Saurichthys and other fossil fishes from the late Smithian (Early Triassic) of Bear Lake County (Idaho, USA), with a discussion of saurichthyid palaeogeography and evolution
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A new marine fish assemblage from the late Smithian (Olenekian, Early Triassic) Anasibirites beds of the Thaynes Formation collected near Georgetown (Bear Lake County, south-east Idaho, USA) comprises actinopterygians (Saurichthys cf.elongatus, Actinopterygii indet.),sarcopterygians (Actinistia indet.), and possibly chondrichthyans.We review the global fossil record of the Triassic lower actinopterygian Saurichthys, which is used herein for a case study of trends in morphological adaptations as well as variations in palaeogeographic distribution and diversity dynamics of Early Mesozoic fishes.In the Early Triassic, Saurichthys already occupied a top position in marine food webs, with some species achieving body lengths of up to 1.5 m.Distribution of morphological characters in Saurichthys during the Triassic suggests trends towards a reduction in squamation, stiffening of the fins and axial skeleton, shortening of the postorbital portion of the cranium, and reduction in the number of dermal skull bones.The postcranial adaptations in particular helped to improve the fast-start ability of these ambush predatory fishes.The palaeogeographic range of Saurichthys changed from a virtually global distribution in the Early Triassic (indicating rapid dispersal within marine and freshwater ecosystems after the end-Permian mass extinction) to an occurrence mainly restricted to the north-western Tethys in the Late Triassic, and also towards increasing rarity within continental deposits.Modifications in the palaeogeographic distribution were accompanied by successive loss in global species richness and were possibly related to intra-Triassic extinction events, environmental alterations and/or competition.Keywords:
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Quantitative lithofacies palaeogeography is an important discipline of palaeogeography.It is developed on the foundation of traditional lithofacies palaeogeography and palaeogeography,the core of which is the quantitative lithofacies palaeogeographic map.Quantity means that in the palaeogeographic map,the division and identification of each palaeogeographic unit are supported by quantitative data and quantitative fundamental maps.Our lithofacies palaeogeographic maps are quantitative or mainly quantitative.A great number of quantitative lithofacies palaeogeographic maps have been published,and articles and monographs of quantitative lithofacies palaeogeography have been published successively,thus the quantitative lithofacies palaeogeography was formed and established.It is an important development in lithofacies palaeogeography.In composing quantitative lithofacies palaeogeographic maps,the key measure is the single factor analysis and multifactor comprehensive mapping method—methodology of quantitative lithofacies palaeogeography.In this paper,the authors utilize two case studies,one from the Early Ordovician of South China and the other from the Early Ordovician of Ordos,North China,to explain how to use this methodology to compose the quantitative lithofacies palaeogeographic maps,and to discuss the palaeogeographic units in these maps.Finally,three characteristics,i.e.,quantification,multiple orders and multiple types,of quantitative lithofacies palaeogeographic maps are conclusively discussed.
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Abstract Palaeogeography is a science that studies the features and evolution of physical geography in geological history and human history. The palaeogeography of China has multiple disciplines and multiple types of palaeogeographic map. These perfectly reflect “a hundred flowers blossom and a hundred schools of thought content”. The palaeogeography of China has three characteristics. The first is multiple disciplines flourishing simultaneously. The second is that lithofacies palaeogeography is in a leading position. The third is that palaeogeography of China is closely connected with industrial practice. It is why palaeogeography, especially lithofacies palaeogeography of China, can flourish continually. We have two journals of palaeogeography, i. e. Journal of Palaeogeography (Chinese Edition) and Journal of Palaeogeography (English Edition). The former primarily publishes articles of Chinese authors regarding Chinese palaeogeography and related disciplines and has a foothold in China. The latter will publish the articles of both Chinese and international authors and caters to foreign readers. These two journals will cooperate together and display their own expertise, which will effectively make a great contribution to the development and innovation of Chinese palaeogeography and international palaeogeography.
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The Permian Basin is the main target of exploration in western Poland. Porous Rotliegendes sandstone and two Zechstein carbonate formations are the most important reservoirs. Every depositional system includes different lithofacies, and interrelations create patterns of trap/reservoir and sealing horizons. Combination traps, with both structural and facial elements involved in their closure, create a comparatively high risk for exploration. Palaeogeographic analysis based on 3D seismic data presents opportunities for improved interpretation leading to a significant reduction of risk in exploration and development drilling. There is no direct information in 3D seismic data, but they allow us to reproduce the palaeogeography and successive stages of structural redevelopment by means of flattened seismic sections and construction of the corresponding maps, i.e. pseudo-palaeogeographical maps.
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Palaeogeography study physical geographical characteristics and evolution of geological and human history,and has close connections with the natural environment.In the first ten years of the 21st century,many sub-disciplines of palaeogeography,such as stratigraphy or geologic history palaeogeography,tectonics palaeogeography,paleontology palaeogeography,sedimentary or petrology palaeogeography,physical geography palaeogeography,and human historical palaeogeography,have been well developed.The trend in development of the palaeogeography is infiltration and matching among the subdisciplines,so that it can better serve the human being and the nature.
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