Mud re-distribution in epicontinental basins - Exploring likely processes

Fine grained clastic sediments are very common in the interior deposits of ancient epicontinental seas. Not only do they make up the gross lithology in these basins, but they can also be traced for more than 1000 km offshore from basin margins. Given that epicontinental seas were overall shallow and in many parts most likely less than 100 m deep, basin floor slopes can safely be expected to be in the 0.01 to 0.001 degrees range for much of depositional history. Known processes that bring muds to the basin margin and beyond are hypopycnal river plumes, hyperpycnal fluvial discharge events, storm-setup relaxation flows, and gravity-driven fluidized muds. With the exception of river plumes, all of these processes require the presence of sufficient slope for sustained movement. Due to that constraint, these processes combined might in the majority of situations have been able to move muddy sediments on the order of 100 km offshore. Whereas this is sufficient to distribute mud across marginal shelf seas, it becomes problematic in the case of much larger epicontinental seas. For example, those of Upper Devonian or Upper Cretaceous times extended in places for thousands of kilometers, and thus a process is needed that can move muddy sediments the rest of the way. Flume studies of the bedload transport of mud, combined with observations from the rock record, suggest that wind or tide induced bottom current circulation was most likely essential for moving muddy sediments from the periphery of epicontiental seas to their interiors. Remobilization of seafloor muds during frequently recurring lowering of sea level is likely to have aided in this process. (C) 2015 Elsevier Ltd. All rights reserved.