Abstract Detailed sedimentological and stratigraphic analyses of a c. 1500 m thick, siliciclastic-dominated slope succession in the Neoproterozoic Isaac Formation at the Castle Creek study area (southern Canadian Cordillera) reveals the occurrence of four well-preserved mass-transport complexes (MTCs) composed principally of slide/slump and debris-flow deposits. The stratigraphically lowest of these complexes is about 60 m thick and crops out for >2.5 km laterally, consisting of slide and debrite. The slide has an irregular erosive base with ramp-and-flat geometry. This is overlain locally by boulder-sized blocks of slightly to moderately deformed strata, bounded by shear surfaces. The slide is overlain by a debrite that pinches and swells laterally, consisting of matrix-supported conglomerate with common metre-scale clasts of mudstone and coarse-grained sandstone embedded in a mudstone-rich matrix with dispersed, pebble quartz grains. Based on its stratigraphic position at the base of the slope, vertical stacking of slide-debrite, lithological distribution, considerable thickness and lateral extent, this MTC is interpreted to be associated with a major episode of continental slope instability and submarine mass-wasting. The close association between the MTC and underlying/overlying mixed carbonate-siliciclastic strata suggests that sea level most likely exerted a key control on sediment supply, which ultimately led to the emplacement of this MTC.

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.