Geochemical and Sedimentary Record of Climate Change from the Paleocene-Eocene Colton and Green River Formations, Southwestern Uinta Basin, Utah
Past work in the southwestern Uinta Basin focused on the Paleocene-Eocene, fluvial-lacustrine, Colton/Wasatch and Green River Formations has resulted in detailed characterization of lithofacies, architecture, stacking patterns, and depositional and correlation models. However, the influence of global and regional climate change, specifically early Eocene hyperthermal events, on the deposition of this succession has not been evaluated. Preliminary geochemical analysis of bulk sedimentary organic matter from mudrock facies in the Colton/Wasatch and Lower to Middle Green River Formations reveals a predominant lacustrine organic matter source (indicated by Corg/Ntot ratios < 10) with δ13Corg values that vary considerably (min. = -28.5‰, max. = -19.8‰, avg. = -25.0‰). Stratigraphic variability in δ13Corg and mudrock mineralogy may reflect multiple early Eocene hyperthermal events that have been documented worldwide. This dataset supports the view that hyperthemal events were a recurring phenomenon during the early Eocene (e.g. Nicolo et al., 2007). The δ13Corg values stabilize at approximately -24.1‰ toward the top of the succession in the Middle Green River Formation, which we interpret as a return to more stable climate conditions. Furthermore, independent sedimentary examination of the same succession using measured sections and architectural analysis of extensive outcrop exposures of the Colton and Lower Green River Formations reveals distinct stratigraphic alternations between two types of alluvial system character and channel fill style, which we hypothesize to reflect the influence of two distinct climatic regimes on the fluvial system. These alternations broadly covary with climate changes documented from the geochemical record. However, further analysis is necessary to 1) confidently correlate the sedimentary and geochemical record, and 2) assess the ability to use the geochemical record as a chemostratigraphic correlation tool.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009