COMMONWEALTH OF AUsrRALIA

1:250,000 GEOLOGICAL SERIES-EXPLANATORY NOTES , Qld

SHEET SG/ 54-8 INTERNATIONAL INDEX

Compiled by C. M. Gregory & R. R. Vine

Published by the Bureau of Mineral Resources, Geology and Geophysics, and issued unde r the authority of the Hon. David Fairbairn, D.F.C., M.P.,. Minister for National Development. COMMONWEALTH OF AUSTRALIA

DEPARTMENT OF NATIONAL DEVEWPMENT llllNISTBR : TRB llON. DAVJD FAIRBAIRN, D.F.C., M.P. SECH!'ARY: R.. W. BoSWW:U., 0.B.E.

BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS DIMCrOll: J. M. RAYlml, O.B.E.

Gl!OLOGtOAL BRANCB: AssnnAlff Dmsoroa: N. H. FJBIIIR

Printed in Australia by the Tasmanian Government Printer, Hobart . Explanatory Notes on the Windorah Geological Sheet

Compiled by C. M. Gregory & R. R. Vine

The Windorah Sheet area was mapped in 1966 by a Bureau of Mineral Resources field party, as part of a programme of regional geological map­ ping in the Great Artesian Basin in .· The area is covered by air-photographs at a nominal scale of 1:250,000, flown by Adastra Airways Ltd in 1958. A topographic base map at 1 :250,000 scale, supplied by the Division of National Mapping, Depart­ ment of National Development, was amended and brought up to date during the geological mapping project. Cadastral maps at 4 miles to 1 inch, pro­ duced by the Queensland Lands Department, also cover the area. The area is serviced by a tar-sealed road (the Diamantina Develop­ mental Road), between Quilpie and Windorah, and by a good gravel road between Windorah and Jundah. Other roads in the area are natural graded earth with gravel only in places. One commercial airline operates a weekly flight to Windorah from and a fortnightly flight from Adelaide. Windorah, the only town in the Sheet area, has a population of about 100.

Previous Investigations The area had not been systematically mapped before the 1966 survey. Understanding had come mainly from basinwide studies (Whitehouse, 1954) and a compendium of the geology of Queensland (Hill & Denmead, eds., 1960). Particular aspects of the late geological history were discussed by Woolnough (1927) and Whitehouse (1940, 1948). Semi-detailed gravity surveys were carried out for L. H. Smart Oil Exploration Co. Ltd and Alliance Oil Development N.L. (SOE, 1962; Staclcler, 1963). A reconnaissance survey of the rest of the Windorah Sheet area, which incorporated the results of previous scattered traverses ( Gibb, (1967), was carried out for the Bureau of Mineral Resources (Lonsdale, 1965). Bouguer anomalies from these surveys are shown on the geological map; contouring was mechanical. Some trends shown in the earlier company reports were based on geological interpretation and show appreciable differ­ ences from the mechanically plotted map, particularly in defining the Cana­ way Ridge.

An aeromagnetic survey of the western third of the Sheet area was carried out for Delhi Australian Petroleum Ltd and Santos Ltd ( 1963).

3 Seismic surveys were carried out for reconnaissance purposes (AOD 1963b), to select drilling sites (SOE, 1962b; AOD, 1964; FPC, 1966), and to check for deep refractors below the drilled depth of Alliance Chan­ dos No. 1 Well while it was temporarily st,1spended (AOD, 1966).

PHYSIOGRAPHY To the north of Windorah town the Thomson and Barcoo Rivers join to hecome . Together with their tributaries they drain prac­ tically all the Windorah Sheet area. In t4Des of heavy flood, water reaches South Australia and, rarely, Lake Eyre. The Bulgroo/eastern Kyabra Creek drainage system in the southeast of the Sheet area drains southwards to an extensive floodout area north of Eromanga. This is mainly an area pf internal drainage, but large floods may overflow along western Kyabra Creek to Cooper Creek. Watercourses are subject to severe seasonal flooding. A large com­ ponent of the floods of the Barcoo and Thomson Rivers originates a long way upstream and results in the introduction of alluvium into the area. The main river gradients are low; for example, the in the nortbeast of the Sheet area is less than 200 feet higher than Cooper Creek in the southwest- a gradient of less than 2 feet per mile. Landscape types in the area reflect the degree to which erosion and deposition have modified a low-relief Tertiary land surface which has been subjected to Cainozoic tectonic movements (Mabbott, Appendix 4 in Gregory et al., 1967). The nearly intact land surface is represented at the present day as a bare rock surface of silcrete (Fig. 1, unit 4), in plateaux or low-angle cuestas. These landforms are characterized by gently sloping summits and prominent bounding escarpments. Away from the escarpments soil processes have formed a red earth cover ( unit 7), with a dense mulga vegetation. More advanced dissection has developed stripped silcrete surfaces ( unit 5) in groups of mesas, buttes, and lower rounded hills, with flanking gravel­ strewn surfaces. Complete stripping of the Tertiary land surface has de­ veloped gently undulating grassy plains with thick soil cover over fresh Cretaceous sediments: the rolling downs (unit 3). These, in turn, are more or Jess modified with local veneers of colluvial or alluvial gravel. Depressions are occupied by the main drainage courses and are areas of sedimentation. The alluvial plains ( unit 1) are characterized by an anastomosing system of steep-sided channels with many billabongs, and by featureless backplains with marginal swamp depressions. Flanking the allu­ vial plains, and locally gradation al with them, are extensive sandplains ( unit 2), possibly representing older areas of alluviation modified by aeolian re­ sorting. Locally, minor dunefields have developed with linear dunes aligned west northwest. The sandplains merge with areas of intact silcrete through transitional belts with part.ial sand cover (unit 6).

4 Sondpfqfns

3 ~ Rolling Ow.s,,,Jth IHO,,#lft ~ Rolling /){Jwns ond Gra,,., 1 C~r

Strlpp,d Sifcr,ld Sudoc,s

Sifcr,11, .-flt, porfklf Sond cw,r

Fig. 1. Physiography of the Windorab Sheet. Compiled by Prof, J. A. Mabbutt and drawn by C. Wilkinson, University of New South Wales. TABLE 1: SUMMARY OF STRATIGRAPHIC UNITS

Age Formation Lithology Thickness Environment of (Letter Symbol) (feet) Deposition Quaternary (Q) (Qa) (Qs) Sand, silt, clay, gravel, in part consoli- Superficial generally, Alluvial, colluvial, aeolian (Qg) (Qc) dated up to 500 feet in val- leys of Cooper Creek and Thomson River ------RELATIONSHIP OBSCURE.------Quaternary (Qp) Limestone, minor chalcedony 0-6 Evaporite in. shallow lakes, pans, and streams PERIOD OF EROSION Tertiary Glendower Quartzose sandstone, siltstone, breccia, Up to 200; very vari- Deposit of continental river (Early) Formation minor quartz-pebble conglomerate. Upper able system, with a few major axes (Tg) . layer ( to 10 ft thick) silicified, forming of sedimentation, and many silcrete. minor short-lived intercon­ necting channels UNCONFORMITY Lower to Winton Labile sandstone, siltstone, mudstone, in 4000 Fluviatile and Iacustrine Upper Formation part calcareous; minor coal, carbonace­ Cretaceous (Kw) ous siltstone and mudstone. Thick altered zone at top (partly stripped) strongly kaolinized, partly ferruginized, with some argillaceous beds silicified to porcellanite. Locally abundant silicified wood. *Mackunda Labile sandstone, siltstone, mudstone, in 200 Paralic Formation part calcareous, grading to impure lime­ (Kim) stone; coquinite *Allaru Predominantly mudstone, siltstone, minor 650-1150 Shallow marine Mudstone sandstone; some calcareous and glaucon­ (Kla) itic beds

*Toolebuc Limestone, calcareous shale 30-120(?) Shallow marine Limestone (Klo) *Wallumbilla Blue-grey mudstone, siltstone, labile 700-900 Shallow marine and paralic Formation sandstone; some beds glauconitic, calcare­ (Klu) ous, and carbonaceous; minor limestone.

Upper *Hooray Sublabile and quartzose sandstone, silt­ 600-900 Fluviatile-deltaic Jurassic to Sandstone stone, mudstone Lower Cretace- ous Upper *Westboume Siltstone, mudstone, quartzose sandston.e, 150-250 Fluviatile-deltaic Jurassic Formation minor· coal Middle to • Adori Quartzose sandstone, minor siltstone and 70-120 Fluviatile Upper Sandstone mudstone, in places carbonaceous Jurassic Middle *Birkhead Carbonaceous mudstone, siltstone, coal, 200-350 Fluviatile-deltaic, paludal Jurassic Formation minor sandstone Lower to *Hutton Predominantly quartzose sandstone, minor 600-1100 Fluvia tile Middle Jurassic Sandstone siltstone, mudstone

UNCONFORMITY Lower *(R) Quartzose sandstone, siltstone, mudstone, 0-1100 Fluviatile, lacustrine Triassic minor coal UNCONFORMITY Upper Permian ( Coal-bearing sandstone and mudstone 0-200 Paludal, fluviatile, lacustrine 1*(P) ) UNCONFORMITY Lower Permian ( Sandstone, siltstone, shale 0-100 Fluviatile and lacustrine, pos­ ) sibly in part glacigene UNCONFORMITY Upper *Buckabie Sandstone, siltstone, shale 0-2500 Redbed sequence; shallow Devonian­ Formation marine and continental Carboniferous? (D-Cb) Middle *Etonvale Siltstone, sandstone, shale; dolomite and 0-1000 Shallow marine, in part Devonian Formation limestone at base evaporitic (De) UNCONFORMITY Middle *Gumbardo Trachyte 0-100 Devonian Formation ( Dg) UNCONFORMITY Lower *(Pz) Indurated shale sandstone, phyllite, schist, Basement Palaeozoic basalt

• Subsurface only STRATIGRAPHY Table 1 summarizes the stratigraphy of the Windorah Sheet area. Only the Winton Formation and younger sediments crop out; information ,on the older rocks has been derived by extrapolation from outcrop studies in adjacent areas and from the results of oil exploration drilling and seismic surveys. Formation tops from the wells, based mainly on Gregory et al. { 1967), are listed in Table 2.

ADAVALE BASIN SEQUENCE Stratigraphic nomenclature for the Devonian-Carboniferous sequence is that of the subsurface Basin (Heikkila, 1966). The present struc­ tural western edge of the Adavale Basin is the Canaway Fault; extension -0f the nomenclature to sediments farther west is based upon the presence of a basal carbonate unit comparable, and identified, with the transgressive Etonvale D3 carbonate member.

Gumbardo Formation Trachyte flows of the Gumbardo Formation had only been encountered in AOD Yongala No. 1. Laing (1966), on seismic evidence, interpn;ted the occurrence as a tracbyte dome.

Etonvale and Buckabie Formations Throughout most of the Adavale Basin, the base of the Etonvale D3 carbonate member is a regional unconformity. Unconformably overlying the Gumbardo Formation in Yongala No. 1 is about 50 feet of fine calcareous sandstone and 50 feet of interbedded argillaceous limestone and dolomite which are equated with the D3 member. West of the Canaway Ridge, in AOD Chandos No. 1 there is about 100 feet of dolomite, grading to dolo­ mitic shale, with some interbedded argillaceous sandstone. This is also equated with the D3 member. Apart from the D3 member, the Buckabie and Etonvale Formations are not divisible on Chandos No. 1. They are a varicoloured (mainly red and green) sequence of fine argillaceous or calcareous sandstone, siltstone, and shale, with some coarser sandstone beds in the lower half. In Yongala No. 1 Laing (op. cit.) makes a somewhat arbitrary division into Buckabie and Etonvale Formations, based upon the presence of con­ glomerate beds in the latter. Both formations are varicoloured, mainly red and green. The Etonvale Formation is fine to coarse and conglomeratic ·sandstone, commonly argillaceous or calcareous, with interbedded shale. The Buckabie Formation contains fine argillaceous or calcareous sandstone with interbedded sh~le and siltstone.

8 TABLE 2: FORMATION TOPS (feet)

Formation Galway 1 Chandos l Canaway 1 Yongala 2 Y ongala 1 KB Elevation 679 738 783 779 683

COOPER BASIN SEQUENCE Martin (1967) proposed a nomenclature of the Permian sequence of the Cooper Basin, comprising the Lower Permian _Merrimelia Formation of elastics with strong glacial affinities, unconformably overlain by the Lower to Upper Permian Gidealpa Formation of elastics and coal measures. Only thin representatives of each formation are present in the wells in the Win­ dorah Sheet area. In the Chandos and Yongala wells palynological determ­ inations indicate that the upper part of the Gidealpa Formation rests directly on the Merrimelia Formation, a situation comparable with the pattern of sedimentation in the (Evans, 1966). No suitable nomenclature yet exists for the Triassic sequence. The thickest recorded section is FPC Galway No. 1, where Jacque & Sweeney ( 1966) recognized a threefold argillaceous-arenaceous-argillaceous division. This is broadly comparable to the ascending sequence Rewan Formation­ Clematis Sandstone-Moolayember Formation of the Galilee and Bowen

9 Basins. However, available palynological determinations so far indicate that the whole of the Cooper Basin Triassic sequence was deposited con­ temporaneously with the Rewan Formation ( Evans, op. cit.). Sandstone varies from fine-grained to coarse and conglomeratic, and from argillaceous to matrix-free. The argillaceous parts of the sequence are siltstone and shale with thin very fine to fine sandstone beds. Redbeds are common.

EROMANGA BASIN SEQUENCE

The Jurassic to early Cretaceous sequence is divided into Hutton Sandstone, Birkhead Formation, Adori Sandstone, Westbourne Formation, and Hooray Sandstone in ascending order (Exon, 1966). The three sand­ stone formations are fluviatile deposits, porous, commonly medium or coarse-grained, .mainly quartzose or sublabile- and characterized by cross­ stratification. They were deposited as extensive blanket sands, easily recog­ nizable throughout a large part of the Eromanga Basin. The intervening Birkhead and Westbourne Formations are dominantly argillaceous- siltstone and mudstone--with thin beds of fine labile sandstone and some carbonace-­ ous beds or coal seams. Much of the labile material in these two formations is derived from acid volcanics, and possibly from contemporaneous vul­ canicity. The basal part of the Hutton Sandstone is mainly argillaceous, with thick interbedded sandstone. Jacque & Sweeney ( 1966) equate this sequence with the Lower Jurassic Precipice and Evergreen Formations of the Surat and southeast Eromanga Basins. Sparse palynological evidence (Evans, 1966) provides some support for contemporaneity of deposition. This lower argillaceous section is not present in AOD Canaway No. 1 on the Canaway Ridge. · Stratigraphic nomenclature of the Cretaceous Rolling Downs Group follows Vine et al., (1967). The Wallumbilla Formation and Allaru Mud­ stone are marine sequences of fossiliferous mudstone and siltstone. Continu­ ous argillaceous sedimentation was interrupted only by a temporary reduc­ tion in the amount of sediment supply, during which time the Toolebuc Limestone was laid down. The change to arenitic sedimentation which produced the Mackunda and Winton Formations was due to an influx of basic or intermediate vol­ canic detritus, presumably due to the onset of contemporaneous vulcan­ icity. Very low proportions of quartz in these arenites indicate that a vol­ canic province was virtually the only source providing sediment. The earliest of these arenites were deposited in paralic environments, but they were laid down faster than the basin was subsiding, and the Winton Formation was deposited in continental environments. By extrapolation from FPC

10 Galway No. 1 the 4000-foot abandoned bore (Reg. No. 154) at Windorah town was drilled entirely in the Winton Formation. This is, therefore, one of the areas of thickest Winton sedimentation in the Eromanga Basin. The Winton Formation was chemically altered to a considerable depth before the Tertiary Glendower Formation was deposited. Upwards through the profile volcanic rock fragments and feldspar within the arenites are increasingly altered, and in the upper part practically all sediments are strongly kaolinized and some beds selectively silicified. The upper part is strongly mottled red and white due to some patchy enrichment in iron oxide. Thin ironstone bands, with up to 90 percent iron oxides, also occur in the profile, but appear to be more common in the lower parts. The succeeding quartzose sandstone sequence, the Glendower Forma­ tion, is also strongly altered in its upper part, but by silicifi.cation to silcrete. 6 LATE TERTIARY TO QUATERNARY ;1Ni\tWL\;}.~f!.;J:d<~{:f~N:\~;t g_u:t/fr~:ii.·:~~~++X}U{/f;WlrW:-tW! h~Nl;tMl~\}\;JWW00 Genl/6 lo/ding qnd erosion, ..,11h deposilion of Ouaternory scdlm1nts In sym;//n1s

5 TERTIARY

Winton Formollon

Wlnton Formation. I.QCol stdppln9 of IOne of chsmlcol olleralio11. 011xu:lllon of Glendowor Formotlon on ~rodtxf surfot, of Sl/crl'Jle dcvol()ped Jn 11ppt1r ron•

4 LATE CRETIICEOVS ! :Z.Z....:-·:.-!·"-.,..:?2~"'.-:~ .-zr__.,,., : ,z,7._-:?r-:.,t.rTJ_,..,,_..,,-~_...._=~ _~_ ___...,_ zr-:,r~-~~~-,,,.._-'-.,,.;.:.z~_-______.,..z..,. -,--.-_.,..,'7 ~:Z""_ ..,~,..,~,,..!.:-J:-__-_,_,-::.~ .,...J.,.._-_..,.,-,-••-_-~ ---_._=-_-_- ,..___ ··-·-...... ----· ------·------'-"-----·· - -- ·- ---

3 .IURIISSIC TO CRE"TIICEOUS .FJ!!!f:IPX\F;~Ntt\\lA;;:~i};·:;ii;;j~r:4~~:-:~il:·:::;:)S?r~ ·:::{?--?~? Trlossic upt/lJ ond ,,oskM foKo,.,,d by d1poslllon of £romon9a Basin sequanc• In o /Jrood shol,,.,, dc•·n-:,qrp, Luis lon lnffiolly In llwiofi/1 o,,d d1llolc 11nvlronmants, lollot,,1d by shallow marina lron.Sf}f'ISlion and r119r1ss

2 ~i@;;n,:t::.:'r;~,;%i4S~'tgl,•· ·?F-:ff -.:~ t.,1~,., uplift Oownworplng of Cooper Basin, O#positlon of sedlm1nts on o r11glonal 4,osionol StJrf

1 OEVONIAN TO CARBONIFEROUS ~!EBNS(·.fB.;~~+zgqqcJ-::~Dnttts-:7¥~~ of Adt:1t10I• Bosln. O,positlon of s•dlm1n1s r,,strlct1d lorpaly to 1ost1rn area). First mtw1m,nl on Oormtttorplng G /AB/l Co11<1""J' Foul/, S4dimentotlon lnltlo/f;, morln,, /of#, c11nllnttntr,I 54 Fig. 2. Geological history of the Windorab Sheet. 11 Lithological differences in the Quaternary rock types reflect different parent materials. Break-up of silcrete sheets produces colluvial silcrete gravel ( map symbol Qc). Dilution by quartz pebbles from the Glendower Formation and ironstone pebbles from the altered Winton. Formation pro­ duce a mixed gravel ( Qg). Sand from the Glen dower Formation, originally deposited as alluvium, has been subjected to aeolian re-sorting into extensive sand sheets and some dunes (Qs). The present alluvium (Qa) along the main watercourses includes a large argillaceous element introduced from farther upstream, but beds of sand derived from the Glendower Formation are common, and rare pebble beds occur. Evaporation in shallow temporary Jakes produced siliceous limestone (Qp). Much of the area of undifferen­ tiated Quaternary deposits ( Q) consists of red earths. Three shallow holes were drilled in 1966 in the northwest of the Sheet area to test the thickness of Quaternary sediments and check for continuity of the silcrete layer in the Glendower Formation. All three were completed in Cainozoic sediments at depths of 240 feet. BMR Windorah Nos 1 & 3 reached the silcrete at 146 and 64 feet respectively and U,us established that the silcrete dips under the Quaternary sediments. Windorah No. 2 was still in poorly consolidated sediments at total depths. This shows either that the silcrete is at greater depth or that Cooper Creek has cut a channel through the silcrete. The geological history of the area is summarized in Figure 2.

STRUCTURE

Distribution of the Winton and younger sediments delineates clearly the major folds of the Windorah Sheet area; detail is emphasized by the alteration zones at the top of the Winton and Glendower Formations. The surface evidence is supported by the result of seis~ic surveys. Thus the Windorah Anticline is represented by an inlier of Glendower silcrete surrounded by lower-lying Quaternary sediments. The Chandos Anticline has a central core of altered Winton Formation rimmed by Glen­ dower Formation but partly obscured by Quaternary sediments. Reflection seismic results (AOD, 1963b) define the position of the axis and show that the anticline is asymmetric. Refraction seismic work shows that the Chandos anticline formed over a basement ridge, but that the crest of the ridge is west of the fold axis (AOD, 1966). Tne north-northwesterly belt of fresh Winton Formation, with flanking belts of altered Winton and of Glendower Formation, marks the site of the Canaway Ridge. It is a major horst-like basement ridge reflected at the surface by marginal faults (e.g. Canaway Fault) and local culmina­ tions ( e.g. Canaway Anticline) . An area of altered Winton and Glendower 12 Formation in the southern half of the Cheviot Range indicates a saddle in the structure. The Windorah Sheet area includes only the northern half of the Canaway Ridge.

The Canaway Ridge forms the structural western margin of the Devonian-Carboniferous Adavale Basin, although Devonian sedimentation once transgressed farther west. Major folds occur in the Adavale Basin (Heikkila, 1966), but within the Windorah Sheet area dips in the Adavale Basin are gentle. AOD Yongala Nos 1 & 2 were drilled on a structural nose against a fault trap. The Canaway Ridge is also the· eastern boundary of the Permian­ Triassic Cooper Basin. All structures in this basin are gentle. Thinning of formations and wedge-out towards anticline show that the folds were developing during and after Permian and Triassic sedimentation. Jurassic and Cretaceous sediments of the Eromanga Basin form a fairly uniform blanket over the whole of the Windorah Sheet area. Evidence of compressional folding is lacking, and structures in this :sequence are best interpreted as drapes, the result of a combination of uplift and compaction over older structures. Synclinal areas are occupied by the main drainage courses and the thickest Quaternary sediments; so the drape folding has continued into Recent times.

Bouguer anomalies have only a broad relation to the regional structure. Both the east flank of the Chandos Anticline and parts of the Canaway Fault cor respond to steep gravity gradients. Likewise the Canaway Ridge and a basement culmination (AOD, 1966) to the west of the Chandos Anticline approximate in position to gravity highs. Differences in values of bouguer anomalies are too great to be due to known variations in the sedimentary cover. They therefore probably reflect major lithological differences in the basement, i.e. distinct basement blocks. Fault boundaries between such blocks would be marked by steep gravity gradients. Where there is correspondence between such gradients and surface-expressed faults or monoclines, it is an indication that the old faults have been reactivated to give inherited structures in the younger sediments.

ECONOMIC GEOLOGY Groundwater

Over 200 non-flowing bores or wells and 9 flowing bores have been · drilled in the Windorah Sheet area. About 20 were drilled to replace bores in which technical difficulties or bore collapse had caused abandonment. About 20 more bores were abandoned because of inadequate supply, salinity of the water, bore collapse, or equipment failure. Five artesian 13 bores 11fe still flowing, one is abctndoned ( original supply of poor quality and inadequate quantity), two have ceased flowing and are now pumped, and one was not located during the geological field work. Records of most bores give no more than the recorded depth; drillers' logs where available, are generally only useful for identifying gross lithology, and the majority do not provide adequate records of aquifers encountered. The following comments are essentially generalizations, based upon interpre­ tation of the drillers' logs, conversations with bore owners, and attempts to relate depths of bores to the stratigraphic sequence. Gamma-ray logs have been obtained from two waterbores drilled in the Winton Formation in the Windorah Sheet area (Jesson, Radeski, & Jewell, 1963). Both show little that could be diagnostic without much closer control. The two deepest bores in the Windorah Sheet area (Bore 154, Windorah town, and 1728, Bulgroo) have obstructions in them which pre­ vented logging. Cainozoic sediments. At least 20 bores or wells tap aquifers in the Glen­ dower Formation and Quaternary sedin1ents. Most are shallow, as the sedi­ ments are thin except below the main watercourses. Water in the Quaternary sediments is commonly brackish to saline, particularly downstream from Windorah, although several bores in the Glendower Formation produce fresh water. Salinity is probably the main factor inhibiting further develop­ ment of the aquifers in the Quaternary sediments. Winton and Mackunda Formations. The majority of bores tap aquifers in the Winton Formation. Recorded supplies are mainly less than 1000 gallons per hour, and quality varies from fresh to saline, but mainly fresh or brackish. Micrologs of the oil exploration wells aid understanding of the aqui­ fers. They show that the basal part of the Winton Formation and the under­ lying Mackunda Formation have generally good permeability over a strati­ graphic thickness of between 200 and 500 feet. The rest of the Winton Formation has only scattered thin intervals with good permeability, although Yongala No. 2 has a second thick permeable interval over 1000 feet above the base. Bores which tap the basal permeable section are mainly where it is shallowest along the Canaway Ridge, and these include 7 bores which originally flowed. The high potentiometric surface for these aquifers implicit from the number of flowing bores, is probably due to good perme­ ability extending to intake areas to the north and east. Water from these aquifers is generally fresh. · By extrapolation from FPC Galway No. 1 Bore 154 in Windorab town reached the aquifer sequence in the basal Winton/Mackunda Forma­ tions. The bore was drilled to 4001 feet in -1905 and a year after comple­ tion it started to flow at less than 100 gallons per day. The water· smelled

14 strongly of kerosene (local report); this combined with paucity of the flow -caused the bore to be abandoned. Despite this, the basal Winton/Mackunda Formations offer the greatest prospect for further development of water resources at economic depths: throughout most of the Sheet area this should be less than 3000 feet. Hooray Sandstone. Bore 1728 (Bulgroo), 5517 feet deep, is the only waterbore in the Windorah Sheet area which has been drilled below the base of the Rolling Downs . Group. The driller's log records five aquifers within the Hooray Sandstone which gave an initial total flow of nearly 20,000 gallons per hour. By 1962 the flow had dropped to less than 8000 _gallons per hour. The Hooray Sandstone can be recognized in all the oil exploration wells of the Windorah Sheet area and should be present at depth througb­ ·out the whole area. On the Canaway Ridge the top of the Hooray Sand­ stone should be in the order of 3000 feet below the land surface. Elsewhere it is much deeper and the cost of drilling would render it uneconomic as a source of stock water. Deeper aquifers. Logs of the oil exploration wells show that thick permeable sequences exist in the Adori and Hutton Sandstones. Drill stem tests were run in these formations in AOD Canaway No. 1; the Adori Sandstone flowed fresh water at 50 gallons per minute and two intervals in the Hutton Sandstone flowed fresh water at 30 and 55 gallons per minute. Drm stem tests of aquifers in older parts of the sequences in other wells generally produced brackish or saline water.

Hydrocarbons Five oil. exploration wells have been drilled in the Windorah Sheet area (Table 3); all are abandoned. Earlier, L. H. Smart Oil Exploration Co. Ltd had drilled a scouthole, SOE Scout Bore No. 2 (Canaway Downs), in the Winton Formation on the Canaway Ridge. Several gas shows were reported, and one confirmed by analysis (GSQ, 1960, p. 55). Most of the area is within the Cooper Basin, in which commercial gas fields have been found farther south; reservoirs to date are in Permian ·sediments. However, good oil shows were found in tl1e Permian and Triassic sequences in Chandos No. 1 and these are encouragement for further search for the heavier hydrocarbons. A further possible target is the sandstone sequence with good perme­ ability in the Mackunda and basal Winton Formations. This is suitably located to receive hydrocarbons from the underlying argillaceous marine Cretaceous sequence if depth of burial has been sufficient to start migra­ tion of petroleum. In the Windorah area the overburden has exceeded 4000 feet; and gas shows in SOE Scout No. 2 (Canaway Downs) are significant in indicating that some generation has taken place.

15 TABLE 3-OIL EXPLORATION DRILLING (For references see Table 2)

Company Well Results (year drilled) Purpose Shows Alliance Oil Canaway No. 1 Stratigraphy, ·and test of Nil Showed Canaway Ridge 'bald­ Development ( 1963) Canaway Anticline headed' below Jurassic sequence; Australia N.L. Jurassic sequence flushed by fresh water.

Alliance Oil Yongala No. 1 Stratigraphy, and test of Signs of gas while Proved presence of Adavale Group Development (1965) fault trap on down-thrown drilling Permian coal sediments on flank of Canaway Australia N.L. side of Canaway Fault and base of Etonvale Ridge. Established that more saline Formation water present in Triassic and basal Jurassic sequence than rest of Jurassic section ;-,. a> Alliance Oil Yongala No. 2 Test of Triassic and basal Nil Target zone water-bearing Development ( 1967) Jurassic up-dip from Yon­ Australia N.L. gala No. 1

Alliance Oil Chandos No. 1 Stratigraphy, and test of 3.5 barrels 53 gravity Established presence of oil in Development ( 1966) Chandos Anticline oil in D.S.T. in Lower northern Cooper Basin, and stimu­ Australia N.L. Triassic. _Oil bleeding lated further search in adjacent from cores in Permian tenements. Provided good evidence for presence of Upper Devonian/ Lower Carboniferous sequence west of Canaway Ridge

French Petroleum Galway No. Stratigraphy, and test of Weak gas shows during Established presence of ·over 1000 Company (Australia) (1966) the Windorah Anticline drilling. Gas-cut fresh feet of Triassic sediments, but Pty Ltd water in D.S.T. in showed that Permian sequence not basal Jurassic sequence. present in crestal zone of fold. Pro­ Gas-cut salt water in vided positive dating of basement D.S.T. of Triassic (see Table 2) sequence Precious Opal Opal has been produced from two mines, now abandoned, in an area. about 10 miles northeast of Bulgroo homestead, but no production figures are available. One other opal prospect occurs 5 miles north of Trinidad homestead. The opal is localized in ferruginized layers in labile sandstone or in ferruginous concretions within the zone of chemical alteration in Winton Formation. Gregory et al. (1967) suggested that precious opaliza­ tion was restricted to areas of chemically altered Winton Formation which were not covered, or only thinly covered, by sediments of the Glendower Formation.

Construction Materials Silcrete is an excellent material for use as a gravel base for road con­ struction, and was used extensively for the sealed Windorah-Quilpie road. Sand is available from the extensive sand sheets, and particularly from the dunes. The sand grains commonly have a very thin ferruginous · coating which may limit usefulness for concrete.

l 'l BIBLIOGRAPHY AOD, 1963a-Completion report for Alliance Oil Development N.L. Canaway Well No. 1, A.P. 98P, ,Queensland.• AOD, 1963b-Final report Bulgroo reflection seismic survey A.T.P. 98P, Queensland. Alliance Oil Developme11t NL.• AOD, 1964--Final report on the Trinidad seismic survey, Authority to Prospect, 98P, Queensland. Alliance Oil Development NL. AOD, 1966--Final report on Cbandos refraction seismic survey, A.R.P. 98P, Queens­ land. Alliance Oil Development N .L . DELHt AUSTRALIAN PETROLEUM LTD and SANTOS LTD, 1963- Final report on Cooper's Creek aeromagnetic survey. EVANS, P. R., 1966--Palynological comparison of the Cooper and Galilee Basins. Bur. Miner. Resour. Aust. Ree. 19661222 (unpubl.). ExoN, N. F., 1966--Revised Jurassic to Lower Cretaceous stratigraphy in the south­ east Eromanga Basin, Queensland. Qld Gol't Mi11 . J., 61, 233-240. FPC, 1966- Windorah-Wolgolla seismic and gravity survey, final report. French Petroleum Company (Austm/ia) Pty Ltd.• GrBB, R. A., 1967-Western Queensland reconnaissance gravity surveys, 1957-1961. Bur. Miner. Resour. Aust. Rep. 129. GREGORY, c. M., SENIOR, B. R., and GALLOWAY, M. c., 1967- The geology of the Connemara, Jundah, Canterbury, Windorah and Adavale l :250,000 Sheet areas, Queensland. Bur. Miner. Resour. Aust. Ree. 1967116 (unpubl.). GSQ, J 960-0ccurrence of petroleum and natural gas in Queensland. Geol. Surv. Qld Pub!. 299. H EtK.KlLA, H. H ., 1966--Palaeozoic of the Adavale Basin, Qld. Proc. 8th Comm. Min. metal/. Cong., 5, 157-165. HtLL, D., and DENMEAD, A. K. (Eds), 1960-The geology of Queensland. J. geol. Soc. Aust., 7. JACQUE, M., and SWEENEY, P. J., 1966--Galway No. l (Queensland) well completion report. French Petroleum Compa11y (Australia) Ltd.* JESSON, E. E., RAX>ESKI, A., and JEWELL, F., 1963- Great Artesian Basin experimental ·bore logging, south-west Queensland, 1960. Bur. Miner. R esow·. Aust. Ree. 1963/ 103 (unpubl.). L ATNG, A. C. M., 1966-Completion report, Alliance Yongala No. l Well, A.P. 98P, Queensland. Allia11ce Oil Deve/op111e11t N.L . * LAINO, A. C. M., 1967-Completion report Yongala Well No. 2, A.P: 98P, Queens­ land. Alliance Oil Del'elopment N.L. * LAING, A. C. M ., and BENEDEK, S .• 1966--Alliance Chandos No. 1 Well-A.P. 98P, Queensland, well completion report Allimzce Oil Development N.L. * LONSDALE, G. F., 1965--Southern Queensland contract reconnaissance gravity survey using helicopter, 1964. B11r. Miner. Resour. Aust. Ree. 1965/251 (unpubl.). MARTIN, C. A., 1967-The Gidgealpn and Merrimelin Formntions in the Cooper's Creek Basin. Aust. Oil Gas /., 14(2), 29-35. SOE, 1962a-Report on a gravity survey of the Eromanga area, 81\P, Queensland. L . H . Smart Oil Erploratio11 Co. Ltd.* SOE, l 926b-Grey Range seismic survey, Queensland, 1959, by L. H . Smart Oil Exploration Company Limited. Bur. Miner. Re.vour. Aust. petrol. Search Subs. Acts Pub/. 29. STACKLER, W. F., 1963-Windorah Gravity Survey, A.P. _98P, Queensland. Alliance Oil Development N.L. * VINE, R. R., DAY, R. W., CASEY, D. J ,, MILl.lGAN, E. N., GALLOWAY, M. C., and EXON, N. F., 1967- Revision of the nomenclature of the Rolling Downs Group in the Eromanga and Surat Basins. Q/d Govt Min. / ., 68, 144-151. WHITEHOUSE, F. W., 1940-Studies in the late geological history of Queensland. Pap. Unil'. Qld Dep. Geol., 2(1). WHITEHOUSE. F. W., 1941 - The surface of western Queen~Jand. Proc. Roy. Soc. Q/d, 53, 1-22.

18 WHITEHOUSE, F. W., 1947-The geology of the of southwestern Queensland. Bull. Bur. Invest. Qld, 1, 10-28. WHITEHOUSE, F. W., 1954-Tbe geology of the Queensland portion of the Great Australian Artesian Basin. Appendix G to Artesian water supplies in Queens­ land. Dep. Co-ord. Ge11. Public Works, Q/d. WOOLNOUGH, W. G., 1927-Presidential Address, Part I-The chemical criteria of peneplanation, Part TI- The duricrust of Australia. J. Roy. Soc. NSW, 61, 17-52.

* Operations subsidized under Petroleum Search Subsidy Acts 1959-64; reports available for study at Bureau of Mineral Resources, Canberra, and Geological Survey of Queensland, Brisbane.

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