Coarse-Tail Graded, Structureless Strata: Indicators of an Internal Hydraulic Jump
Suzanne F. Leclair, R. William C. Arnott, 2013. "Coarse-Tail Graded, Structureless Strata: Indicators of an Internal Hydraulic Jump", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
Download citation file:
Enigmatic strata were observed intercalated with otherwise thin-bedded ‘classic’ turbidites in the Isaac Formation of the Neoproterozoic Windermere Supergroup in the southern Canadian Cordillera. To understand better the origin of these sharp-, planarbased, structureless, coarse-tail graded strata containg grains up to 0.5 mm and bed thickness up to ~0.30 m, experiments were conducted to replicate the conditions during deposition. In particular, the effect of an internal hydraulic jump on deposition from high-density (20% and 35% volume-sediment concentration), silt-sand, turbid bottom currents was investigated. Video records showed that turbulence generated in the hydraulic jump entrained coarse- and fine-grained sediment from the bed and temporarily maintained them in suspension. Analysis of the subsequent deposit, as photographed through the experimental-tank glass walls or seen on sediment epoxy peels, revealed faintly banded, graded strata in which sand grains float in a matrix of silt, similar to that observed in the Neoproterozoic outcrop examples. Strata like these should be easily recognized in core and therein indicate deposition in a hydraulic jump of a high-density sediment-laden flow.