COMMONWEALTH OF AUsrRALIA 1:250,000 GEOLOGICAL SERIES-EXPLANATORY NOTES Windorah, 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 under 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 Queensland.· 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 Brisbane 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 Cooper Creek. 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 Barcoo River 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