Showing papers by "Margaret E. Collinson published in 2013"

Terrestrial cooling in Northern Europe during the Eocene–Oligocene transition

Abstract: Geochemical and modeling studies suggest that the transition from the “greenhouse” state of the Late Eocene to the “icehouse” conditions of the Oligocene 34–33.5 Ma was triggered by a reduction of atmospheric pCO2 that enabled the rapid buildup of a permanent ice sheet on the Antarctic continent. Marine records show that the drop in pCO2 during this interval was accompanied by a significant decline in high-latitude sea surface and deep ocean temperature and enhanced seasonality in middle and high latitudes. However, terrestrial records of this climate transition show heterogeneous responses to changing pCO2 and ocean temperatures, with some records showing a significant time lag in the temperature response to declining pCO2. We measured the Δ47 of aragonite shells of the freshwater gastropod Viviparus lentus from the Solent Group, Hampshire Basin, United Kingdom, to reconstruct terrestrial temperature and hydrologic change in the North Atlantic region during the Eocene–Oligocene transition. Our data show a decrease in growing-season surface water temperatures (∼10 °C) during the Eocene–Oligocene transition, corresponding to an average decrease in mean annual air temperature of ∼4–6 °C from the Late Eocene to Early Oligocene. The magnitude of cooling is similar to observed decreases in North Atlantic sea surface temperature over this interval and occurs during major glacial expansion. This suggests a close linkage between atmospheric carbon dioxide concentrations, Northern Hemisphere temperature, and expansion of the Antarctic ice sheets.

New Observations and Synthesis of Paleogene Heterosporous Water Ferns

Abstract: Premise of research. Reproductive structures of modern genera of heterosporous water ferns (Marsileaceae and Salviniaceae) are widespread and abundant in plant mesofossil assemblages from the Paleogene. For Salviniaceae, whole fertile fossil plants give a good understanding of morphology. These fossils can be applied in paleoenvironmental analysis and to study water fern origin, evolution, and diversification.Methodology. New specimens were examined by SEM and TEM. Synchrotron x-ray tomographic microscopy (SRXTM) is evaluated as a nondestructive tool for investigating Azolla Lam. morphology.Pivotal results. Azolla anglica Martin and Salvinia cobhamii Martin (earliest Eocene, United Kingdom) are fully characterized using SEM and TEM. SRXTM enables digital rendering of the float system in Azolla, but individual floats are difficult to distinguish. Modern water fern genera characterize the Paleogene, but extinct sister taxa characterize the Cretaceous. Literature review documents that water ferns are intoler...

Did fire play a role in formation of dinosaur-rich deposits? An example from the Late Cretaceous of Canada

Abstract: The mid-late Campanian Dinosaur Park Formation outcropping within Dinosaur Provincial Park, Alberta, Canada, contains multiple dinosaur deposits occurring as bone beds, articulated skeletons, isolated bones and microvertebrate deposits. Due to the abundance of dinosaur deposits, the exposure of Cretaceous sediments, and the presence of charcoal, this locality acts as a good test site for investigating the implications of fire-impacted landscapes for the formation of vertebrate deposits. Despite prior palaeontological and geological research being carried out into this Formation, the presence of charcoal in vertebrate deposits has never previously been recorded. This study compares charcoal content in vertebrate deposits (two bone beds, two beds with articulated skeletons), 6 sediment samples with isolated bones and 23 sediments with no bone. Charcoal is more abundant in the vertebrate deposits than in sediments containing isolated bones or no bones, including those in identical lithofacies. This evidence suggests that flooding events following wildfires are likely to have played a role in the formation of some vertebrate deposits.

The Flora of the Insect Limestone (latest Eocene) from the Isle of Wight, southern England

Abstract: Latest Eocene fossil plant remains occur in concentrations within blue-grey micrite known as Insect Limestone near the base of the Bembridge Marls Member (Bouldnor Formation, Solent Group), Isle of Wight, southern England. Some of the previously reported taxa (collections in the Natural History Museum, London) are not preserved within the Insect Limestone. These (e.g., all Arecaceae (palms)) are excluded from the floral list. New non-destructive techniques have yielded additional taxonomic information. Leaves previously assigned to Ficus and Fagus are now incertae sedis. Wetland elements are abundant, particularly Typha, but also Acrostichum, Azolla, Potamogeton, Sparganium and others. Non-wetland elements are rare. Trees and shrubs included representatives of Betulaceae, Caprifoliaceae, Juglandaceae, Lauraceae, Rhamnaceae (the sclerophyllous Zizyphus), other flowering plants and several genera of conifers. There are rare specimens of possible herbaceous plants and propagules with plumes or awns, the latter possibly an early fossil record of Clematis. The common plant remains were probably derived from vegetation near a freshwater body, sometimes with slight brackish influence, whilst rarer elements were probably blown in from a greater distance. There is little evidence of plant–insect interaction; one leaf with small galls, a stem containing an insect larva and a possible association between stratiomyid flies and Typha.

Un curieux microfossile de la Molasse oligocène de Suisse occidentale et de Haute-Savoie (France)

Abstract: Nouvelle description de l’incertae sedis Calcicarpinum? fallax. Determination de son âge oligocene superieur et de sa repartition biogeographique. Il s’agit d’un nucule de Boraginaceae desormais nomme Boraginocarpus fallax (Taugourdeau-Lantz & Rosset 1966) comb. nov.