Marine Studies Group Meeting 11 May, 1971 at 3.30 p.m.

Economic geology of shelf sediments. Chairman—Professor B. M. Funnell.

1. Geophysical identificatlon of shelfments D. M. McCann, Institute of Geological Sciences, and D. Taylor Smith, University College of North Wales.

A knowledge of the geotechnical properties of sea-floor sediments is becoming increasingly important for a variety of economic reasons. These range from the capability of the seafloor to support civil engineering installations, to its place as a source of detrital minerals. For direct economic reasons the important parameters seem to be the thickness and lateral extent of sediment and secondly the mean grain size and size distribution. For indirect economic reasons, such as civil engineering site investigations, information concerning porosity, bulk density, shear strength and settlement properties is also required.

By far the most successful methods for investigating the geology of the sea-floor are geo physical techniques. In particular, those based on acoustic sources and detectors, such as continuous seismic profiling, have yielded considerable information on the sub-bottom geology, including the thickness of sediment. Sea-floor topography is studied using precision echo-sounding and sidescan sonar and considerable research has been carried out into the identification of sediments based on the analysis of the reflected acoustic signals from the sea-floor. Measurement of the acoustical and electrical properties of sea-floor sediments, using in-situ probes, can provide additional information for comparative purposes, since definite relationships have been established between the geophysical and geotechnical properties of marine sediments.

The preparation of geotechnical maps of

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