Lower Eocene alluvial paleosols (Willwood Formation, Northwest Wyoming, U.S.A.) and their significance for paleoecology, paleoclimatology, and basin analysis

摘要: Abstract The lower Eocene Willwood Formation of northwest Wyoming is a 700 m thick accumulation alluvial floodplain and channel mudstones sandstones, nearly all which show paleopedogenic modifications. Pedogenesis sandstones indicated by taproot vertebrate invertebrate bioturbation, early local cementation calcium carbonate, thin illuviation cutans on clastic grains. in plant insect other burrow casts lebensspuren; free iron, aluminum, manganese mobilization, including hydromorphic gleying; sesquioxide calcareous glaebule formation parts the solum; presence clay-rich organic carbon-rich zones; well differentiated epipedons albic spodic horizons. Probable A horizons are also locally developed. Occurrence variegated paleosol units mudstone deposits their association with thin, lenticular, unconnected fluvial central southeast Bighorn Basin suggest that these soils formed during times rapid sediment accumulation. tabular geometry lateral persistence soil as absence catenization indicate floodplains were broad essentially featureless. All paleosols developed parent materials complex B younger commonly superimposed upon mask properties suspected next older paleosols. appear to be wet varieties Spodosol Entisol groups (aquods ferrods, aquents, respectively), though thick, superposed less mottled red, purple, yellow resemble some ultisols. Most warm temperate subtropical form today under alternating dry conditions (or) fluctuating water tables. up-section decrease frequency gley mottles, increase numerical proportion thickness red versus orange coloration, abundance calcrete glaebules better drained probably drier climate late time. This drying believed related creation rain shadows spacing rainfall (but not necessarily absolute rainfall) due progressive tectonic structural elevation mountainous margins Basin.