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ABSTRACT

A high resolution geochronology is possible in Plio-Pleistocene sediments of the outer continental shelf-slope of the Gulf of Mexico (GOM) and other marine basins using isotope chronostratigraphy. This study of Outer Continental Shelf (OCS) Well G-1267 No. A-1 from South Timbalier block 198 represents the first publication of specific δ18O stable isotope data from a GOM exploration well which compares the surface and bottom water signals from the same site. Forty seven (47) δ18O isotope stages are identified in the Plio-Pleistocene section of South Timbalier 198 when integrated with the available biostratigraphy. δ18O stages 24-27 and 48-60 are separated by a hiatuses from 0.9 Ma to 1.41 Ma. δ18O stages 60-104 are missing due to a hiatus from 1.75 Ma to 3.15 Ma. δ18O stages 104-133 are defined in the lower section of the well. This chronostratigraphy makes it possible to derive a detailed record of sediment accumulation rate changes. Comparison of the oxygen isotope records to the resistivity and SP logs reveals a relationship between sand deposition and sea level transgressions and lowstands. Power spectral analysis of the isotope records indicates that the frequencies defined by the Milankovitch orbital parameters are a dominant component of both the benthic and planktonic δ18O data sets. In addition, the benthic δ18O record provides evidence for entrainment of isotopically negative meltwater into bottom water turbidity or density flows as well as several rapid changes in paleobathymetry.

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