Geological Society, London, Special Publications, May 3, 2018
Detailed sedimentological and stratigraphic analyses of a c. 1500 m thick, siliciclastic-dominate... more 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.
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As a genetically related pair, channel-fill and levee deposits are markedly different de- pending on which side of the channel they formed. Along the outer bend, these strata are separated by a sharply erosive, terraced surface that suggests episodic channel-levee growth and long-term migration of the entire channel system toward the northwest. In contrast, along the inner-bend margin, there is a distinct upward change in the spatial association of channel-fill and levee units. The lowermost part of the inner-bend levee is truncated by the channel margin, probably associated with the early, more erosive stage of channel develop- ment. The uppermost part of the inner-bend levee, however, interfingers with channel-fill deposits, suggesting deposition on the lower energy, inner-bend levee of a perhaps narrower, more sinuous channel.
As a genetically related pair, channel-fill and levee deposits are markedly different de- pending on which side of the channel they formed. Along the outer bend, these strata are separated by a sharply erosive, terraced surface that suggests episodic channel-levee growth and long-term migration of the entire channel system toward the northwest. In contrast, along the inner-bend margin, there is a distinct upward change in the spatial association of channel-fill and levee units. The lowermost part of the inner-bend levee is truncated by the channel margin, probably associated with the early, more erosive stage of channel develop- ment. The uppermost part of the inner-bend levee, however, interfingers with channel-fill deposits, suggesting deposition on the lower energy, inner-bend levee of a perhaps narrower, more sinuous channel.