STRUCTURE OF THE CHENAREH ANTICLINE

IN LURESTAN, ZAGROS:

ROLE OF GRAVITY IN FOLDING STYLE

Master en Geología Experimental, Universitat de BarcelonaGroup of Dynamics of the Lithosphere (GDL), Institut de Ciències de la Terra “Jaume Almera”, CSIC

Barcelona, 2007

Mohammad Hasem Hasan Goodarzi

Universidad de Barcelona Facultat de Geología (UB)

Consejo Superior de Investigaciones Científicas (CSIC)

Institut de Ciències de la Terra “Jaume Almera” Departament d’ Estructura i Dinàmica de la Terra

Master en Geología Experimental de la Universitat de Barcelona

STRUCTURE OF THE CHENAREH ANTICLINE IN LURESTAN, ZAGROS:

ROLE OF GRAVITY IN FOLDING STYLE

Mohammad Hasem Hasan Goodarzi

Master's degree (M. Sc.)

Director: Tutor:

Jaume Vergés Masip Francesc Sàbat

Barcelona, March, 2007

4

The research reported in this Master is a contribution of the Group of Dynamics of the Lithosphere (GDL) Department of Structure and Dynamics of the Earth Institute of Earth Sciences “Jaume Almera”, CSIC

5

ACKNOWLEDGMENTS

This study has been financed by a collaborative project between the NIOC

(NATIONAL IRANIAN OIL COMPANY), the Institute of Earth Sciences “Jaume

Almera”, CSIC of Barcelona (Spain) and NORSK HYDRO (HYDRO ZAGROS)

Tehran Iran. I would like acknowledgment the talents and efforts the numerous

individual who have contributed in this study. I am especially indebted to the

Exploration Directorate of National Iranian Oil Company (NIOC) for providing the data

set and field trip facilities. Especial thanks are due to: M. Mohaddes, M.

Zadehmohammadi and A. Ahmadnia for their support of this project over many years. ).

. I am also indebted to the people in the Group of Dynamics of Lithosphere and

especially to Jaume Vergés for his guidance on many and varied aspects in this study…

6

7

ABSTRACT

This structural study explores the geometry of three anticlines in the Pusht-e Kuh Arc

in Zagros, Iran. These are the Chenareh, Kush-Ab and Rit anticlines near the SE

boundary of the tectonic arc. However, this work will mostly concentrate along the

Chenareh anticline. This study presents a combination of field work, seismic

interpretation of old seismic lines and geological corss-section construction to better

define the structure of these anticlines at depth that could represent new targets for HC

exploration.

The nice whale back Chenareh anticline is a NW-SE oriented anticline with 65 km of

length and 8 km of width at the level of Asmari Formation. The anticline is doubly

plunging below the evaporites of the Gachsaran Formation. The anticline can be divided

in three longitudinal segments depending on their different structure: a) the NW

segment very well preserved with little normal faulting; b) the central part defined by

the gravitational collapse of the SW flank of the anticline; and c) the SE segment

showing the oldest rocks at the level of Bangestan Group that seems to be rotated to the

SW.

Using depth projection methods and constant thickness the Chenareh anticline shows

the main detachment level at a depth corresponding to the evaporites of the Dashtak

Formation of Triassic age. This level also corresponds to the main intermediate

detachment in the Kabir Kuh anticline (the next to the SW). Shortening in these cross-

sections give and amount of 7.2% in compression and extension of the SW flank in the

central segment gives 1.06%.

The position of the Chenareh anticline and of its SE termination is favourable for HC

exploration since it plunges beneath the Dezful Embayment from where most of the HC

generate and migrate upwards. This is demonstrated by the occurrence of abundant oil

seeps along the contact between Asmari and Gachsaran Formations along the Bala Rud

Fault near the SE termination of the Chenareh anticline.

In NIOC we benefited from this work because we better understand the need for

good constrained geological cross-sections, as well as combined with other

complementary disciplines of geosciences, to better define and constrain the potential

for HC of other areas outside the Dezful Embayment.

8

9

TABLE OF CONTENTS

ACKNOWLEDGMENTS.............................................................................................. 5

TABLE OF CONTENTS ............................................................................................... 9

FOREWORDS / OBJECTIVE OF RESEARCH...................................................... 11

Flow work and methodology...................................................................................... 12

1. INTRODUCTION .................................................................................................... 15

1.1. Southern Iran and Zagros fold-thrust belt ........................................................... 15 1.2. Timing of tectonic events .................................................................................... 16 1.3. Mechanical stratigraphy of Lurestan Province.................................................... 17

II. SHORT REVIEW OF PREVIOUS WORK ON DETACHMENT FOLDING 23

2.1. Detachments / rounded hinges and axial surfaces ............................................... 25 2.2. Kinematics of detachment folding....................................................................... 25 2.3. The structure of the Competent Group (Lower Structure): folding by multiple stratigraphic units in Lurestan Province with special view on Chenareh anticline .... 28

III. THE CHENAREH ANTICLINE ......................................................................... 29

3.1. Location of Chenareh anticline in Zagros fold-thrust belt .................................. 29 Previous work on the Chenareh anticline ................................................................... 30 3.3. Geometry of Chenareh anticline.......................................................................... 31 3.4. Chenareh cross-section I...................................................................................... 35

3.4.1. First version of cross-section I ..................................................................... 35 3.4.2. Second version of cross-section I ................................................................. 38 3.4.3. Shortening along cross-section I .................................................................. 40

3.5. Chenareh cross-section II .................................................................................... 41 3.6. Chenareh cross-section III ................................................................................... 45

IV. ROLE OF GRAVITY IN PRESENT GEOMETRY OF CHENAREH

ANTICLINE ................................................................................................................. 50

V. CONCLUSIONS...................................................................................................... 58

REFERENCES ............................................................................................................. 60

10

11

FOREWORDS / OBJECTIVE OF RESEARCH

The Zagros Mountains of Southwest of Iran are one of the most prolific fold-and

thrust belts in the World. They contain 8.6% of oil and 15% of gas proven World

reserves.

The occurrences of sediments and traps that generated and preserved hydrocarbons

are linked to the history of the Arabian plate margin evolution. The thick sedimentary

cover of the Zagros orogenic belt records all the stages of evolution of the basin,

evolving from a rift and passive continental shelf to a foreland basin associated to

several stages of deformation related with ophiolitic obduction and continental collision.

The change in hydrocarbon exploration towards deeper targets associated to higher

economical costs requires a better understanding of the structure of the traps at depth.

Seismic and well data acquired during the last decade have shown that the structural

configuration of the deeper objectives often do not match with shallower ones. Some of

the wells located on or near the crest of apparently undisturbed anticlines at surficial

levels went out of the target at depth.

One way to better understand the varying geometry of these anticlines at depth is to

construct accurate sections using available data by means of an integration of different

data bases (field data, geological maps, seismic lines, and oil wells).

The Chenareh anticline is a nicely outcropping fold, which is located in the

Southeastern border of Pusht-e Kuh Arc in the Zagros Mountains in Iran. This anticline

is more than 65 Km long and displays a mean width of about 8 Km. The northwestern

termination changes its name to Kialoo anticline. Its geometry is very regular in

geological map whereas it changes the geometry along the fold strike. The anticline is

double plunging in both extremities below the evaporites of the Gachsaran.

The Chenareh anticline shows a nicely preserved geometry in its NW half and a

rather disturbed geometry in its SE half. This segment of the anticline is disturbed by a

set of normal faults in the proximity of the Mountain Frontal Flexure along the Bala

Rud Fault.

The Khush Ab and Rit anticlines are located to the north of the Chenareh anticline

and these will be included in this work as they show a continuous folded structure.

12

The main objectives of this work are:

1) to determine the geometry of the Chenareh anticline as well as of its northern

Khush-Ab and Rit anticlines

2) to determine the relationships between these anticlines and the Mountain

Frontal Flexure, especially along the Bala Rud Fault

3) to understand the role of the gravity in the SE termination of the Chenareh

anticline

Flow work and methodology

Different methods of study and data bases have been used to accomplish the

objectives of this work:

1) available previous studies, topographic maps, geologic maps, satellite images,

geological cross-sections, oil and gas exploration wells included in an ArcGis project;

2) 2 weeks of field work to better understand key points of the structure of the

anticlines;

3) 4 structural cross-sections were constructed across the Chenareh and Rit anticlines

using about 100 km of old 2D seismic lines and 10 wells by means of drawing programs

like Canvas and cross-section construction programs like 2D Move.

The cross-sections are located perpendicular to the fold axis and close or following

existing seismic lines. In addition, unpublished well data were also used to interpret the

structures at depth. Seismic quality was frequently poor in study area. The oldest rocks

cropping out in the core of the anticline are Upper Cretaceous.

The study of few seismic lines across both the Chenareh anticline and Khush-Ab

anticline to the N shows the implication of two main geological factors that control the

geometry and structure of these anticlines: a) the deep structure of the Mountain Frontal

Flexure (MFF); and b) the rapid pinch-out of the Amiran, Taleh Zang and Kash Kan

Formations along the axis of the Chenareh anticline.

The coupled Chenareh and Khush-Ab anticlines show large outcrops of gently folded

Asmari limestones. The Chenareh anticline to the S displays limestones from the Ilam

13

Fm., whereas the larger and shallower Khush-Ab anticline shows only to the level of the

Amiran Fm. To the N, the core of the Sultan anticline constituted again by Ilam Fm. is

transported above a SW-directed thrust fault.

In order to construct the cross-sections we followed the listed procedures: 1) we

import the JPG files with seismic lines into the Canvas drawing program (similar to

Corel, Illustrator and Freehand) and then we interpret them using the dip domain

technique to select both the position of axial surfaces delimiting the dip domains as well

as to detect potential changes in thickness of selected units; 2) the JPG files are

converted to depth using a uniform velocity of about 2.3 Km/sec, which is probably

correct for shallow levels but slow for the deeper levels of the section; 3) we combine

this interpretation with surficial dips from both geological maps (NIOC geological maps

at scale 1/100,000) and field data.

14

15

1. INTRODUCTION

1.1. Southern Iran and Zagros fold-thrust belt

The NW-SE trending Zagros fold and thrust belt (Fig. 1) extends for about 1,800

kilometer from a location in Taurus Mountain some 300 km SE of the east Anatolian

fault in NE Turkey, through northern Iraq and SW Iran, to the Strait of Hormuz where

the north-south trending Oman Line separates the Zagros belt from the Makran

accretionary prism (Falcon, 1974; Haynes and McQuillan, 1974).

The North –East limit of Zagros belt is marked by the Main Zagros Thrust, which is

rotated about a horizontal axis to form a steeply NE-dipping to sub-vertical reveres

fault with a right lateral component of movement of unknown magnitude (Berberian

and Berberian, 1981; Stöcklin, 1981). However, some of published results (Falcon,

1974; Haynes and McQuillan, 1974; Alavi, 1994) considered the metamorphic rocks,

located to the NE of the Main Zagros Thrust known as Sanandaj. Sirjan Zone to be a

segment of the Zagros Belt

Southern Iran is the area located in Southwest of Neo-Tethys Suture zone and

consist high Zagros and Zagros and all of the Lurestan, Khuzestan and Fars and also

base on geographical data Zagros divides to Lurestan, Khuzestan and Fars area.

Based on Hormuz salt deposit distribution the Zagros is divided in two segments. SE

Zagros or Hormuz Basin and NE Zagros. The boundary between these two parts is the

Ghatar-Kazerun Fault.

16

Fig. 1 Location Map of the Zagros Mountain in SW Iran. The Main Recent fault Zagros Main Thrust is considered as the suture zone between two colliding plate (central Iran and Arabian plate). Imbricated zone correspond to narrow belt between the Zagros fault Zone and Main Recent fault Zagros Main Thrust. It consists of the highest mountain and deepest exposures across the belt. Zagros fold belt with a major topographical step located south of Zagros fault Zone. It shows less deformation and wide variety of folded structures with respect to their size, shape and tectonic complexity. N-S strike-slip faults, like as Kazerun fault, are assumed to be continuation of Arabic trends in to the Zagros basement.

1.2. Timing of tectonic events

Late Cretaceous ophiolites abduction was followed by the closure of Neotethys and

collision between Arabian plate and Central Iran during the early Miocene (e.g., Alavi,

1994, 2004). A major regional angular unconformity between the Agha Jari and

Bakhtyari Formations is generally considered to have marked the late Pliocene climax

of orogeny in the Zagros fold Thrust belt (Haynes and McQuillan, 1974; James and

Wynd, 1965; Kashfi, 1976). Growth strata within the upper Agha Jari Formation show

older movement before this major unconformity.

17

The new seismic data in the inner part of Zagros show also the pinch outs of the

Miocene evaporites (upper Gachsaran Fm.). The seismic reflectors pinch out against

some of the anticlines, which could be related to the beginning of folding process in

Middle Miocene time in the North of Dezful Embayment (Sherkati and Letouzey, 2004;

Sherkati et al., 2005).

Although the upper part of the Agha Jari deposits have been considered as

syntectonic since the very early publications on the Zagros folds and it is only recently

that several workers pointed out its importance for dating the folding development in

different regions of the Zagros fold belt. The magnetostratigraphic study carried out on

2800 m thick Agha Jari deposits filling the Changuleh growth syncline in the Pusht-e

Kuh Arc resolved the timing of folding initiation and its duration (Homke et al., 2004).

Initial folding took place about 8.1-7.2 Ma and had duration of about 6 Myr until the

Pliocene-Pleistocene boundary. This age of initial fold growth is older than the usually

accepted Pliocene times. The duration of deformation includes both folding growth and

uplift related to the development of the Mountain Frontal Flexure, which are difficult to

differentiate.

1.3. Mechanical stratigraphy of Lurestan Province

The stratigraphy of Lurestan Province consists of a 10-12 km thick succession that

encompasses the Paleozoic and Mesozoic Arabian passive margin deposits followed by

the sediments corresponding to the long–lived Cenozoic Zagros orogenic phase. This

tremendous pile of sediments was probably deposited on top of the Proterozoic-early

Cambrian Hormuz evaporates. Most of this stratigraphy of this section is based on

James and Wynd (1965) and Colman-Sadd (1978), (Fig. 2 and Fig. 3).

The Paleozoic sequence is the best documented in the Izeh Zone where it forms the

hangingwall of the High Zagros fault (O'B Perry and Setudenia, 1967). The base of the

hangingwall section is formed by 1160 m of Cambrian rocks followed by 925 m of

Carboniferous and Permian deposits. These thicknesses agree with result from deep

exploration wells in the study area. The Kabir Kuh and the Samand wells penetrated

783 m and 1057 m of Permian rocks, respectively. These Permian corresponds to a new

widespread deposition characterized by little or non deposition. The Permian is

constituted by shallow water carbonates cyclically interbedded with evaporates

18

(Beydoun et al., 1992). Older rocks were only intersected in the Kabir Kuh well where

about 200 m of Ordovician rocks were drilled. The interpretation of deep folded

horizons in the seismic lines across the north-west frontal regions of the Dezful

Embayment strongly suggests that lower Paleozoic siliciclastic deposits with thin

carbonatic units are present beneath the external parts of the Lurestan Province. The

broad extent of the lower Paleozoic is interpreted to have formed within the wide, stable

and long–lived northern passive margin along the paleo-Tethyan border of Gondwana

(e.g., Beydoun et al., 1992). The Mesozoic sequence of the north-eastern Arabian

platform was very stable centre the Late Cretaceous when oceanic obduction took place

along this margin. The succession is about 3 km thick in the Lurestan province and

encompasses the Triassic, the Khami Group (Jurassic-Aptian) and the Bangestan Group

(Albian to middle Campanian) (James and Wynd, 1965). During the Triassic, Jurassic

and Early Cretaceous, the region was dominated by a large carbonate platform (Khami

Group) with associated marls, shales, and argillaceous carbonates interbedded with

episodic plugs of evaporites (e.g., upper Jurassic Gotnia Fm.). These anoxic basins

provided several large areas of potential source rocks through this long sedimentary

sequence (e.g., Murris, 1980; Stoneley, 1981). Shallow marine sedimentation continued

from mid Campanian to Paleocene Gurpi Fm. including two extensive fossiliferous

carbonate members (Emam Hasan and Lofa Members), (Fig. 2 and Fig. 3).

The sedimentary conditions, intensity of folding, variation of thickness and variation

of facies make the geology of the Lurestan (Pusht-e Kuh Arc) very complex. In

Lurestan the Jurassic strata, which consists of dolomite and anhydrite in Fars area,

(Surmeh and Hith formations) change to limestone, shale and anhydrite? (Alan, Mos,

Adayeh, Najmeh, Sargalo and Gotnia Formations).

The Lower Cretaceous sediments are totally different from the Fars Province. The

Fahlian, Gadvan and Darian Formations, which are constituted by carbonates and

shales, change to shales in the Garau Formation. The sediments of middle Cretaceous

are mostly pelagic and consist of Ilam, Surgah, and Sarvak Formations. Upper

Cretaceous and lower Paleogene rocks of Pabdeh and Gurpi Formations contain more

carbonatic members and a thinner limestone horizon in Pabdeh Formation. Eocene

sediments include reefal limestones, which correspond to the Taleh Zang Formation and

some clastic deposit (Kash Kan Formation), which is the result of erosion of radiolarites

in the NE of the Lurestan Province across Main Zagros Reveres Fault (Fig. 3).

19

At the base of Oligocene-Miocene deposits there is an anhydrite unit in Lurestan

area, which disappears towards the NE, and changes to sandstone toward to S (Kalhur

Member and Ahwaz sandstones). In younger sediments such as Gachsaran evaporites,

Agha Jari sandstones and Bakhtyari conglomerates there are also some variation (Fig.

4).

In the North of Lurestan the Pabdeh Formation laterally changes to Amiran

Formation with turbidites, sandstones, marls, shales and clastic limestones. This

stratigraphy unit is the result of compressive deformation, which started after

Coniacian-late Santonian ophiolitic obduction along the strike of Zagros Main reveres

fault (Berberian, 1995; Homke et al., in press). The age of the Amiran Formation in the

centre of the basin is Paleocene (Homke et al., in press). The Amiran Formation pinches

out in the Southern flank of the Chenareh anticline. The Amiran Formation has different

thickness and age along the northern flank of the Khorramabad anticline where 1950 m

of conglomerates showing growth strata patterns are dated as Maastrichtian (Fakhari

and Soleimany, 2003), (Fig. 4).

Fig. 2 Stratigraphy for the pre-Fars Group. The panel crosses from the Kuh-e Kalak to the Kuh-e Sefid anticlines. Datum = Base of Gachsaran Formation

20

Fig. 3 Paleozoic and Mesozoic stratigraphy of the Zagros Fold Belt in the Lurestan Province showing sedimentary facies and dominant structural style.

Fig. 4 Tertiary stratigraphy of the Zagros Fold Belt in the Lurestan Province showing sedimentary facies and dominant structural style.

21

The mechanical behavior of the thick sedimentary pile in response to folding was

firstly discussed by O'Brien (1950) and by Dunnington (1968), and has been the locus

of several recent papers (e.g., Sattarzadeh et al., 2000; Molinaro et al., 2004) and

Sherkati et al., 2005 among others). O'Brien (1950) and Dunnington (1968) used

regional stratigraphy and divided the succession of the Zagros Fold Belt in 5 structural

units with relatively uniform characteristics (Fig. 3 and Fig. 4): 1) Basement

(Precambrian crystalline basement), 2) Lower Mobile Group (Late Proterozoic-early

Cambrian Hormuz evaporites), 3) Competent Group (Palaeozoic and Mesozoic to mid

Tertiary passive margin and early foreland carbonates), 4) Upper Mobile Group (mid-

late Miocene Gachsaran evaporites), and 5) Passive Group (late Miocene-Pliocene

foreland clastics). These groups of strata do not exactly correspond with the large scale

geodynamic cycles that molded the NE margin of the Arabian Plate, especially the

Competent Group (Fig. 3 Fig. 4). This group constitutes the full passive margin period

as well as the early foreland basin period up to the Asmari Formation. Although the

sedimentary pile is grouped in two stiff units and two weak detachments their position

and upper and lower limits are also important for defining the differences in style of

deformation in the different layers. The Competent Group deforms between the Lower

Mobile Group as a basal detachment and the Upper Mobile Group as a roof detachment.

The Upper Mobile Group flows between two rigid and disharmonic units. Finally, the

Passive Group is folded and thrusted disharmonically above the upper detachment

22

23

II. SHORT REVIEW OF PREVIOUS WORK ON DETACHMENT FOLDING

Among the three main classes of folds which are generally recognized, fault-bend

folds, fault-propagation folds and detachment folds, these last ones, though commonly

observed, are the least understood in terms of kinematic evolution. This is due to the

fact that there is no univocal relationship between a given geometry and a kinematic

scenario. The concept of detachment folding was implicitly acknowledged at a very

early stage under concepts such as the “break thrust fold” of Willis (1893) (Fig. 5) or

the “stretch thrust” of Heim (1921), in which the development of a thrust fault was

considered to be the final stage in the fold evolution.

a b

Fig. 5 Break-thrust fold of Willis (1893). Note that in stage (a) preceding the development of the fault, the fold is implicitly depicted as a detachment fold.

The first explicit recognition of detachment folding can probably be attributed to

Buxtorf (1916), with his cross-sections through the Jura Mountains (Fig. 6).

Detachment folds have been documented from numerous other mountain belts around

the world, notably the Parry Islands fold belt (Harrison, 1995), the Pyrenees (Vergés et

al., 1992) and the Zagros fold belt (Colman-Sadd, 1978).

Detachment folds are characterized by a rounded and often symmetrical geometry at

surface and usually display large wavelengths, even at low shortening ratios. De Sitter

(1956) was the first to recognize that in concentric regimes of folding, implicit to

detachment folds, the size of the structure is directly a function of the thickness of the

24

folded panel. Mechanical analyses have demonstrated that the physical properties of the

stronger dominant member in the stratigraphic succession will have a determining effect

on the final size of the structures (Biot, 1961). Dahlstrom (1969a) pointed out that in

concentric regimes of folding, implicit to detachment folds, a fold train is necessarily

bounded by an upper and a lower detachment (Fig. 7).

Fig. 6 Example of detachment anticlines in the Jura Mountains, Switzerland. Redrawn by Epard and Groshong (1993) from Buxtorf (1916). No vertical exaggeration.

Fig. 7 Dahlstrom (1969b) conceptual model explaining why a concentrically folded panel is necessarily bound by an upper (UD) and a lower (LD) detachment zone.

While the lower detachment always exists, sometimes the upper detachment may not

and can correspond to the interface between rock and air/water (Dahlstrom, 1969b). From

(Fig. 7) one can remark that depending of the level of erosion, very different fold

geometries will be observed at surface. Close to the lower detachment one will observe

tight anticlines, with potential internal disharmonic folding, separated by broad gentle

25

synclines, while towards the upper detachment one will have the impression of tight

synclines and broad anticlines.

According to most authors, a prerequisite condition for the generation of detachment

folds is the existence of a high competency contrast between the sedimentary units

involved in the folding process. The simplest model therefore consists of a basal

incompetent layer acting as a detachment zone, such as salt, overlain by a thick

competent unit such as carbonates or sandstones. The basal unit responds in a ductile

manner to fold growth, with migration of ductile material towards the core of the

anticlines causing down warp of the adjacent synclines. The structure will develop more

or less symmetrically depending on the viscosity of the basal detachment: in areas such

as Zagros characterized by ductile detachment horizons (Davis, 1985).

2.1. Detachments / rounded hinges and axial surfaces

The well-exposed anticlines in the Zagros Fold have been used as examples of folds

since long time ago in many articles and books. However, the geometry of these

anticlines at depth remains still unclear.

In the Pusht-e Kuh Arc there is a large number of different anticlines with different

lengths and width mostly formed of the two thick competent limestone units, which in

turn are the two main reservoirs for hydrocarbons in the surrounding oil rich region. The

Kabir Kuh anticline is the largest fold of the Pusht-e Kuh Arc. One third of the total

width the Pusht-e Kuh Arc extends towards the foreland side of the Kabir Kuh anticline

(to the SW). On the hinterland side of the Kabir Kuh anticline (to the NE) there is a

relatively large number of small anticlines whereas to its foreland side (SW) there is a

smaller number of anticlines but larger (Samand and Anaran anticlines among others).

The Kabir Kuh anticline is a 200-km and long anticline is up to 2700 m high and

constitutes the present drainage divide of the Pusht-e Kuh Arc (Vergés, in press 2007)..

2.2. Kinematics of detachment folding

The first author to explicitly discuss the geometric evolution of buckle folds was De

Sitter (1956), who proposed a model where the anticlines grow by increase in limb dip

as the synclinal axes slide toward one another on the underlying detachment (Fig. 8).

However, this model was later shown by Dahlstrom (1990) to violate the law of

26

conservation of volume of Goguel (1952) since it implied a drastic variation in the

location of the detachment horizon with the amount of shortening. With his paper,

Dahlstrom (1990) set the foundations of the modern ideas on the kinematics of

detachment folds by proposing, based upon balancing criteria, an evolution model

“wherein the anticlinal fold limbs are short at the inception of folding and grow longer

as dips increase and the fold grows”

There are two main mechanisms which are now generally thought to contribute to the

growth of a detachment fold: (1) limb lengthening by migration of beds through hinges

and (2) limb rotation. A whole series of papers were published during the last decade

dealing with the kinematics of detachment folds (Homza and Wallace, 1997; Mitra,

2002; Poblet and McClay, 1996; Rowan, 1997). The main debate on these papers

consists of which of these two competing mechanisms is the most important during

different stages of fold development (Fig. 9).

Fig. 8 (De Sitter, 1956) model of geometric evolution of a concentric buckle fold, with illustration of particle trajectories on the flanks of the anticline.

27

Fig. 9 Three possible models of growth of a detachment anticline after Poblet and McClay (1996): Model 1 shows growth by hinge migration; model 2 shows growth by limb rotation; and model 3 displays growth by a combination of hinge migration and limb rotation.

The progression of the detachment fold evolution is generally considered to involve a

thrusting through the forelimb with increasing shortening (i.e. a faulted detachment

fold; Mitra, 2003) (Fig. 10). This is basically the concept that was already implicitly

suggested by Willis (1893).

a

c

b

d

Fig. 10 Typical evolution sequence of a faulted detachment fold, after Mitra (2002). Note that the fold is initiated as a quasi-symmetric structure (a & b) and that the development of the asymmetry coincides with the propagation of a fault (c & d).

28

In the light of our observations and the considerations exposed above, we believe

that these models could be viewed as mere steps in a same continuous process of

folding and ductile flow of the detachment level. The relative importance of each of

these stages will primarily depend on the characteristics of the basal detachment. For a

fold developed over a thin and relatively competent detachment horizon, the stage of

buckling will probably be short lived and will be rapidly replaced by the propagation of

a fault (e.g., Sans and Vergés, 1995). On the other hand, a fold developed over a thick

ductile detachment will likely develop over a longer time by simple buckling. It is only

when all the ductile material available to fill in the core of the anticline has been

completely evacuated from the adjacent synclines that the fault will start propagating

through the forelimb.

2.3. The structure of the Competent Group (Lower Structure): folding by multiple stratigraphic units in Lurestan Province with special view on Chenareh anticline

The Pusht-e Kuh Arc exposes the later passive margin and early foreland basin

folded stratigraphy in the core of the anticlines. The younger foreland basin succession

is only exposed in rare deep synclines in the Pusht-e Kuh Arc and in the entire Dezful

Embayment. Along the folded arc there are main domains distinguished by folding of

different amplitudes. In the north-east, the Khorramabad anticline is cored by the

Bangestan Group and shows high amplitude and wavelength. In the central part of the

Lurestan the outcropping cores of anticlines are mostly constituted by Amiran to

Asmari Formations. The amplitude and wavelength are normally smaller than in the

previous domain. To the south-west, the Kabir Kuh, Chenareh, Samand and Anaran

anticlines show again strata of the Bangestan Group cropping out in their cores. The

different characteristic of these domains are directly related to variation in the

mechanical stratigraphy across the Pusht-e Kuh Arc as previously discussed (e.g.,

Vergés et al:, submitted).

29

III. THE CHENAREH ANTICLINE

3.1. Location of Chenareh anticline in Zagros fold-thrust belt

Previous workers (Berberian and King, 1981; Falcon, 1974; Stöcklin, 1968) divided

the Zagros fold- thrust belt into different sub-divisions, mostly parallel to the strike of

the belt. The division is essentially base on amount of shortening or intensity of

deformation. (Fig. 11) The folded zone forms the most southwesterly deformation zone

of the Zagros orogen. Elevation of the Zagros fold rise gradually to wards northeast the

boundary between folded zone and Imbricated zone is generally abrupt. It corresponds

to high angle thrust fault running parallel to the Zagros range and was named High

Zagros fault. (Berberian 1981). Imbricated zone is a narrow belt, which contains the

highest mountains in the entire range and also exposures of Lower Paleozoic rocks. The

northeastern limit of Imbricated Zone is the Main Zagros reverse fault that was

attributed to the suture zone between Arabian and central Iran by Stöcklin (1968).

The complex evolution of the Zagros basin caused lateral and vertical facies and

thickness variations of sedimentary units. These sediment logical variations, which

caused structural differences during deformation, are the principal reasons to divide the

Zagros folded zone belt into different tectonic sedimentary units, namely Lurestan,

Kohistan and Fars Provinces. (Motiei, 1995).

The Chenareh anticline is located in the Lurestan Province. It is in north of Dezful

and south of Khorramabad cities. The anticline is limited to the south west by the Bala-

Rud Fault that corresponds to the oblique segment of the Mountain Frontal Flexure that

separates the arc from the Dezful Embayment, which contains the major hydrocarbon

reserves of the Iranian Zagros. The Chenareh anticline as well as the Rit and Sultan

anticlines is known for oil and gas exploration in mid Cretaceous and Permian

carbonates. In the west of the Chenareh anticline, the Maleh Kuh anticline is one of the

few discovered oil fields in the Pusht-e Kuh Arc. .

30

Fig. 11 Location Map, Zagros Mountain, SW Iran and study area.

Previous work on the Chenareh anticline

Most of efforts in oil exploration were focused in the Dezful Embayment and Fars

Arc but after first oil discovery in Cretaceous carbonate in the Pusht-e Kuh Arc,

geological exploration started in this tectonic arc. Geological maps at different scale

1.250000 and 1.100000 were produced after field work during several decades by O'B

Perry and Setudenia (1967) and Takin et al. (1970). On the Chenareh anticline there is

only one structural geology report, which was written by (Fakhari et al, 1995). In this

report, the main objective of research was to determine the potential of hydrocarbon for

the group of linked anticlines in this region: the Rit, the Kush-Ab, the Chenareh and the

Marab anticlines. Fig. 12 shows one of the cross-sections, which was constructed in this

report (Fig. 13).

31

Fig. 12 Cross-section from an Internal Report from NIOC (NIOC internal report).

Fig. 13 Geological map showing the location of cross-section and seismic lines.

3.3. Geometry of Chenareh anticline

The Chenareh anticline is a nicely outcropping anticline located in the SE border of

the Pusht-e Kuh Arc (Fig. 14). The anticline has more than 65 kilometer long and

displays a mean width of 8 kilometers at the level of Asmari limestones. Its shape is

quite regular in map view. The anticline plunges in both ends below Gachsaran

evaporites. The. Kush-Ab anticline with wider amplitude together with the Marab

smaller anticlines is located to the north of the Chenareh anticline. The oldest outcrop in

the Chenareh anticline corresponds to the Sarvak Formation (Upper Cretaceous).

32

The Chenareh anticline shows a nicely preserved geometry in its NW segment and

shows a rather disturbed geometry in its SE segment by a set of normal faults. On the

other hand based on field observation in the Kush-Ab anticline there is a local uplift and

likely in this structure the thickness of Amiran formation is not too thick. So, the

geometry of Kush-Ab and Chenareh anticlines at the level of Asmari Formation is

completely different (Fig. 15 and Fig. 16).

The presented geological cross-sections show the variations in fold geometry from

east to west along the Chenareh anticline as observed in . The western segment shows a

very well preserved box folding geometry that is modified by normal faulting that

collapse the southwestern flank of the anticline nearby the Mountain Frontal Flexure

along the Bala Rud Fault (Fig. 17).

Fig. 14 Geological map to show the position of the Chenareh, Kush-Ab and Rit anticlines nearby the Bala Rud Fault. This image is composed with NIOC geological maps and DEM from Google Earth.

33

Fig. 15 Geological map to show the position of the Chenareh, Kush-Ab and Rit anticlines nearby the Bala Rud Fault. This image is composed with NIOC geological maps and DEM from Google Earth.

Fig. 16 Five cross-sections at the level of Asmari limestones to show the strong variation in the style of the folding along the Chenareh anticline. Aerial view towards the SE along the eastern segment of the Chenareh anticline showing the normal faulting that collapses the SW flank of the anticline above the Mountain Frontal Flexure (Bala Rud Fault).

34

Fig. 17 Five cross-sections at the level of Asmari limestones to show the strong variation in the style of the folding along the Chenareh anticline.

35

3.4. Chenareh cross-section I

3.4.1. First version of cross-section I

Cross-section 1 has a length of 28.6 Km and is located 23 Km away from its north-

east plunge (Fig. 18 and Fig. 19). The cross-section crosses the Khush-Ab anticline,

located between the Rit and the Chenareh anticlines. The youngest rocks cropping out

along this section are evaporites of the Gachsaran Formation and the oldest rocks are

Taleh Zang deposits. This cross-section shows the geometry of the eastern segment of

the Chenareh anticline with the normal faults that produce the collapse of the SW flank.

Fig. 18 Map showing location of cross-section I.

36

Fig. 19 Aerial view towards the north-east of the Chenareh anticline with the position of the geological cross-section I

These faults expand the wide of anticline in surface at the level of the Asmari

Formation. So, based on field observations and photos of this area there is no good and

reliable data such as dip and strike. The dip of the Gachsaran Formation in the north of

the Khush-Ab anticline is 5º towards the south-west and there is no surface evidence

showing the other flank of the anticline. For this reason, the Khush-Ab anticline is a

monocline. At the level of the Asmari limestones in the southern flank of the monocline

there are two dip domains: the first one is 5º and the second is 10º. In Chenareh

anticline on the north flank as you see in picture there are 5º dip domain, which put in

contact the Gachsaran and Asmari Formation. The second domain dips 25º, the third is

35º and the fourth is 25º that changes to 13º finally. In the southern flank the Asmari

limestones have been effected by a set of normal fault, However, the anticline shows an

increasing dip downwards reaching 70º-75º dip at the contact with Gachsaran

evaporites. All cross-sections constructed by kink method are based on constant

thickness preservation (Fig. 20).

37

Fig. 20 Geological cross-section I version 1.

38

3.4.2. Second version of cross-section I

In this cross-section I assumed that the topography almost corresponds to the near

top of the Asmari limestones. As well as for the former version of the cross-section I

applied constant thickness for the Amiran, Taleh Zang and Kash Kan Formations that

totalize about 1500 meters along the northern flank of the anticline. Along the crest of

the anticline there is a clear graben with antithetic normal faults that do not propagate

too deep in the culmination. The displacement of the northern fault is about 100 meters

dying about the Asmari-Gurpi contact not affecting the Bangestan Group strata. Also

this cross-section shows a complex geometry in the southern flank of the Chenareh

anticline because the dips between Asmari and Gachsaran are more than 70º and rapidly

change towards the crest of the anticline where are only 10º and 25º.

The wide of anticline in this area expands approximately 600 meters, which seems to

be unreasonable. Otherwise the dip between Gachsaran and Asmari Formations based

on west and east of this section on Asmari is about 45º. The dip on Asmari along the

section is 70º and change to overturned and then change to normal to 45º.

The Bangestan Group crops out in the centre of the anticline showing a disturbed

zone of 980 meter elevation above sea level according longitudinal cross-section. Based

on 2º-dip towards the west of the Asmari formation in cross-section 1 the top of the

Bangestan Group should be located at 300-320 meters of elevation above sea level. So,

in this cross-section the top of the Bangestan Group is located at 320 above sea level

and the thickness of Kash Kan, Taleh Zang, Amiran and Gurpi Formations changed to

1000 meters. This thickness applied for Chenareh anticline increases to the north. In this

version of the cross-section the geometry of the top of the Bangestan Group is

symmetric (Fig. 21)

39

Fig. 21 Geological cross-section I version 2.

40

3.4.3. Shortening along cross-section I

The displacement of the Asmari Formation in the segment of the anticline affected

by the normal faulting, measured along the normal fault, is more than 600 meter

towards the southwest. Shortening is 7.2% only across the Chenareh anticline and

extension is about 1.06%..

41

3.5. Chenareh cross-section II

Cross-section II is 38.5 kilometer long and is located in the middle side of the

Chenareh anticline. The oldest outcrop in the core of the anticline corresponds to the

Sarvak Formation whereas the youngest one corresponds to recent deposits. Cross-

section II is located in a disturbed part of the anticline, which was affected by a set of

normal faults.

I started to draw this section from surface information by using data from the

geological map. Because the level of outcrop in the core of the anticline is at the Sarvak

Formation I complemented this study with a longitudinal section to determine the

structural positions of both the top and bottom of the Asmari Formation on cross-section

II. The top of the Asmari Formation is approximately located at 2500 meters above sea

level (Fig. 22). To complete the cross-section in the anticlines I measured the minimum

thicknesses of outcropping Gachsaran evaporites that turned to be of about 300 meters.

I used all these data together with field observations to construct the geological

cross-section II (Fig. 23 and Fig. 24).

42

Fig. 22 Longitudinal cross-section along the Chenareh anticline.

43

Fig. 23 Aerial picture of the southern part of geological cross-section II.

44

Fig. 24 Geological cross-section II.

45

3.6. Chenareh cross-section III

The geological cross-section III is located across the eastern segment of the anticline

about 7.5 kilometer before its plunge towards the east on top of the Bala Rud Fault (Fig.

25 Fig. 26Fig. 27). This section also crosses an area where the Asmari limestones

change laterally to the Pabdeh Formation. The oldest outcrops correspond to the Gurpi

Formation in the core of the Chenareh anticline and the youngest rocks correspond to

the Labhari Member (Agha Jari Formation) Based on the geological maps and field

observations, the variation in thickness for the Amiran Formation has been taken in

account to build the section. The section also shows that the geometry depicted by the

Asmari Formation is not matched by the rocks of the Bangestan Group at depth.

The geometry of the folds is more difficult to prove along the syncline existing

between the Kabir Kuh and Chenareh anticlines because there are no data in geological

maps nor good observation in the field. Our analysis is based on well data from the

Qaleh Nar oil field where the thickness of the Gachsaran Formation is about 1200

meters (Fig. 27).

According to the well data Qaleh Nar 3, the top of the Asmari Formation should be

located at 2750 m below sea level and the thickness for Pabdeh and Gurpi Formations

should be about 550 m. The Kash Kan Formation is only represented by a thin tong or

rocks. In addition, I assumed 550 m of thickness for the Pabdeh and Gurpi Formations.

The most common variations in the geometry and evolution of detachment fold from

the model in Fig. 28 are: 1) an asymmetric geometry, 2) faulting of limbs to form

faulted detachment fold, 3) complex fold and faulted geometries resulting from multiple

detachment horizons.

In Chenareh anticline you can see all common variation in geometry, also you can

see the evolution of detachment fold (Fig. 28).

46

Fig. 25 Location map to show the situation of the geological cross-section III.

Fig. 26 View to the north-west that shows the central part of cross-section III across the Chenareh anticline.

47

Fig. 27 Geological cross-section III.

48

A

B

C

D

Fig. 28 Cartoon to scale to see the evolution of the Chenareh anticline proposed detachment folding.

49

50

IV. ROLE OF GRAVITY IN PRESENT GEOMETRY OF CHENAREH ANTICLINE

Gravity is one of the important phenomena in modifying the folding structure

especially in those displaying a stratigraphy formed by multilayer sequence with

contrasting mechanical behavior. Among the many authors, who explained complex

structural features in Zagros Mountains, it is worth to mention [Harrison, 1934 #7879] .

These authors recognized the importance of gravity in folds in which a succession of

limestones and marls was exposed creating structural complexity in places where the

underlying structure is simpler. A “flap structure” is one of these spectacular structures,

which were explained by these authors. It is a part of an isoclinally folded limestone

sheet (Fig. 29). For Harrison and Falcon (1934) flaps are purely gravitational structures

resulting from the collapse of over steepened flanks into the eroded valleys synclines).

Fig. 29 Evolution of a flap structure (after Harrison and Falcon, 1934).

Following Saint Bezar et al. (1998), I consider that “flap structures” are recumbent

synclines developed by collapse along the limb of anticlines that maybe enhanced

during the migration of synclinal hinges.

51

In the following I will explain how these gravitational structures observed along the

Chenareh anticline have been included in the geological cross-sections. The Chenareh

anticline displays a strong set of fractures developed in both flanks of the anticline (Fig.

30A). Where dips of the flank are high, thick competent limestones may slide down

above marls using the fractures to detach in the upper part of the slide (Fig. 30B). The

formation of the slide strongly depends on the dip of the anticline flank and on the

correct juxtaposition of limestones and marls that act as detachment levels (Fig. 30C).

In the Lurestan Province, the Amiran, the Gurpi, the Garau and the Dashtak

Formations are potential detachment levels to produce or enhance folds. But in the

study area the larger wavelength of the Chenareh and Rit anticlines seems to suggest

that the fold detachment is located deeper in the section and that the evaporites of the

Dashtak Formation or a deeper units in the Lower Paleozoic are the potential

detachments.

In all these structures in the Zagros Fold Belt a striking characteristic is the absence

or scarcity of thrust faults controlling the geometry and kinematics of the folds: This

scarcity is also observed at the level of subsidiary faults (the so-called “fold-

accommodation faults”, (Mitra, 2002)). Thus the folds presented in this study seem to

correspond also to detachment anticlines. As in the Dezful Embayment, continuing

deformation resulted with the activation of secondary detachment levels. In particular,

there are numerous field examples testifying the role of the Pabdeh-Gurpi marls as a

secondary detachment, which controls the development of minor structures. Different

cases can be separated: Here in the Chenareh anticline the Amiran Formation is the first

detachment level below the Asmari Formation and as you can see the geometry of

structure in Bangestan Group is wider than the one in the Asmari level. The activation

of the Amiran and Gurpi Formations secondary detachment can also trigger the

development of gravity collapse structures as firstly recognised by Harrison and Falcon

(1934). Following these authors, a flap is “a part of a limestone sheet, which has bent

over and backward without breaking” until a completely overturned position has been

attained. We have observed such flaps in the Asmari limestones situated in front of the

Chenareh anticline (Fig. 31). For Harrison and Falcon (1934) flaps are purely

gravitational structures resulting from the collapse of over steepened flanks into eroded

valleys. Following De Sitter (1956), we think that they rather originated during folding.

More precisely and following Saint Bezar et al. (1998), I consider that flap structures

52

along the southern flank of the Chenareh anticline is a recumbent anticline born by the

collapse along the limbs of the anticlines and accentuated during the migration of the

anticline hinges. In any case, the development of a flap structure requires the disruption

by erosion of the Asmari layers involved in the structure (Fig. 32, Fig. 33 and Fig. 34).

This photograph was /taken from the north-west flank of the Chenareh anticline. And

also some times we can see some auxiliary fold which was generated by thrust and

backthrust as you see in photograph in Fig. 32.

53

A

B

C

Fig. 30 A) Oblique fracture system with respect to the anticline axis; B) Opening fractures near the top of a potential new sliding segment of the flank of the anticline; C) Initial movements on the upper part of a gravitational collapse of the flank of the anticline.

54

Fig. 31 Photograph shows sliding of limestone sheet from Asmari on underling marl.

Fig. 32 Photograph shows an auxiliary fold which was generated by back thrust.

55

Fig. 33 A) Photograph and interpretation of a kind of flap structure showing a recumbent fold of Asmari limestones above Gachsaran evaporites. This structure differs from the real flap structures in which the isoclinal syncline faces in the same direction than the anticline flank (Harrison and Falcon, 1934]; B) Line drawing showing recumbent anticline in Oligo-Miocene carbonate (Asmari formation). It has been already described as gravity collapse structure and was named as "flaps" by previous workers (Harrison and Falcon, 1934). I consider that flaps are recumbent anticlines born by collapse along the steep limb of anticlines and accentuated during the migration of the anticlines hinges. So its development requires disruption by erosion of the Asmari carbonate at top structure.

56

Fig. 34 Different helicopter pictures showing the gravitational collapse of the southern flank of the Chenareh anticline.

57

58

V. CONCLUSIONS

The Chenareh anticline outlined at the level of the limestones of the Asmari

Formation is one of the most outstanding whale back anticlines of the Pusht-e Kuh Arc

with a regional NW-SE direction. It is located at the SE border of the Pusht-e Kuh Arc

in Zagros Iran. The anticline has more than 65 km of length and displays at the level of

Asmari Formation a width of 8 km. The Khush-Ab anticline with wider wavelength is

located to the NE of the Chenareh anticline together with an auxiliary fold, which is

called Marab anticline in its south-western flank.

The oldest outcrop in the core of the Chenareh anticline is the Sarvak Formation

(Upper Cretaceous) and the youngest one is Bakhtyari Formation (Pliocene).

The Chenareh anticline exhibits three different segments: a) the NW segment very

well preserved with little normal faulting; b) the central part defined by the gravitational

collapse of the SW flank of the anticline; and c) the SE segment showing the oldest

rocks at the level of Bangestan Group that seems to be rotated to the SW.

In its NW segment, the Chenareh anticline shows a rounded geometry with defined

relatively sharp and rounded hinges bounding steep flanks and flat crestal domains. The

relatively steep flanks and flat crustal domain as well as the rapid decrease in dip at the

base of both NE and SW flanks configure a symmetric box folding geometry, that is

typical of detachment mechanisms.

In the central segment of the anticline, normal faults detach as in many other folds at

the base of the Asmari limestones using marls as detachment horizons. In the lower

parts of the anticline, compressional structures as flaps exist.

The SE segment of the Chenareh anticline is located above the Mountain Front

Flexure along the Bala Rud Fault. The extensive normal faulting affecting the central

segment of the anticline as well as the slight rotation of the SE segment are probably

linked to the Bala Rud Fault. Normal faults and rotation of the anticline can be used to

better define the deep structure of the oblique segment of the Push-e Kuh Arc along the

Bala Rud Fault.

59

Using depth projection methods and constant thickness the Chenareh anticline shows

the main detachment level at a depth corresponding to the evaporites of the Dashtak

Formation of Triassic age. This level also corresponds to the main intermediate

detachment in the Kabir Kuh anticline (the next to the SW).

Shortening in these cross-sections give and amount of 7.2% in compression and

extension of the SW flank in the central segment gives 1.06%.

The Chenareh anticline finally plunges towards the SE beneath the Dezful

Embayment where most of the hydrocarbons are concentrated. These hydrocarbons

migrate upwards and could charge the Pusht-e Kuh Arc anticlines as demonstrated by

the occurrence of abundant oil seeps along the contact between Asmari and Gachsaran

Formations along the Bala Rud Fault near the SE termination of the Chenareh anticline.

In this work I became conscious about the complexities of cross-section construction

using combined data sets. The possibility to constrain the geometry at depth is

important because the Pusht-e Kuh Arc lacks of good seismic data. This is a new area

for exploration that was abandoned long time ago because the repeated dry exploration

wells drilled in the region. Now, with new techniques in exploration from both geology

and geophysics it is worth to start again to explore for smaller oil and gas fields in this

area.

The understanding of the deep structure of the anticlines is needed taking in account

that gas has also a good economical potential nowadays due to the high prices in the

world market. This gas could be used locally in relatively large cities in the Lurestan

Province.

In NIOC we benefited from this work because we better understand the need for good

constrained geological cross-sections, as well as combined with other complementary

disciplines of geosciences, to better define and constrain the potential for HC of other

areas outside the Dezful Embayment.

60

REFERENCES Alavi, M., 1994, Tectonics of the Zagros orogenic belt of Iran: new data and interpretations:

Tectonophysics, v. 229, p. 211-238.

Alavi, M., 2004, Regional stratigraphy of the Zagros fold-thrust belt of Iran and its proforeland evolution: American Journal of Science, v. 304, p. 1-20.

Berberian, M., 1981, Active faulting and tectonics of Iran, in H. K. Gupta, and F. M. Delany, eds., Zagros-Hindu Kush-Himalaya-Geodynamic evolution: Geodynamics Series, v. 3: Washington D.C., American Geophysical Union, GSA and Ed. Board, p. 33-69.

Berberian, F., and M. Berberian, 1981, Tectono-plutonic episodes in Iran, in H. K. Gupta, and F. M. Delany, eds., Zagros-Hindu Kush-Himalaya-Geodynamic evolution: Geodynamics Series, v. 3: Washington D.C., American Geophysical Union, GSA and Ed. Board, p. 5-32.

Berberian, M., 1995, Master "blind" thrust faults hidden under the Zagros folds: active basement tectonics and surface morphotectonics: Tectonophysics, v. 241, p. 193-224.

Berberian, M., and G. C. P. King, 1981, Towards a paleogeography and tectonic evolution of Iran: Canadian Journal of Earth Sciences, v. 18, p. 210-265.

Beydoun, Z. R., M. W. Hughes Clarke, and R. Stoneley, 1992, Petroleum in the Zagros Basin: A Late Tertiary Foreland Basin Overprinted onto the Outer Edge of a Vast Hydrocarbon-Rich Paleozoic-Mesozoic Passive-Margin Shelf, in R. W. Maequeen, and D. H. Lackie, eds., Foreland Basins and Fold Belts, American Association of Petroleum Geologists Memoir 55, p. 309-339.

Biot, M. A., 1961, Theory of folding of stratified viscoelastic media and its implication in tectonics and orogenesis. : Geological Society of America Bulletin, 72, 1595-1620.

Buxtorf, A., 1916, Prognosen und Befundc beim Hanensteinbasis und Grenchenberg

tunnel unde die Bedeutung der Letzeren fur die Geologie de Juragebirges,: Verhand. Naturf. Gesell., Bask, Band XXVII, pp. 185-254.

Colman-Sadd, S. P., 1978, Fold development in Zagros simply folded belt, southwest Iran: The American Association of Petroleum Geologists Bulletin, v. 62, p. 984-1003.

Dahlstrom, C. D. A., 1969a, Balanced cross sections: Canadian Journal of Earth Sciences, v. 6, p. 743-757.

Dahlstrom, C. D. A., 1969b, The upper detachment in concentric folding: Bull. of Can. Pet. Geo., v. 17, p. 326-346.

Dahlstrom, C. D. A., 1990, Geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding: American Association of Petroleum Geologists Bulletin, v. 74, p. 336-344.

Davis, D. M., and Engelder, T., 1985, The role of salt in fold-and-thrust belts: Tectonoph., v. 119, p. 67-89.

De Sitter, L. U., 1956, Structural Geology. McGraw-Hill, , 551 pp.

Dunnington, H. V., 1968, Salt-tectonic features of northern Iraq: Geological Society of America Special Paper, v. 88, p. 183-227.

Epard, J.-L., and R. H. Groshong, Jr., 1993, Excess area and depth to detachment: Am. Asso. Pet. Geol. Bull., v. 77, p. 1291-1302.

Fakhari, M., and B. Soleimany, 2003, Early anticlines of the Zagros Fold Belt, South West Iran: 2003 GSA Seattle Annual Meeting (November 2–5, 2003), Paper No. 156-23.

61

Falcon, N. L., 1974, Southern Iran: Zagros Mountains, in A. M. Spencer, ed., Mesozoic-Cenozoic Orogenic Belts. Data for Orogenic Studies, v. 4, Geological Society of London, Special Publication, p. 9-22.

Goguel, J., 1952, Traité de tectonique. 1 vol. 8, 384 p., 203 fig., Masson, Paris.

Harrison, J. C., 1995, Tectonics and Kinematics of a Foreland Folded Belt Influenced by Salt, Arctic Canada, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., AAPG Memoir 65 on Salt Tectonics: a global perspective, v. Chapter 19, p. 379-412.

Harrison, J. V., and N. Falcon, 1934, Collapse structures: Geological Magazine, v. 71, p. 529-539.

Haynes, S. J., and H. McQuillan, 1974, Evolution of the Zagros Suture Zone, Southern Iran: Geological Society of America Bulletin, v. 85, p. 739-744.

Heim, A., 1921, Geologie der Schweiz. Band I Molasseland und Juragebirge. Tauchniz, Leipzig.

Homke, S., J. Vergés, M. Garcés, H. Emami, and R. Karpuz, 2004, Magnetostratigraphy of Miocene–Pliocene Zagros foreland deposits in the front of the Push-e Kush Arc (Lurestan Province, Iran): Earth and Planetary Science Letters, v. 225, p. 397– 410.

Homke, S., J. Vergés, J. Serra-Kiel, G. Bernaola, M. Garcés, R. Karpuz, I. Sharp, M. H. Goodarzi, and I. M. Verdú, in press, Late Cretaceous-Paleocene formation of the early Zagros foreland basin: biostratigraphy and magnetostratigraphy of the Amiran, Taleh Zang and Kashkan sequence in Lurestan Province, SW Iran: Geological Society of America Bulletin, v. xx, p. xx.

Homza, T. X., and W. K. Wallace, 1997, Detachment folds with fixed hinges and variable detachment depth, northeastern Brooks Range, Alaska: Journal of Structural Geology, Special Issue on Fault-Related Folding, v. 19, p. 337-354.

James, G. A., and J. G. Wynd, 1965, Stratigraphic Nomenclature of Iranian Oil Consortium Agreement Area: Bulletin of the American Association of Petroleum Geologists, v. 49, p. 2182-2245.

Kashfi, M. S., 1976, Plate tectonics and structural evolution of the Zagros geosyncline, southwestern Iran: Geological Society of America Bulletin, v. 87, p. 1486-1490.

Mitra, S., 2002, Fold-accommodation faults: American Assiociaton of Petroleum Geologists Bulletin, v. 86, p. 671-693.

Mitra, S., 2003, A unified kinematic model for the evolution of detachment folds: Journal of Structural Geology, v. 25, p. 1659–1673.

Molinaro, M., J. C. Guezou, P. Leturmy, S. A. Eshraghi, and D. Frizon de Lamotte, 2004, The origin of changes in structural style across the Bandar Abbas syntaxis, SE Zagros (Iran): Marine and Petroleum Geology, v. 21, p. 735–752.

Motiei, H., 1995, Petroleum Geology of Zagros. Publ. Geol. Surv. Iran (in Farsi), 589 p.

Murris, R. J., 1980, Middle East: Stratigraphic Evolution and Oil Habitat: Bulletin of the American Association of Petroleum Geologists, v. 64, p. 597-618.

O'B Perry, J. T., and A. Setudenia, 1967, Küh-e Kamestãn Geological Compilation Map 1:100,000 (Sheet 20821E), National Iranian Oil Company (NIOC).

O'Brien, C. A. E., 1950, Tectonic problems of the oil field belt of southwest Iran: Proceedings of 18th International of Geological Congress, Great Britain, part 6, p. 45-58.

Poblet, J., and K. McClay, 1996, Geometry and Kinematics of Single-Layer Detachment Folds: American Association of Petroleum Geologists Bulletin, v. 80, p. 1085-1109.

62

Rowan, M., 1997, Three-dimensional geometry and evolution of a segmented detachment fold, Mississippi Fan foldbelt, Gulf of Mexico: Journal of Structural Geology, Special Issue on Fault-Related Folding, v. 19, p. 463-480.

Sans, M., and J. Vergés, 1995, Fold development related to contractional salt tectonics: southeastern Pyrenean thrust front, Spain, in M. P. A. Jackson, D. G. Roberts, and S. Snelson, eds., AAPG Memoir 65 on Salt Tectonics: a global perspective, v. Chapter 18, p. 369-378.

Saint Bezar, B., D. Frizon de Lamotte, J. L. Morel, and E. Mercier, 1998, Kinematics of large scale tip line folds from the High Atlas thrust belt, Morocco: Journal of Structural Geology, v. 20, p. 999-1011.

Sattarzadeh, Y., J. W. Cosgrove, and C. Vita-Finzi, 2000, The interplay of faulting and folding during the evolution of the Zagros deformation belt, in J. W. Cosgrove, and M. S. Ameen, eds., Forced folds and fractures: Geological Society, London, Special Publications, v. 169: London, Geological Society of London, p. 187-196.

Sherkati, S., and J. Letouzey, 2004, Variation of structural style and basin evolution in the central Zagros (Izeh zone and Dezful Embayment), Iran: Marine and Petroleum Geology, v. 21, p. 535-554.

Sherkati, S., M. Molinaro, D. Frizon de Lamotte, and J. Letouzey, 2005, Detachment folding in the Central and Eastern Zagros fold-belt (Iran): salt mobility, multiple detachments and late basement control: Journal of Structural Geology, v. 27, p. 1680-1696, doi:10.1016/j.jsg.2005.05.010.

Stöcklin, J., 1968, Structural history and tectonics of Iran: a review: American Association of Petroleum Geologists Bulletin, v. 52, p. 1229-1258.

Stöcklin, J., 1968, Structural history and tectonics of Iran: a review: American Association of Petroleum Geologists Bulletin, v. 52, p. 1229-1258.

Stöcklin, J., 1981, A brief report on geodynamics in Iran, in H. K. Gupta, and F. M. Delany, eds., Zagros-Hindu Kush-Himalaya-Geodynamic evolution: Geodynamics Series, v. 3: Washington D.C., American Geophysical Union, GSA and Ed. Board, p. 70-74.

Stoneley, R., 1981, The geology of the Kuh-e Dalneshim area of southern Iran, and its bearing on the evolution of southernTethys: Journal Geological Society of London, v. 138, p. 509-526.

Takin, M., Y. Akbari, and J. H. Macleod, 1970, Pul-e Dukhtar Geological Compilation Map 1:100,000 (Sheet 20812 E), National Iranian Oil Company (NIOC).

Vergés, J., J. A. Muñoz, and A. Martínez, 1992, South Pyrenean fold-and-thrust belt: Role of foreland evaporitic levels in thrust geometry, in K. R. McClay, ed., Thrust Tectonics: London, Chapman and Hall, p. 255-264.

Vergés, J., in press 2007, Drainage responses to oblique and lateral thrust ramps: a review, in G. Nichols, C. Paola, and E. Williams, eds., Sedimentary processes, environments and basins: a tribute to Peter Friend, v. Special Publication of the International Association of Sedimentologists.

Vergés, J., R. Karpuz, J. Efstatiou, M. H. Goodarzi, H. Emami, and P. Gillespie, submitted 2007, Multiple Detachment Folding in Pusht-e Kuh Arc, Zagros. Role of Mechanical Stratigraphy, in K. McClay, J. Shaw, and J. Suppe, eds., AAPG Memoir on "Thrust Fault Related Folding".

Willis, B., 1893, Mechanics of Appalachian Structure, U.S.G.S. Annual Report 13 (1891-1892), part 2, 217-281, in G. Mitra, and G. Fisher, eds., Structural Geology of Fold and Thrust Belts, v. 5, Johns Hopkins Studies in Earth and Space Sciences, p. 191-206.

63