Palaeohighs: their influence on the North African Palaeozoic petroleum systems
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Abstract We present new insights for the characterization of the petroleum system evolution in North Africa based on a review of the stratigraphic architecture description of some selected North African Palaeozoic basins. During Palaeozoic time, the Gondwana platform was divided into sub-basins bounded by structural highs. Most of the highs were inherited from north–south and SW–NE Pan-African crustal faults which were reactivated during the Palaeozoic and later, in the Austrian and Alpine tectonic phases. We studied the stratigraphic architecture of the Palaeozoic succession around four main highs showing a clear tectonic activity during the Palaeozoic sedimentation. The Gargaff Arch, in Libya, is a major SW–NE broad anticline which slowly grew up during the Cambrian and Ordovician and stopped rising during the Silurian. The activity resumed during Late Silurian and early Devonian and during the Late Devonian. The Tihemboka High is a north–south anticline in between Libya and Algeria. The uplift started during the Cambro-Ordovician then stopped during most of the Silurian. The activity resumed during the Late Silurian and continued until the Lower Carboniferous. The Ahara High, separating the Illizi and Berkine basins in Algeria, has continuously grown during the Cambro-Ordovician, stopped rising during the Silurian, and grew again continuously during the Devonian. The Bled El-Mass High is a part of the Azzel-Matti Ridge separating the Ahnet and Reggane basins in Algeria. The high mostly rose during the Cambro-Ordovician then subsided relatively less quickly than the surrounding basins during the Silurian and Devonian. The uplift timing and chronology of each palaeohigh partly controlled the petroleum systems of the surrounding basins. Topographic lows favoured the occurrence of anoxic conditions and the preservation of Lower Silurian and Frasnian source rocks. Complex progressive unconformities developed around the palaeohighs form potential complex tectonostratigraphic traps. Finally, hydrocarbons could have been trapped around the highs during pre-Hercynian times, preserving reservoir porosity from early silicification. Mixed stratigraphic–structural plays could then be present today around the highs.Cite
This paper contains 50 maps which have been designed for use by the geologic community in preparing paleogeographic, biogeographic, climatologic, and tectonic reconstructions of the Paleozoic periods. Seven maps for each of seven Paleozoic intervals are included, plus a suture map showing the outlines of the Paleozoic continents in their present positions. The intervals chosen are the Late Cambrian (Franconian), Middle Ordovician (Llandeilian-earliest Caradocian), Middle Silurian (Wenlockian), Early Devonian (Emsian), Early Carboniferous (Visean), Late Carboniferous (Westphalian CD), and Late Permian (Kazanian). The paleomagnetic information used to orient the continents is given. For each interval, three types of maps are included, one locality map with place names labelled, four paleogeographic maps with our interpretation of the distribution of mountains, lowlands, shallow seas, and deep oceans, and two outline maps for those who prefer to make their own paleogeographic interpretations. Several projections are used-Mercator, Mollweide, and stereographic polar-to suit the various requirements of paleogeographic work.
Devonian
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Petroleum system
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Currently available Palaeozoic palaeomagnetic data from Gondwanan continents can be interpreted in terms of either (a) a migration of the pole from northern Africa to southern Africa between Ordovician and late Palaeozoic times, or (b) a rapid excursion of the pole from northern Africa to southwest of South Africa during late Ordovician to early Silurian times, followed by a return to central Africa in late Devonian times, thereafter continuing southward again. With respect to this uncertainty, pertinent stratigraphical evidence from western Gondwana includes the distribution of glacial deposits and cold-water and warm-water faunas. This record, although meagre and to some extent contradictory, appears to favour a drift history consistent with the second (b) of the APW alternatives that involves a rapid southerly excursion of the pole by early Silurian times.
Devonian
Excursion
Late Devonian extinction
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Direct evidence of the presence of oil in the region is characteristically widespread within a broad stratigraphic span as well as territorially. This Paleozoic oil is of the naphthene-aromatic type, in contrast with the Mesozoic and Tertiary oils of Uzbekistan, suggesting a justifiable hypothesis of an independent Paleozoic cycle of oleogenesis involving accumulation of hydrocarbons. – IGR Staff.
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Upper Paleozoic sedimentary rocks are widely distributed and probably more fully represented in the Peruvian Andes than in other parts of South America. A reconnaissance study of these rocks and their fossils reported here supplies new and important information on late Paleozoic history of the western part of South America.
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Buried hills of Paleozoic developes in Zhoukou depression .The formation of Paleozoic buried hills is mainly controlled by tectonic movements. The distribution of buried hills is controlled by the stressed field of stretching during Yanshan and Himalayan period ,and the stressed field of compressing during indosinian and Yanshan period mainly makes the inside structure of paleozoic buried hills more complex .The distribution of paleozoic buried hills is controlled by regional fault. Paleozoic buried hills of NW , NE trending developes well in Zhoukou depression.
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The Paleozoic and post-Paleozoic radiations of crinoids present an opportunity to explore genomic and ecological explanations for patterns of morphologic diversification. Analysis of discrete-character data that cover the principal features of the crinoid skeleton shows that both Paleozoic and post-Paleozoic increases in morphological disparity were abrupt; this is consistent with rapid exploitation of open ecological opportunities in both cases. For the post-Paleozoic, this result is sensitive to some aspects of data analysis and sampling, so it cannot be regarded as unequivocal. The deceleration in morphological diversification within each radiation is consistent with an observed decline in rates of taxonomic origination as well as with the attainment of functional or structural limits. Despite these similarities in the two radiations, Paleozoic crinoids exploited a wider range of morphological designs than did their post-Paleozoic successors. Post-Paleozoic crinoids exploited a wide range of ecological strategies despite being stereotyped in many aspects of form. This difference between the radiations is consistent with an increase in the rigidity of genetic and developmental systems. The range of post-Paleozoic designs is not in essence a subset of the Paleozoic spectrum. The two radiations resulted in morphological distributions that are largely nonoverlapping, perhaps reflecting a different range of ecological strategies.
Crinoid
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Adaptive Radiation
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Stratigraphic and geographic distribution, systematic description, S. flexuosa, Arinskian (lower Permian), Western Australia
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A summary of the terminology for the major elements of geologic time since the beginning of the Cambrian is given, with the present standing of those terms in modern usage. It is proposed to combine the Mesozoic and Cenozoic into a single era, the Neozoic, and to divide the Paleozoic into two eras, Eo-Paleozoic and Neo-Paleozoic. The name "Metazoic" is also suggested as a collective term for all time since the pre-Cambrian.
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