Bioclimatic analysis of rodent palaeofaunas reveals severe climatic changes in Southwestern Europe during the Plio-Pleistocene
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Plio-Pleistocene
Paleoclimatology
Early Pleistocene
Peninsula
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Stable oxygen and carbon isotope profiles from fossil scallop shells provide detailed paleoenvironmental information for the Pliocene and early Pleistocene of the Middle Atlantic Coastal Plain. Scallop specimens were collected from strata which represent at least five major marine transgressions. Minimum and maximum paleotemperatures were calculated from the {delta}{sup 18}O ranges recorded in each shell profile, after adjusting for changes in seawater {delta}{sup 18}O related to changes in global ice volume. Paleotemperature ranges from each stratigraphic unit were compared with modern conditions on the shelves of the Middle and South Atlantic Bight, and with paleotemperatures estimated by Hazel (1971b, 1988) from the ostracode faunas. The mollusk-isotope records indicate that the marine climate of the Atlantic Shelf was mild temperate during the deposition of the Sunken Meadow Member of the Yorktown Formation in the early Pliocene. The climate became warm temperate during the middle and late Pliocene transgressions which deposited the Rushmere, Morgarts Beach and Moore House Members of the Yorktown Formation and the Chowan River Formation. During the deposition of the James City Formation in the early Pleistocene, temperatures returned to a mild temperate climate similar to that of the modern Virginia Bight shelf. The character of the isotope profilesmore » indicates that hydrographic conditions were generally stable and similar to those of the modern Middle Atlantic Bight. The {delta}{sup 13}C profiles of most of the shells show trends suggestive of spring phytoplankton blooms and summer water-column stratification. Anomalies in several profiles are interpreted as reduced salinity events, probably related to river discharge, which most commonly occur in the spring. There is no convincing evidence in the shell profiles for upwelling.« less
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The Musselshell Creek flora (12.0-10.5 Ma) of northern Idaho is used to reconstruct paleoclimatic and paleoecologic parameters of the Pacific Northwest during the late Middle Miocene. Other megafossil and microfossil floral records spanning 12.0-6.4 Ma are unknown from this region. The Musselshell Creek fossil flora, previously undescribed, is preserved in lacustrine clays and sediments that accumulated in a narrow valley surrounded by rugged terrain. Dominant taxa include dicotyledons and conifers. Most of the leaves are preserved as impressions or compressions. Some fossil leaves retained their original pigmentation, cellular anatomy, and organic constituents. Other fossils include excellent remains of pollen and spores, dispersed leaf cuticle, pyritized wood, and disarticulated fish bones. A destructive statistical analysis of one block of sediment, approximately 30 cm x 45 cm (1.5 sq. ft) recovered 14 orders, 23 families, and 34 genera of spermatophyte plant fossils. These floral elements are compared with two other earlier Miocene floras which were similarly sampled. Common megafossil genera include Quercus, Zizyphoides, Taxodium, Alnus, Castanea, Magnolia, Acer, Exbucklandia, Sequoia, Populus, and Betula. The rare occurrence of Ginkgo leaves is a first record of this taxon in the Idaho Miocene. Additional plant taxa are represented by palynomorphs. Common pollen taxa are Pinus, Abies, Carya, Quercus, and Tilia. Most of the megafossil and microfossil flora assemblage is characteristic of a streambank to floodplain environment that existed in a warm to cool temperate climate similar to the modern Mid-Atlantic coast of the United States.
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The late Miocene was a critical time in the development of the North American Great Plains marked by paleoclimate-driven biotic change, including faunal turnovers and the spread of C4 dominated grasslands. The large volume of sediment shed from the Rocky Mountain region during this time preserves a record of these transitions, which can be informed by previously undescribed paleosol and trace fossil properties from the Ogallala Formation of the central High Plains. The purpose of this paper is to reconstruct paleoenvironments, paleoclimate, and paleoecology from outcrops of the Ogallala Formation in western Kansas by integrating paleopedology, ichnology, and stable isotope geochemistry. Eleven lithofacies are recognized in the study area, mostly massive to crudely stratified, fine-to coarse-grained sandstone and pebbly gravel with stratigraphically uncommon fine-grained lithofacies restricted to thinly bedded intervals or lens-shaped geometries within the sand-dominated strata. These host five pedotypes: 1) calcic Vertisols developed on overbank fines, 2) Entisols developed on braid bar gravels, 3) Entisols developed on volcaniclastic sediment lenses, 4) calcic Inceptisols developed on coarse sandy channel fills, and 5) calcareous Mollisols developed on fine sandy bedforms and channel fills. We recognize ten ichnogenera within paleosols, including burrows attributed to ants, bees, beetles or hemipterans, vinegarroon-like arthropods, fossorial reptiles, seed caching mammals, and large carnivorous mammals. Organic carbon stable isotopes indicate that the flora consisted entirely of C3 plants, and paleosols and trace-fossil evidence suggest a tree-limited savanna environment with patches of unvegetated soil. Paleoclimate proxies from paleosol and trace fossil properties indicate mean annual air temperatures between 8 °C and 20 °C with seasonal differences of up to 14 °C between mean monthly temperatures of the warmest and coolest months. Mean annual precipitation was likely between 250 mm and 460 mm with a seasonal difference of up to 250 mm between mean monthly precipitation of the driest and wettest months. While hymenopteran tracemakers were active, soil surface temperatures reached at least 30 °C and moisture content was between 10% and 20%. With timing of deposition constrained biostratigraphically to the Barstovian through Hemphillian, our paleoclimate interpretations are most consistent with the period of relative climate stability after Middle Miocene Climate Transition cooling and before Late Miocene Cooling (∼13.8 Ma–7 Ma). The trace-fossil assemblage reveals previously unknown biodiversity among soil arthropods, as well as important trophic connections between the belowground and aboveground components of the terrestrial food web.
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