The Effect of Event Sequences on the Characteristic of Turbidity Current Deposits

Similar submarine canyon systems exist on scales ranging from less than a kilometer to nearly 1000 km. The shallowest end is a submarine canyon and canyon head(s). Further down the canyon is buried by the upper part of a submarine fan with meandering and cross-cutting channels. The fan eventually merges with a nearly flat-lying depositional basin. We have used the deposits associated with these common morphological features to calibrate and verify numerical models. When model parameters are correctly set the characteristic variations of the sediment grain size distributions and bed thicknesses predicted by the model should match patterns observed in cores. This study examines the relationship between the scale of canyon systems created and characteristics of the depositional zones using idealized morphologies. The 2-DV numerical model tracks 5 grain sizes, includes bedload and pelagic sedimentation. One set of experiments represents large systems with long-duration source events. The idealized large system is a composite of the Amazon, Monterey and Congo Canyons. The smaller system represents the submarine canyons along the north central Gulf of Mexico. The modeling shows that deposits in large systems develop as the result of several episodes of reworking by a sequence of turbidity current events. In the upper reaches of the canyon and fan the pattern of grain size sorting is highly variable according to the magnitude of the triggering event. This leads to a distinctive pattern of core layers which show many truncated beds. This pattern is much more subdued in the smaller system because reworking is less intense. Both of these patterns show a strong dependence on the characteristics of the source event and it frequency of occurrence.