Rivers and Submarine Channels: A Comparison of Their Transport Processes and Resulting Stratigraphic Architecture Over Basin Filling Time Scales

Abstract

Channels act as arteries for the transport of sediment across landscapes and seascapes and help distribute this sediment in basins where thick stratigraphic packages accumulate. Quantitative observations of the planform morphologies of channels in terrestrial and submarine settings indicate strong similarity, suggesting similar transport processes and morphodynamics in the two settings. Observations of these systems in cross-section, however, indicate great differences in their morphologies which likely arise from differences in transport processes and morphodynamics. While significant attention has recently been paid to short time scale differences/similarities of open channel flows and turbidity currents (e.g. direction of helical flow in channel bends) here we focus on a comparison of these flow types and their stratigraphic records over basin filling time scales. In the terrestrial, the ratio for the densities of the channelized flow and the ambient fluid it is moving through is roughly 800. This condition leads to one in which rivers are prone to avulse when they superelevate to a value roughly equal to a channel depth. Coupled with the generation of a backwater regime where terrestrial channels approach the shoreline, the strong difference in flow to ambient fluid densities results in abandoned channels which are topographic lows on landscapes. This condition promotes reoccupation of old channel paths following avulsions and the generation of persistent depositional trends, such as channel clustering. In contrast, the ratio of current to ambient fluid density for turbidity currents in the submarine is only slightly greater than unity. In settings where normal flow dominates, this allows submarine channels to superelevate several multiples of their channel depth. These conditions result in abandoned channels that remain high for a time, leading to avoidance of previous channels and an overall tendency to distribute channel bodies. Further complicating matters though, is the widespread occurrence of non-normal flow in turbidity currents, which in terminal fan settings might lead to stratigraphic architecture similar to terrestrial settings. We explore these processes and products using observations from modern systems and ancient stratigraphic architecture in addition to results from reduced complexity models.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015