Tracking organic carbon across the Cascadia Margin: Do the quantity and source of sedimentary organic carbon influence the distribution of gas hydrate?
Stephen C. Phillips
University of New Hampshire, Department of Earth Sciences Durham, New Hampshire, USA
Sedimentary total organic carbon (TOC) plays an important role in the occurrence and rate of methanogenesis in marine sediments and is one of several factors that ultimately influence the formation and accumulation of marine gas hydrate. I hypothesize that in accretionary wedge settings, as fan sediments are uplifted from the abyssal plain and draped with hemipelagic sediment, or eroded into slope basins, overall TOC should increase relative to the original pre-uplift sediments. In this setting, tectonic uplift would allow exported labile marine carbon from surface productivity to accumulate in an environment less diluted by turbidites. In this project, I will measure the TOC quantity and source across the Cascadia margin, using two transects of cores from Deep Sea Drilling Project Leg 18, and Ocean Drilling Program Legs 146 and 204. These two transects provide an ideal opportunity to investigate the fundamental depositional and post-depositional syntectonic evolution of TOC across the Vancouver Island and central Oregon margins where the gas hydrate distribution is well-understood. This work will provide an opportunity to use TOC measurements to predict where in this and other accretionary settings that methanogenesis is likely to flourish and thus have the potential to form and accumulate gas hydrate. I will use these data in conjunction with existing data from Integrated Ocean Drilling Program Expedition 311 to test whether TOC deposition and degradation history influences biogenic methane production, long term rates of AOM, and ultimately the known gas hydrate distribution along these two transects in the Cascadia accretionary wedge.
AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects