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Open accessJournal ArticleDOI: 10.7203/SJP.20.2.20557

Pragian conodont zonal classification in Nevada, Western North America

02 Mar 2021-Vol. 20, Iss: 2, pp 177-206
Abstract: A tripartite global zonal scale for the Pragian Stage (Devonian) was recommended by the Subcomission on Devonian Stratigraphy in 1989. Since that time, additions to the data on the two primary lineages used for the subdivision of the Pragian, Eognathodus and early Polygnathus, have shown: 1) that the Lochkovian-Pragian boundary criterion is useable as defi ned and is applicable on a global scale, but that the boundary-stratotype section in the Barrandian region of the Czech Republic has serious limitations as a reference section; 2) the criteria for the internal subdivision of the Pragian are not globally applicable; and 3) that the taxon that we have used in Nevada to mark the base of the Emsian is Polygnathus lenzi, whose range may be different from that of Australian P. dehiscens, the supposed criterion for the base of the Emsian. This paper reviews the Pragian of Nevada and compares it with Alaska, Canada, eastern Australia, and central Europe and suggests a regional scale for use in the western North American Cordillera. The subdivisions proposed here (irregularis-profunda Zone; profunda–brevicauda Zone; brevicauda-mariannae Zone; mariannae-lenzi Zone) are not the same of the SDS and cannot be applied on a global scale. The first two are based on evolutionary appearances; the last two on the lowest occurrences of distinctive and widespread taxa in North America. One new genus, Masaraella and four new species, Masaraella epsilon, Masaraella riosi, Gondwania profunda, and Pedavis longicauda, are described.

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Topics: Devonian (52%)

19 results found

Book ChapterDOI: 10.1016/B978-0-444-59425-9.00022-6
01 Jan 2012-
Topics: Devonian (71%)

98 Citations

Open accessJournal ArticleDOI: 10.1144/SP423.15
Abstract: The face of Planet Earth has changed significantly through geological time. Dynamic processes active today, such as plate tectonics and climate change, have shaped the Earth’s surface and impacted biodiversity patterns from the beginning. Organisms, on the other hand, have the capacity to significantly alter Earth’s hydrological and geochemical cycles, its atmosphere and climate, sediments, and even hard rocks deep down under the surface. Abiotic– biotic interactions characterize Earth’s system history and, together with biotic competition and food webs, were the main trigger of evolutionary change, innovations and biodiversity fluctuations. Within the Palaeozoic, the Devonian was an especially interesting time interval as it was characterized by the ‘mid-Paleozoic predator revolution’ (Signor & Brett 1984; Brett 2003) and the related ‘nekton revolution’ (Klug et al. 2010), characterized by the blooms of free-swimming cephalopods, including the oldest ammonoids, and fish groups (e.g. toothed sharks and giant placoderms), the rise of more advanced vertebrates, including the oldest tetrapods (e.g. Blieck et al. 2007, 2010; Niedzwiedzki et al. 2010), the most extensive reef complexes of the Phanerozoic (e.g. Kiessling 2008), and the ‘greening of land’ by the diversification and spread of land plants, including the oldest forests (e.g. Stein et al. 2012; Giesen & Berry 2013), which resulted in new soil types and changing weathering. These major evolutionary trends did not unfold in a long interval of environmental stability, but in times of numerous and repeated, geologically brief, global events that punctuated prolonged periods, up to several million years in duration, of relative stability, termed ecological-evolutionary subunits (EE subunits: Boucot 1990; Brett & Baird 1995; Brett et al. 2009). The bounding events, even those of lesser intensity, produced major re-structuring in local to global ecosystems and are seen as critical drivers of long-term evolutionary patterns (Brett 2012). These linked abiotic and biotic events and extinctions of different magnitude have been summarized by House (1983, 1985, 2002), Walliser (1984, 1996) and, more recently, by Becker et al. (2012). The Devonian event succession is summarized in Figure 1. Two first-order mass extinctions at the Frasnian–Famennian boundary (Kellwasser Crisis) and at the end of the Devonian (Hangenberg Crisis), characterized by the loss of major fossil groups (classes and orders) and complete ecosystems (e.g. metazoan reefs, early forests), have to be viewed in the context of a complex global event sequence. There are important similarities between discrete pulses/phases of the major biotic crises and individual smaller-scale events. In our understanding, second-order global events are characterized by sudden extinctions in many groups and ecosystems, including the complete disappearance of several widespread and diverse organism groups (orders and families). Examples are the basal Emsian atopus Event, where the planktonic graptolites finally died out, the Taghanic Crisis, Frasnes events and Lower Kellwasser Event. Third-order global events show globally elevated extinction rates, often at lower taxonomic level (genera and species), but within many clades and in several ecosystems. Examples are the Silurian–Devonian boundary Klonk Event, and the Daleje, Chotěc, Kacak, Condroz and Annulata events. Fourth-order global extinctions refer to the sudden disappearance of relatively fewer but widespread groups, which implies a global, not regional, trigger. This category may include the Lochkovian–Pragian boundary

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Topics: Extinction event (56%), Biodiversity (52%), Devonian (52%) ... show more

50 Citations

Journal ArticleDOI: 10.1002/GJ.1087
01 Nov 2007-Geological Journal
Abstract: Occurrences and distribution of extremely scarce eognathodontids do not facilitate reliable correlation across the European regions. The correlation of the traditional early Pragian of the Prague Synform (a part of the classical Barrandian area) and the Spanish Central Pyrenees (section Segre 1) is based on conodont taxa of the Icriodus steinachensis and the Pelekysgnathus serratus stocks. This correlation has the potential to be extended to other peri-Gondwanan regions where this scarcity of eognathodontid faunas exists as well. Application of the morphotype subdivision in I. steinachensis enables approximation of the beginning of the Pragian in the Pyrenees. It is based on the entry of I. steinachensis beta morphotype; it enters together with early eognathodontid taxa in the Barrandian sections. These correlations show that routine application of certain zonal concepts can lead to misleading conclusions. Copyright © 2007 John Wiley & Sons, Ltd.

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Topics: Conodont (51%)

30 Citations

Journal ArticleDOI: 10.1007/S11430-017-9259-9
Wenkun Qie1, Xueping Ma2, Hong-He Xu1, Li Qiao1  +5 moreInstitutions (2)
Abstract: The Global Boundary Stratotype Sections and Points (GSSPs) for the bases of all seven international Devonian stages have been formally defined and ratified by IUGS till 1996, and nowadays, the main tasks for Devonian stratigraphers include further subdivision of these standard stages, strictly constrained absolute ages for the boundaries, and precise neritic-pelagic and marine-terrestrial correlations using multidisciplinary stratigraphy methods. Establishment of high-resolution Devonian integrative stratigraphy framework and timescale of China would play an important role in improving regional and international correlation, facilitating the recognition of important stratigraphic levels in different paleogeographic settings, and understanding the evolution pattern of biota, paleoclimate and paleoenvironment during this critical interval. Based on well-studied bio- and chronostratigraphy of Devonian in South China and adjacent areas, in combination with recent achievements in carbon isotope stratigraphy, event stratigraphy and radioactive isotope ages, this paper briefly summarize the research history and current status of Devonian chronostratigraphy of China, and for the first time introduce Devonian integrative stratigraphy framework of China. Up to date, few studies have been conducted on the astronomical cyclostratigraphy and high-resolution radioactive isotope dating in Devonian of China, which should be our main focuses in the near future.

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Topics: Devonian (60%), Chronostratigraphy (59%), Stratigraphy (52%)

26 Citations

Open accessJournal Article
Pierre Bultynck1Institutions (1)
Abstract: The most commonly used Lower and Middle Devonian conodont zonations that sometimes have been presented as standard zonations are evaluated. The author questions whether the Frasnian standard conodont zonation based on a phylogenetic succession of species belonging to the pelagic genera Mesotaxis, Palmatolepis and Siphonodella can be used for worldwide correlation. He favours the idea of an international conodont reference scale based on a synthesis of well established and documented conodont successions (with figured specimens of first and last occurrences of index-species) from key areas representing a variety of facies. Graphic correlation is likely to be the most objective and precise method to provide such a synthesis represented by the composite standard. Such standards have been already elaborated for the Frasnian and the Middle Devonian. This point of view does not imply that classical biozonations should be abandoned.

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Topics: Conodont (60%), Devonian (53%)

13 Citations


64 results found

Journal ArticleDOI: 10.1086/628623
Abstract: A compilation of nearly 25,000 rates of sediment accumulation shows that they are extremely variable, spanning at least 11 orders of magnitude. Much of this variation results from compiling rates determined for different time spans: there is a systematic trend of falling mean rate with increasing time span. The gradients of such trends vary with environment of deposition. Although measurement error and compaction contribute to these regressions, they are primarily the consequence of unsteady, discontinuous sedimentation. The essential character of the unsteadiness may be cyclic or random, but net accumulation is characterized by fluctuations whose magnitudes increase with increasing recurrence interval. Ratios of median long- to short-term accumulation rates provide a measure of the expected completeness of sedimentary stratigraphic sections, at the time scale of the short-term rate. Expected completeness deteriorates as finer time scales are considered.

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892 Citations

Open accessBook
13 Oct 1988-
Abstract: Introduction Skeletal anatomy Whole animal anatomy Taxonomy The major conodont groups Paleoecology The phylum Conodonta Evolutionary patterns Appendixes Index

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Topics: Phylum (52%), Conodont (51%), Paleoecology (51%)

382 Citations

Open accessJournal Article
Gilbert Klapper1, J. G. JohnsonInstitutions (1)
Topics: Devonian (57.99%), Biological dispersal (56.99%), Endemism (56.99%)

161 Citations

Open accessOtherDOI: 10.3133/PP276
01 Jan 1956-
Abstract: _____________________ Introduction. _--___-______--___Acknowledgments--.-_---___-_-. Structural setting._______________ Economic significance. _-__._. Cambrian system.________________ Prospect Mountain quartzite.. Pioche shale_______--_-_-_.__. Eldorado dolomite___________ Geddes limestone.___________ Secret Canyon shale._________ Lower shale member. .... Clarks Spring member.._ Hamburg dolomite.___-_.____ Dunderberg shale.___________ Windfall formation.__________ Catlin member._________

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134 Citations

Journal ArticleDOI: 10.1017/S0022336000062466
Abstract: The living members of the Argopecten gibbus stock include the bay and calico scallops, Argopecten irradians (Lamarck) and A. gibbus (Linne), both common in the western Atlantic and Gulf of Mexico; the less common A. nucleus (Born) of the Caribbean, southern Gulf of Mexico, Antilles, and southeastern Florida; and the common A. circularis (Sowerby) and A. purpuratus (Lamarck) of the eastern Pacific. The fossil members of the stock include the ancestors of these living species together with Argopecten eboreus (Conrad), an extinct species or species-group not ancestral to any of the later taxa. This study seeks to determine evolutionary relationships within the Argopecten gibbus stock by working back through the fossil record from a model of the morphological and ecological relationships of living species and subspecies. Biologically, the study is limited to an analysis of the morphology and ecology of the living taxa deduced from population samples. Paleontologically, it is limited to an analysis of morphological variation among samples of fossil populations collected from upper Cenozoic strata (Alum Bluff Group of the middle Miocene through the Pleistocene) exposed on the Atlantic and Gulf Coastal Plains of the United States. The time span investigated is about 18 million years, according to the latest published scale of absolute time. Differences between samples were studied and evaluated by means of morphometric data consisting of 70 measurements and form ratios of the outline, ligamenture, and musculature of each valve. Using an electronic digital computer, data were subjected to univariate and bivariate analyses, and samples were compared using machine-plotted, bivariate scatter diagrams, reduced major axes, and other graphical techniques. Data from right and left valves were treated separately, except that they were recombined in the study of characters that differ between valves, thereby furnishing new information on intervalve features. The postulated phylogeny shows a poorly known species, Argopecten species b, in the early middle Miocene (Oak Grove Sand), that is apparently very near the origin of the stock. This species evolved phyletically through A. nicholsi (Gardner) of the Shoal River Formation and A. choctawhatcheensis (Mansfield) of the Arca Faunizone into A. comparilis (Tuomey & Holmes) of the upper Miocene (Tamiami, Pinecrest, Duplin, and Yorktown Formations). A. comparilis was apparently broadly adapted and widely distributed, living in bays, sounds, and open marine waters in the western Atlantic, Gulf of Mexico, and Caribbean and probably extending through seaway passages to the Pacific, where it gave rise phyletically to A. circularis. By the end of the Miocene, on the eastern side of the Americas, this variable species had split, giving rise to a primitive bay scallop, A. anteamplicostatus (Mansfield), that, like the living bay scallop (its phyletic descendant), was probably ecologically restricted to the semienclosed waters of bays and sounds, and to another species, A. vicenarius (Conrad), probably restricted to open marine waters like the living calico scallop. The primitive bay scallop was apparently unable to reach the Pacific, but the open-marine species seems to have given rise to both the Pacific A. purpuratus and the Atlantic calico scallop, A. gibbus. The living Pacific A. circularis is morphologically primitive in that it resembles the Miocene species A. comparilis more than it does any of the later species on the eastern side of the Americas and is ecologically primitive in that it is broadly adapted and able to live both in bays and sounds and in open marine waters. During the Pleistocene, A. nucleus, a tropical bay scallop, is inferred to have split from A. gibbus and to have become morphologically convergent on the true bay scallop, A. irradians. A. eboreus, a common scallop on the eastern side of the Americas in the Miocene and Pliocene, represents a highly variable yet morphologically persistent lineage that neither split nor gave rise phyletically to other species and that became extinct during the early Pleistocene. In certain features of morphology, the A. gibbus lineage is convergent on the A. eboreus lineage, indicating that the extinct species may also have been restricted to open marine waters. On the basis of the materials analyzed thus far, the evolution (both phyletic change and splitting) of the stock has been faster on the Atlantic side of the Americas than on the Pacific side, with the living Pacific species resembling late Miocene and early Pliocene Atlantic species. Because barrier islands seem to have played a key role in speciation within the stock, it would appear that evolutionary differences may have been caused by the active coastal tectonism of the Pacific side destroying such island barriers before genetic differences between inshore and offshore scallop populations could arise. With regard to nomenclature, the name Argopecten is shown to be a senior synonym of Plagioctenium; the generic name Aequipecten is rejected for American species related to Argopecten gibbus; and it is concluded that the generic name Chlamys, sensu lato, is better applied as the subfamily name Chlamydinae. The species name Argopecten vicenarius (Conrad), unused since 1898, is reinstated as the only available name for an important taxon occurring in the Caloosahatchee Marl of Florida and the Waccamaw Formation of the Carolinas.

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Topics: Argopecten gibbus (68%), Argopecten irradians (59%), Population (53%) ... show more

130 Citations

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