Bonaparte Gulf Basin Research Articles

Carboniferous platyceratid gastropods from Western Australia and a possible alternative lifestyle adaptation

Cook, A.G. & Jell, P.A., September 2015. Carboniferous platyceratid gastropods from Western Australia and a possible alternative lifestyle adaptation. Alcheringa 40, XX–XX. ISSN 0311-5518Platyceratid gastropods, common and in many cases abundant as elements of middle Palaeozoic gastropod faunas worldwide, are rare or absent in Australian Devonian faunas. In Australia, the earliest abundant platyceratids occur in the Lower Carboniferous (Tournaisian) echinoderm-rich Septimus Limestone and Enga Sandstone in the Bonaparte Gulf Basin, Western Australia. Four taxa, each with significant morphological plasticity, are recognized. In Platyceras (Platyceras) tubulosus (de Koninck, 1883), three rows of long radially arranged spines and common pentameral symmetry of re-entrants on the aperture suggest an alternative possibility that a relationship between echinoderms and platyceratids developed, and that this may be with archaeocidaroids that are commonly preserved with the gastropods. Similarly in the singly spinose Platyceras (Platyceras) emmemmjae sp. nov., re-entrants suggest an echinoderm relationship. It is proposed that an echinoderm–Platyceras relationship possibly developed in Australia only after a suitable echinoid host had evolved allowing an alternative way for a gameto- or coprophagous habit to be exploited fully.Alex G Cook [alex.Cook@y7mail.com] and Peter A. Jell [p.jell@uq.edu.au], School of Earth Sciences, The University of Queensland, Queensland 4072, Australia.

Permo-Triassic successions of the Kekneno area, West Timor: implications for palaeogeography and basin evolution

The Permo-Triassic succession of Kekneno, Timor, consists of mixed clastic and carbonate sediments, showing marked local variations in thickness and facies. Sedimentation occured in neritic to deep marine basin environments and was accompanied by fault controlled subsidence. The basin lay close to the northern margin of Gondwanaland but was partly enclosed by land areas to the east and north. Sandstones of the Timor succession are petrologically less mature than their equivalents in the Bonaparte Gulf Basin and the southern part of the Timor Sea, and also contain different heavy mineral assemblages. The implication is that the provenance area of the Kekneno sandstones was separate from the sandstones in the areas to the south. Uplifted carbonate platforms (e.g. the Sahul Platform) may have isolaetd the Kekneno Basin from the quartz rich sandstones which characterise some of the basins closer to the Australian hinterland. Palaeocurrent measurements from the Permo-Triassic sediments of Kekneno show several different flow trends through time. The most significant trends are north-south bimodal (earliest Permian), southeast (Early to Mid-Permian) and west-southwest (Middle to Late Triassic). These data, together with the abundance of terrestrially derived organic matter, suggest that emergent landmasses lay to the east and also to the north or northwest of Kekneno. Part of the northerly landmass may have been removed by Early to Mid-Permian rifting near the northern margin of Gondwanaland. Erosion of nearby shelf areas produced the sediments which infilled the Kekneno Basin. Slump folding and thick debris flows bear witness to active downfaulting of the basin margins, particularly in the Middle to Late Triassic.

A Fresh Look at the Late Palaeozoic Tectonic History of Western-Central Australia

This paper investigates a simple model for the evolution of the central Australian (Amadeus, Officer and Ngalia) basins and the adjacent Canning and Bonaparte Gulf basins at the time of the Alice S...

HYDROCARBON POTENTIAL OF THE UPPER JURASSIC/LOWER CRETACEOUS OF THE AUSTRALIAN NW SHELF

Source‐rock richness, timing of hydrocarbon generation, and thicknesses of potential source shales of the Upper Jurassic/Lower Cretaceous section of the Australian NW Shelf have been examined in order to make predictions as to the hydrocarbon productive of liquid hydrocarbons: the Brows Basin, the Malita Graben/NW Bonaparte Gulf Basin, the Rowley Sub‐basin, and the Vulcan Sub‐basin/Sahul Syncline, respectively.Recent liquid hydrocarbon discorveries in the Vulcan Sub‐basin, probably source by the Upper Jurassic shales, upgrade all four of these areas, and lead to the conclusion that overall, drilling results on the NW Shelf have to date not been indicative the timing of generation as delineated in this study with the timing of structural development in order to improve chances of success, rather than relying on the size of Structures alone.A new method of presenting timing of generation, in the form of a “timing‐of‐generation map”, is introduced, where the timing of the progress of significant hydrocarbon generation is contoured over the NW Shelf for each source‐rock section.

SPORE TETRAD STRUCTURES OF POSSIBLE HEPATIC AFFINITY FROM THE AUSTRALIAN LOWER CARBONIFEROUS

Palynological studies of Early Carboniferous (Viséan) sediments of the Bonaparte Gulf Basin, northwestern Australia, reveal the presence of intact tetrahedral spore tetrads (here described as Sagenotetradites gen. nov.) and, more usually, of their disjunct spore portions which had previously been interpreted as dispersed whole‐miospore species. Two species of the new tetrad genus are recognized: S. bonapartensis (Playford) comb, nov., as type species; and S. spiritensis (Playford) comb. nov. The species are distinguished, as originally, on the basis of sculptural attributes of their distal exoexines. When intact, both species share a common internal “binding” element (“Cadiospora abrupta” Playford, 1971) composed of the fused proximal exoexinal faces of all four spores of a given tetrad. Morphological comparisons with modern hepatic spores suggest an alliance of the microfossils with the order Sphaerocarpales. The occurrence of Sagenotetradites in exclusively marine sediments suggests that its parent plants grew in close proximity to the marine depositional basin. Moreover, the morphological attributes of the tetrads would appear to have facilitated dissemination by water.

Spore Tetrad Structures of Possible Hepatic Affinity from the Australian Lower Carboniferous

Palynological studies of Early Carboniferous (Viséan) sediments of the Bonaparte Gulf Basin, northwestern Australia, reveal the presence of intact tetrahedral spore tetrads (here described as Sagenotetradites gen. nov.) and, more usually, of their disjunct spore portions which had previously been interpreted as dispersed whole-miospore species. Two species of the new tetrad genus are recognized: S. bonapartensis (Playford) comb, nov., as type species; and S. spiritensis (Playford) comb. nov. The species are distinguished, as originally, on the basis of sculptural attributes of their distal exoexines. When intact, both species share a common internal “binding” element (“Cadiospora abrupta” Playford, 1971) composed of the fused proximal exoexinal faces of all four spores of a given tetrad. Morphological comparisons with modern hepatic spores suggest an alliance of the microfossils with the order Sphaerocarpales. The occurrence of Sagenotetradites in exclusively marine sediments suggests that its parent plants grew in close proximity to the marine depositional basin. Moreover, the morphological attributes of the tetrads would appear to have facilitated dissemination by water.

Permian Ingelarellidae (Brachiopoda) from Western Australia and Argentina

Representatives of the Ingelarellidae are described from the marine Permian sequences of the Perth, Carnarvon, Canning and Bonaparte Gulf basins of Western Australia. The subfamily Ingelarellinae Campbell (1959) is raised to family status and the new subfamily Notospiriferinae is proposed; content of the Ingelarellidae is reviewed. New taxa described are Tomiopsis notoplicatus n. sp., T. woodwardi n. sp., T. rarus n. sp., T. pauciplicatus n. sp., T. teicherti n. sp., T. globosus n. sp., T. balgoensis n. sp. and T. hardmani n. sp. Additional material from Western Australia belonging to Tomiopsis and possibly Fredericksia is briefly described. Tomiopsis harringtoni n. sp. is described from the southern hills of Buenos Aires (eastern Argentina).

NeospiriferandTrigonotreta(Spiriferida, Brachiopoda) from the Permian of Western Australia

Representatives of the genera Neospirifer Frederiks and Trigonotreta Koenig are described from the Permian sequences of the Perth, Carnarvon, Canning and Bonaparte Gulf Basins of Western Australia. New or revised taxa are Neospirifer hardmani (Foord), Neospirifer foordi sp. nov., Neospirifer plicatus sp. nov., Neospirifer postplicatus sp. nov., Neospirifer amplus sp. nov., Neospirifer grandis sp. nov., Trigonotreta lyonsensis sp. nov., Trigonotreta neoaustralis sp. nov., Trigonotreta dickinsi sp. nov. and Trigonotreta lightjacki sp. nov. Additional material belonging to Neospirifer is briefly described and a lectotype is designated for Neospirifer timorensis (Martin) from Timor.

New genera of Western Australian Permian Spiriferidae (Brachiopoda)

New genera of the Spiriferidae are described from the Permian sequences of the Carnarvon, Canning and Bonaparte Gulf Basins of Western and northwestern Australia. New taxa described are Latispirifer gen. nov. with type species Latispirifer callytharrensis sp. nov. and Latispirifer amplissimus sp. nov.; Costatispirifer gen. nov. with type species Costatispirifer gracilis sp. nov.; Cratispirifer gen. nov. with type species Cratispirifer nuraensis sp. nov. and Crassispirifer gen. nov. with type species Spirifer rostalinus Hosking (1931) and Crassispirifer pinguis sp. nov. The holotype and only extant specimen of Spirifer kimberleyensis Foord (1890) is re-examined and is assigned to Crassispirifer gen. nov. with a query.

A new late cretaceous megaspore with grapnel‐like appendage tips from Australia and New Zealand

Abstract Grapnelispora evansii, a new megaspore genus and species from the Upper Cretaceous (Maastrichtian) of Australia and New Zealand, is described and illustrated. Although superficially similar to the Paleozoic ancyrospores in possessing appendages with anchor or grapnel‐like tips (a feature not reported previously on Mesozoic megaspores), the new form has significantly longer appendages and a more complex internal wall structure. Specimens have been recovered from wells in the Bass Strait Basins of southeastern Australia, basins along the southern margin of the continent, the Bonaparte Gulf Basin of northern Australia, and from New Zealand surface sections.

Devonian Reef Prospects, Canning and Bonaparte Gulf Basins, Western Australia: ABSTRACT

Middle and Upper Devonian reefs outcrop spectacularly for some 220 mi (350 km) along the northern margin of the Canning basin, in a series of rugged limestone ranges. They extend into the subsurface of the basin, and may originally have continued for some 750 mi (1,200 km) in a belt girdling the Precambrian Kimberley block, to join with similar reefs known in the onshore Bonaparte Gulf basin. There is also evidence that they once extended into the Carnarvon basin, 930 mi (1,500 km) to the south. The Canning basin reefs show similarities to the Devonian reefs of Canada, and for the past 25 years, they have been regarded as prime targets for oil exploration. However, the first potentially commercial discovery was not made in the basin until 1981, when oil was recovered from an Upper Devonian (Famennian) reef complex in the Blina 1 well. This well yielded flows of up to 905 bbl per day from the reefal carbonates. Recent encouragement of oil exploration in Devonian reefs has also been obtained in the Bonaparte Gulf basin, in this case as a result of mineral-exploration activities. More than 20 drill holes, exploring for lead-zinc, encountered significant showings of oil and bitumen in Upper Devonian reefal carbonates and overlying Carboniferous carbonates, in a belt some 95 mi (150 km) long. They are probably the most extensive near-surface oil showings known in Australia. There appears to be a genetic relationship between secondary porosity development, base-metal deposition, and oil emplacement (in that order) in these carbonates. There are strong grounds for optimism that further reef-associated oil discoveries will be made in the northern Canning basin, and the outlook is also promising for similar discoveries in the Bonaparte Gulf basin and the offshore area adjoining the Kimberley block. End_of_Article - Last_Page 981------------

DEVONIAN REEF PROSPECTS IN THE CANNING BASIN: IMPLICATIONS OF THE BLINA OIL DISCOVERY

Devonian reef complexes outcrop spectacularly along the northern margin of the Canning Basin, forming what is probably the best preserved Palaeozoic reef belt in the world. The reefs extend into the subsurface, where they have been prime objectives for oil exploration since the mid 1950s. Exploration was finally successful in 1981, when Home Oil discovered the Blina oilfield in an Upper Devonian reef complex. It is the first potentially commercial field to have been found in the Canning Basin.Blina 1 flowed oil at rates of up to 905 barrels per day from the reef complex and overlying Upper Devonian to Lower Carboniferous dolomite. Two successful step-out wells have now been drilled, and although reserves of the field are still uncertain, economic development seems likely.The Blina reef complex is of Famennian age, belonging to the Nullara Cycle of reef development, while the overlying productive dolomite is within the Famennian-Tournaisian Fairfield Group. The Famennian reef margin is clearly displayed on seismic sections, but an earlier cycle of reefs, the Givetian-Frasnian Pillara Cycle, is more difficult to detect. These older reefs may nevertheless have better overall prospects than those of the Famennian.Positive indications of oil associated with Devonian reefs have also been obtained in the Bonaparte Gulf Basin, where widespread showings have been reported from mineral-exploration boreholes in Famennian reefal carbonates and overlying Lower Carboniferous carbonates.Recent seismic results have disclosed possible reef anomalies in several permit areas. The prospects for making further reef-associated discoveries seem promising along the Blina trend and elsewhere in the Canning and Bonaparte Gulf Basins. Prospective Devonian reefs are also likely to occur in the offshore area skirting the Kimberley Block and possibly extending as far south as the Carnarvon Basin.

THE CAMBRIAN PALAEOGEOGRAPHY OF AUSTRALIA AND OPPORTUNITIES FOR PETROLEUM EXPLORATION

As part of a larger project to re-evaluate the petroleum potential of Australia, it was considered necessary to produce a series of Cambrian palaeogeographic maps. This required the compilation and correlation of a large number of stratigraphic columns, the delineation of sedimentologlcally-significant time intervals, the production of data maps for these same time intervals, and the development of a Cambrian 'tectonic' map. This palaeogeographic study was not undertaken to establish precise exploration targets. However, it does provide new information on where many of the essential components are, what age they are, and why they are there, and as such is a valuable tool in the overall exploration and resource evaluation strategy.The six palaeogeographic maps finally produced illustrate events involving continental drift, tectonics, and climatic and sea-level variations, over a period of 70 million years. Together, these events produced marked changes in the palaeogeography and depositional environments, which in turn profoundly affected the type and distribution of sediments being deposited on and around the palaeo-continent during the Cambrian. Using the palaeogeographic maps and the data accumulated for the project, it is possible to demonstrate that organic-rich sediments, with the potential to be petroleum source rocks, were relatively common during the Cambrian, especially on the eastern cratonic margin during the Lower Cambrian (Officer and possible Amadeus Basins) and the Middle Cambrian (Georgina Basin). There may also be some suitable petroleum source rocks in the Ord Basin. Limestones and dolomites, some of which may constitute potential reservoir rocks, were deposited in a number of Cambrian intracratonic basins (Amadeus, Georgina Basins) and on the shelf (Cooper Basin). Cambrian sandstones in Australia are commonly poor reservoir rocks, but where they have been subjected to shore-line or shelf 'clean-up', for example during the Middle and Upper Cambrian on the northwest side of the craton (Bonaparte Gulf Basin), there may be some potential reservoir rocks. Some sandstones may also be present on the south side of the Cooper Basin. Fine-grained impermeable sediments (potential cap rocks) were deposited throughout the Cambrian, but evaporites were most common during the Early and lower Middle Cambrian. Synsedimentary tectonics may have produced structural and stratigraphlc traps, and a major phase of karsting occurred in the Cambrian. Therefore, the Cambrian of Australia is believed to have many of the prerequisites for the generation, migration and entrapment of hydrocarbons. Especially favourable areas for these features may lie to the southeast of the Georgina Basin and in the offshore region northwest of the Ord and Bonaparte Gulf Basins.

Seismic section from the Bonaparte Gulf Basin

The seismic section presented in Figure 1 illustrates erosional truncation in the Bonaparte Gulf Basin, Western Australia. Figure 2 is an interpretation based upon stratigraphic information obtained from exploratory wells drilled in the vicinity of this feature. Parameters used in acquiring and processing this seismic data are annotated on the section with the final display being presented as a 24-fold stacked section. Shot point 1 (on the right) is to the north-east.

Geochemical Evaluation of Petroleum Source Rock in Bonaparte Gulf-Timor Sea Region, Northwestern Australia

The source-rock potential and maturation history of sediments are critical parameters to the generation, migration, accumulation, and ultimate degradation of hydrocarbons. These parameters, when considered within the constraints of regional tectonics, assist in explaining the absence of commercial reserves in wells drilled to date in the Bonaparte Gulf-Timor Sea region and may subsequently be useful in delineating areas for future exploration. The area now occupied by the Timor Sea is a structural complex of intersecting Phanerozoic tensional features overlain by a thick, Tertiary carbonate platform. Pertinent geochemical data were integrated from analyses performed on cuttings and cores from 25 exploratory wells penetrating the complex. The Bonaparte Gulf basin originated in response to an early Paleozoic rifting phase. Geochemical data from sediments deposited in the basin from the Early Cambrian through Early Permian are very limited. Sedimentary rocks of Late Permian to Middle Jurassic age selectively exhibit source-rock characteristics and maturation levels adequate for the generation of hydrocarbons. The Permian section has yielded significant gas on test. A second rifting phase transpired in the Middle Jurassic and was responsible for creating the prominent tectonic elements that are apparent today in the offshore region. Clastic sediments of Middle Jurassic through Late Cretaceous age which occupied the newly formed depocenters exhibit variable source-rock potential and are sufficiently matured for hydrocarbon generation over an extensive area. Significant hydrocarbons have been noted in wells penetrating this section. The overlying Tertiary carbonate rocks are mainly immature and, except locally, are considered to have poor source-rock potential. Several factors have been detrimental to the accumulation and preservation of hydrocarbons on the relatively positive tectonic features in the Bonaparte Gulf-Timor Sea region. The factors include unfavorable phase relations among structural development, hydrocarbon generation, and subsequent erosion, silicification of sandstone reservoirs, and flushing by meteoric waters. Sediments within major depocenters, however, have had a more continuous maturation history and are believed to have generated significant hydrocarbon reserves.

PETROLEUM IN WESTERN AUSTRALIA: A REVIEW OF EXPLORATION, PRODUCTION, AND FUTURE PROSPECTS

Modern petroleum exploration has been in progress in Western Australia since 1952, and has been concentrated mainly in the Perth, Carnarvon, Canning, and Bonaparte Gulf Basins. Two large onshore fields have been developed, the Barrow Island oilfield in the Carnarvon Basin (found in 1964), and the Dongara gasfield in the Perth Basin (found in 1966). Small gasfields have also been developed at Mondarra, Gingin, and Walyering in the Perth Basin, but Gingin and Walyering are now virtually depleted.Major gas-condensate fields have been found offshore. These are the North Rankin, Goodwyn, West Tryal Rocks, and Angel fields in the northern Carnarvon Basin, and the Scott Reef field in the Browse Basin. They were found during the period 1971 to 1973, but none has yet been developed.Since 1968 the accent has been on offshore exploration, and this reached a peak in 1972. Exploration activity, both onshore and offshore, is currently declining, owing to the lack of recent success and the unfavourable exploration climate prevailing in Australia today.Original reserves in the Dongara gasfield amounted to about 13 billion cubic metres, of which nearly 2.1 billion have now been produced. Current gas production from Dongara and the small adjoining Mondarra field is about 2.2 million cubic metres per day, and production will continue at about this rate until 1981, after which it will begin declining. Production will fall steeply in 1987, when existing contracts expire. At that time about 90% of the reserves will have been depleted.The original in-place reserves of the Barrow Island oil-field amounted to some 750 million barrels, and it is expected that about 240 million will be recovered. Current oil production is around 37,000 barrels per day, compared with the peak of 48.000 barrels per day reached in 1970. Nearly 43% of the original reserves have now been produced.Total reserves of the major fields in the offshore northern Car-narvon Basin (in the proved and probable categories) are more than 345 billion cubic metres of gas and 320 million barrels of condensate. Of these amounts more than 220 billion cubic metres of gas and 180 million barrels of condensate are in the North Rankin field, which is the largest gasfield in Australia and is a giant by world standards. This is followed by Goodwyn (about 65 billion cubic metres of gas and 90 million barrels of condensate), West Tryal Rocks (more than 30 billion cubic metres of gas) and Angel (about 30 billion cubic metres of gas and 50 million barrels of condensate).Further drilling will be required before gas reserves of the Scott Reef field can be estimated, but the results of the first well and the size of the structure indicate that they could be very large. It is clear that future exploration in Western Australia will be mainly concentrated offshore, in the Carnarvon, Browse, Bonaparte Gulf, and Perth Basins. However, there are still some prospective onshore areas in the Perth, Carnarvon, and Canning Basins.The chances of finding giant oilfields in Western Australia have declined markedly in recent years, as It seems that the generative sequences are mainly gas prone, and most of the obvious structures have now been drilled. However, the prospects are good for further large gas discoveries, and there is a reasonable chance that significant oil reserves will also be found.

Tertiary stratigraphy of Western Australia

Abstract This paper is a summary of the present knowledge of the Tertiary stratigraphy of Western Australia. Also included is new information on the Cainozoic of the Carnarvon Basin, a result of petroleum exploration in the area. Tertiary rocks formed during more than one cycle of deposition in three basins (Eucla, Perth, and Carnarvon), and also as thin units deposited in a single transgression along the south coast. The Tertiary stratigraphy of the Bonaparte Gulf Basin is not well known. Drilling in the Eucla Basin has encountered up to 400 m of Tertiary in the south central part, with uniform thinning towards the margins. The section begins with a middle‐upper Eocene carbonate unit which represents the dominant event in the Tertiary sedimentation in this basin. More carbonates were deposited in the late Oligocene‐early Miocene and middle Miocene. Along the south coast, the so‐called Bremer Basin, the Plantagenet Group (up to 100 m) of siltstone, sandstone, spongolite, and minor limestone, was deposited...

Diapiric features of the offshore Bonaparte Gulf Basin, Northwest Australian Shelf

Offshore reconnaissance seismic sparker surveys shot during the midsixties in the Bonaparte Gulf Basin on the Northwest Australian Shelf, outlined a number of diapiric features in the southern part of the Basin. Early aeromagnetic and marine gravity programmes were run on too wide a grid to give clear indications of the nature of the intrus­ ive s . Later, more sophisticated se ismic equ ipment was used to map the plugs and it became possible to date the age of the movement of the intrusives in several cases. A wildcat well, Sandpiper No. 1 was subsequently drilled on the crest of one of the features; it entered massive salt at a fairly shallow depth, as did another well, Pelican Island No. 1, a hundred miles to the south. Hypotheses involving salt migration toward the Basin margins are put forward to explain the Wickham Gravity High, uplift at the SW Basin Margin Fault and the Petrel Structure. The salt is dated as Devonian with salt flowage probably continuous from at least Upper Permian time.

THE REGIONAL GEOLOGY OF THE BONAPARTE GULF TIMOR SEA AREA

The present structural configuration of the Bonaparte Gulf-Timor Sea area is essentially the result of Mesozoic and Tertiary fragmentation of a once relatively simple Permo-Triassic Basin. A northwest-southeast Palaeozoic structural grain in the southeastern portion of the area resulted from early Palaeozoic faulting, possibly tied to aborted rift development. This faulting effectively controlled sedimentation throughout the Phanerozoic. Pronounced northeast-southwest Jurassic to Tertiary structural trends dominate the central and northern area, paralleling the present edge of the continental shelf and swinging south southwest into the northern extension of the Browse Basin. Post-Palaeozoic epeirogenies which had the greatest effect on the regional structural pattern occurred in the mid-Jurassic, Early Cretaceous, within the Eocene and in the Plio-Pleistocene.The Kimberley and Sturt Blocks flanking the basin to the south and east constituted the most important source areas for clastic sedimentation throughout the Phanerozoic. Periodic contributions during the Mesozoic were derived from a postulated source to the northwest in the vicinity of the present-day Timor Trough.The maximum thickness of Phanerozoic sediments present within the Bonaparte Gulf-Timor Sea area exceeds 50,000 ft (15,000 m). Early Palaeozoic to Carboniferous evaporites, carbonates and clastics are unconformably overlain by a thick sequence of Permian deltaic sediments in the southeastern Bonaparte Gulf Basin. This is succeeded by a Triassic to Middle Jurassic transgressive-regressive clastic sequence, grading northwestward to marginal marine and marine clastics and carbonates. The Permian to mid-Jurassic sediments are unconformably overlain by Upper Jurassic sands and shales, mainly fluvial in the southeast and north, becoming more marine westward. These clastics are everywhere succeeded by a monotonous sequence of Cretaceous shales and shaly limestones followed by a generally north to northwesterly thickening wedge of Tertiary carbonates and minor elastics.Hydrocarbon shows have been noted offshore in rocks of Carboniferous, Permian, Late Jurassic, Late Cretaceous and Eocene age. Porous clastics in conjunction with thick and laterally-extensive, organically-rich shales are present within the Palaeozoic and Mesozoic sequences. These sediments, in association with fault- and diapir-related anomalies and stratigraphic plays, combine to make certain provinces of the Bonaparte Gulf-Timor Sea area prospective in the search for viable oil and gas reserves.

Salt and Diapiric Anomalies in the Southeast Bonaparte Gulf Basin

The Southeast Bonaparte Gulf Basin comprises a Phanerozoic sedimentary sequence bordered by Precambrian rocks of the Kimberley, Sturt and Darwin Blocks. This portion of the basin developed as a subsiding graben, in which the flanks are separated from the central collapsed area by terraces that foundered to intermediate depths. Geophysical data acquired in the area since 1965 suggest the existence of large quantities of evaporites in the basin. Wells drilled in the area have confirmed the seismic evaluation. These evaporites were initially deposited across existing terraces and basinal areas prior to the later Devonian. Salt and diapiric structures of various types are widely distributed within the basin. The origin and growth of most of these structures is associated with epeirogenic movements along faults that demarcate the major structural elements of the basin.