Geochemical analysis of source area and climate changes in two fluvial members with bimodal net: gross
University of Wyoming, Department of Geology and Geophysics Laramie, WY, USA
This project will use geochemical analysis to determine if changes in climate and source area were the cause of an abrupt change in channel stacking pattern in the Salt Wash and Brushy members of the Morrison Formation in southeastern Utah and western Colorado. The boundary between the two members is marked by an abrupt change in channel stacking, with the Salt Wash having a higher net:gross than the overlying Brushy Basin.
Samples have been taken from cores and fieldwork, representing three points at varying distance from the source area. Ongoing research will analyze the sample composition using ICP-OES and XRF to determine if there are differences between the two members and spatial trends. Paleoprecipitation trends will be evaluated using a chemical index of alteration minus potassium (CIA-K), which quantifies base loss in paleosol B horizons. Clay mineralogy will also be used as a proxy for paleoprecipitation. The CIA-K of unaltered C horizons will be examined as an indicator of source area and compared with B horizons. If B horizon base loss increases upsection, this would suggest a wetter climate produced more muds in the Brushy Basin. A decrease in C horizon base loss upsection would suggest an increase in volcanic activity caused the change in net:gross, and the muds originated as volcanic ash.
AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects