silurian to Early Devonian age for Tawil Formation on the basis of the Lochkovian-Pragian age of the basal member of Jauf Formation and on the minimum age of the top of Sharawra Formation of Qalibah Group.


The environments evolved from a coastal plain to shallow channels in distal, braided streams characterized



Figure 43. Composite type section of Tawil Formation in Al Qalibah quadrangle (after Janjou and others, 1996c).

by the development of sand bars. Samra Member was deposited as migrating linguoid and transverse bars in a sandy, proximal, braided to straight river bed. The lower part of Ghuwar Member recorded a major transgressive event; the rest represents a cycle of regression and transgression. The sandstones of Tufayhah Member record a return to the alluvial environment of the braided-stream type. Toward the top of the unit, the sedimentary structures reflect renewed transgression. Juraniyat Member is characterized by tidal sand bars emplaced in a deltaic to estuarine complex, marking the Early Devonian transgression.



Samra MemberSamra Member is named after the Samra ‘Anz area in Al Qalibah quadrangle. It comprises fining- and thinning-upward successions consisting of medium- to coarse-grained sandstone. Some layers of fine-grained sandstone within red siltstone show current ripples. The type locality for this member is at lat 28°33’30”N., long 37°57’06”E. for its base and lat 28°33’42”N., long 37°58’00”E. for its top. The member is 29 meters thick. It disconformably overlies Zubliyat Member of Sharawra Formation of Qalibah Group.

Ghuwar MemberGhuwar Member was named after Al Ghuwar area in Al Qalibah quadrangle. The basal part of the member consists mainly of pink clayey-silty sandstone intercalated with tabular layers of coarse-grained sandstone. In some places, its base is a microconglomerate containing quartz gravel, overlain by a thick layer of medium-grained bioturbated sandstone with Tigillites (fig. 44). The base of the complete section (fig. 44) is at lat 28°33’42”N., long 37°58’00”E. and its top is at lat 28°33’54”N., long 37°59’54”E. It is 85 meters thick and conformably overlies Samra Member.

عضو سمرا

عضو الغوار

Figure 44. Tigillite-bearing sandstone in Ghuwar Member of Tawil Formation.

Tufayhah MemberTufayhah Member was named after Hufrat at Tufayhah area in Al Qalibah quadrangle. It is composed of two units. The lower unit consists of medium- to coarse-grained sandstone, with a microconglomerate at the base that contains quartz gravel. The top of this lower unit contains brown or red silty-clayey sandstone, several meters thick and with Tigillites. With coarse-grained basal part, the upper unit consists of medium- to coarse-grained sandstone with microconglomeratic beds towards the top. The base and top of the type locality are respectively located at lat 28°33’13”N., long 38°00’24”E. and lat 28°36’24”N., long 38°03’36”E. The member is 88 meters thick at the type locality and conformably overlies Ghuwar Member.

Juraniyat MemberJuraniyat Member was named after Al Juraniyat area in Al Qalibah quadrangle. It is composed of a homogeneous assemblage of purplish-red, fine-grained sandstone and siltstone. At the bottom, there is a microconglomerate containing small quartz pebbles above which lies a fine-grained sandstone. The type locality is north of Al Qalibah town, at lat 28°36’24”N., long 38°03’36”E. The member is 45 meters thick and conformably overlies Tufayhah Member.

عضو الجرانيات

عضو الطفيحة



JAuf foRmATion

Rock uniT

Jauf Formation

AuThoR

Berg and others

yeAR

1944

oRigin of nAme

Named after the town of Al Jawf

definiTion

Steineke and others (1958) originally proposed a type section for the Jauf Formation and first formally defined it at Al Jawf town. Powers and others (1966) and Powers (1968) amended it by adding a 27.1-m-thick calcareous shale and sansdstone unit at its top. Powers (1968) subdivided the formation into five informal lithologic members from base to top: Shaiba shale member, Qasr limestone member, Sabbat shale member, Hammamiyat limestone member, and the Transition zone member. Helal (1965) used this nomenclature. These five members were formally treated by Wallace and others (1995) and replaced the old name “Transitional zone” with “Murayr Member”. Janjou and others (1996c) followed the same subdivisions for the formation.

TyPe locAliTy

Berg and others (1944) described their section in Al Abd syncline, 4 km. west of Jabal al Abd and 15 km northwest Al Jawf. Steineke and others (1958) described the type locality in Sha’iba Gharisa at lat 29°53’05” N., long 39°37’08” E., about 25 km northwest of Qasr Marid (fort) at Al Jawf town.

RefeRence SecTion

Measured section near the northern edge of Al Qalibah quadrangle and on the west flank of a chain of hills known as Qur Mulayh, the base is at lat 28°58’49”N., long38°18’07”E., and the top is at lat 28°59’18”N., long 38º20’43”E.

ThickneSS

About 299.2 meters thick in the type locality near Al Jawf town (Powers, 1968) and about 307 meters thick in Al Huj area of Al Qalibah quadrangle (Janjou and others, 1996c).

conTAcTS

Upper

Disconformable with the overlying Jubah Formation.

Lower

Disconformable; located at the boundary between the sandstones of Tawil Formation and the siltstone, claystone and sandstone intercalated with fossiliferous limestones of Jauf Formation above.

liThology

The Jauf Formation is subdivided into five members; from bottom to top: Sha’iba, Qasr, Subbat, Hammamiyat, and Murayr (fig. 45).

Age

Devonian, probably lower to middle (Powers, 1968). Vaslet and others (1986b) assigned Jauf Formation in central Arabia to Early Devonian (Pragian - Emsian) although determinable fossils were lacking. On the basis of fish remains, Janjou and others (1996c) assigned to the Jauf Formation in northwestern Arabia a Lochkovian-Pragian to Early-Late Emsian (Late Silurian to ?Middle Devonian) age.


Based on its fossil content, Sha’iba Member was suggested to had been deposited in a shallow marine, near shore setting of low, local relief, in which clastic debris was dominant (Boucot and others, 1989). The carbonate nature of Qasr Member and its lithologic and faunal contents denote deposition in a shallow marine, subtidal environment in the photic zone while beds with fish remains may record brackish-water, estuarine conditions. Subbat Member contains bryozoa, corals, pelecypods, brachiopods, and fragments of fish bones in a mostly shaly facies. This suggests a shallow marine and near-shore environment similar to that of Sha’iba Member. The carbonate nature of Hammamyat Member and its faunal content, which include

متكون الجوف



Figure 45. Composite section of Jauf Formation in Al Qalibah quadrangle (after Janjou and others, 1996c).

corals, crinoids, bryozoa, brachiopods, pelecypods, and stromatolites, suggest a shallow marine environment, far from clastic supply. Murayr Member was deposited in a brackish and esturine environment. Its sandstone beds may represent beach deposits and estuarine channels (Boucot and others, 1989). None of the vertebrate taxons represented in the Jauf Formation is truly characteristic of Eifelian age.



Sha’iba MemberSha’iba Shale Member was named by Pocock and Kopp (1949) after the village of Ash Shuaybah, located south of An Nafud on the Baq‘a’-Turabah highway. It is 33.6 meters thick in the type locality. It is 25 meters thick at the reference section with base at lat 28°58’49”N., long 38°18’07”E. and top at lat 28°58’24”N., long 38°19’15”E. in Al Huj area, Al Qalibah quadrangle. It is composed of green shale, red siltstone, and subordinate impure limestone and sandstone. It disconformably overlies Juraniyat Member of Tawil Formation with a sharp contact but is conformably overlain by Qasr Member of Jauf Formation (fig. 46).

Figure 46. Jauf Formation overlying Tawil Formation in Al Huj area (Al Qalibah quadrangle).

Qasr MemberQasr Limestone Member was named after Qasr Marid in Dawmat al Jandal (Al Jawf town) by Berg and others (1944). The type locality is north of Qasr Marid. The reference section has base at lat 28°58’24”N., long 38°19’15”E. and top at lat 28°59’52”N., long 38°18’48”E., in Al Huj area, Al Qalibah quadrangle (Janjou and others, 1996c). It is 18.8 meters thick in the type locality and about 24 meters thick in the reference section. The Qasr Member is made up of variegated, silty claystone with a few intercalated beds of stromatolitic, dolomitic limestones and sandstones. Its boundary with the underlying Sha’iba Member and the overlying Subbat Member is conformable.

Subbat MemberSubbat Shale Member was named after Subbat al Wadi, east of Al Jawf by Berg and others (1944). Its type locality lies around the gardens of Subbat al Wadi, but a reference section is located between lat 28°59’52”N. to lat 28°59’40”N., and long 38°18’48”E. to long 38°19’04”E. in Al Huj area. It is 113.4 meters thick in the type locality and up to 94 meters in the reference section, where it consists of claystone and micaceous siltstone, with intercalated fine to medium-grained sandstone. The contacts with the underlying Qasr Member and overlying Hammamiyat Member of Jauf Formation are conformable.

Hammamiyat Member Hammamiyat Limestone Member was first named by Boucot and others (1989). However, the formal term was introduced by Helal (1965) in outcrops at Jabal Hammamiyat. Its type locality is in Wadi al Murayr along the northern rim of Al Jawf basin, where it is 106.3 meters thick. It is up to 88 meters thick in the reference section located at lat 28°58’06”N., long 38°20’35”E. in the Al Huj area in Al Qalibah quadrangle.

عضو قصر

عضو حماميات

عضو الشعيبة

عضو صبات



It consists of thin-bedded, tan limestone with local gray-green, silty shale beds. The upper and lower contacts are conformable with the Murayr and Subbat members respectively.

Murayr Member Pocock and Kopp (1949) defined a transitional zone above the Hammamiyat Member and below the obsolete Sakaka Sandstone. It was formally named by Wallace and others (1997) after Wadi al Murayr in Ash Shuwayhitiyah quadrangle, where the type locality is at lat 30°04’22”N., long 39°56’16”E. and where it is 33 meters thick. It is up to 76 meters thick in the reference section located at lat 28°59’21”N., long 38°20’52”E. in the Al Huj area. It consists of reddish to grayish-brown weathered sandstone, light-colored shale and siltstone, and thin beds of platy, impure limestone and dolomite. This level is transitional between the carbonates of Jauf Formation below and sandstones of e Jubah Formation above. Secondary gypsum is common. One thin bed of chert is recorded. It contains plant remains of Prototaxites laganii Dawson (Bahafzallah and others, 1981a, 1981b).

Jubah FormationRock uniT

Jubah Formation

AuThoR

Meissner and others

yeAR

1989

oRigin of nAme

Named after the town of Jawbah

definiTion

This sandstone unit was first named as “Sakaka Sandstone” by Bramkamp and others (1963). The Jubah Formation includes rocks that have had a controversial stratigraphic history: variably dated as Paleozoic through Cretaceous, and variably named “Sakaka”, “Wasia”, and “Wasia-Riyadh”. Bahafzallah and others (1981b), Powers and others (1966) referred to these beds as the “Sakaka Sandstone”. Powers (1968) called these sandstones “Wasia Formation”. Meissner and others (1989) named these sandstones as “Al Jubah Formation” and abandoned the use of “Sakaka Sandstone”.

TyPe locAliTy

The formation has not been given a formal type section. Only an approximate thickness of about 220 meters was estimated from the geographic extent and dip angle. This unit is exposed between the Jal al Jawbah al Gharbi escarpment in the west and the Jal al Jawbah ash Sharqi escarpment in the east, near Sakaka.

ThickneSS

The thickness of Jubah Formation has not been measured accurately because no outcrop showing a total vertical section has been found and it has not been positively identified in drill holes. However, Meissner and others (1989) reported that Jubah Formation is 220 meters thick. In Al Jawf quadrangle, it is at least 250 meters thick in some places (Wallace and others, 1997). In the subsurface, 410 meters were estimated to belong to that unit in the drill-hole S-462 in Ash Shuwayhitiyah quadrangle, although it did not reach the base of Jubah Formation (Meissner and others, 1989).

liThology

Sandstone, white, pale brown, or pale gray to greenish gray, weathered to reddish brown to brownish gray, fine to medium grained, well-sorted, and mostly thin- to medium-bedded. Mica flakes occur along bedding planes. It is calcareous and locally shaly, and contains kaolin. It is interbedded with silty and sandy shale. A few clay beds occur in the upper part of the formation, where casts and plant debris are associated with thin-bedded, shaly sandstone (fig. 47).

conTAcTS

Upper

The upper boundary of Jubah Formation is at the top of sandstones with Prototaxites and fossil fish bones. The sandstones above and below the contact are similar in composition and bedding character. This is a disconformable contact with the overlying Wasia Formation (Wallace and others, 1997).

متكون الجوبة

يرعضو مر



Figure 47. Jubah Formation in Al Jawf quadrangle (from Meissner and others, 1989).

Lower

It is disconformable (Janjou and others, 1996c) and conformably underlain by and with a sharp contact with Murayr Member of Jauf Formation (Meissner and others, 1989).

Age

The most important fossil in Jubah Formation is the tree-like fungus, Prototaxites sp., which is recorded only from Devonian. Plates and bones of acanthodian and anthrodire fresh-water fishes were found near the top of the unit.Meissner and others (1989) and Wallace and others (1998) reported Middle to Upper Devonian (Givetian to Frasnian) age from spore and pollen assemblages.


Cross-bedding and fish remains suggest that Jubah Formation was deposited in brackish water in delta channels or in fluvial environment near the strandline. Local fresh water lakes formed on delta plains. The different facies indicate a continental fluvial environment. The large-scale, inclined, trough cross-stratification of sandstone reflects a high-energy hydrodynamic system in which fluviatile components became predominant over tidal ones. These facies indicate a fluvial to estuarine depositional environment.

RemARkS (JubAh foRmATion)The available data on Jubah Formation are incomplete. More detailed fieldwork will be necessary to determine the contact relations with underlying and overlying rocks, and to determine lateral facies changes relevant to its potential as reservoir rock.



BURAYDAH GROUP

مجموعة بريدة

Figure 48. Lithostratigraphic classification of Buraydah Group in Saudi Arabia. The geological time scale is from the International Stratigraphic Chart (2004).

Rock uniT

Buraydah Group

AuThoR

Vaslet and others

yeAR

1988

oRigin of nAme

The name was derived after Buraydah town, Al Qasim region, central Arabia.

definiTion

“Buraydah Group” was introduced by Vaslet and others (1988) to include, in ascending order, Berwath, Unayzah, Khuff, Sudair, Jilh, and Minjur formations. Berwath, Unayzah, and Khuff (fig. 48) formations are Paleozoic in age and are included in this volume. Khuff, Sudair, Jilh, and Minjur formations are Mesozoic in age and will be covered in the Mesozoic part of this special publication series. Al-Laboun (1987, 1988) named the basal part of Khuff Formation as Unayzah Formation, which he considered as the lowermost formation of Buraydah Group. On the basis of subsurface lithostratigraphic data, the Saudi Stratigraphic Committee included Berwath Formation in Buraydah Group.

TyPe locAliTy

Several composite sections (fig. 49) occur in Shaqra quadrangle (Vaslet and others, 1988).

ThickneSS

The Paleozoic part of Buraydah Group is approximately 1,032 meters thick.

liThology

It is composed mostly of sandstones with minor red to green shale and limestone.



Figure 49. Location map of type and reference sections of formations and members of Buraydah Group.

conTAcTS

Upper

Disconformable below Marrat Formation of Shaqra Group.

Lower

Nonconformable over basement rocks and disconformable over Jubah Formation of Huj Group.

Age

Carboniferous to Triassic.

beRWATh foRmATion

Rock uniT

Berwath Formation

AuThoR

Hemer and Powers

yeAR

1968

oRigin of nAme

Named after Wadi Aba ar Ruwath.

definiTion

The formation is only identified in subsurface sections and is not exposed at the surface. Al-Laboun (1982) also described this formation from the subsurface in the Widyan basin of northern Arabia.

TyPe locAliTy

Described from well ST-8, located at lat 29°53′2”N., long 41°54′44”E. The formation is at well depths between 1,328.3 and 1,518.5 meters.

ThickneSS

The penetrated part is 190.2 meters thick. The base of the formation was not reached.



liThology

Fine- to coarse- grained, argillaceous sandstone; common interbeds of siltstone, some shale.

conTAcTS

Upper

Disconformable below Unayzah Formation, placed at the change from sandstone with Carboniferous microflora below, to the varicolored sandy shale with Late Carboniferous microflora above.

Lower

Not penetrated in the type well, but presumed, on regional considerations, to be underlain by Jauf Formation of Huj Group (Powers, 1968).

foSSilS

Well preserved microspores occur at several levels of the formation.

Age

Early and Late Carboniferous (Mississippian-Pennsylvanian).


Berwath Formation may have been deposited in a non-marine environment based on the presence of abundant spores of vascular plants, its varicolored clastic sediments, and absence of definite marine sediments.

RemARkS (beRWATh foRmATion)Due to the limitations of subsurface information on this formation, more data about its lithology, boundaries, fauna, and age are needed.

unAyzAh foRmATion

Rock uniT

Unayzah Formation

AuThoR

Al-Laboun (Unpublished PhD. thesis)

yeAR

1982

oRigin of nAme

It was named after the town of Unayzah in Al Qasim region.

definiTion

This Unayzah definition includes the mixed carbonate and clastic succession at the Unayzah town site and is applied to approximately the same rocks as Unayzah member of Khuff Formation by Delfour and others (1982), and to the rocks in the basal part of Khuff Formation as defined by Steineke and others (1958) and Powers (1966). The section at Unayzah town had previously been mapped by Bramkamp and others (1963) as Khuff Formation and referred to as Khuff Formation by Lemoigne (1978, 1981).

Delfour and others (1982) first published the name “Unayzah” as the lowermost member of Khuff Formation. It is best represented near the town of Unayzah where the member is 35 m thick, and consists of emerald-green, purplish-red, or varicolored silty gypsiferous claystone, interbedded in its lower part by yellowish or gray silty dolomite and locally white fine-grained cross-bedded sandstone. The section unconformably overlies Saq Sandstone and is conformably overlain by Huqayl member of Khuff Formation. The Unayzah member definition of Delfour and others (1982) maintains the integrity of the formal definition of Khuff Formation (Steineke and others 1958; Powers and others 1966). It is applied to approximately the same rocks as Unayzah Formation of Al-Laboun (1982).

The name “Unayzah Formation” was first described, measured and mapped by Al-Laboun (1982) to include the clastic section, subadjacent to the Khuff carbonates in the area of Al-Qasim. This unit of sandstone and varicolored shales at the base of Khuff Formation was informally referred to as “pre-Khuff Clastics” by Aramco geologists (Bawsher and others,1972). Sharief (1982) referred to the Unayzah shale in a correlation chart, but did not publish additional information. Delfour and others (1982) divided Khuff Formation into five informal members, with the basal member referred to as the Unayzah member. El-Khayal and Wagner (1983) informally proposed the name “Unayzah shale” for the beds unconformably overlain by the Khuff limestone and underlain by the pre-Khuff sandstones. Al-Laboun (1987) formally proposed the name

ةزيمتكون عن



Unayzah Formation.

Unayzah Formation was first described, measured, and mapped by Al-Laboun (1982) to include the clastic section subjacent to the Khuff carbonates in the area of Al Qasim. This unit of sandstones and varicolored shales at the base of the Khuff Formation was informally referred to as “pre-Khuff Clastics” by Bawsher and others (1972). Sharief (1982) referred to the Unayzah shale in a correlation chart but did not publish additional information. Delfour and others (1982) divided the Khuff Formation into five informal members, with the basal member referred to as “Unayzah member”. El-Khayal (1983) informally proposed the term Unayzah shale for the beds unconformably overlain by the Khuff limestones and underlain by the pre-Khuff sandstones. Al-Laboun (1987) formally proposed the term “Unayzah Formation”.

TyPe SecTion

Composite section composed of three sections, along the main road between Unayzah and Buraydah towns. The type section is a composite of three sections located at lat 26º05’10”N., long 43º59’24” E. and measured along the Unayzah-Buraydah main road and in the escarpment of that road 200 meters north of the microwave communication tower.

RefeRence SecTionS

At Wadi Shaqra, Qusayba depression, Al Qasim region, lat 26°52’17.6”N, long 43°36’21.2”E. Ferguson and Chambers (1991) proposed a subsurface reference section in well Hawtah-1 (lat 22°54’38.76”N., long 46°49’40.5”E.).

ThickneSS

In the type section at Unayzah town, it is 32.2 meters thick. In the reference section in the Qusayba depression, it is 34 meters thick.

liThology

Alternating thin-bedded sandstone, siltstone, shale, marl, and minor limestone and anhydrite; varicolored silty, gypsiferous claystone, interbedded in its lower part with yellowish to gray, silty dolomite; locally, white fine-grained sandstone with cross bedding in the middle; dolomite beds are slumped and tinted red by iron oxides and manganese at the top (fig 50). In the subsurface, the Unayzah Formation is subdivided into three informal members A, B, and C, arranged from top to bottom.

conTAcTS

Upper

Disconformably overlain by Ash Shiqqah Member of Khuff Formation. Its upper contact with Khuff Formation was placed at the base of the first massive rubbly weathered fine-grained limestone. El Khayal and Wagner (1985) also recognized a sedimentologic break in the Upper Permian section, and used it as the boundary between Unayzah and Khuff formations.

Lower

Angular unconformity over Carboniferous to Cambrian rocks in the northern part of Widyan basin northern Arabia and nonconformable over Precambrian rocks in central Saudi Arabia. Well ST-8 penetrated Berwath Formation but no data about the presence of the Unayzah Formation was reported. The base of the formation is defined by the well-developed Hercynian unconformity and is not exposed at the type locality.

foSSilS

Unayzah Formation includes fossil plants in outcrops (El-Khayal and others, 1980) and palynomorphs in subsurface samples (Al-Laboun, 1986).

Age

El-Khayal and others (1980) described fossil plants including species of genera Plecopteris, Lobatannularia, Annularia, Cordites, Validopteris and Marattiopsis from the lower part of Unayzah Formation. This assemblage denotes a Late Carboniferous (Pennsylvanian)-Early Permian age. The formation was dated as Late Carboniferous (Pennsylvanian) to Middle Permian (Al-Laboun, 1984, 1986), which was subsequently revised to Late Carboniferous (Pennsylvanian) to Early Permian age (Al-Laboun, 1987). In terms of age, El Khayal and Wagner (1985) distinguished an Early Late Permian (Kazanian) date for the Unayzah plant bed (Unayzah Formation) from later Permian (Tatarian) date for the basal mixed carbonate, shale and sandstone portion of Khuff Formation.


The cyclic nature of the deposits of Unayzah Formation suggests a fluctuating sea level. The basal Unayzah



Figure 50. Type section of Unayzah Formation (Buraydah Group) in Unayzah town, Qasim region (Al-Laboun, 1987).

rocks were deposited over the sub-Unayzah unconformity and reflect swampy or delta-plain conditions. This was followed by shallow-marine deposits with shallow-marine mollusks. The upper part of Unayzah Formation includes forest beds and ripple marks with lenticular sandstones.

RemARkS (unAyzAh foRmATion)The lower part of Unayzah Formation was penetrated by subsurface wells. Subsequent studies may lead to further changes in the age of this problematic and controversial formation.

This definition places the contact between these two formations at the base of the transgressive mixed carbonat-siliclastic unit, which has commonly been included in Unayzah Formation. Senalp and Duaiji



(2001) suggested that this lower unit, which was called “Basal Khuff Clastics”, should be formally defined as a new member of the Khuff Formation. They called it “Ash Shiqqah Member” after its type section in the north of Buraydah town, in Qasim region (Senalp and Al-Duaiji, 1995).

khuff foRmATion

Rock uniT

Khuff Formation

AuThoR

Steineke

yeAR

1937

oRigin of nAme

It was named after ‘Ain Khuff near the old Ar Riyad-Jiddah road.

definiTion

Steineke (1937), in an unpublished report, originally defined the Khuff as the lowest member of Mustawi Formation (obsolete name). Steineke and Bramkamp (1952) first published the “Khuff limestone”; later, Steineke and others (1958) introduced “Khuff Formation” as a formal name. This formal nomenclature was followed by Powers and others (1966) and Powers (1968). Delfour and others (1982) subdivided the formation into five members.

TyPe SecTion

Measured along a traverse southwest from lat 24°58′36”N., long 44°41′48”E. to lat 24°53′12” N., long 44°32′48”E., near the old Ar Riyad-Jiddah road.

RefeRence SecTion

Khuff Formation is exposed between Wadi ar Rayn at lat 23°32′54”N., long 45°34′30”E., and Jabal ath Thuwayr at lat 23°43′00”N., long 45°42′00”E. (Powers and others, 1966).

ThickneSS

The thickness is 177.2 meters at the type locality and 192 meters south of Ad Dawadimi area.

conTAcTS

Lower

Disconformable where it is underlain by older Phanerozoic units (Unayzah Formation or older), and nonconformable with Precambrian basement rocks.

Upper

Disconformable; very sharp contact with the overlying Sudair Formation of Buraydah Group.

liThology

Khuff Formation is composed mainly of limestone and dolomite intercalated with dominantly shale at the middle part (fig. 51). It is subdivided into five members, from oldest to youngest: Ash Shiqqah (which replaced the obsolete “Unayzah member” of Delfour and others (1982), Huqayl, Duhaysan, Midhnab, and Khartam (Vaslet and others, 2005).

dePoSiTionAl enviRonmenTS

A sabkhah environment was suggested for Ash Shiqqah Member, which marks the progressive passage from continental domain to lagoonal environment. This member exhibits very different facies north and south of the central Arabian Arch. North of the Arch, clastic coastal plain and salt-marsh environments dominated. South of the Arch, brackish to evaporitic facies, interpreted as saline deposits, correspond to the flooding of a former coastal plain (Vaslet and others, 2005).

An inter- to sub-tidal sabkhah with a marine transgressive phase towards the top is the environment suggested for Huqayl Member. It represents an intertidal domain with biocalcarenite and locally intraclastic tidal channels (Vaslet and others, 2005). This marine interval represents the first transgressive deposits over the Central Arabian Arch (Le Nindre and others, 1990). These carbonate beds are widespread and continuous. They represent a sharp break between heterogeneous facies below and homogenous marine succession above (fig.51).

Duhaysan Member is marked by abundant and various open-marine fauna consisting of bryozoans, algae,

متكون الخف



Figure 51. Composite type section of Khuff Formation (from Vaslet and others, 2005).

echinoderms, brachiopods, gastropods, bactritids, and cephalopods. Thus a subtidal (littoral to confined) environment is suggested for that member. Vaslet and others (2005), reported an erosional and transgressive marine wedge at the base of Duhaysan Member.

Intertidal to supratidal starting from littoral, and then an extensive well-protected shelf to lacustrine or supratidal is the environment suggested for Midhnab Member. A clear, regressive trend up to continental deposits in the upper part of Midhnab Member was observed by Vaslet and others (2005).

Sub- to intertidal from bottom to top (subtidal to littoral-tidal to intertidal) is the environment interpreted for Khartam Member. Vaslet and others (2005) reported a terminal Permian marine incursion for the lower



Khartam Member. It started with renewed open-marine influence followed by a rapid transgression seen or present just a few meters above major break between Midhnab and Khartam members.

Age

Steineke and others (1958) and Powers and others (1966) suggested a Late Permian age for the Khuff Formation based on microfaunal analysis. Biostudies of the Khuff Formation led Delfour and others (1982) to suggest a Middle to Late Permian age for the Huqayl and Duhaysan members and accurate Upper Permian Murghabian to Djulfian ages for Midhnab and Khartam Members. Manivit and others (1985) assigned a Djulfian (Late Permian) to Scythian (Early Triassic) age to the formation, based on foraminifers and pollen in the Huqayl Member and a serpulid in the Khartam Member. Khuff samples from Dammam Well-43 yielded Colaniella parva (Colani) of early Late Permian age.

Ash Shiqqah Member may be of Middle Permian (Capitanian) age (Vachard and others, 2002; Vaslet and others, 2005), while the Huqayl Member is of Late Permian age (Delfour and others, 1982; Vaslet and others, 1983 and Manivit and others, 1985, Vachard and others (2002, 2005), and Vaslet and others (2005).

Duhaysan Member is of Middle to Late Permian age (Delfour and others, 1982; Vaslet and others, 1983). Midhnab Member is of Late Permian age (Murghabian to Djulfian) as determined by Delfour and others (1982) and of Djulfian age according to Vaslet and others (1983). Manivit and others (1985) dated this member as uppermost Late Permian (Dorashamian). Vaslet and others (2005) gave a Late Permian (Changhsingian-Dorashamian) age.

Khartam Member was initially assigned to Late Permian (Murghabian to Djulfian) by Delfour and others (1982 and to the Djulfian by Vaslet and others (1983). However, Manivit and others (1985) dated this member as Early Triassic (Scythian) and Vaslet and others (1985) re-assigned a Late Permian age to the uppermost of the member. Vachard and others (2002, 2005) believed that lower Khartam Member is late Late Permian (late Changhsingian) in age, while upper Khartam Member contains fossils that are particularly abundant in Early Triassic rocks of Neo-Tethyan areas.

RemARkS (khuff foRmATion)- Prof. Abdulaziz Ibn Laboun suggests that Ash Shiqqah Member to be upper member of Unayzah

Formation (oral communication).

- In their paper in The Saudi Aramco Journal of Technology, Senalp and Al-Duaiji (2001) raised Ash Siqqah member to formation status.

These ideas will be discussed and resolved by the Saudi Stratigraphic Committee and will be published in the second edition of this publication.

Ash Shiqqah MemberFirst defined by Senalp and Al-Duaiji (1995), the name was derived from north of Al Shiqqah at west of Buraydah-Ha’il highway. The type section is located at lat 26°22’44.6”N.. long 43°54’13.8”E. Vaslet and others (2005) replaced Unayzah Member of Delfour and others (1992) with Ash Shiqqah Member. It is 35 meters thick at the reference section and 20 meters at the type locality. The succession consists of four sub-units, in ascending order:

1. Varicolored, silty claystone with secondary gypsum in the lower part and yellowish/gray silty dolomite; 10.5 meters thick.

2. White, fine-grained, cross-bedded sandstone; 2.5 meters thick.

3. Red and green, silty claystone interbedded with pinkish/yellowish dolomite; locally slumped and tinted red by iron oxides; 15 meters thick.

4. Clayey, locally finely bioclastic dolomite with beige patina, algal laminites and fentral fabrics; 7 meters thick.

The member lies disconformably above the Unayzah Formation and conformably below Huqayl Member of Khuff Formation.

Huqayl MemberThe type section of Huqayl Member was measured by Delfour and others (1982) at Safra Huqayl in Ad Dawadimi quadrangle, between lat 24°44’25”N., long 44°39’08”E., and lat 24°45’37”N., long 44°39’15”E.

عضو حقيل



by Delfour and others (1982), where it is 40 meters thick. It consists of two successions. The lower succession has bluish, silty bioclastic dolomite with a gravelly dolomitic bed at the base; green or yellow, gypsiferous claystone in the middle, and blue-gray, blocky, fine-grained, laminated dolomite at the top. The upper succession is composed of bluish, granular, bioclastic dolomite and fine-grained, laminated dolomite at the base. Blue-gray, blocky clayey dolomite, terminating in a layer of bioturbation burrows and algal mats, lies at the top. The lower and upper contacts are conformable with the Ash Shiqqah and Duhaysan Members respectively.

Duhaysan MemberThe type section of Duhaysan Member was measured to the east of Jabal Duhaysan, between lat 24°40’35”N., long 44°45’58”E. and lat 24°40’37”N., long 44°47’46”E. (Delfour and others, 1982), where it is 20 meters thick. The member consists of three lithofacies, from base to top: gray dolomitic limestone with pebbles overlain by bioclastic pelletoid dolomite, white gypsiferous dolomitic clay, and gray, flaggy limestone with bioturbation at the top. The lower and upper contacts are conformable with Huqayl and Midhnab Members respectively.

Midhnab MemberThe type section of Midhnab Member was measured by Delfour and others (1982) along Wadi Maghib near Khuff town, between lat 24°55’28”N., long 44°36’47”E. to lat 24°58’20”N., long 44°638’19”E. by Delfour and others (1982), where it is 60 meters thick. The name was derived from Wadi Midhnab. The member is composed of three lithofacies: conglomeratic, lithoclastic dolomitic limestone in the lower part; alternating laminated, clayey dolomite and yellow to blue, gypsiferous, dolomitic claystone in the middle; and light gray, lacustrine limestone in the upper part. Lower and upper contacts are conformable with Khartam and Duhaysan Members respectively.

Khartam MemberThe type section of Khartam Member was measured by Delfour and others (1982) from lat 24°58’20”N., long 44°38’19”E. to lat 24°59’52”N., long 44°40’42”E., northeast of Khuff town, where it is 37 meters thick. The name was derived from Khartam escarpment in Al Qasim region. The member consists of two lithologic successions. The lower succession has bioclastic limestone and blue, laminated, dolomitic claystone at the base, yellowish dolomitic claystone in the middle, and ferruginous, bioclastic dolomite at the top. The upper succession consists of beige, powdery, calcitized dolomite and flaggy, microcrystalline limestone with stromatolitic patches, overlain by interlayered silty claystone, flaggy dolomite, and lumachelle dolomite with an oolitic limestone bed and an uppermost claystone at the top. The lower and upper contacts are conformable with the Midhnab Member of Khuff Formation and Sudair Formation respectively.

عضو دحيسان

بنمذالعضو

طمعضو خر



REFERENCES Al Hajri, S.A. and Owens, B., 2000, Stratigraphic Palynology of the Paleozoic of Saudi Arabia, results

of a joint study between Saudi Arabian Oil Company (Saudi Aramco) and the Commission International de Microflore du Paleozoique (CIMP), Special GeoArabia Publication 1 by Gulf PetroLink, 231p.

Al-Hajri, S., 1995, Biostratigraphy of the Ordovician Chitinozoa of northwestern Saudi Arabia: Review of palaeobotany and palynology, no. 89, pp. 27-48.

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3+$1(52=2,& 675$7,*5$3+< 2) 6$8', $5$%,$ 3$57 … · Berwath Formation ... Siq Formation is exposed...

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Transcript of 3+$1(52=2,& 675$7,*5$3+< 2) 6$8', $5$%,$ 3$57 … · Berwath Formation ... Siq Formation is exposed...