Abstract

The Middle America Trench is a tectonically unstable area in which sediments have accumulated rapidly. Sediments from the upper part of the continental flank are folded and faulted within a perched basin and impounded by a ridge at the outer part of the basin. Little sediment accumulates permanently on the continental flank seaward of this basin. Sediments from the seaward flank have more biogenous material due to a lower rate of terrigenous deposition.

Heavy minerals, coarse sands in the trench, facies similarities, displaced Foraminifera, and a textural gradation along the trench axis suggest that the sediments in the trench were deposited by turbidity currents. Carbon-14 dates indicate sedimentation rates as high as 146cm/1000 yrs in the trench bottom. Assuming constant conditions, the sediments found in the trench bottom would have taken only 4.5 × 106 yrs to accumulate. Sediment thicknesses vary along the trench axis but are consistent with present ideas of plate tectonics.

Sedimentary facies of the Middle America Trench and the Gulf of California are similar due to the predominance of tectonic factors over depositional factors in these areas. In the Gulf of Mexico, the opposite is true, since the source regions have low relief and are subjected to stronger weathering.

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