Syn-Sedimentary Deformation Processes Driven by Debrite Emplacement from a Deep-Water Basin Floor
Willem C. Van der Merwe, David Hodgson, and Steve Flint
Earth and Ocean Sciences, Liverpool University, Liverpool, United Kingdom
A rare example of deepwater MTDs exposed at seismic scale in the Vischkuil Formation, Laingsburg Karoo Basin, South Africa allows detailed analysis and interpretation of deformation processes and emplacement history. Detailed correlation and isopach mapping of volcanic ash and other marker beds over more than 500 km2 indicate minimal inter-marker thickness changes, hence a flat basin floor setting. Down-dip facies transitions of deformed intervals within this correlation framework indicate spatial transition of emplacement process from proximal deformed bodies into thick, graded mud-prone turbidites over a down dip distance of 55 km. A 50 m thick chaotic unit, continuously exposed for 2 km passes from extensionally deformed material up dip (clastic dykes and down-dip facing low-angle shear surfaces) to large (10’s of metres amplitude) folds dissected by steep, up-dip facing shear planes. The compressional shears sole out onto a highly sheared interval and cross-cutting relationships indicate an up-dip younging in fold dissection. A large debrite, spatially related to the folds, is interpreted to have driven the large-scale deformation. This debrite is directly overlain by a thick turbidite sandstone that shows widespread vertical foundering into the debrite. The whole stratigraphic exposure preserves the evolution of a slump from undeformed, through extensional to a compressional toe zone. The Vischkuil Formation study shows that intensely deformed strata can be generated by negligible amounts of down-dip movement in a low gradient, mud-rich basin floor setting with the driver for movement and deformation being the mass imbalance resulting from emplacement of episodic debris flows.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery