Micropaleontology and Mineralogy of a Tertiary Sediment Core from the Sigsbee Knolls, Gulf of Mexico

摘要

The Sigsbee knolls are deep-sea hills which rise as much as 300 meters from the flat floor of the Sigsbee abyssal plain in the Gulf of Mexico. Although they are a favored coring site, only one core interpreted to contain pre-Pleistocene sediments has been obtained from their flanks. Studies of the calcareous nannoplankton and planktonic foraminifera in this core, number 64-A-9-5E, indicate that it contains sediments of Miocene, Pliocene, and Recent ages. The compressed nature of the stratigraphic section and the presence of authigenic minerals point to a very low sediment accumulation rate, roughly estimated to be about 1 mm per 1000 years. The low rate is interpreted to be due to accumulation on a topographic high which existed prior to the Middle Miocene. However, water content of five samples from the core averages 38% of wet weight and may be indicative of previous burial of these sediments at a depth of several tens of meters below the sediment-water interface. Two possible explanations of this apparent contradiction are discussed. Analysis of the depth ranges of the benthonic foraminifera suggests that the sediments were deposited in at least 1000 meters of water and provides further evidence of the invalidity of the hypothesis of Pleistocene-Recent downfaulting of the Gulf of Mexico. (Author)