Chinchilla, Qld
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COMMONWEALTH OF AUSTRALIA STATE OF QUEENSLAND 1:250,000 GEOLOGICAL SERIES-EXPLANATORY NOTES Chinchilla, Qld SHEET SG/56-9 INTERNATIONAL INDEX COMPILED BY R. F. REISER Published by the Bureau of Mineral Resources, Geology and Geophysics, and issued under the authority of the Honourable R. W. C. Swartz, M.B.E., E.D., M.P., Minister for National Development 1971. COMMONWEALTH OF AUSTRALIA DEPARTMENT OF NATIONAL DEVELOPMENT MINISTEll: THE HON. R. W. C. SWAIITZ, M.B.B., E.O., M.P. SECUTUY: L. F. BOTT, D.S.C. BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS D1ucroa: N. H. FISH!!&. GEOLOGICAL BllANCH; ASSISTANT DlllECTOR: J. N. CASEY. STATE OF QUEENSLAND DEPARTMENT OF MINES MINISTl!a: THE HoN. R . L. A. CAKII, M.L.A. UHDE& SEClll!TARY: E. K . HEALEY. GEOLOGICAL SURVEY OF QUEENSLAND CHIEF GEOLOGIST: J. T . WOODS. Printed in Australia by the Tasmanian Government Printer, Hobart Explanatory Notes on the Chinchilla Geological Sheet Compiled by R. F. Reiser (Geological Survey of Queensland.) The main centres of population are Chinchilla (population 3300), Miles (population 1500) , and Jandowae. The southern half of the Sheet area is well served by sealed roads. Chinchilla and Miles lie on the W arrego Highway linking Brisbane and Roma; from Dalby, a major town to the south of the Sheet area, the Jandowae-Dalby road gives access to the southeast, and the Condamine Highway to the far south and southwest; the Leichhardt Highway gives access to the western edge of the Sheet area. There are few sealed roads in the northern half, but formed roads are generally closely spaced, giving ready access to most areas. Chinchilla, Miles, and Condamine all have regular air services. The Western Railway serves Chinchilla and Miles and a branch line from Dalby runs to Jandowae; the Barakula Tramway runs from Chinchilla to the sawmills of the Barakula area, and a branch line from Miles runs to Wandoan. The area was mapped during 1967 as part of a regional mapping pro gramme of the Surat Basin (Exon, Reiser, Jensen, Burger, & Thomas, 1968) conducted jointly by the Bureau of Mineral Resources and the Geological Survey of Queensland. Rivereau (1966) prepared a photogeo logical map of the area before field work began. The heavy clay soil of the alluvial plains of the Condamine River system once supported dense brigalow scrub; this has now been cleared and cultivated for cash and feed crops. The sandy soils developed on the sand stone, granite, and metamorphic terrain of the north and west are covered by open forest suitable for cattle grazing. Forest reserves in this area supply several sawmills. In the southwest, where relief is less rugged, sheep are raised. Vine scrub dominated the vegetation of the basalt-covered areas of the southeast; where relief is not too extreme, this scrub has been cleared and the area now supports an intensive dairying industry. Air photographs at 1:85,000 nominal scale flown by Adastra Airways in 1963 cover the area. A topographic map at a scale of 1:250,000 is currently being produced by the Royal Australian Survey Corps. 3 PREVIOUS INVESTIGATIONS Geological Jack & Maitland (1894) covered the area as part of a geological reconnaissance of inland Queensland. Jack (1896) suggested a Triassic Jurassic age for the basalts of the eastern part of the Sheet area, and recorded Palaeozoic rocks in the far north at Cadarga (grid ref. 396756). Coal occurrences at Jimbour ( 424653) and Chinchilla were investigated by Cameron (1910) and Marks (1910) respectively. Walkom (1918) showed the distribution in Queensland of the Walloon Series, which included most of the Jurassic of the Chinchilla Sheet area. Jensen's (1926a) reconnaissance included part of the Sheet area north and west of Chinchilla. He mapped the Upper Triassic Bundamba Series and the Jurassic Walloon Series. Ball (1931) identified fossil plants from Guluguba (296738), and commented on deep weathering effects in this area. Coal at Warra (391657) was examined by Cribb (1944), who also noted fossil vertebrate bones in sand and gravel. These deposits, together with those at Chinchilla and Brigalow, were grouped by Bryan & Jones (1946) with the Pleistocene Diprotodon beds; Woods (1956, 1960) has since shown that these are more probably of Pliocene age. Sturmfels (1954) mapped the Miles-Wandoan area. Isbell (1962) worked on the soils of the brigalow lands of Eastern Australia, including the Chinchilla Sheet area. The Sheet area was mapped at a regional scale by McTaggart (1963a) ; the findings of Exon et al. (1968) agree broadly with those of McTaggart. Webb, Stevens, & McDougall (1967) determined isotopically the age of contiguous Tertiary basalts to the south and east of the Sheet area as early Miocene. Casey, Gray, & Reiser (1968) briefly reviewed the Lower Mesozoic stratigraphy. Geophysical Geophysical surveys by companies and the Bureau of Mineral Resources are listed in Table 1; the surveys are concentrated in the sedimentary areas of the west and south. Bouger anomaly contours shown on the geological map are from a survey by the Bureau of Mineral Resources (Lonsdale, 1965). Aeromagnetic work for Union Oil Development Corporation, which defined the eastern flanks of the Mimosa Syncline, was summarised and interpreted by Aero Service Corporation (1963). Seismic surveys for Union Oil Development Corporation (e.g. Kahanoff, 1962b; United, 1964, 1966) and for Phillips Petroleum Company (Fjelstul & Beck, 1963) showed detailed structure, particularly the faulting on the east flank of the Mimosa Syncline. Seismic surveys in the centre of the Sheet area were completed for Condamine Oil Ltd (McQueen & Warner, 1962; Warner & Klaudt, 1963), and re-interpreted by Companie Generale de Geophysique (1963). 4 TABLE 1.-GEOPHYSICAL SURVEYS IN THE CHINCHILLA AREA Short Title Survey Organisation Reference Central and South- Gravity along seismic Bureau of Mineral Darby, 1965 em Queensland lines; far south of Resources Sheet area Southern Queens- Regional gravity Bureau of Mineral Lonsdale, 1965 land Resources NE New South Regional gravity Bureau of Mineral Langron & van Wales, SE Resources Son, 1967 Queensland Surat-Bowen Basin Aeromagnetic Union Oil Develop Union, 1960 ment Corp. Moree-Miles Aeromagnetic Union Oil Develop Kahanoff, 1962a ment Corp. Moree-Miles Aeromagnetic Union Oil Develop Aero Service Corp. ment Corp. 1963 Miles-Dulacca Reconnaissance Union Oil Develop Kahanoff, 1962b seismic ment Corp. Yuleba Reconnaissance Union Oil Develop Kahanoff, 1963 seismic ment Corp. Chinchilla area Detailed seismic; Condamine Oil Ltd McQueen & small area in Warner, 1962 centre of Sheet Barakula Detailed refraction Burmah Oil Co. Warner & Klaudt, seismic; small area 1963 in centre of Sheet Chinchilla area Reinterpretation of Condamine Oil Ltd CGG, 1963 earlier seismic in central area Western ATP 71P Reconnaissance and Phillips Petroleum Fjelstul & Beck, detailed seismic; Co. 1963 southeast Moonie River Detailed seismic; Union Oil Develop- United, 1964 west ment Corp. Condamine Detailed seismic; Union Oil Develop- United, 1966 southwest ment Corp. Exploratory drilling for petroleum The earliest wells in the area were Murilla Oil Company 1 (Boyanda) near Miles and Condamine Oil Ltd 1 (Speculation): both reported minor shows. In the early 1960's, the Union Oil Development Corporation began prospecting for oil in' an area which included the western part of the Sheet area. Promising results in wells in adjacent areas (gas shows in UKA Buranga 1 and oil in UKA Cabawin 1 and UKA Conloi 1) led to the drilling of fourteen wells in the Sheet area, sited from geophysical evidence on the culmination of small fault-controlled anticlines on the eastern flank of the Taroom Trough; they were aimed at the Precipice Sandstone in structural traps or pinchouts in anticlinal flanks. Results are summarised in Table 2. PHYSIOGRAPHY The physiography of the Sheet area is summarised in Fig. 1. Drainage is to the Condamine, Burnett, and Dawson Rivers. The Condamine River is part of the Darling River System; the Burnett and Dawson Rivers flow 5 into the Pacific. The main stream divide constitutes part of the so-called Great Dividing Range; the name is difficult to justify in the mainly flat western part. 0 10 20 30 KI LOMETRES G 54/A/3 0 10 20 MILES Boso/I-copped mesas Vnduloling sandy § , l[&J country Rood Rounded hills Vnduloling clayey ~ ~- country --- Roilwoy Sandstone m,so$ Sand ond soil / [TIIJ D plains / Oivide Figure 1. Physiography The most rugged country in the Sheet area is in the east and north east, and relief decreases to the west and south. In the southeast, there are basalt-capped mesas separated by valleys of rich clay soil. The basalts were flows filling valleys developed in the soft Marburg sediments; the sediments have since been extensively eroded to give the present reversed relief; in a few areas, topographic reversal is not complete, and sandstone mesas remain. In the northeast, the granite and metamorphic rocks have weathered to a terrain of rounded hills with V-shaped valleys. Elevation falls to the north, following the Boyne River, from 1500 feet to 700 feet. The topography of the remainder of the Sheet area has resulted from more or less intensive erosion of once extensive pediplain developed during 6 TABLE 2.-EXPLORATORY DRILLING IN THE CHINCHILLA AREA Total Depth Name of Well Year Drilled Grid Reference (Feet) Hydrocarbon Shows Reference Murilla Oil Co. 1 (Boyanda) 1935-1953 304691 ?4721 Gas at some levels Condamine Oil Ltd (Specula 1948-1963 363713 2885 Some oil and gas shows Mott