Late Pleistocene-Holocene sedimentation surrounding an active seafloor gas-hydrate and cold-seep field on the Northern Gulf of Mexico Slope

摘要

A chronostratigraphic framework is constructed from sediments surrounding an active gas-hydrate and coldseep field, situated on the northern Gulf of Mexico slope within federal offshore lease block Mississippi Canyon 118 (MC118). Accelerator mass spectrometer (AMS) radiocarbon dating, foraminiferal biostratigraphy and nannofossil biostratigraphy are used to constrain the age of sediments from 10 gravity cores collected around the field. X-ray fluorescence (XRF) core scanning is employed to develop continuous down-core elemental profiles, which are used to evaluate biogenic calcium and siliciclastic titanium sediment inputs, and provide a means to correlate sediments across the study area and infer changes in sedimentation through time. Spatial reconstruction of sedimentation surrounding the field indicates the following: (1) a consistent pattern of stratigraphic thinning in close proximity to the field over the past 14,000 yrs and (2), temporal changes in sedimentation that primarily reflect deglacial sea-level rise as well as regional factors such as Mississippi delta lobe switching. These results highlight the variability of sedimentation along a continental slope setting where marine cold seeps and gas hydrate persist, yet do not suggest slope failure or destabilization of the seafloor at this site, at least during the past 14,000 yrs. The evaluation of sedimentation at this location provides an important context for ongoing biogeochemical and geophysical monitoring of the MC118 site, which has been designated the first National Gas Hydrate Seafloor Observatory by the Gulf of Mexico Hydrate Research Consortium.