Analysis of deposition, erosion, and landscape stability during the late Quaternary using multi-proxy evidence from Owl Creek, Central Texas, USA.
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Meier, Holly A., 1979-
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Episodes of fluvial deposition and incision preserved in Quaternary sediments are valuable archives of environmental change, but have been understudied in low order streams in central Texas, USA. An exposure along Owl Creek a tributary of the Brazos River was examined using geological and pedological approaches, including stratigraphic and soil description and characterization. Eight stratigraphic units were identified, described, and constrained in time based on relative stratigraphy and optically stimulated luminescent (OSL) ranging in age from ~120 ka to <8 ka. Despite the dynamic nature of fluvial systems, the Owl Creek record has uniquely preserved sediment spanning the late Quaternary with major erosional events that may reflect the advance and retreat of the Laurentide ice sheet and the southward displacement of the jet stream and ensuing wetter conditions as recorded by regional climate proxies. Compilation of the proxies presented shows evidence for a cooler and wetter late Pleistocene climate, followed by a warmer and drier climate dominating during the Holocene. Regional proxies become more abundant into the Holocene with Owl Creek and other local stream preserving sediment of different ages and are likely responding to intrinsic variables. Buried soils formed in association with low-order tributary streams are valuable archives of past climates, but have not been studied extensively in central Texas, USA. Four buried soils exposed along Owl Creek, within the larger Brazos River drainage basin, were examined using soil morphology and micromorphology, optically stimulated luminescence (OSL) dating, soil characterization, whole-soil geochemical and stable isotope analyses of soil organic matter and pedogenic carbonate. These buried soils provide a record of changes in paleoecological and paleo-alluvial conditions spanning ~14 ky. Morphological and geochemical differences between buried soils reflect changes in landscape attributable to climate, with a distinct 5‰ increase in δ13C values of soil organic matter corresponding to the onset of drier conditions during the Holocene. Paleoecological reconstructions coupled with depth to Bk horizon suggest possible amounts of erosion of ~1 m for each of the buried soils.