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Nigel R. Ainsworth - One of the best experts on this subject based on the ideXlab platform.
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Stratigraphy of the Triassic, Lower Jurassic and Middle Jurassic (Aalenian) from the Fastnet Basin, Offshore South-west Ireland
Marine and Petroleum Geology, 1991Co-Authors: Noel J. Murphy, Nigel R. AinsworthAbstract:Abstract The stratigraphy of the Triassic, Lower Jurassic and Middle Jurassic (Aalenian) of the Fastnet Basin is described. The sequence has been divided using wireline log criteria. Six rock units are recognized in the Triassic and 12 in the Lower Jurassic and Middle Jurassic (Aalenian). None of these major rock units shows any significant diachroneity. Apparent breaks in the sequence due to unconformities or condensed sections have been identified within or bounding three of the rock units: the Liassic Limestone, Liassic Marl and Liassic Sandstone. Dating is provided by both microfaunas and microfloras extracted from ditch cuttings and sidewall cores. The ages of the Triassic rock units are mainly determined by correlation with dateable sequences in the North Celtic Sea Basin, whereas the Jurassic rock units yielded abundant short-ranging microfossils.
Ján Schlögl - One of the best experts on this subject based on the ideXlab platform.
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Jurassic submarine troglobites: is there any link to the recent submarine cave fauna?
Hydrobiologia, 2011Co-Authors: Roman Aubrecht, Ján SchlöglAbstract:Recent submarine caves are inhabited by endemic faunas adapted to oligotrophism, darkness and a tranquil environment. Many of their representatives are archaic types of animals resembling fossils from very early times in evolution. This article compares fossil fauna from Jurassic neptunian dykes (originally sea bed clefts) from the Western Carpathians with the Recent cave-dwelling fauna. The ostracods Pokornyopsis feifeli are particularly important. In the Western Carpathians, these were exclusively found in the Middle/Late Jurassic fissure fillings, but in the non-Tethyan Germanic Jurassic this species was found in deep-marine claystones. They are phylogenetic forerunners of the recent genus Danielopolina inhabiting both anchialine caves and deep seas. This indicates a Jurassic migration of deep-marine fauna to cryptic habitats. Other examples of cryptic communities include the Upper Jurassic cavity-dwelling fauna dominated by serpulids and scleractinian corals. Associated suspension feeders include thecideidine brachiopods, oysters, bryozoans, sponges, crinoids and sessile foraminifers. Serpulid-dominated bioconstructions have recent analogies in the Mediterranean and Carribean seas. Different type of dyke communities represent the Late Jurassic fauna of small sized ammonites which originated from both Tethyan and Boreal paleobioprovinces. It has not been established whether these amonites were juvenile, dwarfed specimens adapted to limited cave space or size-sorted adult specimens.
Henrik I. Petersen - One of the best experts on this subject based on the ideXlab platform.
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HYDROCARBON POTENTIAL OF MIDDLE Jurassic COALY AND LACUSTRINE AND UPPER Jurassic – LOWERMOST CRETACEOUS MARINE SOURCE ROCKS IN THE SØGNE BASIN, NORTH SEA
Journal of Petroleum Geology, 2011Co-Authors: Henrik I. Petersen, A.c. Holme, Erik Thomsen, M.f. Whitaker, T. Brekke, Jørgen A. Bojesen-koefoed, K.h. Hansen, B.t. LarsenAbstract:The Sogne Basin in the Danish-Norwegian Central Graben is unique in the North Sea because it has been proven to contain commercial volumes of hydrocarbons derived only from Middle Jurassic coaly source rocks. Exploration here relies on the identification of good quality, mature Middle Jurassic coaly and lacustrine source rocks and Upper Jurassic – lowermost Cretaceous marine source rocks. The present study examines source rock data from almost 900 Middle Jurassic and Upper Jurassic – lowermost Cretaceous samples from 21 wells together with 286 vitrinite reflectance data from 14 wells. The kerogen composition and kinetics for bulk petroleum formation of three Middle Jurassic lacustrine samples were also determined. Differences in kerogen composition between the coaly and marine source rocks result in two principal oil windows: (i) the effective oil window for Middle Jurassic coaly strata, located at ∼3800 m and spanning at least ∼650 m; and (ii) the oil window for Upper Jurassic – lowermost Cretaceous marine mudstones, located at ∼3250 m and spanning ∼650 m. A possible third oil window may relate to Middle Jurassic lacustrine deposits. Middle Jurassic coaly strata are thermally mature in the southern part of the Sogne Basin and probably also in the north, whereas they are largely immature in the central part of the basin. HImax values of the Middle Jurassic coals range from ∼150–280 mg HC/g TOC indicating that they are gas-prone to gas/oil-prone. The overall source rock quality of the Middle Jurassic coaly rocks is fair to good, although a relatively large number of the samples are of poor source rock quality. At the present day, Middle Jurassic oil-prone or gas/oil-prone rocks occur in the southern part of the basin and possibly in a narrow zone in the northern part. In the remainder of the basin, these deposits are considered to be gas-prone or are absent. Wells in the northernmost part of the Sogne Basin / southernmost Steinbit Terrace encountered Middle Jurassic organic–rich lacustrine mudstones with sapropelic kerogen, high HI values reaching 770 mg HC/g TOC and Ea-distributions characterised by a single dominant Ea-peak. The presence of lacustrine mudstones is also suggested by a limited number of samples with HI values above 300 mg HC/g TOC in the southern part of the basin; in addition, palynofacies demonstrate a progressive increase in the abundance and areal extent of lacustrine and brackish open water conditions during Callovian times. A regional presence of oil-prone Middle Jurassic lacustrine source rocks in the Sogne Basin, however, remains speculative. Middle Jurassic kitchen areas may be present in an elongated palaeo-depression in the northern part of the Sogne Basin and in restricted areas in the south. Upper Jurassic – lowermost Cretaceous mudstones are thermally mature in the central, western and northern parts of the basin; they are immature in the eastern part towards the Coffee Soil Fault, and overmature in the southernmost part. Only a minor proportion of the mudstones have HI values >300 mg HC/g TOC, and the present-day source rock quality is for the best samples fair to good. In the south and probably also in most of the northern part of the Sogne Basin, the mudstones are most likely gas-prone, whereas they may be gas/oil-prone in the central part of the basin. A narrow elongated zone in the northern part of the basin may be oil-prone. The marine mudstones are, however, volumetrically more significant than the Middle Jurassic strata. Possible Upper Jurassic – lowermost Cretaceous kitchen areas are today restricted to the central Sogne Basin and the elongated palaeo-depression in the north.
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Coal facies studies in Denmark and Greenland
International Journal of Coal Geology, 2004Co-Authors: Henrik I. PetersenAbstract:Abstract Coal of Jurassic age occurs onshore Denmark and in the Danish North Sea, whereas coal of Carboniferous and Miocene age only occurs in the Danish North Sea and onshore Denmark, respectively. The Lower–Middle Jurassic coals are the most widespread and best documented. Onshore Denmark the coals are of low rank while the Jurassic coals in the North Sea are thermally mature and hydrocarbon generating in the Sogne Basin. The Jurassic coals have a maximum thickness of ∼2 m and were formed in coastal plain mires and in inland fresh water mires. The Miocene brown coals, up to ∼2 m thick, were formed in an overall deltaic setting. Lower Carboniferous and Palaeogene coals occur in northern Greenland, Middle Jurassic coals in northeast Greenland, and Cretaceous coals in western Greenland. The Middle Jurassic low rank coals have been investigated in detail. The up to ∼3.5-m-thick coal seams accumulated in coastal mires and they may have an extraordinary resinite-enriched composition. Only a single Cretaceous coal seam has been investigated with regard to the depositional environment; the seam records drowning of a peat mire. The Lower Carboniferous and Palaeogene coals have not been investigated.
Noel J. Murphy - One of the best experts on this subject based on the ideXlab platform.
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Stratigraphy of the Triassic, Lower Jurassic and Middle Jurassic (Aalenian) from the Fastnet Basin, Offshore South-west Ireland
Marine and Petroleum Geology, 1991Co-Authors: Noel J. Murphy, Nigel R. AinsworthAbstract:Abstract The stratigraphy of the Triassic, Lower Jurassic and Middle Jurassic (Aalenian) of the Fastnet Basin is described. The sequence has been divided using wireline log criteria. Six rock units are recognized in the Triassic and 12 in the Lower Jurassic and Middle Jurassic (Aalenian). None of these major rock units shows any significant diachroneity. Apparent breaks in the sequence due to unconformities or condensed sections have been identified within or bounding three of the rock units: the Liassic Limestone, Liassic Marl and Liassic Sandstone. Dating is provided by both microfaunas and microfloras extracted from ditch cuttings and sidewall cores. The ages of the Triassic rock units are mainly determined by correlation with dateable sequences in the North Celtic Sea Basin, whereas the Jurassic rock units yielded abundant short-ranging microfossils.
Roman Aubrecht - One of the best experts on this subject based on the ideXlab platform.
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Jurassic submarine troglobites: is there any link to the recent submarine cave fauna?
Hydrobiologia, 2011Co-Authors: Roman Aubrecht, Ján SchlöglAbstract:Recent submarine caves are inhabited by endemic faunas adapted to oligotrophism, darkness and a tranquil environment. Many of their representatives are archaic types of animals resembling fossils from very early times in evolution. This article compares fossil fauna from Jurassic neptunian dykes (originally sea bed clefts) from the Western Carpathians with the Recent cave-dwelling fauna. The ostracods Pokornyopsis feifeli are particularly important. In the Western Carpathians, these were exclusively found in the Middle/Late Jurassic fissure fillings, but in the non-Tethyan Germanic Jurassic this species was found in deep-marine claystones. They are phylogenetic forerunners of the recent genus Danielopolina inhabiting both anchialine caves and deep seas. This indicates a Jurassic migration of deep-marine fauna to cryptic habitats. Other examples of cryptic communities include the Upper Jurassic cavity-dwelling fauna dominated by serpulids and scleractinian corals. Associated suspension feeders include thecideidine brachiopods, oysters, bryozoans, sponges, crinoids and sessile foraminifers. Serpulid-dominated bioconstructions have recent analogies in the Mediterranean and Carribean seas. Different type of dyke communities represent the Late Jurassic fauna of small sized ammonites which originated from both Tethyan and Boreal paleobioprovinces. It has not been established whether these amonites were juvenile, dwarfed specimens adapted to limited cave space or size-sorted adult specimens.
