Print this pageHigh-Latitude Canyon Development and Associated Depositional Element Evolution; Southwest Grand Banks Upper Slope, Canada
Dominic A. Armitage1, David T. McGee2, William R. Morris2, and David J. W. Piper3
1Geological and Environmental Sciences, Stanford University, Stanford, CA
2ConocoPhillips Co, Houston, TX
3Geological Survey of Canada (Atlantic), Dartmouth, NS, Canada
Analysis of sediment cores, 2D Huntec and 3D shallow seismic-reflection data reveal two main canyon types: 1.) those that have relatively broad, flat bottoms, which are probably formed by glacial outburst floods with inner terraces likely to be formed by proglacial failures. These canyons are principally erosional in their axes, their floors are dominated by winnowed conglomerates and stiff Pleistocene muds with terraces recording recent axis bypass; 2.) canyons that do not extend updip to the shelf margin but terminate locally and appear to be created by retrogressive failure (modifying aggradational deposits) and are draped by Holocene and Pleistocene muds.
The shallow 3D data reveals upper slope accommodation space created by large-scale mass wasting events, reflecting a period of slope failure. These events are succeeded by a complex history of deposition dominated by smaller-scale mass transport deposits and canyon/channel overbank deposits. The slope failure and associated deposits fundamentally setup the canyon configuration that is observed on the modern seafloor. Two interrelated processes controlled canyon development: 1.) the failure scarps resulting from the mass wasting event created accommodation space available for canyon ridge aggradation and 2.) the scarps captured subsequent sediment gravity flows necessary for their construction. It is demonstrated that these scarps act as a precursor to canyon development. Large slide blocks (up to ~2 km3) created topography on the paleo-seafloor and were preferential sites for locally ponded deposition.
The canyon ridges internally record a complex history of overall aggradation via sediment gravity flow deposits and degradation by erosive flows and slumping. Isopach maps and reflection geometries of individual packages indicate offset stacked overbank wedges in the construction of these ridges.
AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas