Plasticity Characteristics of the Quaternary Sediments of the Guatemalan Continental Slope, Middle America Trench, and Cocos Plate—Leg 67, Deep Sea Drilling Project

Abstract

The plasticity characteristics of the Quaternary sediments of the Guatemalan continental margin were determined from five sites drilled during Leg 67 of the Deep Sea Drilling Project. The 64 samples analyzed are from various marine environments, including the Cocos Plate, Middle America Trench, and the trench lower slope to midslope of the Guatemalan continental slope. The sediments are primarily hemipelagic muds and trench-fill turbidites and include quantities of siliceous and calcareous biogenic components. The sediments are generally classified as organic clays of medium to high plasticity, containing micaceous sands and silts, with 14% classed as inorganic clays of medium to high plasticity. High sedimentation rates in Quaternary sediments are the result, in part, of sediment gravity flows that depend upon rheological properties, i.e., sediment plasticity. Mudflows and cohesive debris flows appear to be significant downslope transport mechanisms in these highly plastic sediments.

In-situ water contents, liquid limits, and submarine mass flows due to a high liquefaction potential of slope sediment (results from DSDP and subaerial counterparts)

“…The validity of Atterberg limits, determined on old sediment cores, was tested by resampling site 496, where the same investigation had previously been carried out (FAAS, 1982). Taking into account that (1) the method in itself is not very accurate and that (2) not exactly the same samples could be investigated, the results appear to be satisfactory (compare Fig.…”