Abstract
Two distinct sedimentary sections were drilled by the Deep Sea Drilling Project using the hydraulic piston core, and were subjected to geotechnical testing in an effort to document the physical changes related to sediment burial. Site 532, located on a flank of the Walvis Ridge off Southwestern Africa, drilled approximately 200 meters of hemipelagic carbonates of Recent to Pliocene age. Site 576, located in the Northwest Pacific, drilled nearly 55 meters of pelagic, red clay sediments before bottoming in Cretaceous calcareous ooze. Geotechnical testing of the sedimentary sections showed both sites to be primarily responding to the effects of mechanical compaction, or consolidation. The upper portion of both sediment columns is overconsolidated, following typical marine sediment behavior. However, Site 576 remains overconsolidated to a sub-bottom depth greater than 20 meters, possibly as a result of increased strength of the sediment formed by a fabric containing numerous clay aggregates. Sediments from the lower portions of both sections are normal to underconsolidated. The changing character of geotechnical properties with depth was used to construct a stratigraphic sub-division of the sediment columns to reflect intervals having different mechanical behavior or sedimentary history. This sub-division resulted in the geotechnical stratigraphic definition of both sites. Correlation of the geotechnical stratigraphic units to conventional stratigraphic divisions shows the value of relating the mechanical aspect of sediments to other features. Boundaries between geotechnical units are correlated to seismic reflectors and to contacts of lithostratigraphic and bio-chronostratigraphic units. Factors controlling most geotechnical variability at these sites are sediment composition and sedimentary hiatuses. Compositional changes at Site 532 reflect altering upwelling intensities, locus of upwelling, terrigenous input and biogenic composition of primary producers in the water column. The geotechnical stratigraphy of Site 576 is strongly correlated to widespread existing hiatuses and major changes of sediment source and supply rates. The chronostratigraphy at Site 576 is greatly enhanced by matching geotechnical stratigraphic contacts to dated events of hiatus maxima, refining biostratigraphic dating.
Taylor, Elliot (1984). Oceanic sedimentation and geotechnical stratigraphy : hemipelagic carbonates and red clays. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -409371.