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Poul Emsbo - One of the best experts on this subject based on the ideXlab platform.
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chitinozoan biostratigraphy of the silurian wenlock ludlow boundary succession of the long mountain powys wales
Geological Magazine, 2016Co-Authors: Thomas Steeman, Jan Zalasiewicz, David J. Siveter, Thijs R.a. Vandenbroucke, Jacques Verniers, Vincent Perrier, James G. Wilkinson, Poul EmsboAbstract:Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the Graptolites enables a local three-fold subdivision of the late Homerian lundgreni Graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens Graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new Graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in Graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.
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Chitinozoan biostratigraphy of the Silurian Wenlock–Ludlow boundary succession of the Long Mountain, Powys, Wales
Geological Magazine, 2015Co-Authors: Thomas Steeman, Jan Zalasiewicz, David J. Siveter, Thijs R.a. Vandenbroucke, Jacques Verniers, Vincent Perrier, James G. Wilkinson, Poul EmsboAbstract:Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the Graptolites enables a local three-fold subdivision of the late Homerian lundgreni Graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens Graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new Graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in Graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.
Jan Zalasiewicz - One of the best experts on this subject based on the ideXlab platform.
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early silurian llandovery Graptolite assemblages of saudi arabia biozonation palaeoenvironmental significance and biogeography
Geological Quarterly, 2016Co-Authors: Mark Williams, Jan Zalasiewicz, Hani Boukhamsin, Christian CesariAbstract:Analysis of Silurian Graptolite assemblages from 1017 sample horizons in 132 cores (from 65 boreholes) through the Qusaiba Member, Qalibah Formation of Saudi Arabia, provides a refined Graptolite biostratigraphy for the Arabian Peninsula comparable in its resolution to that from the British Isles and the Czech Republic. Over 150 Graptolite species characterize 11 biozones from the lowermost Rhuddanian lubricus Biozone to the lower Telychian guerichi Biozone, with sub-zonal resolution for several intervals. Graptolite biozonal boundaries and the Rhuddanian-Aeronian and Aeronian-Telychian stage boundaries can be placed with high precision. Detailed analysis of Graptolite spatial distribution suggests persistent depth-stratified assemblages across the Silurian palaeo-Arabian Plate. Near-surface-dwelling assemblages probably occupied the mixed-layer of Silurian oceans, enabling colonization of shallow shelf environments. They are low-diversity (1-2 species) assemblages characterized by Neodiplograptus, Coronograptus, Neolagarograptus and Stimulograptus species and often are preserved in strata with extensive shelly faunas. Deeper marine assemblages are of higher diversity (up to 15 species per horizon), and are characterized by dorsally curved or helically coiled species of Spirograptus , Demirastrites , Lituigraptus , Rastrites and Torquigraptus . Recognition of depth-stratified Graptolite assemblages provides an important tool for establishing palaeo-basin topography and water depth at the time of sedimentary deposition. At the species level, the Graptolite assemblages of Saudi Arabia are remarkably similar to contemporaneous faunas from peri-Gondwanan Europe and, from the middle Rhuddanian onwards, also to the Avalonian and Laurentian Llandovery Graptolites of the UK.
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chitinozoan biostratigraphy of the silurian wenlock ludlow boundary succession of the long mountain powys wales
Geological Magazine, 2016Co-Authors: Thomas Steeman, Jan Zalasiewicz, David J. Siveter, Thijs R.a. Vandenbroucke, Jacques Verniers, Vincent Perrier, James G. Wilkinson, Poul EmsboAbstract:Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the Graptolites enables a local three-fold subdivision of the late Homerian lundgreni Graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens Graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new Graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in Graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.
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Chitinozoan biostratigraphy of the Silurian Wenlock–Ludlow boundary succession of the Long Mountain, Powys, Wales
Geological Magazine, 2015Co-Authors: Thomas Steeman, Jan Zalasiewicz, David J. Siveter, Thijs R.a. Vandenbroucke, Jacques Verniers, Vincent Perrier, James G. Wilkinson, Poul EmsboAbstract:Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the Graptolites enables a local three-fold subdivision of the late Homerian lundgreni Graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens Graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new Graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in Graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.
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Graptolite studies in honour of Barrie Rickards (1938–2009): an introduction
Proceedings of the Yorkshire Geological Society, 2011Co-Authors: Andrea M Snelling, Denis E. B. Bates, Jan ZalasiewiczAbstract:Barrie Rickards was a fisherman, biographer and, most pertinently in this context, a teacher of geology and palaeontology. As a fisherman, especially of pike, he was almost legendary, writing many books on the subject including some regarded as classics within the angling community. As a teacher of geology and palaeontology, he was known for his inspirational qualities in the field (and could, almost to the end, outpace his young proteges across hill and valley). In the narrower world of palaeontology, he was one of the world's leading researchers on those graceful, useful, but equally bizarre and baffling fossils, the Graptolites. While the fishing and the fieldwork might have been foreseen in his youth (as a child he was happy to be outdoors), the academic achievement was a less obvious outcome. By his own admission he was not the most diligent of pupils, but he nevertheless got into sixth form, and then went to Hull University to study chemistry (Woodcock & Page 2010). There, he switched to geology. An undergraduate mapping project in the Howgill Fells introduced him to mudrocks and Graptolites and was followed by a Ph.D. on the same area, the work soon being published, much of it in a Palaeontographical Society monograph. This was the beginning of a formidable publishing career, mostly at the Sedgwick Museum of the University of Cambridge where he had been lured early in his career by the eminent Graptolite worker, Oliver Bulman, who recognized a good man when he saw one. Barrie's interest in Graptolites was total and broad. He was interested in the taxonomy of Graptolites, both at the small scale – he wrote many papers detailing the morphology and characteristics of this or that Graptolite or group of Graptolites – and more widely where, for example, his magisterial account of the …
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using x ray images to analyse Graptolite distribution and alignment in welsh mudrocks
Scopus, 2010Co-Authors: Jan Zalasiewicz, Andrea M Snelling, Ian ReedsAbstract:SUMMARY X-ray imaging of Graptolites is here shown to enhance greatly the amount and type of fossil evidence available, both for biostratigraphical study and for palaeoceanographical and palaeoecological analysis. The technique requires there to be sufficient density contrast between the fossils and the enclosing rock, as with the pyritized Graptolites within the Silurian (Llandovery, Aeronian) mudrocks of central Wales investigated herein. Graptolite species previously not encountered using traditional collecting techniques were recorded in significant numbers using X-ray imaging and include two species recorded for the first time in Britain. Stratigraphic variation has been found in the numbers of pyritized Graptolites, and this is inversely related to the amount of free aggregated pyrite within the rock. Biserial Graptolite specimens show systematic patterns of alignment by currents, and construction of stereo and anaglyph images enables 3-dimensional visualisation of spatial information, allowing the geometry and microstratigraphic relationship of one Graptolite to another to be discerned. CT-scan techniques show better-resolved 3D morphology, but digital X-ray techniques, being more rapid, may remain optimal for many routine uses in palaeontology.
Thomas Steeman - One of the best experts on this subject based on the ideXlab platform.
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chitinozoan biostratigraphy of the silurian wenlock ludlow boundary succession of the long mountain powys wales
Geological Magazine, 2016Co-Authors: Thomas Steeman, Jan Zalasiewicz, David J. Siveter, Thijs R.a. Vandenbroucke, Jacques Verniers, Vincent Perrier, James G. Wilkinson, Poul EmsboAbstract:Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the Graptolites enables a local three-fold subdivision of the late Homerian lundgreni Graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens Graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new Graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in Graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.
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Chitinozoan biostratigraphy of the Silurian Wenlock–Ludlow boundary succession of the Long Mountain, Powys, Wales
Geological Magazine, 2015Co-Authors: Thomas Steeman, Jan Zalasiewicz, David J. Siveter, Thijs R.a. Vandenbroucke, Jacques Verniers, Vincent Perrier, James G. Wilkinson, Poul EmsboAbstract:Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the Graptolites enables a local three-fold subdivision of the late Homerian lundgreni Graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens Graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new Graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in Graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.
David K. Loydell - One of the best experts on this subject based on the ideXlab platform.
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the panghkawkwo Graptolite bed llandovery silurian myanmar and the location of the sibumasu or sibuma terrane in the silurian
Palaeogeography Palaeoclimatology Palaeoecology, 2017Co-Authors: David K. Loydell, Kyi Pyar AungAbstract:Abstract The “Panghkawkwo Graptolite bed” is shown to comprise several graptolitic horizons extending through the Aeronian (middle Llandovery) and into the lower Telychian (upper Llandovery). Graptolite assemblages are diverse indicating an outer shelf (or deeper) depositional environment. They are similar to those of Bohemia and Saudi Arabia (peri-Gondwanan Europe and core Gondwana respectively), but include also taxa (Agetograptus and species of Metaclimacograptus) not known from these regions, but which characterize lower latitude Llandovery Graptolite assemblages. The evidence for the Silurian location of the Sibuma(su) Terrane is discussed. The presence of Monograptus belophorus and Cyrtograptus rigidus in the lower Sheinwoodian (Wenlock) of western Yunnan suggests a non-equatorial palaeolatitude. The Panghkawkwo Graptolites suggest a location for Sibuma(su) between Gondwana and South China.
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the early ludfordian leintwardinensis Graptolite event and the gorstian ludfordian boundary in bohemia silurian czech republic
Palaeontology, 2014Co-Authors: Petr Storch, Stěpan Manda, David K. LoydellAbstract:The late Gorstian to early Ludfordian hemipela- gic succession of the south-eastern part of the Prague Syn- form preserves a rich fossil record dominated by 28 species of planktic graptoloids associated with pelagic myodocopid ostracods, pelagic and nektobenthic orthocerid cephalopods, epibyssate bivalves, nektonic phyllocarids, rare dendroid Graptolites, brachiopods, crinoids, trilobites, sponges and macroalgae. Faunal dynamics have been studied with parti- cular reference to Graptolites. The early Ludfordian leintwar- dinensis Graptolite extinction Event manifests itself as a stepwise turnover of a moderate diversity Graptolite fauna rather than an abrupt destruction of a flourishing biota. The simultaneous extinction of the spinose saetograptids Saeto- graptus clavulus, Saetograptus leintwardinensis and the rare S. sp. B. at the top of the S. leintwardinensis Zone was preceded by a short-term acme of S. clavulus. Cucullograptus cf. aver- sus and C. rostratus vanished from the fossil record in the lower part of the Bohemograptus tenuis Biozone. No mass proliferation of Bohemograptus has been observed in the postextinction interval. Limited indigenous speciation gave rise to Pseudomonoclimacis kosoviensis and Pseudomonoclima- cis cf. dalejensis. Egregiograptus (the only novel element of cryptic origin) made its earliest occurrence in association with the latest cucullograptids. A postextinction Graptolite assemblage of moderate diversity, composed for the most part of long-ranging taxa, persisted through the middle and upper tenuis Biozone until new rediversification in the Neo- cucullograptus inexpectatus Biozone. Unlike the graptoloids, the planktic, epiplanktic, nektonic and nektobenthic shelly fauna did not suffer significant extinction in the early Lud- fordian. The Gorstian-Ludfordian boundary is placed at the lowest occurrence of S. leintwardinensis in spite of the very modest Graptolite record available from the Ludfordian GSSP where no Graptolites occur below the basal bed of the Lower Leintwardine Formation. Elsewhere, the Gorstian-Ludfordian boundary has been placed at the base of the Saetograptus linearis Biozone which has been considered roughly correla- tive with the leintwardinensis Biozone. Indeed, our morpho- metric study places the worldwide biozonal index species S. linearis in synonymy with S. leintwardinensis and thus considerably enhances the biostratigraphical utility of the lat- ter index species. Pseudomonoclimacis antiqua sp. nov. is described.
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Graptolite biozone correlation charts
Geological Magazine, 2011Co-Authors: David K. LoydellAbstract:Charts are presented showing the correlation of Graptolite biozonations for the Lower Ordovician to Lower Devonian, i.e. for the entire stratigraphical range of the planktonic graptoloid Graptolites. Regions chosen are those for which the most detailed biostratigraphical studies have been undertaken. For Baltica, average Graptolite zone (chron) duration appears to vary from c . 300000 years (Ludlow Epoch) to 2.4 Ma (Lochkovian Epoch).
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Graptolites from the Deerhope Formation, North Esk Inlier
Scottish Journal of Geology, 2005Co-Authors: David K. LoydellAbstract:The Deerhope Formation of the Pentland Hills, near Edinburgh, is generally considered to be of late Telychian (late Llandovery) age (e.g. Robertson 1989; Bull & Loydell 1995; Clarkson et al. 2001). Evidence for a precise level in the Graptolite biozonation has, however, thus far been lacking. The only published record of Graptolites is that of Mykura (1960, p. 166) from the Deerhope Burn. Clarkson & Taylor (2002, p. 32) described this material as comprising ‘rare unidentifiable monograptids’. Bull & Loydell (1995) described Graptolites from the underlying Reservoir Formation, exposed in the Gutterford Burn, and assigned the assemblage to the middle part of the Oktavites spiralis Biozone. The author has recently examined all of the Deerhope Formation fossils housed in the British Geological Survey collections. These collections contain a small number of biostratigraphically significant Graptolites that form the subject of this short paper. Mark Dean (BGS Edinburgh) kindly arranged the loan of a very large number of Deerhope Formation fossils. Hugh Barron and Euan Clarkson advised on the lithostratigraphy, particularly on changes to the definition of the formation's base. Claire Mellish (NHM) arranged the loan of Girvan Graptolites.
Petr Storch - One of the best experts on this subject based on the ideXlab platform.
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the early ludfordian leintwardinensis Graptolite event and the gorstian ludfordian boundary in bohemia silurian czech republic
Palaeontology, 2014Co-Authors: Petr Storch, Stěpan Manda, David K. LoydellAbstract:The late Gorstian to early Ludfordian hemipela- gic succession of the south-eastern part of the Prague Syn- form preserves a rich fossil record dominated by 28 species of planktic graptoloids associated with pelagic myodocopid ostracods, pelagic and nektobenthic orthocerid cephalopods, epibyssate bivalves, nektonic phyllocarids, rare dendroid Graptolites, brachiopods, crinoids, trilobites, sponges and macroalgae. Faunal dynamics have been studied with parti- cular reference to Graptolites. The early Ludfordian leintwar- dinensis Graptolite extinction Event manifests itself as a stepwise turnover of a moderate diversity Graptolite fauna rather than an abrupt destruction of a flourishing biota. The simultaneous extinction of the spinose saetograptids Saeto- graptus clavulus, Saetograptus leintwardinensis and the rare S. sp. B. at the top of the S. leintwardinensis Zone was preceded by a short-term acme of S. clavulus. Cucullograptus cf. aver- sus and C. rostratus vanished from the fossil record in the lower part of the Bohemograptus tenuis Biozone. No mass proliferation of Bohemograptus has been observed in the postextinction interval. Limited indigenous speciation gave rise to Pseudomonoclimacis kosoviensis and Pseudomonoclima- cis cf. dalejensis. Egregiograptus (the only novel element of cryptic origin) made its earliest occurrence in association with the latest cucullograptids. A postextinction Graptolite assemblage of moderate diversity, composed for the most part of long-ranging taxa, persisted through the middle and upper tenuis Biozone until new rediversification in the Neo- cucullograptus inexpectatus Biozone. Unlike the graptoloids, the planktic, epiplanktic, nektonic and nektobenthic shelly fauna did not suffer significant extinction in the early Lud- fordian. The Gorstian-Ludfordian boundary is placed at the lowest occurrence of S. leintwardinensis in spite of the very modest Graptolite record available from the Ludfordian GSSP where no Graptolites occur below the basal bed of the Lower Leintwardine Formation. Elsewhere, the Gorstian-Ludfordian boundary has been placed at the base of the Saetograptus linearis Biozone which has been considered roughly correla- tive with the leintwardinensis Biozone. Indeed, our morpho- metric study places the worldwide biozonal index species S. linearis in synonymy with S. leintwardinensis and thus considerably enhances the biostratigraphical utility of the lat- ter index species. Pseudomonoclimacis antiqua sp. nov. is described.
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the late aeronian Graptolite sedgwickii event associated positive carbon isotope excursion and facies changes in the prague synform barrandian area bohemia
Geological Magazine, 2012Co-Authors: Petr Storch, Jiři FrýdaAbstract:Study of the lower Silurian black shale succession of the Prague Synform has enabled detailed insight into Graptolite faunal dynamics and diversity trends from the mid-Aeronian diversity maximum through to the late Aeronian crisis. Graptolite diversity decreased from 33 taxa in the Lituigraptus convolutus Biozone to 17 taxa in the upper part of the Stimulograptus sedgwickii Biozone and newly erected Lituigraptus rastrum Biozone. The Graptolite assemblages of the latter biozones exhibit low species richness along with high dominance. Many Graptolite species that became extinct in the early part of the sedgwickii Zone were promptly replaced by new forms. In the later part of the sedgwickii Zone, however, replacement of extinct species by new forms considerably decelerated. The increased rate of Graptolite extinction recorded in the convolutus–sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in δ 13 C org (of 2.2 ‰) compared to baseline values. Sea-level drawdown can be inferred from siltstones and/or temporary nondeposition in the middle sedgwickii Zone. This level also sees total organic carbon (TOC) fluctuations and a strong positive δ 13 C org excursion with a peak shift of at least 7 ‰. The sedgwickii Event exhibits substantial reorganization of the Graptolite fauna, its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre-extinction assemblage. Associated changes in lithology, TOC and the pronounced δ 13 C org excursion suggest a relatively extended and probably multi-phase period of stressed conditions that affected the pelagic realm inhabited by Graptolites in the course of the late Aeronian interval.
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Graptolite biostratigraphy of the lower silurian llandovery shelf deposits of the western iberian cordillera spain
Geological Magazine, 1998Co-Authors: Juan Carlos Gutierrezmarco, Petr StorchAbstract:Eight Lower Silurian Graptolite biozones (triangulatus, convolutus, linnaei, turriculatus, cris- pus, griestoniensis, tullbergi and spiralis) and three subzones (runcinatus-gemmatus, palmeus and hispani- cus) have been recognized in the Sierra Menera, Nevera, and Tremedal massifs in the Castilian Branch of the Iberian Cordillera (Western Iberian Cordillera). Early Silurian, Rhuddanian low-diversity normalograp- tid faunas are also present and these, together with the rich Graptolite faunas of the Aeronian triangulatus and convolutus biozones, come from black, shaly intercalations within the quartzose sandstones of the upper part of the Los Puertos Quartzite. Telychian Graptolite biozones have been recognized in the succeeding black-shale sequence of the Badenas Formation. Diachroneity of the transition from sandstones to black shales is dated by Graptolites. It ranges from about the base to at least the top of the linnaei Biozone. We sug- gest that the Lower Silurian black shales of the Western Iberian Cordillera were deposited in a shallow, shelf environment, not much deeper than that of presumably storm-influenced sandstones of the Los Puertos Quartzite.
