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Helen Lever - One of the best experts on this subject based on the ideXlab platform.
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Cyclic sedimentation in the shallow marine Upper Permian Kennedy Group, Carnarvon Basin, Western Australia
Sedimentary Geology, 2004Co-Authors: Helen LeverAbstract:Abstract The Upper Permian Kennedy Group of the Carnarvon Basin, Western Australia, was deposited while the Merlinleigh Sub-Basin was undergoing thermal subsidence, and the global climate was warming from the Carboniferous–Permian glaciation to the Mesozoic Greenhouse conditions. The Kennedy Group comprises siliciclastic sedimentary rocks, dominated by sandstones in the lower part, with coarsening-up cycles from mudstones to very coarse sandstones and granule conglomerates in the upper part. Cycles were observed and logged in the field, and although many types of cycles were found, three main motifs describe most of the cycles. Cycle motifs are defined based on the dominance of the various facies: Mooka motif cycles are dominated by fine-grained and bioturbated facies (interpreted as deposition during relative sea-level highstand) with only thin laminated or cross-bedded sandstones (interpreted as deposited during relative sea-level fall); Binthalya motif cycles are dominated by laminated and cross-bedded sandstones; and Coolkilya motif cycles consist of alternating laminated and bioturbated beds. A hierarchy of cycles was observed in the field, and this correlated well with spectral analysis of logged parameters. Spectral analysis of section log data and data sets corrected for the effects of compaction and sedimentation rates detected regular cyclicity. Geochronology of the Kennedy Group is not well enough constrained to allow the cycle periods in time to be calculated, but ratios of the different scale cycle thicknesses correlate well with ratios of the Milankovitch orbital cycles that have been calculated for the Permian. The presence of regular cyclicity and even bed thicknesses across large distances are not consistent with tectonic or autocyclic models of cycle formation. The cycles are more likely to have been caused by fluctuating eustatic sea levels, perhaps enhanced by changing amounts or seasonality of precipitation. Both sea levels and climatic fluctuations would ultimately be controlled by the Milankovitch orbital cycles.
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Climate Changes and Cyclic Sedimentation in the Mid-Late Permian: Kennedy Group, Carnarvon Basin, Western Australia
Gondwana Research, 2004Co-Authors: Helen LeverAbstract:Climate has an important direct and indirect influence of sedimentation, and especially on the development of cyclic sedimentation. Climate influences both accommodation and supply, the major controls on the architecture of sedimentary sequences. The Permian paleoclimate is the subject of increasing controversy, giving rise to numerous differing models developed and an expanding database of fossil evidence for climatic conditions. Western Australian Basins, in particular the Carnarvon Basin, are unique among nearby Gondwanan Basins in that they do not have extensive coal measures within their Permian successions. The Kennedy Group, the uppermost unit in the onshore Carnarvon Basin Permian succession, has a detrital composition indicative of arid weathering conditions. Within the Kennedy Group, even lagoonal and very nearshore sediments are devoid of plant debris or indications of the nearby presence of extensive flora. Presumed surfaces of subaerial exposure do not show paleosol development or root-traces. There has been little development of clay and chemical grain degradation is almost entirely related to diagenetic cementation and dissolution phases, rather than transport and source weathering. Nearby Basins, at similar latitudes, in India and East Australia contain coal measures, consistent with the humid climates that are predicted for this latitude. It is suggested therefore that the inferred aridity in the climate of the Carnarvon Basin and other Western Australian Basins is due to local climatic effects, probably related to an interruption in atmospheric circulation caused by tectonic rifting and uplift to the west. Cyclicity in the Kennedy Group indicates regular Late Permian, Milankovitch scale eustatic sea-level change, and may signify the presence of some ice at the poles. The development of cycles may have been enhanced by shifting climate belts controlled by Milankovitch cyclicity.
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Alunite alteration of tuffaceous layers and zircon dating, Upper Permian Kennedy Group, Carnarvon Basin, Western Australia
Australian Journal of Earth Sciences, 2004Co-Authors: Helen Lever, Christopher FanningAbstract:Alunite layers were found in two locations in the Binthalya Formation, Upper Kennedy Group, of Late Permian age, in the Merlinleigh Sub-Basin, onshore Carnarvon Basin. Alunite has not previously been reported from the Kennedy Group, or from a similar setting in Western Australia. The alunite occurs in discrete layers that have different chemical signatures to surrounding, unaltered sedimentary rocks. The lack of alteration in surrounding sedimentary rocks suggests that alteration was localised by initial differences in lithology, rather than by fortuitous localisation of alteration in a single layer. Alunite is thought to be the product of alteration of K-feldspars, clay minerals and pyrite under acidic, specifically sulfuric, conditions. It is found in hydrothermal systems and weathering profiles. Because the precursor minerals of alunite are believed to be feldspars, clays and sulfur-rich minerals, tuffaceous layers are the probable precursors of the alunite layers. Sulfur for the reaction was derived from within the tuffaceous deposits or from the oxidation of pyrite, which was probably present as cementation of trace fossils in other beds. The alteration is thought to have occurred during extensive oxidation, weathering and laterite formation during the Cenozoic, because the low density and powdery nature of the alunite indicates that it developed at a shallow depth. U-Pb dates obtained from zircons extracted from the alunite layers returned ages ranging from ca 2690 Ma to ca 270 Ma. The majority of zircons are inherited from the same source as the Kennedy Group sediments, indicating mixing of the initial tuffaceous layers with background sedimentation, either during the sedimentation process or afterwards by reworking or biological disturbance.
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Stratigraphy of the Upper Permian Kennedy Group of the onshore Carnarvon Basin (Merlinleigh Sub-Basin), Western Australia
Australian Journal of Earth Sciences, 2002Co-Authors: Helen LeverAbstract:Upper Permian strata contain many examples of cyclic deposition, despite the prevailing view that greenhouse conditions existed at the time. The shallow marine Upper Permian Kennedy Group, onshore Carnarvon Basin, has been studied in detail in the Kennedy Range 150 km east of the town of Carnarvon, Western Australia. The Kennedy Group exhibits cyclicity on a scale of 3-10 m, and also some larger scale changes in sedimentation. In this study, the Kennedy Group is divided into twelve informal units, designated with letters from A to L. The small-scale cyclicity consists of stacked regressive cycles that comprise only thin highstand systems tracts and regressive systems tracts. Transgressive systems tracts are only sometimes represented by highly bioturbated green sandstone layers at cycle boundaries. Cycle tops are planar and often have extensive vertical trace fossil development down from them, as well as surface traces on them. The twelve informal units can be interpreted as being caused by changes in relative sea-level.
Arthur J. Mory - One of the best experts on this subject based on the ideXlab platform.
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Lower Carboniferous (middle Visean) foraminifers and algae from an interior sea, Southern Carnarvon Basin, Australia
Geobios, 2014Co-Authors: Daniel Vachard, David W. Haig, Arthur J. MoryAbstract:Abstract A moderate diversity biota of foraminifers, algae and calcareous microproblematica is recorded from the Lower Carboniferous Yindagindy Formation within the intracratonic Southern Carnarvon Basin in Western Australia. Very shallow metahaline to hypersaline conditions are suggested. The palaeobotanical components are sporadic calcitarcha, tuberitinaceans, codiaceans Orthriosiphon? sp. 1, dasycladaleans? Koninckopora tenuiramosa, and algosponges Issinella devonica, Serrisinella cf. serrensis, Issinella? sp. 1, Kamaena cf. awirsi, Proninella? sp. and Stacheoides spp. The foraminiferal assemblage is dominated by a new koktjubinid taxon: Praekoktjubina yindagindyensis nov. gen., nov. sp. Subordinate associated foraminifers are more sporadic Salpingothurammina? sp. 1, Plectinopsis michelseni nov. gen., nov. sp., Rectopravina multifida nov. gen., nov. sp. (with 4 morphotypes), and scarce Endothyra spp. Despite many of these taxa being endemic, a middle Visean age is probable, based on: (1) the maximum global geographic extent of K. tenuiramosa reached during the middle Visean, (2) the disappearance of Plectinopsis nov. gen. in Palaeotethys and the Urals, and (3) the first occurrence of Praekoktjubina nov. gen. in Palaeotethys. An age no older than the middle Visean is supported by sparse conodonts from the Formation and comparison to episodes of carbonate deposition in the Bonaparte Basin, further north in the East Gondwana rift system. Absence of middle Visean archaediscoids may be due to high salinity. The following algal and foraminiferal families and superfamilies are emended: Scribroporellaceae (a lectotype is selected for Orthriosiphon saskatchewanense); Palaeospiroplectamminidae (due to the creation of Plectinopsis nov. gen.); Haplophragminoidea (due to the creation of Rectopravina nov. gen.); and Globivalvulinoidea and Koktjubinidae (due to the creation of Praekoktjubina nov. gen.).
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Modeling petroleum generation in the Paleozoic of the Carnarvon Basin, Western Australia: Implications for prospectivity
AAPG Bulletin, 2005Co-Authors: K. Ameed R. Ghori, Arthur J. Mory, Robert P. IaskyAbstract:Maturity and petroleum generation modeling of the Paleozoic succession in the Carnarvon Basin shows that most potential source rock intervals reached their maximum generation migration during the Carboniferous–Permian and could have charged traps developed during rifting in the middle Carboniferous to Early Permian except for the Peedamullah Shelf, where generation peaked during the Cretaceous. However, identification of such traps is challenging because it is difficult to differentiate between the deformation associated with middle Carboniferous–Early Permian rifting and that of the Early Cretaceous breakup rifting. Given the presence of suitable reservoir and sealing units in most of the Paleozoic, the prime risks for this section are the volume of available source rock, trap integrity because of the long period of preservation required, and relative timing of generation vs. trap formation, such that charging of younger traps requires secondary migration.The best Paleozoic oil-prone source beds identified in the Carnarvon Basin are thin beds in carbonate-dominated Silurian and Devonian units on the Gascoyne Platform, but Devonian source beds are restricted to the northern parts of the platform. The maturity of these units progressively increases from immature in the south-southeast to mature in the north-northwest, following increasing depth of burial in that direction. The best gas-prone source beds lie within the Lower Permian of the Merlinleigh SubBasin, and their maturity ranges from immature along the margins of the subBasin to overmature toward the center. Within the Upper Permian, the best source beds for oil and gas are in the Peedamullah Shelf, where they range from immature in the southeast to mature in the northwest.Commercial Paleozoic petroleum has yet to be discovered in the Paleozoic of the Carnarvon Basin, but the assessment of this part of the Basin is limited because few, if any, of the exploration wells drilled to date were valid tests of these objectives.
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Anhydrite cements after dolomitization of shallow marine Silurian carbonates of the Gascoyne Platform, Southern Carnarvon Basin, Western Australia
Sedimentary Geology, 2003Co-Authors: Mohamed El-tabakh, Arthur J. Mory, B. Charlotte Schreiber, Raza YasinAbstract:Abstract Carbonates and evaporites in the Dirk Hartog Group were deposited in subtidal, peritidal and shallow-marine evaporitic mudflat environments across the Gascoyne Platform within the Southern Carnarvon Basin, Western Australia. The carbonates are composed of ooids, peloids and minor bioclastic fragments, with early cements. They have been extensively dolomitized and replaced, in part, by late anhydrite sparry cements. Four types of dolomite which range from early to burial types are identified, incorporating re-equilibration or re-crystallization from Basin brines. Accordingly, they exhibit distinctive petrographic features and isotopic signatures of carbon and oxygen. Evaporites deposited are present as discrete beds and displacive nodules in carbonate and siliciclastic beds, and show δ34SCDT values and 87Sr/86Sr ratios indicative of variable marine and non-marine conditions. Late dissolution of evaporites has produced satin spar gypsum veins in the shallowest section of the platform, whereas blocky and sparry anhydrite cements and void fillings formed deeper within the platform. Dissolution of the evaporites and formation of anhydrite cements post-date dolomitization.
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carboniferous permian facies and tectono stratigraphic successions of the glacially influenced and rifted Carnarvon Basin western australia
Sedimentary Geology, 2003Co-Authors: Carolyn H. Eyles, Arthur J. Mory, Nicholas EylesAbstract:Abstract The Carnarvon Basin of Western Australia is a rift Basin that contains a thick (up to 5 km) succession of late Carboniferous–early Permian glacially influenced marine sedimentary strata. These rocks accumulated in near-polar paleolatitudes along the uplifted and glaciated margin of the west Australian Shield (Pilbara Craton). Three stratigraphic successions (I, II, III) can be recognised, each characterised by distinct facies associations that record different stages in the tectonic evolution of the Basin and associated changes in the rate of Basin subsidence and sediment accommodation. A lowermost succession (I) comprises rapidly deposited (30 m/Ma) glacially influenced marine strata (Lyons Group) containing palynomorphs of Westphalian–Tastubian (early Sakmarian) and possibly older age. Strata are dominated by subaqueously deposited sediment gravity flow facies. Succession II is composed of richly fossiliferous cool water shales (Callythara and Cordalia formations) that record much reduced sedimentation rates (2 m/Ma). In turn, shales are overlain by an uppermost succession (III) of shallow marine, wave- and storm-influenced sandstone (Moogooloo Sandstone). Comparison with other rift Basin fills indicates that Succession I likely records initial Basin infilling where abundant coarse debris was produced by faulting and glaciation of the adjacent Pilbara Craton. Shales of Succession II mark a phase of ‘sediment underfilling’ characterized by rapid tectonic subsidence, an increase in relative sea level and reduced sediment supply. Shallow water sandstone facies of Succession III record a late stage in the tectonic cycle when subsidence rates had decreased and sediment supply outpaced accommodation. Such successions, where found in other late Paleozoic Basins, are widely interpreted in terms of glacioeustatically driven changes in sea level resulting from deglaciation events across Gondwana. Instead, the three successions within the Carnarvon Basin are argued to reflect a dominantly tectonic control on sedimentation and preservation.
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Carboniferous–Permian facies and tectono-stratigraphic successions of the glacially influenced and rifted Carnarvon Basin, western Australia
Sedimentary Geology, 2002Co-Authors: Carolyn H. Eyles, Arthur J. Mory, Nicholas EylesAbstract:Abstract The Carnarvon Basin of Western Australia is a rift Basin that contains a thick (up to 5 km) succession of late Carboniferous–early Permian glacially influenced marine sedimentary strata. These rocks accumulated in near-polar paleolatitudes along the uplifted and glaciated margin of the west Australian Shield (Pilbara Craton). Three stratigraphic successions (I, II, III) can be recognised, each characterised by distinct facies associations that record different stages in the tectonic evolution of the Basin and associated changes in the rate of Basin subsidence and sediment accommodation. A lowermost succession (I) comprises rapidly deposited (30 m/Ma) glacially influenced marine strata (Lyons Group) containing palynomorphs of Westphalian–Tastubian (early Sakmarian) and possibly older age. Strata are dominated by subaqueously deposited sediment gravity flow facies. Succession II is composed of richly fossiliferous cool water shales (Callythara and Cordalia formations) that record much reduced sedimentation rates (2 m/Ma). In turn, shales are overlain by an uppermost succession (III) of shallow marine, wave- and storm-influenced sandstone (Moogooloo Sandstone). Comparison with other rift Basin fills indicates that Succession I likely records initial Basin infilling where abundant coarse debris was produced by faulting and glaciation of the adjacent Pilbara Craton. Shales of Succession II mark a phase of ‘sediment underfilling’ characterized by rapid tectonic subsidence, an increase in relative sea level and reduced sediment supply. Shallow water sandstone facies of Succession III record a late stage in the tectonic cycle when subsidence rates had decreased and sediment supply outpaced accommodation. Such successions, where found in other late Paleozoic Basins, are widely interpreted in terms of glacioeustatically driven changes in sea level resulting from deglaciation events across Gondwana. Instead, the three successions within the Carnarvon Basin are argued to reflect a dominantly tectonic control on sedimentation and preservation.
Robert P. Iasky - One of the best experts on this subject based on the ideXlab platform.
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Modeling petroleum generation in the Paleozoic of the Carnarvon Basin, Western Australia: Implications for prospectivity
AAPG Bulletin, 2005Co-Authors: K. Ameed R. Ghori, Arthur J. Mory, Robert P. IaskyAbstract:Maturity and petroleum generation modeling of the Paleozoic succession in the Carnarvon Basin shows that most potential source rock intervals reached their maximum generation migration during the Carboniferous–Permian and could have charged traps developed during rifting in the middle Carboniferous to Early Permian except for the Peedamullah Shelf, where generation peaked during the Cretaceous. However, identification of such traps is challenging because it is difficult to differentiate between the deformation associated with middle Carboniferous–Early Permian rifting and that of the Early Cretaceous breakup rifting. Given the presence of suitable reservoir and sealing units in most of the Paleozoic, the prime risks for this section are the volume of available source rock, trap integrity because of the long period of preservation required, and relative timing of generation vs. trap formation, such that charging of younger traps requires secondary migration.The best Paleozoic oil-prone source beds identified in the Carnarvon Basin are thin beds in carbonate-dominated Silurian and Devonian units on the Gascoyne Platform, but Devonian source beds are restricted to the northern parts of the platform. The maturity of these units progressively increases from immature in the south-southeast to mature in the north-northwest, following increasing depth of burial in that direction. The best gas-prone source beds lie within the Lower Permian of the Merlinleigh SubBasin, and their maturity ranges from immature along the margins of the subBasin to overmature toward the center. Within the Upper Permian, the best source beds for oil and gas are in the Peedamullah Shelf, where they range from immature in the southeast to mature in the northwest.Commercial Paleozoic petroleum has yet to be discovered in the Paleozoic of the Carnarvon Basin, but the assessment of this part of the Basin is limited because few, if any, of the exploration wells drilled to date were valid tests of these objectives.
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Gnargoo: a possible 75 km-diameter post-Early Permian – pre-Cretaceous buried impact structure, Carnarvon Basin, Western Australia
Australian Journal of Earth Sciences, 2005Co-Authors: Robert P. Iasky, Andrew Y. GliksonAbstract:The Gnargoo structure is located on the Gascoyne Platform, Southern Carnarvon Basin, Western Australia, and is buried beneath about 500 m of Cretaceous and younger strata. The structure is interpreted as being of possible impact origin from major geophysical and morphometric signatures, characteristic of impact deformation, and its remarkable similarities with the proven Woodleigh impact structure, about 275 km to the south on the Gascoyne Platform. These similarities include: a circular Bouguer anomaly (slightly less well-defined at Gnargoo than at Woodleigh); a central structurally uplifted area comprising a buried dome with a central uplifted plug; and the lack of a significant magnetic anomaly. Gnargoo shows a weakly defined inner 10 km-diameter circular Bouguer anomaly surrounded by a broadly circular zone, ∼75 km in diameter. The north – south Bouguer anomaly lineament of the Giralia Range (a regional topographic and structural feature) terminates abruptly against the outer circular zone which is, i...
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gnargoo a possible 75 km diameter post early permian pre cretaceous buried impact structure Carnarvon Basin western australia
Australian Journal of Earth Sciences, 2005Co-Authors: Robert P. Iasky, Andrew Y. GliksonAbstract:The Gnargoo structure is located on the Gascoyne Platform, Southern Carnarvon Basin, Western Australia, and is buried beneath about 500 m of Cretaceous and younger strata. The structure is interpreted as being of possible impact origin from major geophysical and morphometric signatures, characteristic of impact deformation, and its remarkable similarities with the proven Woodleigh impact structure, about 275 km to the south on the Gascoyne Platform. These similarities include: a circular Bouguer anomaly (slightly less well-defined at Gnargoo than at Woodleigh); a central structurally uplifted area comprising a buried dome with a central uplifted plug; and the lack of a significant magnetic anomaly. Gnargoo shows a weakly defined inner 10 km-diameter circular Bouguer anomaly surrounded by a broadly circular zone, ∼75 km in diameter. The north – south Bouguer anomaly lineament of the Giralia Range (a regional topographic and structural feature) terminates abruptly against the outer circular zone which is, i...
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Woodleigh, Carnarvon Basin, Western Australia: a new 120 km diameter impact structure
Earth and Planetary Science Letters, 2000Co-Authors: Arthur J. Mory, Robert P. Iasky, Andrew Y. Glikson, Franco PirajnoAbstract:Abstract The Woodleigh multi-ring structure, buried by Cretaceous and, at its centre, Lower Jurassic lacustrine sediments, east of Hamelin Pool, Carnarvon Basin, Western Australia, is identified as an impact structure, the largest discovered to date on the Australian continent. An impact origin is indicated by: a central core of uplifted granitoid basement probably less than 25 km in diameter, which displays shock-induced planar deformation features in quartz, pervasive diaplectic vitrification of feldspar and penetrative pseudotachylite veining; and an inner ring syncline containing a ∼70 m thick thermally modified diamictite overlain by ∼380 m of Lower Jurassic lacustrine deposits. An outermost diameter of 120 km, defined by gravity, magnetic and surface drainage, indicates a ring fault that sharply intersects the NS-striking regional structure. At the centre of the basement uplift shock metamorphosed granitoid was intersected at a depth of 171 m, at least 1800 m higher than the gravity-modelled level of regional basement. Pseudotachylite vein systems within the shocked granitoid are strongly enriched in Al, Ca, Mg, Ni, Co, Cr, V and S, and depleted in K and Si, suggesting chemical fractionation attendant on shock volatilisation, enrichment by an injected and volatilised meteoritic component, and potentially of sulfide mineralisation. The impact age is constrained by overlying Lower Jurassic strata, reworked Early Permian palynomorphs in the Jurassic lacustrine section, and deformed Lower Devonian and older units. A regional thermal event identified by apatite fission track at 280–250 Ma hints at a possible Permian–Triassic boundary age for the impact, although the lack of Triassic fossils in the crater fill favours a late Triassic age.
Nicholas Eyles - One of the best experts on this subject based on the ideXlab platform.
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carboniferous permian facies and tectono stratigraphic successions of the glacially influenced and rifted Carnarvon Basin western australia
Sedimentary Geology, 2003Co-Authors: Carolyn H. Eyles, Arthur J. Mory, Nicholas EylesAbstract:Abstract The Carnarvon Basin of Western Australia is a rift Basin that contains a thick (up to 5 km) succession of late Carboniferous–early Permian glacially influenced marine sedimentary strata. These rocks accumulated in near-polar paleolatitudes along the uplifted and glaciated margin of the west Australian Shield (Pilbara Craton). Three stratigraphic successions (I, II, III) can be recognised, each characterised by distinct facies associations that record different stages in the tectonic evolution of the Basin and associated changes in the rate of Basin subsidence and sediment accommodation. A lowermost succession (I) comprises rapidly deposited (30 m/Ma) glacially influenced marine strata (Lyons Group) containing palynomorphs of Westphalian–Tastubian (early Sakmarian) and possibly older age. Strata are dominated by subaqueously deposited sediment gravity flow facies. Succession II is composed of richly fossiliferous cool water shales (Callythara and Cordalia formations) that record much reduced sedimentation rates (2 m/Ma). In turn, shales are overlain by an uppermost succession (III) of shallow marine, wave- and storm-influenced sandstone (Moogooloo Sandstone). Comparison with other rift Basin fills indicates that Succession I likely records initial Basin infilling where abundant coarse debris was produced by faulting and glaciation of the adjacent Pilbara Craton. Shales of Succession II mark a phase of ‘sediment underfilling’ characterized by rapid tectonic subsidence, an increase in relative sea level and reduced sediment supply. Shallow water sandstone facies of Succession III record a late stage in the tectonic cycle when subsidence rates had decreased and sediment supply outpaced accommodation. Such successions, where found in other late Paleozoic Basins, are widely interpreted in terms of glacioeustatically driven changes in sea level resulting from deglaciation events across Gondwana. Instead, the three successions within the Carnarvon Basin are argued to reflect a dominantly tectonic control on sedimentation and preservation.
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Carboniferous–Permian facies and tectono-stratigraphic successions of the glacially influenced and rifted Carnarvon Basin, western Australia
Sedimentary Geology, 2002Co-Authors: Carolyn H. Eyles, Arthur J. Mory, Nicholas EylesAbstract:Abstract The Carnarvon Basin of Western Australia is a rift Basin that contains a thick (up to 5 km) succession of late Carboniferous–early Permian glacially influenced marine sedimentary strata. These rocks accumulated in near-polar paleolatitudes along the uplifted and glaciated margin of the west Australian Shield (Pilbara Craton). Three stratigraphic successions (I, II, III) can be recognised, each characterised by distinct facies associations that record different stages in the tectonic evolution of the Basin and associated changes in the rate of Basin subsidence and sediment accommodation. A lowermost succession (I) comprises rapidly deposited (30 m/Ma) glacially influenced marine strata (Lyons Group) containing palynomorphs of Westphalian–Tastubian (early Sakmarian) and possibly older age. Strata are dominated by subaqueously deposited sediment gravity flow facies. Succession II is composed of richly fossiliferous cool water shales (Callythara and Cordalia formations) that record much reduced sedimentation rates (2 m/Ma). In turn, shales are overlain by an uppermost succession (III) of shallow marine, wave- and storm-influenced sandstone (Moogooloo Sandstone). Comparison with other rift Basin fills indicates that Succession I likely records initial Basin infilling where abundant coarse debris was produced by faulting and glaciation of the adjacent Pilbara Craton. Shales of Succession II mark a phase of ‘sediment underfilling’ characterized by rapid tectonic subsidence, an increase in relative sea level and reduced sediment supply. Shallow water sandstone facies of Succession III record a late stage in the tectonic cycle when subsidence rates had decreased and sediment supply outpaced accommodation. Such successions, where found in other late Paleozoic Basins, are widely interpreted in terms of glacioeustatically driven changes in sea level resulting from deglaciation events across Gondwana. Instead, the three successions within the Carnarvon Basin are argued to reflect a dominantly tectonic control on sedimentation and preservation.
Mike Middleton - One of the best experts on this subject based on the ideXlab platform.
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Heat flow and thermal maturity modelling in the Northern Carnarvon Basin, North West Shelf, Australia
Marine and Petroleum Geology, 2002Co-Authors: Mike MiddletonAbstract:Abstract The Northern Carnarvon Basin is located at the southern end of the North West Shelf of Australia. It was developed by rifting during the Jurassic–earliest Cretaceous. Heat flow and thermal maturity in seven wells, from three sub-Basins, Rankin Platform and Exmouth Plateau of the Northern Carnarvon Basin, were modelled using BasinMod 1D program. Multiple thermal maturity parameters were used to constrain the influence of anomalously low vitrinite reflectance. Those T max data with reliable quality can be applied to correlate with vitrinite reflectance, establish thermal maturity and calibrate the modelled results. The modelled results indicated that the measured maturity data in some wells were consistent with the rift heat flow model (Jarvis & McKenzie) associated with the Jurassic rift and the earliest Cretaceous seafloor spreading events. The maximum values of heat flow were in the range from 67 mW/m 2 (Jurabi-1) to 105 mW/m 2 (Bowers-1) in the Exmouth and Barrow Sub-Basins. On the Exmouth Plateau, the maximum values of heat flow were modelled to be 72 mW/m 2 in the Jupiter-1 well and 78 mW/m 2 in the Investigator-1 well. These maximum values were modelled to occur during syn-rift phase, which were 29–88% and 33–37% greater than their current heat flow values in the sub-Basins and on the Exmouth Plateau, respectively. This study suggests that maturity indicators are less diagnostic of rifting thermal histories if the maximum thermal effect is associated with Cretaceous and Cainozoic burial in this Basin.
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A thermal maturation study of the Carnarvon Basin, Australia and the northern North Sea, Europe
Exploration Geophysics, 1998Co-Authors: Jörgen Samuelsson, Mike MiddletonAbstract:The suppression of vitrinite reflectance can cause problems for the oil industry if not properly considered. The scope of this paper is to emphasise the errors that suppression could lead to in the estimation of heat flow and transformation ratio of hydrocarbons. Two cross-sections from the Carnarvon Basin, North West Shelf, Australia, are modelled and compared to a model from the North Sea of Europe, in order to study the effect of suppressed vitrinite reflectance in a sedimentary Basin. The North Sea modelling implies that neglecting the suppression effect of the vitrinite reflectance could lead to the heat flow being erroneously estimated by as much as almost 40% (40 mW/m2 instead of 55 mW/m2). Further, modelling of the Australian profiles suggest that the local effect might be even higher. This will lead to an underestimation of source u rock maturity. As a result of this underestimation of the source rock maturity. maior errors will occur in the predictions of the transformaratio of hydrocarbons and thereby the quantity of generated hydrocarbons.