The origin of near-seafloor "crust zones" in deepwater

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Conference Proceeding

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In recent years, geotechnical site investigations for deepwater oil and gas developments have disclosed the presence of a thin "crust zone" of anomalous high strength immediately below the seabed in several deepwater regions around the world. The origin of the crust zone, however, has not been satisfactorily explained with conventional soil mechanics. The sediments within the crust do not have physical property values or definable trends in water content, density, plasticity and grain size distribution that explain why the crust exists. Previous marine biological studies have shown that biological activity or bioturbation affects geotechni-cal properties including soil shear strength. A variety of sedimentological and geochemical tests together with geotechnical tests were performed on cores recovered at two deepwater sites offshore Nigeria where a crust is present. This paper presents the test results that suggest that the "crust zone" is both a product of intense bio-turbation and early geochemical alteration of burrow walls and pelletized burrow fills. The paper begins with a literature review on the effects of biological activity on sediment physical properties. © 2005 Taylor & Francis Group.

Publication Source (Journal or Book title)

Frontiers in Offshore Geotechnics, ISFOG 2005 - Proceedings of the 1st International Symposium on Frontiers in Offshore Geotechnics

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