Carboniferous Sediments from Sigsbee Knolls, Gulf of Mexico: GEOLOGICAL NOTES

Abstract

A violet siltstone determined by K-Ar methods to be Carboniferous (318 × 106 years old) was dredged from one of the Sigsbee Knolls in the southwest Gulf of Mexico. This is by far the oldest material ever recovered from the deep Gulf or any other oceanic basin. Analyses by atomic absorption spectrometry, X-ray diffraction, and electron microscopy reveal that the siltstone is composed primarily of quartz with lesser amounts of kaolinite, talc, and hematite. Glauconite, anatase, and rutile are present in trace amounts. The delicate lath work of the glauconite crystals indicates that this material was formed in place and is not detrital. In view of the geologic structure of the Sigsbee Knolls, it is probable that the siltstone was transported from the point of its formation to the knoll's surface by processes related to salt flow.