Download - Alton Downs Gravity Survey Birdsville-LakeFrome Gravity Survey · ALTON DOWNS GRAVITY SURVEY SUMMARY OF DATA AND RESULTS. SUMMARY A gravity survey of 3883 stations covering an area

COMMONWEALTH OF AUSTRALIA

DEPARTMENT OF NATIONAL DEVELOPMENT

BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS

Petroleum Search Subsidy Acts

PUBLICATION No. 67

SUMMARY OF DATA AND RESULTS

GREAT ARTESIAN BASIN, QUEENSLAND

AND SOUTH AUSTRALIA

Alton Downs Gravity Survey

Birdsville-Lake Frome Gravity Survey

OF

DELHI AUSTRALIAN PETROLEUM LTD

Issued under the Authority of the Hon. David Fairbairn

Minister for National Development1965'''r

COMMONWEALTH OF AUSTRALIA

DEPARTMENT OF NATIONAL DEVELOPMENT

MINISTER: THE HON. DAVID FAIRBAIRN, D.F.C., M.P.

SECRETARY; R. W. BOSWELL

BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS

DIRECTOR: J. M. RAYNER

THIS REPORT WAS PREPARED FOR PUBLICATION IN THE PETROLEUM EXPLORATION BRANCH

ASSISTANT DIRECTOR: M. A. CONDON

Published by the Bureau of Mineral Resources, Geology and Geophysics

Canberra, A.C.T.

/65-L

FOREWORD

Under the Petroleum search Subsidy Act 1959-1961. agreements relating tosubsidized operations provide that the information obtained maybe published by the Commonwealth Government six months after the completion of field work.

The growth of the exploration effort has greaUy increased the number of subsidized projects and this increase has led to delays in publishing the results of operations.

The detailed results of subsidized operations may be examined at the officeof the Bureau of Mineral Resources in Canberra (after the agreed period) and copies of the reports may be purchased.

In order to make the main results of operations available early. short summariesare being prepared for publication. These will. be grouped by area and date of completionas far as practicable. Drilling projects and geophysical projects will be grouped separately.In due course. full reports will be published concerning those operations which have producedthe more important new data.

This Publication contains summaries of data and results of two geophysicaloperations undertaken in the Great Artesian Basin. Queensland and South Australia: AltonDowns GraVity Survey. and Birdsville - Lake Frome Gravity Survey. The information hasbeen abstracted by the Petroleum Exploration Branch of the Bureau of Mineral Resourcesfrom final reports furnished by Delhi Australian Petroleum Ltd.

J.M. RAYNERDIRECTOR

CONTENTS

ALTON DOWNS GRAVITY SURVEY

SUMMARY 1

METHODS OF OPERATION 2

GEOLOGY 2

GEO PHYSI CS 3

FIELD PROCEDURES 3

INTERPRETATION METHODS 4

RESULTS 5

ADDITIONAL DATA FILED IN THE BUREAU OF MINERAL RESOURCES 6

BIRDSVILLE - LAKE FROME GRAVITY SURVEY

SUMMARY 9

METHODS OF OPERATION 10

GEOLOGY 11

FIELD PROCEDURES 12

INTERPRETATION METHODS 13

RESULTS 14

REFERENCES 15

ADDITIONAL DATA FILED IN THE BUREAU OF MINERAL RESOURCES 16

ILLUSTRATIONS

Figure 1:Figure 2:

Plate 1:Plate 2:

Plate 3:

Plate 4:

Plate 5:

Location Map. Alton Downs Gravity SurveyLocation Map. Birdsville - Lake Frome Gravity Survey

Bouguer Gravity Map. Alton Downs Gravity SurveyBouguer Gravity Map. Lake Frome Area.Birdsville - Lake Frome GraVity Survey .•Magnetic Map. Lake Frome Area.Birdsville - Lake Frome Gravity SurveyBouguer Gravity Map. Gidgealpa Area.Birdsville - Lake Frome GravityJiurveyMagnetic Map. Gidgealpa Area.Birdsville - Lake Frome GraVity Survey

Frontispiece8

At back of report

At back of report

At back of report

At back of report

At back of report


by



Fig. 1

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Windorah

• Boulio

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QUEENSLANDAUTHORITY TO PROSPECT

66 a 67P

• Leigh Creek

LICENCE

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SUMMARY OF DATA AND RESULTS.

SUMMARY

A gravity survey of 3883 stations covering an area of 4000 square miles wasconducted in southern Queensland and northern South Australia by GeophySical serviceInternational's Party 662 for Delhi Australian Petroleum Ltd, from July to December. 1962.Most of the gravity stations were approximately one-half mile apart. but 824 were one-quartermile stations. In general, stations wel'e set in a four by fifteen-mile grid, although insome areas, particularly in the south-eastern portion of the survey. closer control wasestablished.

The survey was designed to determine the major gravity anomalies in theprospect area. and to seek structural leads in an area almost devoid of outcrop.

Fifteen gravity anomalies of significance were discovered. eight of which arerelated to basement topography while the remainder indicate features within the sedimentarysection. Computed sedimentary thicknesses ranging from 3500 feet to 21.500 feet wereobtained. Seven major anomalies related to basement features are recommended for furtherdetailed geophysical investigation.

In this summary, the results of the survey are presented on the Bouguer gravitymap at a scale of 1:250.000.

The geophysical operation undertaken in the Alton Downs area of the GreatArtesian Basin. Queensland and South Australia, was subsidized under the Petroleum SearchSubsidy Act 1959-1961.

• Abstracted from: Final Report "Interpretation of Reconnaissance Gravity Survey. AltonDowns Area, Queensland and South Australia," by R.A. Geyer. Geophysical service International, March, 1963.

1

METHODS OF OPERATION

General Data

Operator:

Contractor:

Location:

Basin:

Tenement Holder:'

Field Operations

Date survey commenced:

Date survey completed:

Total field party work time:

Coverage:

Average density of gravitystations:

Equipment

Gravity Meters:

Surveying instruments:

Vehicles:

Camp:

Delhi Australian Petroleum Ltd.32 Grenfell Street,Adelaide. S.A.

Geophysical Service International

Oil Exploration Licences Nos 20 and 21, issued bythe State of South Australia; Authorities to ProspectNos 66P and 67P. issued by the State of Queensland.Survey area south-west gf Birdsville'oQueensland• andbounded by lathtudes 25 58' and 27 00' South,longitudes 138 15' and 139 30' East.

Great Artesian

Delhi Australian Petroleum Ltd and Santos Limited

7th July. 1962

19th December. 1962

1369.75 hours

3883 gravity stations over an area of 4000 square miles

0.97 station per square mile

Worden No. 317Worden No. 342

Keuffel and Esser transits

Five Landrovers;One 7-ton Bedford supply truck

One air-conditioned office caravan;Tented camp for 13 men.

GEOLOGY

by

Delhi Australian Petroleum Ltd

General

With the exception of some small areas of "gibbers" representing weatheredduricrust. the Alton Downs area is blanketed by sand and soil and. as a consequence. anysurface expression of geological structure is confined to drainage anomalies. The meagre

2

586-2

knowledge of the stratigraphy of the area is inferred from water bores along the MarreeBirdsville Track, and other widely scattered water bores and test wells. from outcrops inthe Amadeus Basin region, and from data compiled into regional subsurface geological maps.From these sources of information a general stratigraphic column for the Alton Downs areahas been derived.

Stratigra2hy

Rocks of the Lower Cretaceous Winton. Tambo. and Roma Formations and theTransition Zone are likely to attain an aggregate thickness of 4800 feet. and to be underlainby 700 feet of Upper Jurassic Blythesdale Group sediments. Below the Blythesdale. theWalloon Formation of Middle Jurassic age is expected to be of the order of 500 feet thick.Below the Jurassic there may be some 500 feet of Triassic sediments resting on a thicksequence of Permian and older Palaeozoic rocks. From aeromagnetic data the "true" (inagnetic) basement, very generally. occurs at depths of 12.000 feet and more in this area. Athickness for the Palaeozoic strata of 5500 feet can thus be postulated, subtracting the 6500feet of Mesozoic sediments. and assuming Palaeozoic sediments of essentially no magneticsusceptibility. It is qUite likely that in addition to Perm,ian. the Palaeozoic sequence mayinclude rocks of Devonian. Ordovician. and Cambrian ages, as suggested by studies of themany thousands of feet of beds of these ages present in the Amadeus Basin to the north-west.

GEOPHYSICS

byDelhi Australian Petroleum Ltd

Both aeromagnetic and seismic surveys covered all parts of the Alton Downsarea prior to the 1962 gravity survey. The Innamincka-Betoota reconnaissance airbornemagnetometer survey flown in 1961 included this area in a regional mapping programme.The Clifton Hills seismic survey. conducted in part concurrently with the gravity survey,overlapped the eastern half of the gravity survey area.

A comparison of the Bouguer anomaly map and the total magnetic intensitymap shows a fairly good correlation in as much as the areas of greater depth to basement onthe latter map agree well with the location of the strongest negative Bouguer anomalies. andindicated structural anomalies often coincide. Computations of depth to basement made onthese negative anomalies give figures which are in agreement with those on the total magneticintensity map. The Bouguer anomaly map shows a close correlation also with the seismiccontour maps on the' (J and' 'l! horizons. On the seismic maps the location and strike ofthe axes of the major folds agree remarkably well with the main positive and negative Bougueranomalies in the overlap area. In this regard. particularly. the graVity method is shown to bea reliable tool in this area for the detection of structural leads prior to the more costlymapping in detail by the seismic method.

FIELD PROCEDURES

General

Surveying was begun at horizontal and vertical control points in Birdsville. Thesewere National Mapping Astrofix NMA 41 and bench mark 50/57 (elevation 161.00 feet.

3

Queensland Level Datum). A control line of one-quarter mile stations was double-surveyedsouth along the Birdsville Track to station 333. All other stations were surveyed in a seriesof closed loops extending away from the control line, tied and adjusted to South AustralianDepartment of Lands tellurometer stations where possible.

The observed gravity datum is based on an adopted value of 979.103.59 milligalsfor the BMR pendulum station at Birdsville (this value, 100 milligals greater than the BMRvalue, was assigned so that all Bouguer values of this survey would be positive). Observedvalues for 120 other gravity base stations were determined from two or more measurementsof the difference between adjacent bases in overlapping "drifts" (Le., for bases A. B. C, •••.•gravity meter readings in the sequence ABABCBC••.••.... ). These base stations were set inclosed loops with the closure error prorated. The average closure error of the 29 loopsinvolved waf;l 0.026 milligal, Without regard to sign.

Sand dunes afford the only Significant topographic relief in the ~urvey area.A density profile over one dune indicated an average density of 1.8 gm/cm • However,in keeping with prior BMR e¥erience in the Great Artesian Basin. an average surfacematerial density of 1.9 gm/cm was adopted. The Bouguer gravity values were calculatedwith the corresponding elevation correction factor, 0.06982 milligal per foot.

INTERPRETATION METHOrn

General

Both profile analysis and contour migration. methods were used to interpretthe Bouguer graVity map in terms of its geolOgical significance. Profiles were drawn approximately normal to the prevailing strike of the gravity anomalies to facilitate both theirqualitative and quantitative study. Anomalies found on the profiles were corroborated bycontour migration before they were accepted as being real. geologically. Their axes werethen plotted on the geologic summary map.

The major emphasis in interpreting the geological significance of the anomalieson the Bouguer gravity map was to classify them in terms of their origin - such as intrabasement features, basement topography, and structure or igneous intrusions in the sedimentary section. Pertinent information from the aeromagnetic map was also used as corroborative evidence in this phase of the interpretation.

Bouguer Gravity Map

A half-milligal contour interval was used except where the gradient was sosteep as to necessitate a 1-milligal interval. There is evidence in the configuration of thegravity contours for a number of major structures that are confined to the sedimentary section.These include large anticlines, structural noses. and individual faults. as well as horst andgraben systems. In addition. by a comparative study of the aeromagnetic map. severalgravity anomalies indicative of structure in the section that could also be controlled to amajor extent by basement topography were define'd.

• . Contour migration is essentially the same as the fictitious contour method described in''Introduction to Geophysical Prospecting". by M.B. Dobrin. p. 244. McGraw-Hill BookCompany, Inc.• New York. 1960 (second edition).

4

There is also corroborative evidence in the gravity data for areas where theaeromagnetic data indicate the basement is deep. particularly near the eastern boundary ofthe survey. The deeper portions of the basement appear to be interrupted at a number ofplaces by local basement uplifts. Some of these appear to control major structural featuresin the overlying sedimentary section.

Aeromagnetic Mal!

Several magnetic anomalies of intrabasement orIgm dominate this map. Oneoccurs along the eastern boundary ofthe survey and was used for a depth-to-basement determination in this area. It centres near the axis of a major negative gravity anomaly.

A depth-to-basement computation on this negative gravity anomaly, assuming anaverage diqerence in density between the basement rocks and the sedimentary section of0.1 gm/cm, yields a value of approximately three miles. This figure is in reasonableagreement with that obtained by computing the depth-to-basement on the aeromagneticanomaly.

RESULTS

General

The purpose of the report was to interpret the geological significance of thevarious types of gravity anomalies mapped by the survey. Evidence available from theaeromagnetic survey and density data of key geological formations was also considered inpreparing this interpretation.

The significant geological features of the area and their relationships as interpreted from the gravity survey and additional aeromagnetic and density data are shown on thegeologic summary map. These include major positive and negative structural axes, faultsand fault-systems.

The Bouguer gravity map of the survey area shows at least two large positivegravity anomalies believed to be caused primarily by density contrasts within the basement.Each of these anomalies is associated with a well-defined positive magnetic anomaly whichis also of intrabasement origin. The first is a regional anomaly situated in the centre ofthe survey area; the second occurs near the southern central part of the area. In addition,there is a positive, intrabasement, magnetic anomaly with no associated positive gravityanomaly. It is near the central part of the eastern boundary.

There is evidence in the configuration of the Bouguer gravity contours along theeastern and western boundaries for two major synclines. However, profile analysis indicatesthe western one may in part be a pseudo-negative effect caused by the adjoining positive,intrabasement, gravity anomaly.

A number of positive structural axes are shown on the geologic summarymap. These were interpreted from those positive gravity anomalies believed to be causedby either structure in the section or basement uplift, considering also the magnetic information.

5

A series of fault type anomalies including horst and graben systems also appearon the summary map. Additional gravity information would be reqUired over these anomaliesbefore a more definitive quantitative interpretation as to depth and displacement could be made.

It is evident from the interpretation that additional information regarding thedensity of key formations in the survey area is necessary before a more quantitative interpretation can be made of the geological significance of the gravity anomalies. It would thenbe oossible to give a more direct answer as to the depth to basement, the thickness ofthe sedimentary section in variOUS parts of the survey area. and the displacement of thefaults.

ADDITIONAL DATA F1LED IN THEBUREAU OF MINERAL RESOURCES

The follOWing additional data relating to the Alton Downs Gravity Survey havebeen filed in the Bureau of Mineral Resources. Canberra. and are available for reference:

(i) Final Report, by RA. Geyer 14 pp.

Appendix A:Appendix B:

Field operationsGeology and geophysics, by Delhi AustralianPetroleum Ltd

6 pp.

2 pp.

(ii) Geologic summary map (1". 10.000 it)

(Hi) Representative Bouguer profiles

(iv) Station location map, shOWing station numbers, elevations.and station locations

(v) Computation sheets, shOWing station numbers. elevations,observed gravity values~ latitude corrections. elevationcorrections. and Bouguer values

(vi~ Topographic survey field sheets

(vii) Gravity meter field notes

6

2 sheets

1 sheet

9 sheets


by



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50Me

o142

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QUEENSLANDAUTHORITY TO PROSPECT

66 8 67P

AUSTRALIALICENCE 20

GRAVITY SURVEY

AREA

NORTHERN

TER RITORY

SOUTHOIL EXPLORATION

~ BETOOTA No.l-----____ __ • Birdsville

---'-'-':~:~;D~~::;~-'-'-'-'-;---;rjl-_--f----__260;

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8


SUMMARY OF DATA AND RESULTS.

SUMMARY

A gravity survey of two areas in the Birdsville - Lake Frome region of theGreat Artesian Basin was conducted by Geophysical Service International's Party 662 forDelhi Australian Petroleum Ltd, during the period April to October, 1963.

In the first survey, over the Lake Frome area of eastern South Australia.gravity observations were taken at 2870 stations that formed loops of approximately five byten-mUe dimensions. and were spaced at one-half mile intervals along trails and fence lines.Thirty-four anomalies were outlined, including features of interest to petroleum exploration,and features such as intrusive material. that might limit the prospective areas. Some of themore interesting anomalies indicate regions where 5000 to 15,000 feet of sediments mayoverlie the basement. Vertical magnetic intensity measurements were recorded at thegravity stations, and the results were used to aid the gravity interpretation.

The second survey was made over the Gidgealpa area in north-eastern SouthAustralia, where both gravity and magnetic observations were taken on 1189 one-half milestations located in an estimated area of approximately 2000 square miles. Eighteen anomalieswere outlined. Nowhere was the sedimentary section computed to be less than 6000 feet.Of particular interest is a large graVity "high" anomaly that appears to outline the structureupon which the Gidgealpa gas field is located.

The vertical magnetic intensity contours show that some of the magnetic anomaliescannot be correlated directly with graVity anomalies. The variance between gravity and magnetic anomalies is discussed in general terms, and it is concluded that:

(i) Magnetic estimations of deep basement are valid;

(ii) Gravity anomalies reflect mainly Permian-Cambrian topography and shallowdensity anomalies; and

(iii) The major negative gravity anomalies indicate thickening of sedir;tients.

The geophysical operation undertaken in the BirdsvU1e- Lake Frome area of theGreat Artesian Basin, South Australia, was subsidized under the Petroleum Search SubsidyAct 1959-1961.

• Abstracted from: Final Report "Birdsville - Lake FromeGravity Survey, Parts I and 11".by N. Harding, M.L. Brown. and R.A. Geyer. Geophysical service International. November.1963.

9

METHODS OF OPERATION

General Data

Operator:

Contractor:

Location:

Basin:

Tenement Holder:

Field ~rations

Date survey commenced:

Date survey completed:

Total field party work time:

Coverage:

Average .density of gravitystations:

Gravity Meters:

Surveying instruments:

Vehicles:

Camp:

Delhi Australian Petroleum Ltd,32 Grenfell Street,Adelaide, S.A.

Geophysical service International

Oil Exploration Licences Nos 20 and 21, issued by theState of South Australia. Lake Frome area - bounded

o 0by latitudes 29

045' and 31

030' South,

longitudes 139 00' and 140 30' East.Gidgealpa ares - bounded 8Ylatitudes 27 30' and 28 30' South.,

o 0longitudes 139 25' and 140 20' East.

Great Artesian

Delhi Australian Petroleum Ltd and Santos Limited

3rd April, 1963

11th October, 1963

1338.75 hours

4059 gravity stations over an area of 6750 square miles

0.6 station per square mile

Worden No. 317

Worden No. 342

Keuffel and Esser transits

Six Landrovers;One 4 x 4 Bedford supply truck

One air-conditioned office caravan;Tented camp for 15 men.

10

GEOLOGY

by

Delhi Australian Petroleum Ltd

Lake Frome Area

Objective of survey:

The Lake Frome portion of the Birdsville-Lake Frome Gravity Survey wasdesigned as a means of confirming the existence and determining the extent of a postulatedstructural trough adjacent to the eastern flank of the northern Flinders Ranges. and to detectleads to possible structural traps for hydrocarbons which might be mapped further by seismicmethods.

Prior geological information:

Extensive areas of outcrop of very thick (up to 20.000 feet) Lower and MiddleCambrian marine sediments occur along the eastern flank of the northern Flinders Ranges.within the south-western margin of the survey area. Meagre structural indications from afew aeromagnetic profiles and scattered shallow water bores have suggested that a deep structural depression parallel to and immediately east of the ranges is present. The presenceof Cambrian sediments in the downwarp is indicated by regional stratigraphic studies whichshow that marine sedimentation was widespread during the Cambrian period. with shorelinesfar from the area under consideration.

Gidgealpa Area

Objective of survey:

The primary objective of the survey in the Gidgealpa area was to acquire basicgravity and ground magnetic information in an area believed to have considerable potentialfor hydrocarbons. At the time the survey was undertaken the area was one in which onlyreconnaissance aeromagnetic and seismic surveys had been carried out. A deep off-structurestratigraphic test was being drilled at the time the survey was initiated and conducted. Itwas expected that the gravity and ground magnetic information in conjunction with theprevious geophysical data. and data resulting from the drilling of the Gidgealpa No. 1 Well.would provide a means for more reliable mapping of the subsurface structural and stratigraphic features of this area.

Prior geological information:

Previously drilled wells nearest to the survey area are the Delhi-FromeSantos Innamincka No. 1 Well located 60 miles to the north-west of Gidgealpa No. 1 and theDelhi-Santos Dullingari No. 1 Well located 50 miles to the south-east. Reconnaissancereflection and refraction seismic surveys had related the sedimentary column as encounteredin these wells to the present survey area and. in conjunction with reconnaissance aeromagneticdata, indicated that a thick sequence of Permian and older Palaeozoic sediments is ofWidespread occurrence in this region.

11

Conclusions regarding the stratigraphy of the Permian sediments in the reg'ionof the gravity and ground magnetic survey were based primarily on the results of the twowells previously mentioned. both of which encountered interbedded sandstones. shales. andcoals of Permian age. At least some of the shales appear to be of marine origin. althoughthis is not proven. and the section in general appears to be representative of a fluctuatingmarginal-to-marine environment. and to bear a favourable aspect for the generation andaccumulation of hydrocarbons.

With regard to pre-Permian sediments in the general Gidgealpa area it wasexpected that marine units of Lower Palaeozoic age would be present. but it was impossibleto predict their age or nature. At Innamincka No. 1. red-beds of probable Devonian age. andmore than 5000 feet thick. were encountered below the Permian. At Dullingari No. 1. marineshales of Ordovician age. and in excess of 2000 feet stratigraphic thickness. were found tounderlie the Permian sequence. Widespread Lower Palaeozoic marine sedimentation isbelieved to have occurred across the north-eastern portions of South Australia. based onstudies of sediments of these ages which occur in outcrop in the northern Flinders Rangesof South Australia. the Mootwingee area of north-western New South Wales. and the Amadeusand Georgina regions of the Northern Territory and Queensland.

Gidgealpa No. 1 Well penetrated 6942 feet of Mesozoic sediments, 1000 feet ofPermian, 420 feet of undifferentiated Palaeozoic sediments, and 4004 feet of Cambrian sediments to total depth of 13,114 feet. In the Cambrian section, Middle Cambrian rocks arethrust over Upper Cambrian, which continue in downward sequence into Middle Cambrian attotal depth.

Gidgealpa No. 2. located two miles west of No. 1 Well. and near the axis of theanticline. found volcanic rocks immediately underlying the Permian sediments and these werepenetrated for 2152 feet to total depth at 9020 feet. Gidgealpa No. 2 was completed as thediscovery well of the Gidgealpa gas field. with a calculated absolute open flow potential of29.5 million cubic feet of gas per day from Permian sands.

FIELD PROCEDURES

Lake Frome Area

Vertical control was initiated at Reaphook Hill trigonometrical station with anelevation of 1272 feet (M.S.L. Port Augusta). National Mapping Astrofixes NMA 37 andNMA/E/54 provided the horizontal control.

The observed graVity base network was composed of seventy-six bases formingsixteen base loops with an average misclosure of less than .!. 0.02 milligal. Misclosureerrors were prorated. Observed values for bases were determined from two or moremeasurements of the difference between adjacent bases in overlapping "drifts" (i.e•• forbases A. B. C•.•.... gravity meter readings in the sequence ABABCBC) and are relative to anassumed value of 500.00 milligals for Base A. A tie to a pendulum station was not deemedpractical. With the exception of the foothills of the Flinders Ranges along the western sideof the prospect, the terrain is generally flat. Only two suitable grarty meter density profileswere obtained in the area. Both yielded a density of 2.0 gm/cm indicative of an elevationcorrection factor of 0.06854 milligal per foot. No surface rock samples were submitted.

12

Gid~ealpa Area

The entire prospect is dominated by north-south oriented sand dunes spaced atapproximately one-half mile intervals. These rough-surfaced dunes rise 30 to 60 feet abovethe general terrain which has little relief. A large percentage of the surveying was alongseismic lines with station spacing at one-half mile intervals. The majority of the lineswere oriented in a north-south direction because of the sand dunes. Accessibility andanomalous conditions were the criteria used to decide loop sizes.

The horizontal and vertical datum originated on United Geophysical CorporationShot Point L-llO, which has an established elevation of 168.00 feet. The horizontal controlfor Shot Point L-110 was derived from the Delhi Australian Petrol~um Ltd Gidgealpa No. 1astrofix, located 820 feet from this shot point on a bearing of 064 05' True. The verticaldatum was derived by United Geophysical Corporation seismic survey, using as a basedatum the value of Innamincka No. 1 Well: 401.68 feet (L.W.O.S.T... 0' Port Adelaide).This well had previously been tied by a level traverse to the Marree-Birdsville 1883 Railway Survey.

A network of 41 bases was established from an adopted value of 200.00 milligalsfor Base A located on station No. 8. Two or more measurements of the observed gravitydifference between adjacent bases were taken by use of overlapping "drifts" (i.e. ABAB, whereA and B are readings on+two distinct points used as base locations). The nine base loops'average misclosure was - 0.027 milligal. The errors were prorated in proportion to thenumber of bases on the loop.

When running stations, "drift" was determined from readings on previouslyestablished bases at not more than two and one-half hour intervals. The drift correctionswere applied in proportion to time.

One density profile was run which indicated an elllvation correction factor of0.06982 milligal per foot, corresponding to a density of 1.9 gm/cm •

INTERPRETATION METHODS

Lake Frome Area

The interpretation of the Bouguer gravity maps was made using profile analysisand contour migration methods. Gravity and magnetic profiles were drawn perpendicularto the gravity contours.

An attempt was made to classify each anomaly's source as to its geologicalorigin, based on the combined evidence from the gravity, magnetic, and density data.

Because of the extremely steep gradient in several parts of the area, a 1.0milligal contour interval was used. The Bouguer gravity maps show a wide range of anomalytypes from large circular anomalies associated with basement geology to small, sharp,irregular shaped contour variations due to shallow intrusions or near-surface sedimentarydensity contrasts.

13

The magnetic maps made it possible to eliminate from further considerationthe entire northern quarter of the surveyed area - the part dominated by intruswes andflows. The general basement configuration can be seen from depths to basement computedfrom the magnetic anomalies. Magnetic depth determinations in the south-western part ofof the map were not made because of the absence of suitable anomalies.

Gidgealpa Area

Profile analysis was used to interpret the Bouguer gravity map. Profiles weredrawn approximately normal to the prevailing strike of the gravity anomalies to facilitatetheir qualitative and quantitative study. The gravity and magnetic maps were used to traceout the axes shown on the geologic summary map.

Because of the steep gravity gradient along the eastern side of the centralanticlinal axes. a contour interval of one milligal was chosen. The gravity map substantiatesevidence shown on the magnetic map for large areas where the basement is relatively deepsuch as in the north-western and south-eastern sections.

RESULTS

Lake Frome Area

The results of the survey are presented in this summary on two maps: Bouguergravity map. and magnetic map. each drawn at a scale of 1:250,000.

The examination and interpretation of all data obtained from the survey indicatethat the Lake Frome area can be divided into three provinces: (i) an area in the south-westernpart bounded on the east by a major fault and on the west by the northern Flinders Ranges.(H) the north-eastern part containing very shallow intrusions of igneous plugs and flows intothe sedimentary section, and (Hi) a basin area having a maximum thickness of sediments ofabout three miles.

Thirty-four anomalies are drawn on the geologic summary map. Their interpretations are based upon profiles drawn perpe~dicularto the gravity contours and by contourmigration. A density contrast of 0.2 gm!cm was used to compute maximum depths to thetop of the geological feature causing the anomaly. Specific gravity determinations made bythe Australian Mineral Development Laboratories on top Lower Cambrian (Billy Cree~)

and Lower Cambrian (Parara) spec~en rocks. resulted in densities of 2.60 and 2.78 gm!cm ,density contrast of 0.18 gm!cm. These rocks crop out along the eastern flank of thenorthern Flinders Ranges. It is also thought that the Billy Creek Formation is overlain by200 to 300 feet of limestone (probable density of 2.6 to 2.7) and a very thick Middle Cambriansection of sands (probable density of 2.4). resulting i?3 a probable density contrast betweenMiddle Cambrian and top Lower Cambrian of 0.2 gm!cm •

gid~alpa Area

The results of this survey are presented on the follOWing maps (scale 1:250,000)Bouguer gravity map; and magnetic map.

14

The geologic summary map shows the significant geological featuresof the area as interpreted from the gravity and magnetic maps. These features are majorpositive and negative structural axes, faults, and fault systems; a total of 18 gravity anomaliesare drawn on the map.

The most striking characteristic of the magnetic map is the enormous regionalextent of the magnetic positive anomaly which dominates at least 60 percent of the surveyedarea. This great elliptical-shaped anomaly has its symmetry interrupted in only two places.by a deep basement fault which runs northeast-southwest across it, breaking its axial continuityat 27

057' S, 140

000' E, and by the large magnetic negative with its axis at approximately

280

13' S, and 1400

13' E. Because of the relatively genUe magnetic gradients over the entiremap, except on the eastern flank ofthe huge magnetic positive, it can safely be concluded fromthe magnetic data alone that (i) the basement is at considerable depth, or (ii) the properties ofthe Precambrian rocks in general change very gradually horizontally.

An inspection of the Bouguer gravity map and a subsequent comparison of itsanomalous areas with those of the magnetic map reveal that in general there is a minimumcorrelation. From this fact, it can be concluded that many of the positive and negative graVityanomalies originate entirely from horizontal density contrasts within the sedimentary section.Specific gravity determinations of cores (1-17) from Gidgealpa No. 1 revealed that positivedensity contrasts do exist in the section.

The Bouguer gravity map shows a major anticlinal axis running northeastsouthwest across the central part of the area. Gravity lows of considerable areal extentflank the sides of this axis. Profile B-B' was selected to cross the axis perpendicularly.This major positive gravity anomaly is no doubt associated with the Gidgealpa structure.Its trend coincides very nearly with the crest of the structure.

The positive gravity anomalies vary in amplitude from three milligals to 16milligals. As an objective test, depths were calculated on all significant positive anomaliesusing symmetrical models of two dimen~ionalprisms and circular cylinders and a conservativepositive density contrast of 0.2 gm/cm • No depth was shallower than 6000 feet.

REFERENCES

DELHI AUSTRALIAN PETROLEUMLTD,


DELffi AUSTRALIAN PETROLEUMLTD,


1961a: Final Report, Innamincka - Betoota aeromagnetic survey (Unpubl.).

1961b: D.F.S. Innamincka No. 1 Well. South Aust-ralia. Bur. Min. Resour• Aust. Petrol.Search Subs. Acts Pub1, 9.

1961c: D.F.S. No. 1 Betoota. Queensland. Bur. Min.Resour. Aust. Petrol. Search Subs. ActsPubl.10.

1962 Well completion report, Delhi-Santos Dullingari No. I, South Australia (Unpubl.).

15

REFERENCES (Cont'd)



SKEELS, D.C••

VACQUIER, V., STEENLAND, N.C.,HENDERSON, R.G., and ZIETZ, I.,

1963: Final report, Diamantina - McGregor seismicsurvey (Unpubl.).

1964 Well completion report, Delhi-Santos Gidgealpa No. 1, South Australia (Unpubl.).

1962 An approximate solution of the problem ofmaximum depth in gravity interpretation.Society of Exploration Geophysicists, 32ndInternational Meeting. Calgary, Alberta.

1951 Interpretation of aeromagnetic maps. Geol.Soc. Amer. Mem. 47.

ADDITIONAL DATA FILED IN THEBUREAU OF MINERAL RESOURCES

The following additional data relating to the Birdsville - Lake Frome GravitySurvey have been filed in the Bureau of Mineral Resources, Canberra, and are availablefor reference:

Lake Frome Area

(i) Final Report, by N. Harding and R.A. Geyer

Appendix A: Field operations

12 pp.

9 pp.

Appendix B: Geological summary, by Delhi AustralianPetroleum Ltd 3 pp.

Appendix C: Table of Principal Facts 6 pp.

(H) Bouguer graVity map,

(Hi) Magnetic anomaly map,

(iv) Geologic summary map.

(1" '" 5000 it)

(1"" 5000 ft)

(1" .. 10,000 it)

6 sheets

6 sheets

3 sheets

(v) Station location and elevation map. (1" = 5000 ft)

(vi) Density profile results

(vii) One-mile photo mosaics showing 100 permanentlymarked stations

16

6 sheets

1 sheet

1 sheet

L

Gidge'llpa Area

(i) Final Report, by M.L. Brown and R.A. Geyer

Appendix A: Field operations

Appendix B: Geological summary, by Delhi AustralianPetroleum Ltd

Appendix C: Correlation of geophysical data, byM. Mazzolini

Appendix D: Table of Principal Facts

11 pp.

6 pp.

8 pp.

5 pp.

10 pp.

(ii) Geologic summary map, (1" .. 10,000 ft) 1 sheet

(iii) Station location and elevation map, (1" ..

(iv) Density profile results

(v) Gravity profile B-B'

(vi) Topographic survey notes

(vii) Magnetometer calculation sheets

(viii) Gravity meter drift and dial corrections

(ix) GraVity meter drift curves

(x) Bouguer calculation sheets

17

5000 ft) 4 sheets

1 sheet

1 sheet

27'00'

26'15'

26'00'

26' 3d

PLATE

140'00'

PARTY CHIEF: L. WERLE

DATE' MARCH, 1963

FIELD WORK DONE·

GRAVITY SIJRVEY

MAP PROJECTION, PO~Y~~~~COECEMBER 1962

BOUGUER GRAVITY MAP

? SCALE 1 : 250,000

[=:::::I;;;;;;;;;;;;c:~~::~~~b~~~~::e;;;;;;3:=::J;;;;;;;;;;dCONTOUR MILEs .....-30

INTERVAL 0,5 MILLlGAL

GEOPHYSICAL SERVICE INTERNATIONAL

OELHI AUSTRALlAN PETROLEUM LTO,

ALTON DOWNSOUTH S GRAVITY SURVEYAUSTRALIA AND QUEENSL AND

PARTY NO. 662

INTERPRETATION: R A GEYER

139"45'

Observed gravity datumStation. Bouguer gravlt based on adopted valuebased on ado led y values calculated w of 979,103.59 mill' 01gravity farm~la. prr:~~b~ensity of 1.9 gm/C~~ e~e~~t,on correction gfa;t::rafBi~dsvllle Pendulum

e accuracy of graY1t;val~ "~f ca"ectians from 1930·069B2 m.lhgal/ft.es. _ 0.10 mill1gal. International I

139'45'

TI/49211>

TI/47211>

n/482IJI,

139'30'

~I~al paint of harl~:~~a\n miles Probable accu~a:tadla distances. Probable acB.M ·5g;~~ ~t ~iar~d: .~,,"ur~~re~:~' ~~~:~~~~ ~apPln~ ~stv..:n:aMur~ey 0.3 ft~:;~~~:a::ehlarl,en,al

VI e (Queensland Level· 0 ertical surVey based I at Blrdsville with ~imlles.atum), on elevation 011

161.00 f~S f~~

TOPOGRAPHIC

Surveyed by transit . SIJRVEYsurvey: 100 ft. Jd 1st With magnetic bearings an

TI/550161

BouQuer gravitmilllgol interv~ls~ontourSI at one-naif

0 Positive Anomaly.

= Negative Anomaly.

LEGENO

NMA 41 are S A point, 011 except

Tellurometer ·s;a~~~:·.of Lands

~ 139'15'

TI/482'

l:1 Horizontal control

~;, Gravity Station wIn milligals Slontel~h Bouguer valueunderneath. 1 station number

INDEX

_____~. QUEENSLANDS~AUSTRALIA

138'00'

26' 00' ---11---

27'00'~~--b~~~~138°00' 138°15' 138°30'

I

PLATE 2

1390

00'

30' 30'

Homestead or outstation.

Permanently·marked stationwith gravity base

@IS••-t

•


DA.TE: NOVEMBER. 1963

GRAVITY SURVEYAIJSTRALlA

",r:P/80UgUer gravity contours at/" one-mill1gol Intervals.

o Posilive Anomaly

c:J Negative Anomaly.

• Water well.

70POGRAPHIC SURVEY

LEGEND

Surveyed by transit with magnetic bearings and stadia distances. Probable ac

curacies of horizontal and vertical surveys: 100 ft Idlstance In miles and0.3 ft ..Idlstance in miles respectively. Initial points of horizontal survey,National Mapping Astroflxes NMF 37 and NMA/E/54. Vertical survey basedon sea level datum, with origin at Reaphook' Hill (printed elevation onaeronautical Chart).

LAKE FROMESOIJTH

.u T'

1&''''rI .0

",110

,...

PARTY NO. 662

INTERPRETATION: R. A. GEYER

DELHI AUSTRALIAN PETROLEUM LTo.

BOUGUER GRAVITY MAP

SCALE " 250,000

O~=::::E;;;;;3==:E;;;;;;;;;(=;;;15~~!C==r~~C=:::E=;::i'OL MILES E""'3CONTOUR INTERVAL: I MILLlGAL

GEOPHYSICAL SERVICE INTERNA710NAL

FIELD WORK DONE: APRIL- JULY 1963MAP PROJECTION - POLYCDNIC

Observed gravity origin at Base A with an assumed value of 500 ml1l1oall.

80uguer gravity values calculated with elevation correction factor of 0.06854milligallft (density 2.00m./cm.3 ) based on two density profiles surveYQd In thearea. Latitude corrections fr~m 1930 International gravity formula. P.robableaccuracy of gravity va.u8l: - 0.10 mllllgal.

.''\~ Station locatIon with station number,.. underneath and the Bouguer value

above. Stations with no va lue notmetered

111""76 Horizonta I control point, National Map-

pinQ Astrofix

l:H",A.IJl\rig station Not used as control

DDlnr.

"LlI'," tI

• 111. ,.•••11...:

• ...11.,-..........

:.\1............• .,'f

.'

.16!11

....:",t.,_-~"l

ell .".. ,---././

/' ..../' /'

/ ...cfJ/

€l~:,"_1

FAEELING HEIGHTS

ClTAIG

" .~:o

o• "OElUCII

Cl

,.,0.'

9000---::~.o-l--- _---..........•"1°__4---__

310

00'

139'00' 139-111' 139'30' 140'00'

3

1390

00'

distances. Initial

NMF 37 and NMA/E/54.

Mme

Homestead or outstation

Permanently-marked station With

gravIty base.

10

E=""3

•

PARTY CHIEF: L WERLE

DATE: NOVEMBER, .963

PETROLEUM LTD.

GRAVITY SURVEY

AUSTRALIA

LEGEND

PositIve Anomaly.

NegatIve Anomaly_

Water well.

MAGNETIC MAP

SCALE I : 250,000

E=""3 5MIr;;--t t-----4

CONTOUR INTERVAL' 20 GAMMA

TOPOGRAPHIC SURVEY

Po~itlonlnQ by transit With maPOints of borizontal surve Ngnetlc bearings and stadia

Probable horizontal accuraYc'y. I~~o;a I M.applng AstroflXes. t .)dlstance in miles.

,.,00 " Magnetic vertical Intensit

~ontour lines at 50- gomm~Intervals.

DELHI AUSTRALIAN

LAKE FROME

SOUTH

. '

oI

noo.- IIlt


PARTY NlO. 662

INTERPRETATION: R. A. GEYER

,-";....", ...." ....."

• ..."' ... 0_ ..0 1.u,o- ut'••• M.Z@·."O

2111}'

-----_--1_.....-:.-,..

Station location With statunderneath and relative ~;on:~~bervalue, vertical component /obove. Stafions J postedmetered With no value not

HOfllontal control points, NatIonalMopping Astrofl1l:

Trig stotpaint. IOn. Not used as control

ZUOD_'''lIoO-ITI

LfV'1, 't-----'-., ,, ,I .!

LOCATION

FIE L 0 WORK DONE: APRIL-JULY .963MAIP PROJECTION - POLYCONIC

Q

MAGNETIC SURVEY

All observed magnetIc voluesat •Ma.gnetometer Base "A'.' ObS::latlve to an assumeddevlat,on of '4.3 gommo, ved va'ue, co"ected fva.ue of 1000 gommo,accuracy of magnetic value,p~r±m

611e, N 6 E (BMR R or normal regional. gammas eport No. 62), Apparent

''[,''

.....Z@)_·'lIo.-.".-".

0-"1

Z~1I1 ._,'

'-," ,::T:I•\'JIt't'" .._.Tl

t ..iO 2440

0_""

.',',".

,_0"

_",1_,,1

"'T'O~_OII

••no 0..1'"._TTI • .,OT - '00

~_-.o,.....

140°00'

~&O

139°45'

1404@

'\401

..

IlO4

1210.'f.T ..

FR££L6 HEIGHTS

TR';

TIO.·"""

~'O_.~

~OElUCK

Tlm;

-400

3111

00'

30' 00'

.,-------

PLATE 4

140'00'

OELHI AUSTRALIAN PETROLEUM LTO,GRAVITY a MAGNETIC SURVEYS

28· 15'

28' 00'

•

.•...•. I~O·· .11 •• 11

11. 'I'•.:.0. 11

...'", ~

,.o'V .._

..... ,,.".... ,,0

if,. ••to .p........

..Iro ••

• 1:0 11

..

=

..11111

140" 15'

GRAVITY SURVeY

"'~""..- r1' Q::i.'" ··...if

.']••"j.... ~....,,."

.', .p

0·... .",0·" .....'"- .'."..._-,----...0 ."}" ~

.'"

.'f' ~,", J'••.,.•-f',

.p'11.0

...o~',,'

Observed gravity origin at Ba .. 11 A 11 with an assumed value of 200.00 mllllgall. Bououergravity value. calculated with el.vation correction fac10r of 0.06982 milllgal/ft. (density

1.9 vm,/cm.3 ) baled on one denslt~ profile lurv.eyed In the area. ~atitude car-l'lctionsfrom 1930 Internat Iona I gravity formula. Probable accurac~ of gravit, v.a'ues: - 0.10 mllligal.

gg

140' od

12: ~ United Geophysical shot point and linenumber.

,.rJ'// BouQuer gravl t)" contours at I mllllQol

Intervals.

ri,'or;F

LEG~ND

~ Po.itlve Anomaly.

t:J ·Negative Anomaly.

-?- Dry Hol.,

Gravity bases marked with Iron@ pickets. Number undernea th..S·p· doubl-e clrcle Indicate. perman

ently marked station.

Station location with station numberunderneath and the Bouguer valueabove .totlons,

.'...~50'

"..HI'I"0Horlzontal control point, National6. Mapping Astroflx.

TOPOGRAPHIC SURVEY

10

Surveyed by transit with magnetic bearings and stadia distances.Probable Qccurocles of horizontal Qnd vertical surveys: 100 ft,';distance In miles and 0.3 ft.v'dlstonce In miles relpectively.Initial points of both horizontal and vertical survey, UnitedGeophysical Ihot point L-IIO. Previously establtshed elevation ofL-1I0, 168.00 feet.

Malt of seismic Ihot point locations omitted to prevent crowdingof data.

PARTY CHIEF: L, WERLE

DATE: MARCH, 1964

MILES

CONTOUR INTERVAL I MILLIGAL

80UGUER GRAVITY MAP

SCALE I : Z50,OOO

5

...... t-....c:.'--t"'.....+-----l


o

BIROSVILLE-LAKE FROME AREASOUTH AUSTRALIA

oI

'FIELD WORK DONE: AUGUST- OCTOBER, 1963MAP PROJECTION: PDLYCONIC

LOCATION

PARTY NO, 662

INTERPRETATION: R, A. GEYER

...:~",'".""... ,,0'. .',.

••• ·,..I'(§) .....,.111'1· ..0,.

'",.~.

cj:) .".,....1°' • ,,","

11'00

".'•..·0·...•.' J'.0

0-

- ,._--------+-----.......'"II.·..~'"

.'", .'..-.'.' __-----~l82.00 -,::,,0..'."

010· 11

28' 3d

28' 00'

____I

PLATE 5

139 30' 14000'

B/RDSV/LLE-LAKE FRaME AREASOUTH AUSTRALIA


FIELD WORK DONE: AUGUST-OCTOBER, 1963

MAP PROJECTION: POLYCONIC

28 od

• .,. ••• "" • ,~o 4>'• • 0,..

. .'1!O· •

....ll~ •

., .M'

="0" .0.,' .'"5IlCld .'~..'

-".'~'.'.,'..,.u,? •

\-<.'"I "",~10..,......:j

LTD.


DATE: MARCH, 1964

MAP

SCALE I : 250,000

5..,......:j

MAGNETIC

Ml LES

CONTOUR INTERVAL. 25 GAMMA

DELHI AUSTRALIAN PETROLEUMGRAVITY a MAGNETIC SURVEYS

oI

PARTY NO. 662

INTERPRETATION' R. A GEYER

28' 30'

28' 00

LOCATION TOPOGRAPHIC SURVE Y LEGENO

140 od 140' 15'

MAGNETIC SURVE Y

PositIoning by transit with magnetic bearings and stadia distances.Initial points of horizontal survey. United Geophysical shot point

L-1I0. Probable horizontal accuracy: 100 ft. Jdistance in miles

Most of seismic shot point locations omitted to prevent crowding

of data.

q,'"- Station location wIth statIon number,..."'0 underneath and relative magnetic

value, vertical component, posted

above.

N"~70Horizontal control POints, NotionalMopping Astroflx.

Gravity bases marked with Irono pickets Number underneath double

as "Q" circle indicates permanently

marked station.

o Positive Anomaly.

c:::J Negative Anomaly

-9- Dry Hole

Magnetic vertical intensity contour linesat 25 gamma intervals.

UnIted GeophYSical shot point and linenumber.

:~lseOb~~r.yel~CO~:3ne~b~ vf~~Utess::tlhat~;ede~~lt~n P~~~~I~edStVa°t'i~en O~o.I?~O OgbOs~~vOeSd a~a~~~netometercorrected for normal regIonal deviation derived from BMR Report No 62 7 1I1somogneticMops of Australia:'

+Probable accuracy of magnetic values: - 10 gammas.