Ben Creisler
Some new dino-related papers:
Nora Noffke, James Hagadorn & Sam Bartlett (2019)
Microbial structures and dinosaur trackways from a Cretaceous coastal environment (Dakota Group, Colorado, U.S.A.).
Journal of Sedimentary Research 89 (11): 1096-1108
DOI:
https://doi.org/10.2110/jsr.2019.57https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/89/11/1096/575262/Microbial-structures-and-dinosaur-trackways-from-a Microbially induced sedimentary structures may help preserve unique glimpses of ancient shoreline habitats, but are little known from Mesozoic epicontinental settings. To help fill this knowledge gap, we describe a diverse suite of microbial structures from the Upper Cretaceous "J" Sandstone (South Platte Formation, Dakota Group) that are spectacularly exposed at Dinosaur Ridge in Morrison, Colorado, USA. Structures include "tattered" bed surfaces and ferruginous sand chips in supratidal flat facies. A large over-flip structure is preserved in a channel locally known as Crocodile Creek. In upper-intertidal facies, multidirectional ripple marks occur. Perhaps the most well-known microbial structures are exposed on extensive bedding surfaces known as "Slimy Beach," where lower supratidal-flat facies are dominated by decimeter-scale erosional remnants and pockets. Morphologies and superposition of the structures allows identification of three generations of erosional pockets. Generation A of these erosional pockets exhibit size similarities to ornithomimid, sauropod, and ornithopod dinosaur tracks from adjacent bedding planes, raising the question of whether initial disturbance of the mat-bound surface could have been from track making. Generation B erosional pockets are older and record continuous erosion of the initial pockets until they were eventually overgrown and sealed by microbial mats. Generation C pockets are the oldest ones, exposing wide areas of barren sediment that could not be overgrown by microbial mats anymore. In concert, the microbial structures point to seasonally variable meteorological conditions along the coastline of the Western Interior Seaway and indicate that the "Slimy Beach" bedding plane represents a multi-year record of dinosaur locomotion.
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How large must an extraterrestrial impact be to cause a peak episode of increased extinctions of life? Impact energies â 3âÃâ107 Mt TNT (associated with terrestrial impact craters with final diameters â 100âkm) seem to be required to generate significant widespread climatic effects from sub-micron dust and soot in the atmosphere, leading to a distinct extinction episode (â 15% extinction of marine genera). Impacts creating craters smaller than ~100âkm in final diameter (in the 106 to 107 Mt TNT range) are capable of mostly regional destruction, with minimal impact on global climate or biota. These results are supported by the fact that the ages of the four known â 100-km diameter craters of the last 260 My (Popigai, Chicxulub, Morokweng, and Manicouagan) are all correlative with times of documented extinction episodes, whereas smaller craters are not. The largest crater, the 180âkm diameter Chicxulub crater (a ~108 Mt TNT event) is associated with the more severe "major" mass-extinction event (â 45% extinction of genera) at the end of the Cretaceous.
The percent species extinctions show a significant linear relationship with final crater diameter and impact energy. The very large Chicxulub impact lies close to the predicted curve of percent extinction versus impact-crater diameter (and energy), but the low-angle of impact, an unusual composition of the target area (with thick sediments rich in carbonates, sulfates and organic material), and a large excavated transient crater, may have led to the generation of unusually large amounts of CO2, widely distributed dust, soot and sulfate aerosols, and a uniquely severe impact-related environmental disaster. Chicxulub may thus be the only large-body impact associated with a "major" mass extinction in the Phanerozoic. Target sensitivity may apply to large impacts into ocean crust having only a thin cover of organic-poor and carbonate-poor pelagic sediments, and thus even large oceanic impacts (which are still unknown) may not produce enough dust, soot and aerosols to cause environmental crises leading to global extinction peaks above background levels.
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Chris Mays, Vivi Vajda, Tracy D. Frank, Christopher R. Fielding, Robert S. Nicoll, Allen P. Tevyaw & Stephen McLoughlin (2019)
Refined PermianâTriassic floristic timeline reveals early collapse and delayed recovery of south polar terrestrial ecosystems.
Geological Society of America ÂBulletin (advance online publication)
DOI:
https://doi.org/10.1130/B35355.1https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B35355.1/575264/Refined-Permian-Triassic-floristic-timeline The collapse of late Permian (Lopingian) Gondwanan floras, characterized by the extinction of glossopterid gymnosperms, heralded the end of one of the most enduring and extensive biomes in Earthâs history. The Sydney Basin, Australia, hosts a near-continuous, age-constrained succession of high southern paleolatitude (~65â75ÂS) terrestrial strata spanning the end-Permian extinction (EPE) interval. Sedimentological, stable carbon isotopic, palynological, and macrofloral data were collected from two cored coal-exploration wells and correlated. Six palynostratigraphic zones, supported by ordination analyses, were identified within the uppermost Permian to Lower Triassic succession, corresponding to discrete vegetation stages before, during, and after the EPE interval. Collapse of the glossopterid biome marked the onset of the terrestrial EPE and may have significantly predated the marine mass extinctions and conodont-defined PermianâTriassic Boundary. Apart from extinction of the dominant Permian plant taxa, the EPE was characterized by a reduction in primary productivity, and the immediate aftermath was marked by high abundances of opportunistic fungi, algae, and ferns. This transition is coeval with the onset of a gradual global decrease in Î13Corg and the primary extrusive phase of Siberian Traps Large Igneous Province magmatism. The dominant gymnosperm groups of the Gondwanan Mesozoic (peltasperms, conifers, and corystosperms) all appeared soon after the collapse but remained rare throughout the immediate post-EPE succession. Faltering recovery was due to a succession of rapid and severe climatic stressors until at least the late Early Triassic. Immediately prior to the SmithianâSpathian boundary (ca. 249 Ma), indices of increased weathering, thick redbeds, and abundant pleuromeian lycophytes likely signify marked climate change and intensification of the Gondwanan monsoon climate system. This is the first record of the SmithianâSpathian floral overturn event in high southern latitudes.
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