Leonid Popov | National Museum of Wales (original) (raw)
Papers by Leonid Popov
Scientific Reports , 2019
The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions w... more The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions with tropical water surface temperature estimates, interpolated from oxygen isotopes, approaching 40 °C. In the mid-latitude Baltoscandian Basin, conodonts displaying low δ 18 O values, which suggest high temperatures (>40 °C) in the water column, are in contrast with the discovery of contemporaneous glendonite clusters, a pseudomorph of ikaite (CaCO 3 ·6H 2 O) traditionally considered as indicator of near-freezing bottom-water conditions. The massive precipitation of this temperature sensitive mineral is associated with transgressive conditions and high organic productivity. As a result, the lower Tremadocian sediments of Baltoscandia apparently contain both "greenhouse" pelagic signals and near-freezing substrate indicators. This paradox points to other primary controlling mechanisms for ikaite precipitation in kerogenous substrates, such as carbonate alkalinity, pH and Mg/Ca ratios, as recently constrained by laboratory experiments. Preservation of "hot" conodonts embedded in kerogenous shales rich in δ 18 o-depleted glendonites suggests both the onset of sharp thermal stratification patterns in a semi-closed basin and the assumed influence of isotopically depleted freshwater yielded by fluvial systems. Except one rather controversial note 1 , the record of glendonites displays an apparent gap from Neopoterozoic 2 to Permian 3 times. However, similar calcareous nodular aggregates embedded in Tremadocian black shales of the East Baltic (Fig. 1a), the so-called "antraconites", have been known for more than 150 years. These aggregates are documented from 24 geographical localities in the Türisalu and Koporiye formations (Cordylodus angulatus-Paltodus deltifer pristinus zones) and sporadically in the Orasoja Member (upper part of the Kallavere Formation; Cordylodus angulatus-Paltodus deltifer pristinus zones), exposed along 600 km of the Baltic-Ladoga Glint 4 , a transect linking North Estonia to the eastern St Petersburg area (Fig. 1b). All these units were accumulated in the
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The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar... more The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar (Boghu Mountains), Tabas (Derenjal Mountains, Ozbak-Kuh), Anarak (Pole Khavand) and Kerman regions is reviewed and updated. The current state of knowledge of the Silurian in the Zagros Basin, Alborz, Kopet-Dagh and Talysh regions, as well as in a few areas scattered across the Sabzevar Zone, and the Sanandaj-Sirjan terranes is also reviewed. Silurian volcanism in various parts of Iran is briefly discussed. The end of the Ordovician coincided with a widespread regression across Iran synchronous with the Hirnantian glaciation, and only in the Zagros Basin is there a continuous Ordovician–Silurian transition represented by graptolitic black shales of the Sarchahan Formation. In the Central-East Iranian Platform marine sedimentation re-commenced in the early to mid Aeronian. By the Sheinwoodian, carbonate platform depositional environments were established along its northeastern margin. In other parts of Iran (e.g., Kopet-Dagh and the Sabzevar Zone), siliciclastic sedimentation continued probably into the late Silurian. The Silurian conodont and brachiopod biostratigraphy of Central Iran is significantly updated facilitating a precise correlation with the Standard Global Chronostratigraphic Scale, as well as with key Silurian sections in other parts of Iran. The Silurian lithostratigraphy is considerably revised and two new lithostratigraphical units, namely the Boghu and Dahaneh-Kalut formations, are introduced.
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Acta Geologica Polonica, 2017
Popov, L.E. and Cocks, L.R.M. 2017. Late Ordovician palaeogeography and the positions of the Kaza... more Popov, L.E. and Cocks, L.R.M. 2017. Late Ordovician palaeogeography and the positions of the Kazakh ter-ranes through analysis of their brachiopod faunas. Acta Geologica Polonica, 67 (3), 323–380. Warszawa. Detailed biogeographical and biofacies analyses of the Late Ordovician brachiopod faunas with 160 genera, grouped into 94 faunas from individual lithotectonic units within the Kazakh Orogen strongly support an archipelago model for that time in that area. The Kazakh island arcs and microcontinents within several separate clusters were located in the tropics on both sides of the Equator. Key units, from which the Late Ordovician faunas are now well known, include the Boshchekul, Chingiz-Tarbagatai, and Chu-Ili terranes. The development of brachiopod biogeography within the nearly ten million year time span of the Late Ordovician from about 458 to 443 Ma (Sandbian, Katian, and Hirnantian), is supported by much new data, including our revised identifications from the Kazakh Orogen and elsewhere. The Kazakh archipelago was west of the Australasian segment of the Gondwana Supercontinent, and relatively near the Tarim, South China and North China continents, apart from the Atashu-Zhamshi Microcontinent, which probably occupied a relatively isolated position on the southwestern margin of the archipelago. Distinct faunal signatures indicate that the Kazakh terranes were far away from Baltica and Siberia throughout the Ordovician. Although some earlier terranes had joined each other before the Middle Ordovician, the amalgamation of Kazakh terranes into the single continent of Kazakhstania by the end of the Ordovician is very unlikely. The Late Ordovician brachiopods from the other continents are also compared with the Kazakh faunas and global provincialisation statistically determined.
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Journal of Paleontology, 2005
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Journal of the Geological Society, 2013
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Geobios, Jan 1, 2001
The Tritoechiidae are redefined following study of nine species of the genera Tritoechia, Eremoto... more The Tritoechiidae are redefined following study of nine species of the genera Tritoechia, Eremotoechia, Martellia Pomatotrema, Protambonites and Korinevskia nov. gen. in Kazakhstanian brachiopod faunas from the upper Tremadoc to lower Caradoc. Six species are new: Tritoechia crassa, T. tokmakensis, Eremotoechia inchoata, E. spissa, Martellia reliqua and Pomatotrema fecunda. In key characters of shell morphology the Tritoechiidae demonstrate close affinity with billingsellids and are therefore reassigned to the superfamily Billingselloidea.La Famille Tritoechiidae est redéfinie sur la base de l'étude de neuf espèces appartenant aux genres Tritoechia, Eremotoechia, Martellia Pomatotrema, Protambonites et Korinevskia nov. gen. de la faune de brachiopodes du Kazakhstan du Trémadoc supérieur au Caradoc inférieur. Six nouvelles espèces sont décrites Tritoechia crassa, T. tokmakensis, Eremotoechia inchoata, E. spissa, Martellia reliqua et Pomatotrema fecunda. Les caractères diagnostiques de la coquille des Tritoechiidés attestent de fortes affinités avec les Billingsellidés; de ce fait les Tritoechiidés sont rapportés à la Superfamille Bilingselloidea.
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Palaeoworld, 2006
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Journal of Paleontology, 2005
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Philosophical Transactions of The Royal Society B: Biological Sciences, 1996
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Two trilobite faunas of late Ordovician (Sandbian and Katian) age are described from the silicicl... more Two trilobite faunas of late Ordovician (Sandbian and Katian) age are described from the siliciclastic Karagach Formation, western Tarbagatai Range, eastern Kazakhstan. They comprise 15 families and 24 genera and include the new taxa Agerina acutilimbata sp. nov., Birmanites akchiensis sp. nov., Dulanaspis karagachensis sp. nov. and Kimakaspis kovalevskyi gen. et sp. nov. Most of the Karagach Formation yields graptolites characteristic of the Diplograptus foliaceus [multidens] Biozone, which are associated with the older trilobite fauna; the uppermost part, which is the source of the younger trilobite fauna, contains Orthograptus quadrimucronatus and
Dicranograptus hians which suggest a younger age, equating with the lowermost Ensigraptus caudatus Biozone, and the base of the Katian Stage. Most of the trilobite genera in both faunas have a wide geographical distribution in the late Ordovician, although Dulanaspis and Sinocybele are characteristic
of low latitude eastern peri-Gondwanan faunas.
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The Llandovery deposits of Iran preserve an important record of the biotic recovery of the benthi... more The Llandovery deposits of Iran preserve an important record of the biotic recovery of the
benthic faunas in temperate latitude Gondwana after the Terminal Ordovician Mass Extinction.
During that time, the terranes of Kopet-Dagh and Central Iran probably formed part of the
Gondwana domain. Genera characteristic of the open shelf are mostly derived from pan-tropical
Rhuddanian faunas and contain a significant proportion of taxa which survived the Terminal
Ordovician Mass Extinction. A significant number of taxa from shallow shelf biofacies show
links to contemporaneous and older faunas of South China. Major components of the benthic
fauna including tabulate and rugose corals, brachiopods, bryozoans and ostracods, as well as
cephalopods, were new to the region and show clear links to contemporaneous low latitude
faunas (e.g. Laurentia, Baltica and South China). During the Aeronian, peri-Gondwanan terranes
of Central Iran, Kope-Dagh and Afghanistan supported shallow water faunas bearing a common
biogeographical signature, suggesting that they were positioned in relatively close proximity to
each other, and probably lay in temperate southern palaeolatitudes. Data from Iran also show
that major patterns of biofacies differentiation known for the most of the Silurian Period were
developed during the Aeronian Age.
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Alcheringa: An Australasian Journal of Palaeontology, 1994
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The Early Triassic (late Induan to early Olenekian) Lingula borealis Bittner, from the Russkii Is... more The Early Triassic (late Induan to early Olenekian) Lingula borealis Bittner, from the Russkii
Island on the Pacific cost of south-eastern Russia is revised, based on re-examination of the type material.
Although this species, like most described Triassic lingulids, has remained very poorly understood due to
the lack of information on important characters, such as musculature and mantle canals, it has been commonly
recorded in subsequent studies and included in attempts at understanding the patterns of extinction
and recovery at around the Permian–Triassic boundary. Linguliform brachiopods are some of the notable
survivors of this significant mass extinction event. Lingula borealis has previously been referred to Lingularia
and provisionally synonymised with Lingularia similis Biernat & Emig. Here, it is shown that it
differs from Lingularia similis mainly in characters of mantle canals, musculature and most importantly
in details of the pedicle nerve impression. In Lingularia borealis, the impression of the pedicle nerve is
symmetrical and goes almost straight between the individual ventral umbonal muscle scars, whereas in
Lingularia similis it is asymmetrically positioned towards the smaller left component of the ventral umbonal
muscle scar. Shell structures and details of preserved ontogenies have also proven to be important
for the discrimination of lingulid taxa, but cannot be provided from the types of Lingularia borealis.
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Despite many major advances in recent years, three key challenges remain in bringing clarity to t... more Despite many major advances in recent years, three key challenges remain in bringing clarity to the early history of the phylum: (1) identifying the origin, morphology and life modes of the first brachiopods; (2) understanding the relationships of the major groups to each other and higher sister taxa; and (3) unravelling the roles of the Cambrian and Ordovician radiations that set the agenda for much of subsequent brachiopod evolution. Since some 95% of all brachiopod taxa are extinct, the fossil record is the primary source of data to frame and test models for the evolution of the phylum. The acquisition of new, and the redescription of existing faunas, in precise spatial and temporal frameworks, using new and well-established analytical and investigative techniques, are as important as ever.
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Palaeogeography, Palaeoclimatology, Palaeoecology, 2011
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Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 2014
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This paper reviews the global biogeography and affinities of the Bradoriida, a group of Cambrian–... more This paper reviews the global biogeography and affinities of the Bradoriida, a group of Cambrian–early Ordovician arthropods. Bradoriida appear in the fossil record during the early Cambrian, just prior to the earliest trilobite faunas. Seven families may form a natural (monophyletic) group of Bradoriida sensu stricto, comprising Cambriidae, Kunmingellidae, Comptalutidae, Bradoriidae, Hipponicharionidae, Beyrichonidae and Svealutidae. Amongst the Bradoriida sensu lato, some forms that lie outside these families have carapace designs that suggest an ostracod affinity, particularly Altajanella and Vojbokalina. Bradoriida formed a major element of the 'Cambrian evolutionary fauna' and are components of the Chengjiang, Burgess Shale, and Buen Formation Lagerstätten. Bradoriida achieved global distribution from the Atdabanian (early Cambrian). Their diversity peaked during the early and middle Cambrian, with highest diversity at the species and genus level amongst the palaeo-tropical faunas of the South China (17 genera) and east Gondwana palaeocontinental regions (23 genera). By contrast Laurentian faunas were of much lower diversity (10 genera for the whole Cambrian). Bradoriid diversity declined rapidly from the latest middle Cambrian, a trend that may be related to the major extinction of trilobites at the base of the late Cambrian. The youngest Bradoriida comprise a few, rare Ordovician forms. Bradoriids appear to have occupied well-oxygenated marine shelf facies. The biogeographical patterns of early and middle Cambrian Bradoriida suggest climatic control on their distribution (temperate and tropical faunas), together with palaeogeographical constraints that also reflect trilobite provinciality. Kunmingellids and comptalutids were restricted to palaeo-tropical/subtropical sites, but migrated between South China, Siberia and eastern Gondwana palaeocontinents. They are absent from the mid-and high latitude faunas of the western Gondwana, Avalonia and Baltica palaeocontinental areas that were dominated by hipponicharionids, beyrichonids and Bradoriidae. The Laurentia palaeocontinent was isolated from the main zones of bradoriid diversity, but its faunas include a number of early and middle Cambrian Bradoriidae (Indota, Bradoria, Walcottella), and the region was colonised by cosmopolitan cambriids during the early Cambrian and by supposed pelagic svealutids (Liangshanella and Anabarochilina) during the middle Cambrian. The genera Walcottella, Dielymella and Bullaluta were endemic to Laurentia. One species of Anabarochilina that possibly dwelt near the sea-surface achieved an equatorial to high southern latitude (70° S) distribution during the late middle Cambrian (Lejopyge laevigata Biozone), perhaps reflecting a reduced latitudinal temperature gradient for near surface ocean waters.
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Scientific Reports , 2019
The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions w... more The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions with tropical water surface temperature estimates, interpolated from oxygen isotopes, approaching 40 °C. In the mid-latitude Baltoscandian Basin, conodonts displaying low δ 18 O values, which suggest high temperatures (>40 °C) in the water column, are in contrast with the discovery of contemporaneous glendonite clusters, a pseudomorph of ikaite (CaCO 3 ·6H 2 O) traditionally considered as indicator of near-freezing bottom-water conditions. The massive precipitation of this temperature sensitive mineral is associated with transgressive conditions and high organic productivity. As a result, the lower Tremadocian sediments of Baltoscandia apparently contain both "greenhouse" pelagic signals and near-freezing substrate indicators. This paradox points to other primary controlling mechanisms for ikaite precipitation in kerogenous substrates, such as carbonate alkalinity, pH and Mg/Ca ratios, as recently constrained by laboratory experiments. Preservation of "hot" conodonts embedded in kerogenous shales rich in δ 18 o-depleted glendonites suggests both the onset of sharp thermal stratification patterns in a semi-closed basin and the assumed influence of isotopically depleted freshwater yielded by fluvial systems. Except one rather controversial note 1 , the record of glendonites displays an apparent gap from Neopoterozoic 2 to Permian 3 times. However, similar calcareous nodular aggregates embedded in Tremadocian black shales of the East Baltic (Fig. 1a), the so-called "antraconites", have been known for more than 150 years. These aggregates are documented from 24 geographical localities in the Türisalu and Koporiye formations (Cordylodus angulatus-Paltodus deltifer pristinus zones) and sporadically in the Orasoja Member (upper part of the Kallavere Formation; Cordylodus angulatus-Paltodus deltifer pristinus zones), exposed along 600 km of the Baltic-Ladoga Glint 4 , a transect linking North Estonia to the eastern St Petersburg area (Fig. 1b). All these units were accumulated in the
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The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar... more The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar (Boghu Mountains), Tabas (Derenjal Mountains, Ozbak-Kuh), Anarak (Pole Khavand) and Kerman regions is reviewed and updated. The current state of knowledge of the Silurian in the Zagros Basin, Alborz, Kopet-Dagh and Talysh regions, as well as in a few areas scattered across the Sabzevar Zone, and the Sanandaj-Sirjan terranes is also reviewed. Silurian volcanism in various parts of Iran is briefly discussed. The end of the Ordovician coincided with a widespread regression across Iran synchronous with the Hirnantian glaciation, and only in the Zagros Basin is there a continuous Ordovician–Silurian transition represented by graptolitic black shales of the Sarchahan Formation. In the Central-East Iranian Platform marine sedimentation re-commenced in the early to mid Aeronian. By the Sheinwoodian, carbonate platform depositional environments were established along its northeastern margin. In other parts of Iran (e.g., Kopet-Dagh and the Sabzevar Zone), siliciclastic sedimentation continued probably into the late Silurian. The Silurian conodont and brachiopod biostratigraphy of Central Iran is significantly updated facilitating a precise correlation with the Standard Global Chronostratigraphic Scale, as well as with key Silurian sections in other parts of Iran. The Silurian lithostratigraphy is considerably revised and two new lithostratigraphical units, namely the Boghu and Dahaneh-Kalut formations, are introduced.
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Acta Geologica Polonica, 2017
Popov, L.E. and Cocks, L.R.M. 2017. Late Ordovician palaeogeography and the positions of the Kaza... more Popov, L.E. and Cocks, L.R.M. 2017. Late Ordovician palaeogeography and the positions of the Kazakh ter-ranes through analysis of their brachiopod faunas. Acta Geologica Polonica, 67 (3), 323–380. Warszawa. Detailed biogeographical and biofacies analyses of the Late Ordovician brachiopod faunas with 160 genera, grouped into 94 faunas from individual lithotectonic units within the Kazakh Orogen strongly support an archipelago model for that time in that area. The Kazakh island arcs and microcontinents within several separate clusters were located in the tropics on both sides of the Equator. Key units, from which the Late Ordovician faunas are now well known, include the Boshchekul, Chingiz-Tarbagatai, and Chu-Ili terranes. The development of brachiopod biogeography within the nearly ten million year time span of the Late Ordovician from about 458 to 443 Ma (Sandbian, Katian, and Hirnantian), is supported by much new data, including our revised identifications from the Kazakh Orogen and elsewhere. The Kazakh archipelago was west of the Australasian segment of the Gondwana Supercontinent, and relatively near the Tarim, South China and North China continents, apart from the Atashu-Zhamshi Microcontinent, which probably occupied a relatively isolated position on the southwestern margin of the archipelago. Distinct faunal signatures indicate that the Kazakh terranes were far away from Baltica and Siberia throughout the Ordovician. Although some earlier terranes had joined each other before the Middle Ordovician, the amalgamation of Kazakh terranes into the single continent of Kazakhstania by the end of the Ordovician is very unlikely. The Late Ordovician brachiopods from the other continents are also compared with the Kazakh faunas and global provincialisation statistically determined.
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Journal of Paleontology, 2005
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Journal of the Geological Society, 2013
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Geobios, Jan 1, 2001
The Tritoechiidae are redefined following study of nine species of the genera Tritoechia, Eremoto... more The Tritoechiidae are redefined following study of nine species of the genera Tritoechia, Eremotoechia, Martellia Pomatotrema, Protambonites and Korinevskia nov. gen. in Kazakhstanian brachiopod faunas from the upper Tremadoc to lower Caradoc. Six species are new: Tritoechia crassa, T. tokmakensis, Eremotoechia inchoata, E. spissa, Martellia reliqua and Pomatotrema fecunda. In key characters of shell morphology the Tritoechiidae demonstrate close affinity with billingsellids and are therefore reassigned to the superfamily Billingselloidea.La Famille Tritoechiidae est redéfinie sur la base de l'étude de neuf espèces appartenant aux genres Tritoechia, Eremotoechia, Martellia Pomatotrema, Protambonites et Korinevskia nov. gen. de la faune de brachiopodes du Kazakhstan du Trémadoc supérieur au Caradoc inférieur. Six nouvelles espèces sont décrites Tritoechia crassa, T. tokmakensis, Eremotoechia inchoata, E. spissa, Martellia reliqua et Pomatotrema fecunda. Les caractères diagnostiques de la coquille des Tritoechiidés attestent de fortes affinités avec les Billingsellidés; de ce fait les Tritoechiidés sont rapportés à la Superfamille Bilingselloidea.
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Palaeoworld, 2006
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Journal of Paleontology, 2005
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Philosophical Transactions of The Royal Society B: Biological Sciences, 1996
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Two trilobite faunas of late Ordovician (Sandbian and Katian) age are described from the silicicl... more Two trilobite faunas of late Ordovician (Sandbian and Katian) age are described from the siliciclastic Karagach Formation, western Tarbagatai Range, eastern Kazakhstan. They comprise 15 families and 24 genera and include the new taxa Agerina acutilimbata sp. nov., Birmanites akchiensis sp. nov., Dulanaspis karagachensis sp. nov. and Kimakaspis kovalevskyi gen. et sp. nov. Most of the Karagach Formation yields graptolites characteristic of the Diplograptus foliaceus [multidens] Biozone, which are associated with the older trilobite fauna; the uppermost part, which is the source of the younger trilobite fauna, contains Orthograptus quadrimucronatus and
Dicranograptus hians which suggest a younger age, equating with the lowermost Ensigraptus caudatus Biozone, and the base of the Katian Stage. Most of the trilobite genera in both faunas have a wide geographical distribution in the late Ordovician, although Dulanaspis and Sinocybele are characteristic
of low latitude eastern peri-Gondwanan faunas.
Bookmarks Related papers MentionsView impact
The Llandovery deposits of Iran preserve an important record of the biotic recovery of the benthi... more The Llandovery deposits of Iran preserve an important record of the biotic recovery of the
benthic faunas in temperate latitude Gondwana after the Terminal Ordovician Mass Extinction.
During that time, the terranes of Kopet-Dagh and Central Iran probably formed part of the
Gondwana domain. Genera characteristic of the open shelf are mostly derived from pan-tropical
Rhuddanian faunas and contain a significant proportion of taxa which survived the Terminal
Ordovician Mass Extinction. A significant number of taxa from shallow shelf biofacies show
links to contemporaneous and older faunas of South China. Major components of the benthic
fauna including tabulate and rugose corals, brachiopods, bryozoans and ostracods, as well as
cephalopods, were new to the region and show clear links to contemporaneous low latitude
faunas (e.g. Laurentia, Baltica and South China). During the Aeronian, peri-Gondwanan terranes
of Central Iran, Kope-Dagh and Afghanistan supported shallow water faunas bearing a common
biogeographical signature, suggesting that they were positioned in relatively close proximity to
each other, and probably lay in temperate southern palaeolatitudes. Data from Iran also show
that major patterns of biofacies differentiation known for the most of the Silurian Period were
developed during the Aeronian Age.
Bookmarks Related papers MentionsView impact
Alcheringa: An Australasian Journal of Palaeontology, 1994
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The Early Triassic (late Induan to early Olenekian) Lingula borealis Bittner, from the Russkii Is... more The Early Triassic (late Induan to early Olenekian) Lingula borealis Bittner, from the Russkii
Island on the Pacific cost of south-eastern Russia is revised, based on re-examination of the type material.
Although this species, like most described Triassic lingulids, has remained very poorly understood due to
the lack of information on important characters, such as musculature and mantle canals, it has been commonly
recorded in subsequent studies and included in attempts at understanding the patterns of extinction
and recovery at around the Permian–Triassic boundary. Linguliform brachiopods are some of the notable
survivors of this significant mass extinction event. Lingula borealis has previously been referred to Lingularia
and provisionally synonymised with Lingularia similis Biernat & Emig. Here, it is shown that it
differs from Lingularia similis mainly in characters of mantle canals, musculature and most importantly
in details of the pedicle nerve impression. In Lingularia borealis, the impression of the pedicle nerve is
symmetrical and goes almost straight between the individual ventral umbonal muscle scars, whereas in
Lingularia similis it is asymmetrically positioned towards the smaller left component of the ventral umbonal
muscle scar. Shell structures and details of preserved ontogenies have also proven to be important
for the discrimination of lingulid taxa, but cannot be provided from the types of Lingularia borealis.
Bookmarks Related papers MentionsView impact
Despite many major advances in recent years, three key challenges remain in bringing clarity to t... more Despite many major advances in recent years, three key challenges remain in bringing clarity to the early history of the phylum: (1) identifying the origin, morphology and life modes of the first brachiopods; (2) understanding the relationships of the major groups to each other and higher sister taxa; and (3) unravelling the roles of the Cambrian and Ordovician radiations that set the agenda for much of subsequent brachiopod evolution. Since some 95% of all brachiopod taxa are extinct, the fossil record is the primary source of data to frame and test models for the evolution of the phylum. The acquisition of new, and the redescription of existing faunas, in precise spatial and temporal frameworks, using new and well-established analytical and investigative techniques, are as important as ever.
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Palaeogeography, Palaeoclimatology, Palaeoecology, 2011
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Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 2014
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This paper reviews the global biogeography and affinities of the Bradoriida, a group of Cambrian–... more This paper reviews the global biogeography and affinities of the Bradoriida, a group of Cambrian–early Ordovician arthropods. Bradoriida appear in the fossil record during the early Cambrian, just prior to the earliest trilobite faunas. Seven families may form a natural (monophyletic) group of Bradoriida sensu stricto, comprising Cambriidae, Kunmingellidae, Comptalutidae, Bradoriidae, Hipponicharionidae, Beyrichonidae and Svealutidae. Amongst the Bradoriida sensu lato, some forms that lie outside these families have carapace designs that suggest an ostracod affinity, particularly Altajanella and Vojbokalina. Bradoriida formed a major element of the 'Cambrian evolutionary fauna' and are components of the Chengjiang, Burgess Shale, and Buen Formation Lagerstätten. Bradoriida achieved global distribution from the Atdabanian (early Cambrian). Their diversity peaked during the early and middle Cambrian, with highest diversity at the species and genus level amongst the palaeo-tropical faunas of the South China (17 genera) and east Gondwana palaeocontinental regions (23 genera). By contrast Laurentian faunas were of much lower diversity (10 genera for the whole Cambrian). Bradoriid diversity declined rapidly from the latest middle Cambrian, a trend that may be related to the major extinction of trilobites at the base of the late Cambrian. The youngest Bradoriida comprise a few, rare Ordovician forms. Bradoriids appear to have occupied well-oxygenated marine shelf facies. The biogeographical patterns of early and middle Cambrian Bradoriida suggest climatic control on their distribution (temperate and tropical faunas), together with palaeogeographical constraints that also reflect trilobite provinciality. Kunmingellids and comptalutids were restricted to palaeo-tropical/subtropical sites, but migrated between South China, Siberia and eastern Gondwana palaeocontinents. They are absent from the mid-and high latitude faunas of the western Gondwana, Avalonia and Baltica palaeocontinental areas that were dominated by hipponicharionids, beyrichonids and Bradoriidae. The Laurentia palaeocontinent was isolated from the main zones of bradoriid diversity, but its faunas include a number of early and middle Cambrian Bradoriidae (Indota, Bradoria, Walcottella), and the region was colonised by cosmopolitan cambriids during the early Cambrian and by supposed pelagic svealutids (Liangshanella and Anabarochilina) during the middle Cambrian. The genera Walcottella, Dielymella and Bullaluta were endemic to Laurentia. One species of Anabarochilina that possibly dwelt near the sea-surface achieved an equatorial to high southern latitude (70° S) distribution during the late middle Cambrian (Lejopyge laevigata Biozone), perhaps reflecting a reduced latitudinal temperature gradient for near surface ocean waters.
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The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions w... more The Tremadocian (Early Ordovician) is currently considered a time span of greenhouse conditions with tropical water surface temperature estimates, interpolated from oxygen isotopes, approaching 40°C. In the high-latitude Baltoscandian Basin, these data are in contrast with the discovery of glendonite, a pseudomorph of ikaite (CaCO3•6H2O) and valuable indicator of near-freezing bottom-water conditions. The massive precipitation of this climatically sensitive mineral is associated with transgressive conditions and high organic productivity. Surprisingly, the precipitation of glendonite is contemporaneous with the record of conodonts displaying low δ18O values, which would suggest high temperatures (>40°C) in the water column. Therefore, the early Tremadocian sediments of Baltoscandia contain both “greenhouse” pelagic signals and near-freezing substrate indicators. This apparent paradox suggests both the influence of isotopically depleted freshwater yielded by fluvial systems, and the onset of sharp thermal stratification patterns in a semi-closed basin, which should have played an important role in moderating subpolar climates and reducing latitudinal gradients.
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