Full Title: Clay Water Diagenesis during Burial: How Mud Becomes Gneiss
Authors: Charles E. Weaver and Kevin C. Beck
From the original introduction: It has been noted by a number of people that montmorillonite-rich clays tend to lose their ability to expand with depth. It has been concluded that montmorillonite alters to illite with depth. Little data, other than X-ray analysis, is available. The nature of the clay minerals, chemical changes, and mechanisms responsible for the changes are speculative. There is little or no data on the chemistry of the interstitial water and the exchangeable cation in deeply buried clays. The relation between the porewater chemistry of muds and sandstones is inferred almost entirely from sandstone data. The mechanism of clay compaction, dewatering, and fluid pressure is not well understood. In order to obtain additional data on these problems and hopefully some answers, a series of sidewall cores of muds and silty muds was obtained from a deep well in the South Pass Area of Louisiana. The cores and information about the well were kindly supplied by the Chevron Oil Company. Supplemental information from Gulf Coast and Paleozoic sediments is based on data acquired by the senior author while employed by the Shell Oil Company. The samples from the Chevron well range in depth from 4233 ft to 16,450 ft. The top of the Pliocene is at approximately 4000 ft and the top of the Miocene approximately 9000 ft. The well bottomed in the upper Miocene. Chevron paleontologists report that the depositional environments systematically increase from inner neritic at 4233 ft to outer neritic at 9100 ft. All deeper samples indicate a bathyal environment. There is a marked increase in numbers of tests of deep-water benthonics from 10,930 ft to total depth. Abnormally high fluid pressures were encountered at 10,230 ft and continued to total depth.
Published: 10/15/1971
ISBN Number: 0813721342
Pages: 106
Product Category: EBooks