Architectural Attributes from Ancient (Neoproterozoic) Deep-Marine Sinuous Channel Complex: Styles of Erosion, Deposition and Termination

Bill Arnott
Earth Sciences, University of Ottawa, Ottawa, ON, Canada

Channel complex 2 exposes a network of vertically-stacked and laterally-offset, sharp-based sinuous channel fills. In many places channels fills are characterized by lateral-accretion deposits (LAD), which are inclined up to 7-12^o toward the channel base.

Grain size changes little obliquely-upward along an individual LAD, or vertically upward through the channel fill. LADs consist of two repeating and interstratified kinds: coarse-grained LADs consisting of strata up to granule conglomerate, and fine-grained LADs composed of thin- to medium-bedded finer-grained turbidites. Rhythmic intercalation of coarse- and fine-grained LADs is interpreted to be related to temporal changes in the nature of sediment deposition along the point-bar of a deep-marine sinuous channel. Lateral accretion was terminated abruptly in one of two ways: incision by a younger sinuous channel fill, or detachment related to gravitational sliding. In one example, incision is made evident by an extensive mudstone-clast breccia zone separating the channel fills. Clasts were likely sourced from fine-grained deposits that had accumulated in the older channel fill following channel deactivation and then eroded during rejuvenation of the channel fairway. Channel fills truncated by slide detachment are characterized by surfaces that cut obliquely downward and across the mudstone-rich upper part of the LADs, soling-out in the lower amalgamated sandstone part of the channel fill. Gravitational instability was most likely enhanced by the steep angle of the lateral accretion surfaces, the intercalation of sediment of contrasting mechanical strength, and possibly also the reduction of transport activity within the channel. Recognition of lithological characteristics and styles of channel termination may provide help explain some puzzling seismic attributes from deep-marine sinuous channel systems.

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