Near-Bottom Observations of the Middle America Trench off Guatemala

Deep-tow data across the Middle America Trench and the lower part of the landward Trench slope off Guatemala provide high-resolution information on the geological setting of four Leg 67 drill sites. Our 6-kHz profiler data resolve stratified sediments seaward of the Trench floor, which we interpret as deposits of Trench turbidites that flowed part way up the seaward slope of the Trench. Reflectors in the Trench fill are laterally continuous and relatively undisturbed. The Trench is segmented into diamond-shaped basins by ridges that intersect it at oblique angles. The acoustic stratigraphy in the Trench fill in these sub-basins is different on either side of an oblique ridge. A mound of variable height and width occurs at the base of the lower Trench slope; the mound could be either deformed Trench strata or an accumulation of debris that slumped from the Trench slope. The lower part of the landward Trench slope is steep and is linear along strike. There is no evidence on our 6-kHz or side-scan sonar data of large gravity slides in this area. Slope sediments are ponded on a bench along the landward Trench slope. They are acoustically stratified, but are not as continuous laterally as are the Trench strata. The structure parallel to the strike of the Trench slope is variable, with many small-scale folds and faults