JOURNAL and. PROCEEDINGS of The Royal Society of New South Wales Volume 142 ‘Parts 1 and 2 Numbers 431-432 2009 THE ROYAL SOCIETY OF NEW SOUTH WALES OFFICE BEARERS FOR 2009-2010 Patrons Her Excellency Ms Quentin Bryce AC Governor-General of the Commonwealth of Australia. Her Excellency Professor Marie Bashir AC CVO Governor of New South Wales. President Mr J.R. Hardie, BSc Syd, FGS, MACE Vice Presidents Em. Prof. H. Hora Ms R. Stutchbury Mr C.M. Wilmot Hon. Secretary (Gen.) Mr B.R. Welch Hon. Secretary (Ed.) Prof. J. Kelly, BSc Syd, PhD Reading, DSc NSW, FAIP, FInstP Hon. ‘Treasurer Ms M. Haire BSc, Dip Ed. Hon. Librarian vacant Councillors Mr A.J. Buttenshaw Mr J. Franklin, BSc ANU Ms Julie Haeusler Dr M. Lake, PhD Syd A/Prof. W.A. Sewell, MB, BS, BSc Syd, PhD Melb FRCPA Southern Highlands Rep. Mr C.M. Wilmot EDITORIAL BOARD Prof. J. Kelly, BSc Syd, PhD Reading, DSc NSW, FAIP, FInstP Prof. P.A. Williams, BA (Hons), PhD Macq. Dr M. Lake, PhD Syd Mr J. Franklin, BSc ANU The Society originated in the year 1821 as the Philosophical Society of Australasia. Its main function is the promotion of Science by: publishing results of scientific investigations in its Journal and Proceedings; conducting monthly meetings; awarding prizes and medals; and by liason with other scientific societies. Special meetings are held for: the Pollock Memorial Lecture in Physics and Mathematics, the Liversidge Research Lecture in Chemistry, the Clarke Memorial Lecture in Geology, Zoology and Botany, and the Poggendorf Lecture in Agricultural Science. Membership is open to any person whose application is acceptable to the Society. Subscriptions for the Journal are also accepted. The Society welcomes, from members and non-members, manuscripts of research and review articles in all branches of science, art, literature and philosophy for publication in the Journal and Proceedings. Acknowledgements The Royal Society of New South Wales gratefully thanks the NSW State Government for their financial suppport of this publication. Copyright The Royal Society of New South Wales does not require authors to transfer their copyright. Authors are free to re-use their paper in any of their future printed work and can post a copy of the published paper on their own web site. Enquiries relating to copyright or reproduction of an article should be directed to the author. ISSN 0035-9173 Journal & Proceedings of the Royal Society of New South Wales, Vol. 142, p. 1-3, 2009. ISSN 0035-9173/09/01001-3 $4.00/1 Editorial go iC \THo Zo ONIAN ~~ LIBRAR'ES See eI JAK KELLY A WELL KNOWN MEMBER It is not often that one of the members of The Royal Society of New South Wales has an ‘International Year of ...’ devoted to them. Even the Pinhole Camera only rates a day (www.pinholeday.org). However, 2009 is such a year and Charles Darwin is the member. In the vast Darwin literature little is made of his visit to Australia on his voyage in the Beagle. He is locally commemorated by having Darwin Harbour, named after him in 1839, as was the town, now the capital of Australia’s Northern Territory, established there in 1911. Most people would however be unaware of his membership of our society. His gracious letter accepting membership of the RSNSW is reproduced for the first time ever in this issue as our original contribution to this year’s joint celebration of his birth in February 1809 and his publication of ‘On the Origin of Species’ in November 1859. He was well aware of the trouble that his ideas could cause in religious circles and in ‘Species’ he intentionally minimised discussion of men and apes. In vain, as it turned out. It is difficult to believe that disputes about creation and natural selection are still with us 150 years on but they are. Creationism has become Intelligent Design. This recent change of title was clearly intended to sound like a scientific subject rather than a dogma confined to religious extremists. Most countries have given up burning heretics and most of us believe in the freedom to publish what we like, subject to a few restrictions. Why worry about the teaching of ID? The problem is the push to have ID taught as a science. This movement is largely confined to some US states but there are a few Australian schools attempting it. If you think ID in Australia is dead, Google ‘Intelligent Design in Australia. I got 1,240,000 entries. The ID claims that the world is 6000 years old and men and dinosaurs coexisting will not stick for most students but it will waste their time and make a scientific career less likely. I am unaware of any moves to have Fred Flintstone or the Wiggles banned for supporting our coexistence with dinosaurs. As for the age of the earth, on his way to Bathurst Darwin is said to have looked out over the valleys of the Blue Mountains, which are clearly eroded from the plateau and remarked that this must have taken aeons longer than the biblical 6000 years. The powerful US text book industry has modified some science books so as not to offend the ID people, many of whom are on state boards such as the Kansas State Board of Education. ‘To avoid the expense of printing different versions, some of these books are used in other states and in other countries. History shows that even if most people don’t believe in an idea a few determined and fanatical people can do serious damage to a society. The Nazi eugenics theories are a recent example. They were falsely claimed to be supported by Darwin’s ideas. International Years are great for publishers, perhaps they invented them, and Darwin’s year is no exception. The current deluge of articles and books, for and against Darwin, is over- whelming. We are all familiar with evolution and natural selection but you may wish to know what the ID people are claiming. - € (1969) Carroll (1982) | i 3 = <'E (2285 m) Meadow Tank | & = ao Formation =| | EMSIAN | } Glen (1982a) | | e Bindian Event~Regional Unconformity | | a ~Seismic Marker Reflector (Horizon-B) boi me Mt Daubeny | ________. Glen (1979, 1982b) ---------- Amphitheatre) {| = POVIIALIOR ¢ Poeecntacotuier tec cess Seteeance llores dsc Group 1 a Gundaroo | Unit-Al (40 m) 2 > Neef et al 5 Sandstone | Andrews ee PRAGIAN (1989) (90m) | Unit-A2(50m) (1913) 55 and i = and s= Week and E Sawmill Tank Siltstone (500 m) Rayner (1962) 3 x LOCHKOVIAN oi = | Buckambool Sandstone 26 (1000 m) S 3 LATEST SILURIAN Bowning Event~Angular Unconformity | | ~Seismic Marker Reflector (Horizon-A) ee. L = —»-- Table 2. Lithostratigraphic units nomenclature correlation of the latest Silurian to Devonian sequence in the Darling Basin. Seismic marker unconformities (A, B, C, D) from Evans (1977) are correlated with the three informally named ‘Intervals’ described by Bembrick (1997a, b). The Mulga Downs Group, which is the main focal point of this study, is one of the major thick clastic successions of late Early Devonian to Late Devonian age in western New South Wales. This Devonian sequence, originally referred to as the Mulga Downs Stage (Mulhol- land 1940) but re-defined as the Mulga Downs Group by Rayner (1962, cited in Conolly et al. 1969), has been subdivided into several forma- tions and mapped by authors such as Conolly (1962), Rose (1968), Ward et al. (1969) and Glen (1979, 1982a, 1986). Bembrick (1997a, b) also suggested that the Mulga Downs Group required re-definition based, among other as- 34 MOHAMED KH. KHALIFA pects, on regional mapping by Glen (1986), and avoided using the term in his discussion. Such a framework, based on mapping and correlation of seismically defined units, also provide a useful stratigraphic framework for the present study. Winduck Interval and Equivalents The Winduck Interval is widespread throughout the Darling Basin, both in outcrop and in the subsurface. These strata are represented by the Mt Daubeny Formation in the western part of the basin (Neef et al. 1989), the Winduck Group in the central to eastern part (Glen 1982a, b; Scheibner 1987), and the Amphitheatre Group in the eastern part of the basin (Andrews 1913; Rayner 1962) (Table 2). The depositional environment of the Win- duck Interval shows an overall regressive na- ture from west to east across the Darling Basin. It generally ranges from alluvial /fluvial in the Mt Daubeny Formation through fluvial to deltaic/shoreline in Winduck Group (Glen 1982a,b; Neef 2005; Neef et al. 1989; Neef and Bottill 1991) and deeper marine within Amphitheatre Group in the east (Glen 1982b, 1986). Snake Cave Interval and Equivalents The lower part of the Mulga Downs Group was formally proposed as the Snake Cave Interval by Bembrick (1997a, b). This interval is equivalent to the Snake Cave Sandstone in the Mt Wright area (Rose 1968), and in the eastern part of the Bancannia Trough (Packham 1969; Carroll 1982). It also includes the Coco Range Beds (now Coco Range Sandstone, Neef et al. 1995) on the western flank of the Bancannia Trough (Ward et al. 1969). In the east the interval has been subdivided into a lower part, the Meadows Tank Formation, a middle part, the Merrimerriwa Formation, and an upper part, the Bulgoo Formation, in the Buckambool area (Glen 1979, 1982a) (Table 2). The depositional sequence of the Snake Cave Interval was initiated by braided and alluvial fan input from the west within the Valley Tank Member in the western part of the basin and from the south-west for the Meadows Tank Formation in the eastern and central parts of the basin (Glen 1979, 1982a). At this time, the central parts of the Darling Basin were relatively free of coarse siliciclastic sediments and minor carbonates were developed locally (Rose 1968; Conolly et al. 1969; Carroll 1982; Neef and Larsen 2003). Ravendale Interval and Equivalents The upper part of the Mulga Downs Group is. equivalent to the subsurface Ravendale Interval proposed by Bembrick (1997a, b). The interval is equivalent to the Ravendale Formation named by Rose (1968). Conolly et al. (1969) has described the Ravendale Formation near the Bancannia Trough. The unit is synonymous with Units A, B and C mapped by Carroll (1982) on the eastern side of the Bancannia Trough. The Ravendale Formation is equivalent to the Nundooka Sandstone, mapped on the western flank of the Bancannia Trough by Ward et al. (1969). The lower part is also equivalent to the Bundycoola Formation and the upper part to the Crowl Creek Formation in the Buckambool area, west of Cobar (Glen 1982a), as shown in Table 2. In general the Ravendale Interval is initiated by an influx of coarse siliciclastic sediments in both the western and eastern parts of the basin (Ward et al. 1969; Conolly et al. 1969; Neef et al. 1995, 1996). Few coarse clastic types of sediment reached the central regions of the basin (Neef et al., 1995; Bembrick 1997a, b). The depositional environment of the Ravendale Interval is dominantly fluvial, but closes with — a Famennian marine episode encountered in the structural troughs where the thicker Late Devonian section is preserved (Neef and Larsen 2003; Bembrick 1997b). Late Carboniferous to Early Permian Sequence In the southern part of the Darling Basin, rocks of Late Carboniferous to Early Permian age have been recognized in several different studies (Byrnes 1985; Bembrick 1997b). Horizon D was considered to mark the Kanimblan event, a regional unconformity of Late Carboniferous age (Evans 1977) (Table 2). Areas in which TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN 35 such beds have been noted include the Blan- tyre Sub-basin. The lithology of these strata is dominated by interbedded siltstones and sandstones, which are variably micaceous and carbonaceous. Thick sections of Late Carbonif- erous to Early Permian strata have also been encountered in wells drilled in the Wentworth and Tararra Troughs (Evans 1977). Evans (1969) and Veevers and Evans (1975) considered from microfloras in the sequence that the rocks are mainly Late Carboniferous in age. However, rocks of Early Cretaceous age are known in the subsurface of the northern Bancannia Trough, and have also been encountered in wells to the south near Wentworth and Mildura (Evans and Hawkins 1967). STRUCTURAL FRAMEWORK Integration of lineament data within the Darling Basin shows that the boundaries are marked by a complex of major structural features as shown in Figure 1. The basin can be divided into six structural zones and one sub-zone, each representing distinct fault-bounded blocks (Scheibner 1993), and perhaps into several less distinct geologic terranes (Scheibner 1972, 1976; Evans, 1977; Glen et al. 1996; Glen and Walshe 1999; Pearson 2003; Neef 2005; Cooney and Mantaring 2007). The basin appears to be bounded in the north and east by the Tibooburra-Louth Zone (Scheibner 1989; Scheibner and Basden 1996, 1998), the Olepoloko Fault (Stevens and Craw- ford 1992) and the Paddington Line (Glen et al. 1996) (Figure 1). The western margin, against the Broken Hill Block, is represented by the NW-trending Nundooka Fault in the Bancannia Zone, and by the southwest trending southern margin of the Redan Zone (Scheibner 1993) (Figure 1). Significant faults and other features within the basin include the NW-SE trending Koonen- berry Fault (Rose and Brunker 1969; Leitch et al. 1987; Neef and Larsen 2003; Neef 2005), the prominent ENE-trending Darling River Lin- eament (Hills 1956), and the Bynguano Fault (Buckley 2001) on the eastern side of the Bancannia Trough. The Lake Wintlow Line separates the Bancannia Trough and the Pondie Range Sub-basin in the north and the Menindee Trough and Blantyre Sub-basin in the south- western part of the basin. The structural features of the Blantyre Sub- basin were described by Glen et al. (1996). The Manara Fault changes from NW trending in the SE part of the sub-basin to NW-trending near the Nelyambo Sub-basin. Uplift of the Wilcannia High, as defined by Evans (1977), appears to indicate the development of another major structural feature within the sub-basin. The Lake Wintlow Line provides a well-defined feature separating the Blantyre Sub-basin from the Menindee Sub-basin (Encom Technology Pty Ltd 1994; Glen et al. 1996; Alder et al. 1998). The Neckarboo High, along the southeastern margin of the Neckarboo Sub- basin and the southern margin of the Blantyre Sub-basin, is a narrow, elongate feature, which is approximately 60 kilometres long (Alder et al. 1998; Pearson 2003) (Figure 1). DATA COLLECTION AND METHODOLOGY Database The database used for this study consists of data from five exploratory petroleum wells and approximately 800 km of conventional two- dimensional seismic reflection profiles drawn from four different data sets (Figure 2). The Appendices summarize seismic data acquisition and processing parameters. This seismic data set was then integrated with Bouguer gravity data in order to identify and map the major structural features within the Blantyre Sub- basin (Figure 2). 36 MOHAMED KH. KHALIFA erie 143 OO E 700000M E Seismic line with Syncline Anticline Shotponit nN 143 30E 740000M E Stratigraphic Well Petroleum Weli Contour in mGal ! o / 144.00 E 14410E 6460000M N 6420000M N C.1. 50 mGal =“ eS Manara Fault ¢ y - 6380000M N 780000M E Cross-section of Figures 11 & 12 Sub-basin Boundary scemeewe, “No 400 \ Figure 2. Map showing gravity anomaly with distribution of two-dimensional (2-D) seismic profiles. Location of wells drilled within the Blantyre Sub-basin (modified after NSW Department of Mineral Resources, 2003). Also shown are hinge surface traces of structural highs (anticlines H-1, H-2 and dome H-3) and structural lows (synclines L-1 and L-2) and the Manara Fault as determined in Figures 3, 4 and 5. The two-dimensional seismic reflection data sets were integrated and re-interpreted using a range of computer-based techniques, par- ticularly the Kingdom® processing suite. In- formation from the seismic and well studies was integrated using CorelDraw® 11 (e.g. for preparation of seismic cross-sections) and Surfer 8 for preparation of contour maps and three- dimensional geologic evaluations. i The two-way travel time at selected shot points, about 100 metres apart on each of the seismic sections, was estimated for each reflector. The resulting data (the eastings and northings of each shot point and the two-way travel time to the reflector at that shot point) were input to the Surfer 8 graphic modelling package, to develop contour maps of the individ- ual horizons. Areas where the relevant horizons were not present, especially in modelling the base of the Ravendale Interval, were excluded from the modelling process. Interpretation Methods The data were interpreted in four steps. It should be noted, however, that tectonostrati- graphic modelling is very much an iterative process between the different steps, and hence dhe succession of processes was repeated several times in developing the final output of the study area. The first step was to describe the major structural features of the sub-basin, based on time-structure contour maps of the bases of the Winduck, Snake Cave and Ravendale Intervals. The second step involved comparison of the time-structure maps with the most recently available gravity data of the area, compiled by the New South Wales Department of Mineral Resources in 2003 (Figure 2). A good corre- lation was observed between the gravity data and the two-way travel time contours to the TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN of key horizons, especially those on the base of the Winduck Interval. This indicates that the grav- ity data mainly reflect the sub-basin structure, and do not appear to be significantly affected by variations in basement density or rock type. The third step was to compare the isochore map for each lithostratigraphic unit (in terms of two-way travel time) to the time-structure ft ° ‘ 143 OOE 143 30E SSD Zz TE : © CS we AW 700000M E 740000M E Reverse/Thrust fault Normal fault Syncline Anticline Nagi, OO Ss “Sema Stratigraphic Well patterns, especially for the Winduck and Snake Cave Intervals. The fourth step was to interpret the tectonostratigraphic evolution of the area, as indicated by a study of the contour maps and a closer look at the individual seismic cross- sections. This suggested a history involving three separate phases of tectonic activity. is) i °o / 144 00E 144 10E TWT (ms) 6460000M N 6420000M N C.1. 200 milliseconds . « 0 10 20 ° ee Kilometres 8 6380000M N 780000M E Petroleum Well Contour of two-way Sub-basin Boundary Position inferred -& time. milliseconds 9 ema ee MR 2200 \ Figure 3. Two-way time structure map of the base of the Winduck Interval within the Blantyre Sub-basin showing hinge surface traces of structural highs (anticlines H-1, H-2 and dome H-3) and structural lows (synclines L-1 and L-2) and the Manara Fault as discussed in the text. RESULTS AND DISCUSSION Subsurface Map Construction On the basis of the interpretation of the newly acquired data, the Blantyre Sub-basin can now be divided into a number of distinct structural provinces; these provinces are shown in the three two-way time structure maps (Figures 3, 4 and 5), supplemented by the two isochore maps (Figures 6 and 7). Structure Map Interpretation The data analysed includes both stratigraphic and seismic data. The three two-way time struc- ture map interpretations in Figures 3, 4 and 5 are consistent with a reconstructed pattern of sub-basin evolution. 38 MOHAMED KH. KHALIFA i a i fo) f ’ 143 00 E 443 30E 144 00 E 144 10 E 6460000M N 6420000M N Cross-section Figure 9 F1 ee, ¢o C.1. 200 milliseconds 0 10 20 eee Kilometres 6380000M N 700000M E 740000M E 780000M E Reverse/Thrust fault Normal fault Syncline Anticline Stratigraphic Well Petroleum Well Contour of two-way Sub-basin Boundary Erosion Position inferred MSc f ot time, milliseconds on, Sseacc vw ge Pig ane s + Nano Se mae ant *s 9 Carty Saale Figure 4. Two-way time structure map of the base of the Snake Cave Interval within the Blantyre Sub-basin showing hinge surface traces of structural highs (anticlines H-1, H-2 and dome H-3) and structural lows (synclines L-1 and L-2) and the Manara Fault as discussed in the text. TWT (ms) ° ' 9 1 143 OO E 143 30E 6460000M N 6420000M N Cross-section Figures 8&9 EM Sees (: et 3230S C.1. 200 milliseconds 0 10 20 | Kilometres i] 6380000M N 700000M E 740000M E 780000M E Reverse/Trust fault Normal fault Syncline Anticline Stratigraphic Well Petroleum Well Contour of two-way Sub-basin Boundary Erosion Position inferred ~. / time. milliseconds an ~., — A + cee foe. mene es Riss see 1600S as ahaa To Sea a ened) Figure 5. Two-way time structure map of the base of the Ravendale Interval within the Blantyre Sub-basin showing hinge surface traces of structural highs (anticlines H-1, H-2 and dome H-3) and structural lows (synclines L-1 and L-2) and the Manara Fault as discussed in the text. TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN 39 o t ° oO ! te ‘ 143 OOF 143 30 E 144 00E 14410E 250 6460000M N 450 600 Isochron Thickness(milliseconds) 6420000M N 750 C.1. 50 milliseconds o +r 3230S 0 10 20 nn eeevaeververweccereerers| Kilometres 6380000M N 700000M E 740000M E 780000M E Stratigraphic Well Petroleum Well Contour of two-way = Sub-basin Boundary —_ Erosion surface Position inferred Cross-section Figure 10 ist + time, milliseconds _~ eons ey F5 300 A semmene, ee SEO RCE 2 i ee Beas F6 Figure 6. Isochore map of the Winduck Interval, showing the response of the latest Silurian to late Early Devonian sequence to subsidence within the Blantyre Sub-basin. ° ’ 0 t ’ ‘ 143 00 E 143 30 E 144 00E 144 10 E 100 rm xo) £ °o 6460000MN & fe} f 3200S 2 ann = e (so B | .f 450 Blantyre 165 es 6 . a ES tog cS fe : ck 600 [o) = pl ox} o °o a1) 6420000M N 800 Erosion surface C.1. 50 milliseconds Qo #¥ 3230S 6 a0 20 Nn neeeevenveveoceerreews] Kilometres 6380000M N 700000M E 740000M E 780000M E Stratigraphic Well Petroleum Well Contour of two-way Sub-basin Boundary _—__ Erosion surface Position inferred Cross-section Figure 10 Ss time, milliseconds Lam, ) F5 em meee on BS, =a ™~ i! ". ced : Se ee Figure 7. Isochore map of the Snake Cave Interval, showing the response of the late Early Devonian to early Middle Devonian sequence to subsidence within the Blantyre Sub-basin. AO MOHAMED KH. KHALIFA (A) Two-way time structure contours on Farther east again there is a second struc- base of Winduck Interval 7 tural low (L-2), centred near the eastern end of seismic profile DMR03-05. The eastern part of this structure is poorly defined, due to a lack of seismic coverage. However at the eastern end of DMR03-05 there is an up-to-the-east high angle reverse fault (see Figure 9). A second structural high (H-2) is mapped in the northern part of the Blantyre Sub-basin, running east and then SE from Booligal Creek-1 and Booligal Creek-. 2 (Figure 2). This corresponds to the feature identified by Evans (1977), Alder et al. (1998), Pearson (2003), Neef (2005), Cooney and Man- taring (2007) Khalifa (2005) and Khalifa and Ward (2009) as the Wilcannia High. It curves southwards to link up with the NE-SW high (H- 1) through the Mount Emu-1 well site. Smaller structural highs are noted west of the Booligal Creek wells, east of the Wilcannia High around the Kewell East well, and west of the main NE- SW high, around the Snake Flat well (H-3) (see Figures 2 and 3). The two-way time structure contours on the base of the Winduck Interval (Figure 3) shows a NE-SW oriented structural low (L-1) in the western part of the Blantyre Sub-basin, centred around the Blantyre-1 exploration well. To the east of this is a NE-SW trending high, lying approximately along seismic profile $S$134>HD- 114. This contains two smaller high areas, one of which (H-1) is immediately SW of the Mount Emu-1 site. The base of the Winduck Interval is widespread throughout the Blantyre Sub-basin. Its depth ranges between 200 to 2600 millisec- onds of two-way travel time, being shallowest near the northern margin and deepest in the faulted central part of the Blantyre Sub-basin (Figure 3). The strata of the Winduck Interval, as defined from seismic profile DMR0O3-05, have an estimated thickness in this area of approxi- mately 1,400 metres (Figure 8). S$S134>HD-125 SP 859.53 $S134>HD-114} | _ SP 268.58 | FF enennaER 9Am S 1SGNN G me S a g ge Mount Emu-1 Weill T.D. 1450.5 m $S134>HD-110 $S134>HD-124 $S134>HD-116| $S134>HD-115 SP 716.16 SP 937.66 SP 882.96 SP 425.27 DMR03-05 $S134>HD-114 SP 318.63 SP 1331.48 {Boundary Inferred) Neckarboo Sub-basin— > Kewell East-1Well T.D. 1224m SP 1425 1225 1025 825 1400 % 1600 0.0 puarrironie = 0 a 0.5 =e : bE oe SS B 1000 w Re 2S p ary SS i wy & oS Re J ee Bi eS BE 5 ce EO 5A z 2 3 NGF * RS i954 © 3 ae S 3 St SRS oc BIEN As SA = 9 1.08 +} be EIR BS 2000 = ” LES % 3 EAS G BE WZ 5 c RS 4 eee § SF ca = a i a ER ERS Se g e165 Ss Soy 3000 £ nase DON, = OS ce NOR A Dineen x a ors es | es SNE o DROME POOR Se a CISC SNS L Fa eee RESALE LON % SI : > Es = SS RENE ONS eNO aS CSRS Lelie | = 2.0 Ses SRN 4000 « ° Rae aon £ 3 Sos a = Soe @ 2.5 SSR 5000 SAY 3.0 6000 Figure 8. Interpreted seismic section F3-F4, through east part of the Blantyre Sub-basin linked to the Neckarboo Sub-basin showing how thickening of Winduck, Snake Cave and Ravendale Intervals is compartmentalized on either side of the Wilcannia Uplift by complex faults. Section is based on well data, gravity data, and seismic profiles SS134>HD-114, 116 and DMR03-05. Location of seismic section is shown in Figure 5. TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN Al Snake Flat-1 Well Mount Emu-1 Well (Projected) T.D. 353.5 m 0 Kilometres 6-5 T.D. 1450.5 m (EER ERNNE TCE H.Scale SP 0.0 0 nD 1000 S 3 0.5 7 8 —E @ c pie 1.0 2000 = @ = — x > 1.5 3000 2 = 2. o < = 2.0 4000 € ® Q 2.5 5000 SS 143>HD-202 SS 134>HD-125 SP 350.59 SP 524.13 SS 143>HD-218B) |SS 143>HD-201 SP 877.37 P 1191.64 FE] wanenneneeneees> $$143>HD-21BB-n-n=-4-=----- |--SS143> |--SS134>HD-125-|-41DMRO3-05----- F2 SS 134>HD-110 SP 655.27 Snake Flat-1 Well HD-201— Mount Emu-1 Well 0 Kilometres 6.5 (Projected) T.D. 353.5 m T.D. 1450.5 m ad eeesseefeceeesseets QAYIKIMN cseeeessseeeenseeen H.Scale a 5 SP 400 -- 600 x 1000 600 800) fy 400 0.0 oh % oy ~ o w Ye Ta & + 5 g 05 AE = : Zee i E / re ro) = 1.0 5 Oe: = = ; ; os ; [= = - x De 3 ° = 3 eet LEGEND ae ror o x : 21 ucs | Undifferentiated Cenozoic sediments BX3 HD-218B and 201 showing the most deformed part of Snake Flat anticline with several high angle reverse faults. Also interpreted part of seismic profiles $S134>HD-125 and DMR0O3- 05, showing anticlinal folding and a associated thrust fault, indicating stratigraphic geometry and absence of the Ravendale Interval in the Mount Emu-1 well. A2 MOHAMED KH. KHALIFA (B) Two-way time structure contours on base of Snake Cave Interval © The two-way time structure contours on the base of the Snake Cave Interval (Figure 4) display a similar structural pattern to those on the base of the Winduck Interval (Figure 3). The surface for the base of the Snake Cave Interval has been mapped using data from all of the available shot points on the seismic profiles in Figure 2, except where the unit has been completely removed by erosion. Figure 9 displays a part of seismic profiles SS134>HD-125 and DMR03-05, which indicate in greater detail the setting of the anticlinal folding and associated thrust faulting close to the Mount Emu-1 Well. Figure 3 also shows a NE-SW oriented structural high (H-1) around the Mount Emu-1 Well, representing the Mount Emu Anticline (cf. Mullard 1995, Khalifa 2005). The base of the Snake Cave Interval recog- nised in the two-way time structure contours within the Blantyre Sub-basin, ranges in depth between 200 and 2100 milliseconds of two-way time, being shallowest near the northern margin of the sub-basin and deepest in the faulted region in the central part of the study area (Figure 4). The strata of the Snake Cave Interval, as shown in Figures 8 and 9, has been mapped by combining information from seismic profiles and well logs. In the wells, the greatest known thickness of the Snake Cave Interval (243.1 metres) has been recorded in Mount Emu-1 (cf. Khalifa 2005, Khalifa and Ward 2009), and the minimum thickness (about 100 metres) in Blantyre-1 (cf. Bembrick 1997b) is shown in Table 1, but thickness reaches an estimated 1,600 metres in the western Blantyre Sub-basin (e.g., at about 1.4-2.2 sec. TWT around SP 400 in seismic profile $$143>HD-218B; Figure 9). (C) Two-way time structure contours on base of Ravendale Interval The two-way time structure contours on the base of the Ravendale Interval (top of Snake Cave Interval) show a similar pattern to Win- duck Interval and Snake Cave Interval although there are extensive areas where the Ravendale Interval is not present (Figure 5). The Wilcan- nia High in the northern part of the sub-basin clearly exposed the Ravendale Interval, running SE from the Booligal Creek-1 and Booligal Creek-2 wells. The Wilcannia High is also seen to curve southwards and link up with the NE- SW oriented structural high (H-1) controlled by the Mount Emu Anticline (Figure 9). The base of the Ravendale Interval is widespread throughout the Blantyre Sub-basin, at a depth ranging from 250 to 1400 milliseconds of two-way travel time. It is shallowest in the southeastern and northern parts of the sub- basin, and deepest in the faulted region in the central part of the study area (Figure 5). The Ravendale Interval is absent in the Mount Emu- 1, Snake Flat-1, Booligal Creek-1, and Booligal Creek-2 well sections (Table 1). The strata of the Ravendale Interval reach a maximum thickness of approximately 1200 metres in the western Blantyre Sub-basin (e.g., at about 0.6— 1.1 sec. TWT between SP 600 and 1000 in seismic profile SS143>HD-201, Figure 9). The base of the Ravendale Interval is missing in part of the area (Figure 5), especially in the north-east, due to erosion after deposition and uplift. This is also shown on seismic section F3- F4 (Figure 8). Integration of Data from Structure Contour and Gravity Structure Maps The gravity contours of the area can be com- pared with the two-way travel time contours on the base of the Winduck Interval (Figures 2 and 3). The gravity data also reflect the main structural features indicated on the two- way time structure contour maps. Two gravity lows, with NE-SW orientations are interpreted in the western part of the sub-basin, and a NW-SE oriented structural low occur near the eastern end of seismic profile DMR03-05. These correspond to positive structures on the travel- time contour map of the base of the Winduck Interval (Figure 3). A positive gravity anomaly, corresponding to the Wilcannia High, is clearly identified on the northern margin of the Blantyre Sub- basin, around the Booligal Creek-1 and Booli- gal Creek-2 wells. This appears to link with TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN 43 gravity high (H-1) through the Mount Emu-1 well (equivalent to the Mount Emu anticline in Figure 9). The NE-SW oriented structural high around the Snake Flat-1 well corresponds to a similar structure inferred from the travel- time structure map (Figure 3) at the base the Winduck Interval. Further detail of the structural high (H-3) around the Snake Flat- 1 Well, representing the Snake Flat Anticline (cf. Mullard 1995, Khalifa 2005), is shown in Figure 9. This is the most deformed part of the anticline, and is marked by a high angle reverse fault and an asymmetrical fold. Comparison of Structure Contour and Isochore Maps Isochore maps have been constructed for the Devonian sequence in the Blantyre Sub-basin, $$134>HD-111]/SS134>HD-112| |SS134>HD-116 SP 1424.52 SP 429.68 SP 184.24 $S143>HD-205 SP 778.24 FE wnsanopenene-SS134>HD+1 23 -neeeennes $S134 Blantyre Sub-basin based on the seismic data. The units evaluated were of the Snake Cave and Winduck Inter- vals. (A) Thickness of the Ravendale Interval The thickness of the Ravendale Interval in many parts of the Blantyre Sub-basin is incomplete, due to removal of strata by erosion follow- ing uplift associated with the faults and folds that have deformed the strata since deposi- tion (e.g. seismic section F5-F6, Figure 10). This and other sections have been used to identify those parts of the region where the Ravendale Interval, and in some cases other units, are partly or completely removed by post- structure erosion, and to separate those areas from areas with the full (un-eroded) interval thickness. $S134>HD-113 $S134>HD-116 $S134>HD-115 SP 545.28 SP 882.96 SP 425.27 0 Kilometres 12 TT $$134>HD-114 SP 1331.48 H. Scale Sa en SUSU SH Det (Been procitcnestrceaiartcsotennrsisshncnonnctentaaennrne F6 (Boundary Inferred) Neckarboo Sub-basin > Kewell East-1Well T.D. 1224 m SP 442 900 432 186 300 600 1500 S 0.0 lw . ——e cee DATOS eer —O0 = pg i eee u 2, Sues ee by: S ao} ie. “ ese KO D dra ee) S eS SEP iS z S 0.5 ee ee SON 28 1000 & ® * SS ‘ % : q Ses x — = s Ss ee RASS oe Se PAO = c y Zar SS ~¢: ys Save SS 1: 2 7 J S es , We 7 > ser} @ N ima & \ : SA : © E 1.0=f eS SEWN: 2000 £ zs ° Bae eee Ue ies A | 5 doe 8 3 ee ae ek Ge a & a = 1.5 Undifferentiated Upper Carboniferous! 3 a ] ° i Q 3000 < = 5 ey Se = HD-123, 112 and 116. See Figures 6 and 7 for location of seismic section F5-F6. 44 MOHAMED KH. KHALIFA (B) Thickness of the Snake Cave and Winduck Intervals The isochore maps for the Winduck and Snake Cave Intervals (Figures 6 and 7) show a broad similarity to the structure contour maps of their boundary horizons (Figures 3 and 4), with some degree of thickening and thinning in areas where the travel-time structure contours show low and high elevations respectively. The structure contour map on the base of the Winduck Interval (Figure 3) indicates struc- tural lows, or synclinal areas, along the sub- basin axis (a NE-SW oriented feature identified as L-1 and a NW-SE oriented feature identi- fied as L-2), and the corresponding thickness variations (Figure 6) indicate that these areas subsided more rapidly during Winduck Interval deposition. Similar structural lows or synclinal areas are observed by thickening in the isochore map of the Snake Cave Interval (Figure 7), although the extent is more limited due to erosion of the unit within the sub-basin (Figure 6). Nevertheless, there are clear increases in thickness of the Winduck and Snake Cave In- tervals from near the western and eastern edges of the Blantyre Sub-basin towards its centre. Figure 10 shows thinning of the Winduck and Snake Cave Intervals-on to the Wilcannia High in the west in seismic section F5-F6, and a remarkable thickening of the late Early Devonian to early Middle Devonian Snake Cave Interval in the Blantyre Sub-basin to the east of this structure, towards the Kewell East-1 well. It also indicates that the base of the Ravendale is present farther to the east, around shot point 1800 on seismic profile SS134>HD- 116, where the Snake Cave Interval is again of more ‘normal’ thickness. Figure 9 illustrates the stratigraphic and present-day structural configuration of the Blantyre Sub-basin. Lithostratigraphic unit relationships within the east-central Blantyre Sub-basin are similar to those in the west- central portion of the study area. Although the nature of the sequence is poorly documented due to limited well pene- tration, the Winduck Interval and the Mulga Downs Group (Snake Cave and Ravendale In- tervals) show little variation in thickness, sug- gesting tectonic quiescence within the region during the period of sediment accumulation. The most prominent feature is the alternate thickening and thinning of the area adjacent to the faults identified by this study in regional seismic sections, F3-F4 and F5-F6 (Figures 8 and 10). However, the characteristics of the Winduck, Snake Cave and Ravendale Inter- vals are particularly evident where sequences are thicker, in the central part of the section (between SP 400 and 800, Figure 9). They gradually disappear where the Winduck and Snake Cave Intervals become thinner, near the Wilcannia High, close to the northern margin of the sub-basin, for example between shot points 186 to 432 in seismic profile $S134>HD-112 (Figure 10). Tectonstratigraphic Evolution of the Blantyre Sub-basin Figures 11 and 12 provide a simplified recon- struction of the deformation history for the Winduck, Snake Cave and Ravendale tectonos- tratigraphic packages within the Blantyre Sub- basin. Four stages of tectonic evolution are suggested for the study area: (a) rapid sub- sidence, (b) compression associated with con- tinued subsidence (Tabberabberan Event) (c) compression associated with uplift and erosion (Alice Springs/Kanimblan Event) and (d) ex- tension associated with slow subsidence. Cross-section through the Mount Emu High Cross-section T1-T2 (Figure 11) represents a section across the Mount Emu-1 well, extend- ing from seismic profile DMR03-05 near struc- tural low L-2 (Figure 3) through the Mount Emu anticline, and north-east to seismic profile SS134>HD-125 and the end of seismic pro- file SS143>HD-204 (for location see Figure 2). High subsidence rates are interpreted during deposition of the Winduck, Snake Cave and Ravendale Intervals over the two low areas (i.e. the two ends of cross-section T1-T2), and lesser subsidence rates (smaller thicknesses) across the structural high (i.e. the Mount Emu anticline). TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN 45 NW E 1 Te Blantyre Sub-basin —————————————_—_—__———————————————— sP 537.5 300 600 852.5 600 900 1200 1500 0.0 — 0 an 1000 # E : be 5 —E o 1.0 2000 — it) n 8 £ 3 £ E a 2 1.5 3000 © amt — ° = hes > & © 2.0 4000 3 = c {o) - 3 o F 2.5 5000 & 3.0 6000 NW E T1 ; T2 «___-.- HFOmOROOeOemnNRONrrwm=r”™”1 rer ee ees=HD-125 E SP 853.01 mM §S143>HD-204——-|| — $$ 1345-125 rs MRO 80 Sa Mount Emu-1 Well T2 Blantyre Sub-basin————(T.D. 1450.5 m lt Erosional surface SP 537.5 300 600 B5215,8 600 900 1200 1500 0.0 SKS ‘ x < SK APS S MAIL ALM SS LONE. AT - & x g Ss 74 OY > VIRION IE. 0 BSS es BOSS Undifferentiated Cenozoic sediments7.2 x % “~\ SR PEER E 7D SLI BR YRS. PSS S GOOG CP. MYT A igi Nilay Gs RD xs x SS S x, rte. dep “ . f "ate ance - > =<, Undifferentiated Upper Carbo Is Cee Fo BARE Mot Permian sedimen ~~ Es pass , D 0.5 4 - 134 ea ; ~ ~~ 3335 1000 ry ; = g j g 3 3 Oo 1.0 2000 = a ” 2 £ e | Gati's 15 3000 £ g E = 2 = a WA em BOCs III, Cee “OOOO a4 Reeamamaee 4000 $ STONER . : : Fe 2.5 oat SH > <$ 2a Patg - ore = ey oe : : @ 5000 Oo o, 2 = d ~ Undifferentiated Proterozoic complex/Ordovician sediments?-—~ 3.0 nO nOn kat ata Sa tatatnlatntaPatatatalatatatntees 6000 NW E T1 T2 Blantyre Sub-basin SP 537.5 300 600 852.5 600 900 1200 1500 —_ = 0 1000 % = ) —E 2000 c 2 ~~ E 3000 = ean ° a o 4000 < = ~~ o 5000 4 Tyzetece Savas 6000 Figure 11 c & d. Cross-section T1-T2, showing the tectonic development of the Blantyre Sub- basin (See location of cross-section in Figure 2). (c) More compression, showing further anticlinal folding associated with the Mount Emu structure to create complex reverse faults (d) Further development of the Mount Emu thrust fault, followed by extension, erosion and deposition of the Cenozoic sediments. Cross-section through the Wilcannia High Cross-section T3-T4 (Figure 12) is a dip sec- tion across the Wilcannia High, extending from the Kewell East-1 well in the east (part of the Neckarboo Sub-basin) through seismic pro- file SS134>HD-116 and part of seismic profile 5S134>HD-114 (between shot points 937.66 to 1331.48), as shown in Figure 2, to the end of seismic profile $S134>HD-124. Figure 12a represents a schematic recon- struction of the section during the rapid sub- sidence phase of sub-basin development. Lower subsidence rates are interpreted across the high area in the central part of cross-section T3-T4 during deposition of the Winduck, Snake Cave and Ravendale Intervals (Figure 12a). Higher subsidence rates during Winduck, Snake Cave and Ravendale deposition are interpreted in the trough area farther to the west on the same cross-section. TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN AT SW E T3 es f 3 (Boundary Inferred) Blantyre Sub-basin ; Neckarboo Sub-basin sP 200 400 600 800 800 1000 1200 1000 1400 1600 0.0 == on = 0 0.5 1000 2 3 33-B eI ee ra 5 £ 0 1.0 2000 = : E £ e i> 1.5 3000 © gam £ x — o _— = a. ~ Q = 2.0 , 4000 ¢ ‘ 529.0 £ S Seat +. ® F 25a Kt eaeate peatatatatece tatecate 5000 Q cesta satesetetesusetctatetetetecesesetetetetscetstesccesetstetetesece SO OIA OO OS Undifferentiated Proterozoic complex/Ordovician sediments? Co ae > - rp Ce egg ee e* we s_ > ; 3.0 6000 SW = T3 (Boundary Inferred) 14 Blantyre Sub-basin Neckarboo Sub-basin SP 200 400 600 800 800 1000 1200 1000 1200 1400 1600 0.0 ' " ' Feearaee 0 mY Meawon wn Ravendale Interval 0.5 149 1000 ° ” 3 = me) : ® 3 £ o 1.0 2000 = @ 4 yk men can o were eee! Or eeeeees 2 £ : © @ 1.5 3000 £ =< E 3 - na a ~ rom = 2.0 4000 < g £ FE ORR O RAIA RAM OO ETHER = 2.5 5000 O Ns OP mh Gary aay a Nek il ky bl a Sad al Nae a Ne ee er a PR ane, Cow oe PENNS A Und omplex/Ordovician sediments?\>< <0 Kilometres 8-5 3.0 poatatate 4 Oc Onel ee beepommmaee 6000 a H.Scale Figure 12 a & b. Cross-section T3-T4, showing the tectonic development of the Blantyre Sub- basin (See location of cross-section in Figure 2). (a) High subsidence rates in the trough areas (b) Compression and localized deformation associated with further subsidence, especially in the southwest. (Figure 12 c & d on next page.) The lithostratigraphic units representing the Winduck, Snake Cave and Ravendale Intervals are of similar thickness in the two synclinal areas, but the three tectonostratigraphic pack- ages appear from the seismic data, where a complete section is preserved, to be thinner on the Wilcannia High itself, for example around shot points 1000 to 1200 on cross-section ‘T3- T4 (Figure 12a). 48 MOHAMED KH. KHALIFA $S134>HD-124 $S134>HD-124 SP 193.95 SP 937.66 $S134>HD-116 $S134>HD-115 SP 882.96 SP 425.27 SW (Boundary Inferred) E $S134>HD-114 c eee ay, Neckarboo Sub-basin T3 Rican me in aenncnwnenewennows | wnmewwannmnnn SS134>HD-114--~--2---a- | ----nnn nnn nnnnnnnnnn anne panne ef --eemne- SS 1 34>HD-116- TA Kewell East-1Well Blantyre | Sub-basi Eosional “TD. 4 =, an SP DO 400 600 800 800 1000 1200 1400 F160 i ay > Ms OO COOK Wo 5 ~ 0 0.0 oats aged Ne Ao : OY Ncanhnwiee 6 o. VSS . Se 0.5 1000 = ® 3 5 c ® 8 1.0 2000 & ® D 6 Gea oe 15 3000 £ 11> £ * = = g g 2.0 4000 = 4 ro) =< = a Fos 5000 & O20, 0 one & 3.0 S526: Wiometres 8. 5 er 5-4 6000 H.Scale. aa Sw E T3 (Boundary Inferred) T4 —— Blantyre Sub-basin Neckarboo Sub-basin SP 200 400 600 800 800 1000 1200 1000 1200 1400 1600 0.0° 0 ° wn 1000 2000 3000 aii 4000 Depth Approximation (metres) 5000 3.0 6000 Figure 12 c & d. Cross-section T3-T4, showing the tectonic development of the Blantyre Sub- basin (See location of cross-section in Figure 2). (¢) More compression with maximum movement of the Wilcannia Uplift contrast in complex thrust and normal-faults in the east (d) Extension, enhancement of horst-graben structures, erosion and deposition of the Cenozoic sediments. Figure 12b shows a reconstruction of the highly faulted area on the eastern end of sec- tion T3-T4, suggesting that major subsidence occurred around the eastern margin of the Blan- tyre and the western margin of the Neckarboo Sub-basins. The more structurally complex zone of normal and reverse faults in between the sub-basins is associated with later compression forming a relatively symmetrical synclinal fold. Figure 12c suggests that, by the end of the second tectonic stage, the Wilcannia Uplift had begun to develop in the area, with the Win- duck, Snake Cave and Ravendale Intervals being partly or completely removed by post-structure erosion. The extent of erosion of the Ravendale Interval is further indicated in Figure 5. TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN AQ The last stage of tectonic development repre- sents extension, enhancement of the fault struc- tures, regional uplift, erosion and deposition of the Cenozoic sediments over the whole of the Blantyre Sub-basin. However, Figure 12d shows extension with faults after the Devonian, and then deposition of the overlying Upper Carboniferous/Permian sediments during a tec- tonically quiet period with broad slower subsi- dence. Cenozoic sediments were deposited over the whole section following erosion. The high on the eastern side of cross-section T3-T4 is part of the Kewell East Anticline, bounded on the west side by fault zones (com- plex of normal and reverse faults) and a near symmetric synclinal fold (Figure 12d). This high was drilled by the Kewell East-1 well (Clark et al. 2001). Basement Surface A change in basement dip is evident on re- gional seismic sections across kilometer-scale wavelength fold structures (e.g. Mount Emu and Snake Flat anticlines) and a basement ‘pop- up’ feature that was formed in post-Devonian time. Also shown on the regional sections that integrate the gravity data and the seismic profiles (Figures 11 and 12) is a strong onlap and thinning of the Winduck and Snake Cave Interval on to palaeo-basement highs, indicating that many of the present sub-surface highs were highs during sediment deposition. How- ever, the faults bounding these paleo-highs had northwest-southeast, east-west and north-south strike orientations, supporting a suggestion that all of these fault systems were co-active during the extensional part of the sub-basin history and controlled differential subsidence. Similarly, ‘palaeo-basement’ character is inferred for the Mount Jack High and the Lake Wintlow Highs by Glen et al. (1996), Alder et al. (1998), Willcox et al. (2003) and Cooney and Mantaring (2007). The basement structure may have influenced thickness variations in the Winduck and Snake Cave Interval. There are hints of this on the seismic data, where the basal Winduck Interval is interpreted to be faulted or gently warped (Figures 11 and 12). In turn, the shape and thickness of the Winduck Interval may have influenced fold development, such as across the Mount Emu anticlinal fold. In con- trast, for areas to the northwest and southeast, gravity lows do correspond to basement depth estimated from seismic profiles SS134>HD- 123, 124, $S143>HD-204, 218B and DMR03-05 (Figure 2). Structural Aspects and Implications for Hydrocarbon Potential The hydrocarbon potential of the Darling Basin has been discussed by Evans (1977), Brown et al. (1982), Byrnes (1985), Bembrick (1997a, b) and Wilcox et al. (2003), and described in more detail by Alder et al. (1998), Pearson (2003), Cooney and Mantaring (2007), Khalifa (2005), and Khalifa and Ward (2009). Herein, I summarize the specific structural aspects of the hydrocarbon potential prospects in the Blantyre Sub-basin related to the folding and associated complex faulting that have affected the latest Silurian-Devonian stratigraphic geometry. The anticlinal crests of Snake Flat, Mount Emu and Kewell East folds are the primary targets for any future exploration (Figures 8 and 9), with additional potential for stratigraphic pitch-out plays on the flanks of some structures. Individual structures have areal closure of up 100 square kilometres, with more than 2000 metres of section under closure. The different models of fold formation described in this paper would influence any prospects. A tectonostrati- graphic model of anticlinal geometry is assumed to have developed, as the fold translated over a fault, bending would predict a repetition of the deep section within the core of the fold structure. The fracture patterns predicted by the tectonostratigraphic model (Figures 11 and 12) also would be quite different, an important point considering that fracture permeability may play a significant role in developing viable hydrocarbon targets across the folds. The extent of these major folds beneath the Up- per Carboniferous/Permian sediment and their possible hydrocarbon potential are important unanswered questions in the Blantyre Sub- basin. 50 MOHAMED KH. KHALIFA CONCLUSIONS This paper has attempted to integrate the data from the seismic profiles, several maps and wells into a consistent geologic picture, in order to add some new insights into the structural styles and tectonostratigraphic framework of the Blantyre Sub-basin. A geological model has been derived from interpretation of two-way travel time structure contour maps, in conjunction with the regional gravity contour map. Several major structures have been identified and named. These include a large structure situated at the junction of three major high complexes, referred to as the Wilcannia High (H-2), and two smaller high areas. One of these, the Mount Emu High (H-1), is an anticlinal fold with thrust fault; the other, the Snake Flat High (H-3), is an asymmetric anticlinal fold with a number of high angle reverse faults. Two structural lows have also been identified, aided by cor- relations between the structure contour data and the gravity map, especially the structure contours on the base of the Winduck Inter- val. In the central part of the Blantyre Sub- basin, around the Blantyre-1 exploration well, there is a structural low (L-1). This is an elongate, synclinal fold, and covers an area of approximately 400 square kilometres. There is a second generally smooth structural low (L-2) within the Blantyre Sub-basin. This is also shown on the gravity contour map and the structure contour map on the base of the Winduck Interval, and is seen on seismic profile DMR03-05. Isochore maps for each stratigraphic interval (in two-way travel time) have been compared with the travel-time structure contour patterns, especially for the Winduck and Snake Cave Intervals, to identify any thickening and thin- ning associated with structural development. Improved isochore maps will provide control for structure mapped on seismic profiles, especially the Wilcannia, Mount Emu and Snake Flat structural highs. Key seismic cross-sections, T1-T2 and T3-T4, were also constructed to assist the analysis process, and further inves- tigation of relationships between the tectonos- tratigraphic sequences, sub-basin geometry, and the development of complex structures within the study area. The following broad history has been iden- tified from these interpretations and a review of the basin’s tectonic evolution: (a) high sub- sidence rates in the trough areas, (b) compres- sion and localized deformation associated with further subsidence, (c) extension, enhancement of normal and reverse faults, including the Wilcannia Uplift and (d) erosion and deposition of the undifferentiated Permo-Carboniferous, Early Cretaceous and Cenozoic (Tertiary and Quaternary) sediments, identified at shallow depths within the main Blantyre Sub-basin. A tectonostratigraphic model has been put forward to address the variation in compres- sional and extensional fault and fold-related stresses that created the observed differences in the deformation of the original normal and re- verse faults, and the synclinal and anticlinal fold structures. The positive subsidence patterns are always fault-controlled, as shown in cross- sections T1-T2 and T3-T4 (Figures 11 and 12). Understanding the ongoing structural processes within interpreted seismic data should help to decrease the risk of hydrocarbon exploration by applying up-to-date concepts throughout the Blantyre Sub-basin. ACKNOWLEDGMENTS This work was originally carried out during 2005 at University of New South Wales in collabora- tion with the Petroleum Group of the Geological Survey of New South Wales as part of PhD thesis under the joint supervision of Professor Colin Ward and Dr Derecke Palmer. This thesis was supported by a scholarship from the Sev- enth of April University in Libya. Thanks are also expressed to the New South Wales Depart- ment of Primary Industries, Mineral Resources Division (Coal & Petroleum Development) for providing all of the data for this study. Special thanks to Senior Geophysicist Phillip Cooney (Consultant), Dr Brian Jones (University of Wollongong) and Dr Paul Lennox (University of New South Wales) for reviews of an early version of this manuscript. I am grateful to Dr Kingsley Mills (Geological Survey of NSW) for the review of the final version and his many sug- gestions and useful amendments. Finally, many thanks to Dr Michael Lake (Journal Typeset- ter) and anonymous journal reviewers for their suggestions that improved the manuscript. ol TECTONOSTRATIGRAPHIC EVOLUTION OF THE BLANTYRE SUB-BASIN ‘abod 7xaU UO panuljzUoy) aouepedull aseaIOU] wd /sa0e1} ()T 90s /WU9 QT pezienba aoe1], dd prepueys SPpUOdasTT[IU QOG IMAG Joye pue s10joq eiyoodg A}IOO[VA AAOCT S,ULODSTAaS Spuodvas /19}0UL YOOE SalJOU YOT SUOI}JEAV[9 JOATIVII PUL 9dINOS SpUOdIAST]IIU YOR Spuoossi{ [IU P SpuOdasI]IUL Z eAsoqyur ajdureg SpuOodv—as G :Y4SUs] p1ooVyY ADS JULIO} P1OIBY yuasoidar syeog aaeyo0/qp ZL edo[s ZH BZ] 39 YS a]eos [eWOZIIOT] aaeyo/qp edojs ZH LAO Wo MoT SIOY TA a]eos [ROL}IOA, dnoss sed Z] (ZHOL) G0% SH OSD sauoydoas) ad J, sutayskg Aeldsiq{ 6 UOTyeJUSUINASUT “EF SPpuooeste O2> “WIS ANE °8 S[BAIOJUT SoI}OUL (Cp I 96 sdnois Jo Jaquinyy ed4q, ape IS 2 Saljoul (861-001-dS-00T-O86T peoidg yysug] ayer) suoryestpenby oer], “9 sorjoul ee ==: yySuay dnor3 auoydoar juaurysn{pe sorye4s %OOZT SUIPIOIII JO Ploy JUd4}STISUOD sata: IMAC “S Aajoutoesy) Surpr0v0y °*Z poyndurog SOI}IIOTo ‘sasAyeuy AYIO0TOA * V iaaaecdaes cold ai aaa AYDOTOA Tee Pte eer uoryeys Jad sdvaMs OT Aeire 9oInos wnyeq daomsdn ZH 96-91 Aduanbaly daams SUOT}IIIIOI OT}LYS soryeys UNyeq “E ate 9 eee evar yysug] ayer) :uoryesipenby soe], *Z einer Sour I sa ae "ps sel], ; : a,duresoy ‘SSOD01g [RII "] eomMog Asieuq *T ONISSHDOUd NOLLISINOOV GZI ‘PZT ‘E21 ‘9TT ‘PIT-GH