The Stratigraphic and Geomorphic Evolution of the Bull Creek Valley, Oklahoma: Implications for Paleoclimate Studies and Nanodiamond Occurrence.

摘要

The Younger Dryas is a well-recognized climatic event, but researchers have yet to agree upon which mechanism was responsible for the rapid cooling in the northern hemisphere. A spike in nanodiamond presence at the Younger Dryas boundary has been reported in sediments from the Bull Creek valley in Oklahoma and used to support a recently proposed impact hypothesis. However, this record was compiled from a heterogeneous mix of sediment from different fluvial subenvironments. In order for the significance of a unique occurrence of nanodiamonds to be determined, a full appreciation of the other changes that occurred within the valley throughout its evolution must be taken into account. These changes may have impacted sediment character as well as sediment preservation and the processes governing deposition, all of which could impact nanodiamond accumulation and preservation.;The purpose of this study is to build an evolutionary model for the Bull Creek valley spanning the last 16,000 years in order to place nanodiamond occurrence into stratigraphic context. Fluvial terraces were mapped and their sediments described within the valley. Results indicate the valley has undergone at least four cycles of cutting and filling, creating five sets of discontinuous fluvial terraces. The sedimentary sequence preserved in the terraces records the transition from a perennial fluvial system during the late glacial to a cool yet dry environment during the Younger Dryas, followed by an arid environment dominated by eolian processes and punctuated by flooding events. Although the sediment character of the Younger Dryas soil is unique, the occurrence of nanodiamonds within it is not. No correlation was found between nanodiamond abundance and landscape exposure time.