The lower Permian(Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial plain.Locally,mudstones display a ...The lower Permian(Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial plain.Locally,mudstones display a variety of pedogenic features.Common mudstone fabrics vary from platy to prismatic;some beds display prominent pedogenic slickensides.Drab-colored root traces are common throughout the section,as are calcareous nodules,which vary from small bodies with diffuse boundaries to vertically stacked,discrete,cm-scale nodules(rhizocretions),and less commonly form coalescing horizons.Vertisols occur only in the lower portion of the ca.90-m measured section.Most of the mudstone beds contain calcretes that are immature(calcic Protosols to calcic Argillisols),but the lower to middle portion of the section also contains mature calcrete horizons(argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces,are of laterally variable thickness and grade to nodular calcretes.These are interpreted as floodplain pond carbonates that have undergone pedogenic alteration(palustrine limestones),indicating long periods of exposure under strongly seasonal climatic conditions.The isotopic composition of the pedogenic carbonate displays a substantial range of values,but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate(both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking(palustrine carbonate).During the early Permian,northern New Mexico was situated in a near equatorial position(ca.4° N).The overall character of the paleosols suggests a persistent warm,semi-humid,seasonal climate throughout most of the interval of deposition during the Wolfcampian,but with episodically increased aridity during formation of the more mature calcretes.No long-term trend of climate change is evident in the stratigraphic section examined for this study.展开更多
Gomphotheriid proboscideans reached South America as Late Cenozoic immigrants from North America. However, disagreements over alpha taxonomy, age dating and phylogenetic relationships have produced three competing hyp...Gomphotheriid proboscideans reached South America as Late Cenozoic immigrants from North America. However, disagreements over alpha taxonomy, age dating and phylogenetic relationships have produced three competing hypotheses about this immigration: (1) a single gomphothere immigration took place soon after the～3 Ma closure of the Panamanian isthmus; (2) two separate gomphothere immigrations took place after closure of the isthmus; or (3) an earlier, Late Miocene (before 9 Ma) immigration brought gomphotheres into South America. A critical re-evaluation of the alpha taxonomy, age dating and phyloge-netic relationships of Neotropical gomphotheres identifies two valid genera of South American gomphotheres, Cuvieronius and Notiomastodon (="Haplomastodon",="Stegomastodon" from South America) and recognizes "Amahuacatherium" as an invalid genus likely based on a specimen of Notiomastodon. The oldest well-dated South American gomphothere fossil is Marplatan, ～2.5 Ma, from Argentina. The case for an age of "Amahuacatherium" older than 9 Ma is refuted by mammalian biostratigraphy and a re-evaluation of the relevant magne-tostratigraphy. North American Rhynchotherium descended from Gomphotherium during the Late Hemphillian (～5-6 Ma) and gave rise to Cuvieronius in North America by the end of the Blancan (～2 Ma) time. Notiomastodon evolved from Cuvieronius in South America during the Pleistocene. The case for a close relationship between the Neotropical gomphotheres and Sinomastodon from China is rejected. Central America was not a center of endemic gompho-there evolution and merely acted as a pathway for the immigration of gomphotheres from north to south: Gomphotherium into Central America during the Miocene, Cuvieronius to Central America by Early Pleistocene time and on to South America. After closure of the Panamanian isthmus, Cuvieronius immigrated to South America, where it gave rise to Notiomastodon by Middle Pleistocene time. The South American history of gomphotheres was thus a modest evolutionary diversification from a single Plio-Pleistocene immigration.展开更多
The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctio...The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates（amphibians and reptiles）, though some workers advocate a sudden endTriassic（TJB） extinction of land plants. Nevertheless, an extensive literature does not identify a major extinction of land plants at the TJB, and a comprehensive review of palynological records concluded that TJB vegetation changes were non-uniform（different changes in different places）, not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP（Central Atlantic Magmatic Province） eruptions, which caused significant environmental perturbations（cooling, warming, acidification） through outgassing, but the effects on the nonmarine biota appear to have been localized, transient and not catastrophic. Long-term changes in the terrestrial biota across the TJB are complex,diachronous and likely climate driven evolutionary changes in the context of fluctuating background extinction rates, not a single, sudden or mass extinction.展开更多
Permian charophytes are known from the Ukraine, Russia, Kazakhstan, Germany, Saudi Arabia, China, the USA, Brazil, Paraguay and India. Most of these records are of Middle- Late Permian Age and are the basis of local b...Permian charophytes are known from the Ukraine, Russia, Kazakhstan, Germany, Saudi Arabia, China, the USA, Brazil, Paraguay and India. Most of these records are of Middle- Late Permian Age and are the basis of local biostratigraphic zonation in southern Russia and China. Development of a robust Permian charophyte biostratigraphy will require a more extensive record. Triassic charopbytes are known from Germany, Sweden, Poland, Slovenia, Bulgaria, the Ukraine, Russia, Morocco, Congo, the USA, Argentina, Kazakhstan and China. This encompasses records from all Triassic stages and has been the basis of detailed biostratigraphic zonation in southern Russia-Kazakhstan-eastern Europe. Permian and Triassic charophyte biostratigraphy at the level of genus does not provide detailed correlations beyond local or regional schemes. Nevertheless, it does identify some important evolutionary datums that constrain the timing of important biotic events in the Permian-Triassic evolutionary history of the Charophyta, including： （1） Early Permian extinction of the Palaeocharaceae; （2） Late Permian extinction of the ＂Trochiliscales＂ （Moellerinales）; （3） Carboniferous origin of the paraphyletic Porocharaceae, soon followed during the Permian by the origin of the multicellular basal plate; and （4） an important generic turnover of charophytes across the Triassic-Jurassic boundary, though there are insufficient data to identify this as a mass extinction.展开更多
文摘The lower Permian(Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial plain.Locally,mudstones display a variety of pedogenic features.Common mudstone fabrics vary from platy to prismatic;some beds display prominent pedogenic slickensides.Drab-colored root traces are common throughout the section,as are calcareous nodules,which vary from small bodies with diffuse boundaries to vertically stacked,discrete,cm-scale nodules(rhizocretions),and less commonly form coalescing horizons.Vertisols occur only in the lower portion of the ca.90-m measured section.Most of the mudstone beds contain calcretes that are immature(calcic Protosols to calcic Argillisols),but the lower to middle portion of the section also contains mature calcrete horizons(argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces,are of laterally variable thickness and grade to nodular calcretes.These are interpreted as floodplain pond carbonates that have undergone pedogenic alteration(palustrine limestones),indicating long periods of exposure under strongly seasonal climatic conditions.The isotopic composition of the pedogenic carbonate displays a substantial range of values,but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate(both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking(palustrine carbonate).During the early Permian,northern New Mexico was situated in a near equatorial position(ca.4° N).The overall character of the paleosols suggests a persistent warm,semi-humid,seasonal climate throughout most of the interval of deposition during the Wolfcampian,but with episodically increased aridity during formation of the more mature calcretes.No long-term trend of climate change is evident in the stratigraphic section examined for this study.
文摘Gomphotheriid proboscideans reached South America as Late Cenozoic immigrants from North America. However, disagreements over alpha taxonomy, age dating and phylogenetic relationships have produced three competing hypotheses about this immigration: (1) a single gomphothere immigration took place soon after the～3 Ma closure of the Panamanian isthmus; (2) two separate gomphothere immigrations took place after closure of the isthmus; or (3) an earlier, Late Miocene (before 9 Ma) immigration brought gomphotheres into South America. A critical re-evaluation of the alpha taxonomy, age dating and phyloge-netic relationships of Neotropical gomphotheres identifies two valid genera of South American gomphotheres, Cuvieronius and Notiomastodon (="Haplomastodon",="Stegomastodon" from South America) and recognizes "Amahuacatherium" as an invalid genus likely based on a specimen of Notiomastodon. The oldest well-dated South American gomphothere fossil is Marplatan, ～2.5 Ma, from Argentina. The case for an age of "Amahuacatherium" older than 9 Ma is refuted by mammalian biostratigraphy and a re-evaluation of the relevant magne-tostratigraphy. North American Rhynchotherium descended from Gomphotherium during the Late Hemphillian (～5-6 Ma) and gave rise to Cuvieronius in North America by the end of the Blancan (～2 Ma) time. Notiomastodon evolved from Cuvieronius in South America during the Pleistocene. The case for a close relationship between the Neotropical gomphotheres and Sinomastodon from China is rejected. Central America was not a center of endemic gompho-there evolution and merely acted as a pathway for the immigration of gomphotheres from north to south: Gomphotherium into Central America during the Miocene, Cuvieronius to Central America by Early Pleistocene time and on to South America. After closure of the Panamanian isthmus, Cuvieronius immigrated to South America, where it gave rise to Notiomastodon by Middle Pleistocene time. The South American history of gomphotheres was thus a modest evolutionary diversification from a single Plio-Pleistocene immigration.
文摘The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates（amphibians and reptiles）, though some workers advocate a sudden endTriassic（TJB） extinction of land plants. Nevertheless, an extensive literature does not identify a major extinction of land plants at the TJB, and a comprehensive review of palynological records concluded that TJB vegetation changes were non-uniform（different changes in different places）, not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP（Central Atlantic Magmatic Province） eruptions, which caused significant environmental perturbations（cooling, warming, acidification） through outgassing, but the effects on the nonmarine biota appear to have been localized, transient and not catastrophic. Long-term changes in the terrestrial biota across the TJB are complex,diachronous and likely climate driven evolutionary changes in the context of fluctuating background extinction rates, not a single, sudden or mass extinction.
文摘Permian charophytes are known from the Ukraine, Russia, Kazakhstan, Germany, Saudi Arabia, China, the USA, Brazil, Paraguay and India. Most of these records are of Middle- Late Permian Age and are the basis of local biostratigraphic zonation in southern Russia and China. Development of a robust Permian charophyte biostratigraphy will require a more extensive record. Triassic charopbytes are known from Germany, Sweden, Poland, Slovenia, Bulgaria, the Ukraine, Russia, Morocco, Congo, the USA, Argentina, Kazakhstan and China. This encompasses records from all Triassic stages and has been the basis of detailed biostratigraphic zonation in southern Russia-Kazakhstan-eastern Europe. Permian and Triassic charophyte biostratigraphy at the level of genus does not provide detailed correlations beyond local or regional schemes. Nevertheless, it does identify some important evolutionary datums that constrain the timing of important biotic events in the Permian-Triassic evolutionary history of the Charophyta, including： （1） Early Permian extinction of the Palaeocharaceae; （2） Late Permian extinction of the ＂Trochiliscales＂ （Moellerinales）; （3） Carboniferous origin of the paraphyletic Porocharaceae, soon followed during the Permian by the origin of the multicellular basal plate; and （4） an important generic turnover of charophytes across the Triassic-Jurassic boundary, though there are insufficient data to identify this as a mass extinction.
