Sedimentation and mass physical properties of marine sediments, western Gulf of Mexico

Abstract

This study is an investigation of the mass physical properties of marine sediments from the western Gulf of Mexico. Sixty-one cores from the continental shelf, continental slope, and the abyssal plain were analyzed to provide the data. The physical properties of marine sediments may be divided into two broad categories: 1. Parameters which allow direct measurement of sediment shear strength. 2. Parameters which are referred to in this paper as index properties (porosity, grain size, plasticity index, mineralogy, and water content). The index properties give an indirect indication of sediment shear strength. Both types of parameters may also be used to describe and classify sedimentary deposits. Sediments from the continental slope and shelf in the western Gulf of Mexico were tested to determine the shear strength, stability, consolidation characteristics, and index properties. To approximate in situ conditions, a direct shear test machine was used to measure shear strength and an Anteus Back-Pressure Consolidometer was used to determine consolidation. Although the topography of parts of the continental slope has been attributed to local slumping of unconsolidated and unstable marine sediments, no evidence was found that indicated instability of sediments in the present environment. The Sabine River Delta samples are under consolidated in contrast to the continental shelf and slope samples which are overconsolidated. The overconsolidation of these samples and the high values of shear strength are assumed to be the results of low deposition rates and incipient cementation of the mineral grains. Evidence can be found which indicates that some of the sediments in the Campeche Canyon were deposited as the result of slumping and turbidity currents during the Pleistocene, however, test results show that the sediments are stable in the present environment. The abyssal plain sediments range from normally consolidated to underconsolidated and have low values of shear strength. There is evidence that the rate of deposition plays a role in the development of shear strength and the consolidation characteristics of these sediments. Carbonate content and volcanic debris also affect shear strength and consolidation.