CLIMATE DRIVEN CHANGES IN RIVER CHANNEL MORPHOLOGY AND BASE LEVEL DURING THE HOLOCENE AND LATE PLEISTOCENE OF SOUTHEASTERN WEST VIRGINIA

摘要

Rivers commonly respond to climate change by aggrading or incising. This iswell documented for North American rivers in arid and proglacial regions, but is alsotrue of rivers in unglaciated, humid-temperate regions. Here, we present a record ofHolocene hydroclimatology for a humid, temperate watershed in the AppalachianMountains of eastern North America. We use stable isotope geochemistries of astalagmite and clastic cave sediments to reconstruct Holocene climate and ecology in theGreenbrier River catchment (3,600 km~2) of southeastern West Virginia. Independently,we use river-deposited cave sediments to construct a history of incision, aggradation, andmorphological change in the surface channel. The clastic cave deposits display enriched(less negative) values of sedimentary δ~(13)C_(org)during the Holocene Climatic Optimum(HCO), which regional pollen records indicate was warm compared to later climes. Theriver channel had aggraded by >4 m during or prior to the HCO and adopted an alluvialmorphology, probably due to the mobilization of hillslope sediments accumulated duringthe colder, drier full-glacial conditions of the Late Pleistocene. As climate moistenedduring the Holocene, the Greenbrier River incised through channel-filling sediments andback onto bedrock, but not until ~3,500 cal. years B.P. Therefore, the bedrockmorphology of many streams in the Appalachian Mountains may not have existed formuch of the Holocene, which highlights the effect of climate variability on channelprocesses. The base-level rise is more evidence that bedrock incision by rivers is oftenepisodic and that slow, long-term incision rates reported for Appalachian Rivers areprobably not representative of short-term incision rates.