Case Studies of Massive Gravity Slides Imaged in 3D Seismic Volumes: Passive Margin and Basinal Settings (West Africa and Northwest Europe)
Abstract
Regionally extensive scour surfaces on continental margins and in epeiric basins develop due to two major processes: submarine landslides, mainly affecting slopes in excess of 1 degree and subglacial scour beneath ice streams draining alpine or continental ice sheets. Both types of surfaces can extend for tens to hundreds of kilometres in the dip and strike directions, with tens of metres relief across tens of kilometres long scours and ridges. Correct interpretation within a sediment system tract enlightens models of synchronous glacial, marine and climatic conditions. We present four megaslides imaged in, and interpreted from 3D seismic volumes acquired in diverse settings: 1: On the passive margin shelf of Cameroon, large-scale, downslope-oriented striations extend 40 km from the upper slope to the deep basin area. Individual striations are 20-50 m wide, 8 km long, 5-10 ms TWT deep, and broadly arcuate. The striations present in two sets and mark the base of a chaotic-to-discontinuous, high-amplitude package with chaotic, low amplitude reflections in the unstriated area. The facies is interpreted as a zone of repeated gravity sliding during the early Pleistocene in response to tectono-climatic forcing. 2: A basal surface from the Moray Firth, UK Central North Sea, tentatively dated as Paleocene in age. It is 20 km in width, over 40 km long and displays parallel grooves measuring typically 100-1000 m wide, 10-20 km long, of sinuous form along the section imaged in the dataset and with evidence of post-slump failure along the margins of the slide zone. It is interpreted as scour caused by a single sliding event. 3: An areally extensive scoured surface measuring 45x45 km that is part of a larger Pliocene system on the Angolan margin. The basal shear surface is marked by divergent scours. The geometry and spatial location of this flow are confined by listric faults and salt-cored folds with compressional thrusts within the distal toe of deposits on the flanks of salt diapirs. The system evolved through instabilities triggered by increased Pliocene uplift of the hinterland, an increased sediment flux, and oversteepening of fold limbs. 4: Ice stream scours on the present land surface and seafloor, and in the geological record display mega-scale lineations with elongation ratios proportional to ice streaming velocity within troughs measuring several km to more than 100 km across. Individual landforms are up to a few km across and 10-100 km long with the majority of grooves observed seismically being 1-100 m wide and 1-10 km long. Depth of grooves and height of erosional remnants are 10-100 m depending on substrate erodibility. Groove sets are parallel, converging or diverging depending on lateral constraints, flow path deviation and substrate properties. We utilise seismic geomorphologic and morphometric analyses of these basal scour surfaces to develop distinguishing characteristics which can be used as predictive tools in inferring causative mechanisms of gravity-related processes. This provides a discriminative framework for shelf-edge glacial, interglacial and aglacial sequences.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMOS21H..02B
- Keywords:
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- 3045 MARINE GEOLOGY AND GEOPHYSICS / Seafloor morphology;
- geology;
- and geophysics;
- 3070 MARINE GEOLOGY AND GEOPHYSICS / Submarine landslides;
- 3075 MARINE GEOLOGY AND GEOPHYSICS / Submarine tectonics and volcanism;
- 8122 TECTONOPHYSICS / Dynamics: gravity and tectonics