Submarine Channel Initiation and Maintenance from Seafloor Geomorphology and Morphodynamic Modeling

Covault, Jacob A.; Kostic, Svetlana; Paull, Charles K.; Ryan, Holly F.; and Fildani, Andrea
[email protected]

USA Acoustic imagery acquired with Autonomous Underwater Vehicle technology provides high-resolution perspectives of the geomorphology and shallow stratigraphy of the San Mateo submarine channel system, offshore of southern California. The channel system comprises a train of crescent-shaped bedforms in the thalweg of the lower channel reach. Similar channel-thalweg bedforms have been observed in active submarine channel systems worldwide. Herein, we combine morphodynamic numerical modeling with interpretations of seafloor and stratigraphic imagery to demonstrate that these bedforms are likely to be turbiditic cyclic steps molded by associated internal hydraulic jumps. Weakly asymmetric to near symmetric aggradation of seismic reflections across the bedforms suggests that the cyclic steps maintaining the San Mateo channel are net-depositional and relatively fine-grained in nature. Numerical modeling further reveals that an incipient, proto-San Mateo channel comprises a train of relatively coarse-grained net-erosional cyclic steps, which nucleated out of seafloor perturbations across the tectonically active lower slope. Thus, the interaction between turbidity-current processes and seafloor rugosity appears to be fundamentally important to channel initiation, particularly in high-gradient systems. We hypothesize that in this, and analogous, tectonically active, deep-water basins, channel inception and maintenance can be strongly linked to the development of morphodynamic instability manifested as different flavors of cyclic steps.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013