Erosion and Bypass Records in Upper Slope Submarine Canyons

Abstract

Submarine canyons on the shelf-edge and upper slope are known as regions of repeated deposition and erosion, and locations where slope channels initiate. Recent modern seafloor studies suggest the active depositional and erosional bedforms commonly demonstrating upslope-migration at the base of canyons. Modern studies also show that tributary channels at the shelf-edge transform downslope into large canyons where the stable conduits initiate. Outcrop record is essential to complement this morphological understanding and the dynamics of flow process in order to understand the long-term canyon evolution.

This presentation focuses on submarine canyon outcrops of the La Jolla Group in southern California exhibit a 100 m thick and 5 km long exposure in a paleoflow oblique direction. We compare to the submarine canyon outcrops on Svalbard that display similar lithological relationships. This study aims to describe three orders of bypass and erosive architectures and structures. The first-order scale can be correlated with the seismic scale. Individual channels, 15-100 m thick and 150-750 m wide, indicate overlapped and cross-cutting channel margin relationships. The second-order within the channel fills demonstrates the variability of muddy to conglomeratic channel fills. These channel fills show drape like to a few to 10s of m cross-cutting geometries. Commonly variable sandstone-dominated to heterolithic mudstone lithologies occur. The third-order are bedforms, ranging from tens of cm to 10 m thick. The bedforms display backset bedded and scour-and-fill structured conglomeratic, sandy and heterolithic muddy bedforms.

Compared to the modern sea-floor examples, these outcrop data agree on the updip migration of supercritical bedforms. The outcrop data also indicate avulsive channel behavior. All these features give us insight into the slope channel development where sediments bypass and erosion occurred on multiple scales.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018