--> Abstract: Source Control Over Calciturbidite Facies Distributions in the Lower Isaac Carbonate, Windermere Supergroup, Canada; #90063 (2007)

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Source Control Over Calciturbidite Facies Distributions in the Lower Isaac Carbonate, Windermere Supergroup, Canada

 

Gammon, Paul R.1, Bill Arnott2 (1) Carleton University, Ottawa, ON (2) University of Ottawa, Ottawa, ON

 

The informally named lower Isaac carbonate (LIC) is the only calcareous unit in ~3 km of Neoproterozoic Windermere Supergroup strata in eastern British Columbia. In general, deepwater calcareous turbidites (calciturbidites) are uncommon in most turbidite or limestone systems. The LIC is a mix of three facies: coarse sand to gravelly turbidites that form shallow channel fills dominated by Ta (Bouma A-division) deposits that have a quartz (~70%) – carbonate (~30%) composition. Channel fills are generally surrounded by calciturbidite levee deposits that laterally grade into non-calcareous, Tde overbank mudstone turbidites. Proximal levees consist of laminated Tdebc calcarenites to thick-bedded Tbc calcilutites that are generally >70% carbonate clasts plus cement. The calciturbidites display m-scale coarsening and fining-upward trends; between calcarenite and calcilutite lithologies. On the distal levee these fine to siliciclastic mudstone – calcilutite cycles, with locally well developed bypass surfaces. The origin of the three facies can be ascribed to compositional differences between grainsize classes in a mixed siliciclastic-carbonate continental shelf source region. Subsequently, turbidity current dynamics distributed the grainsize classes into different depositional environments, and hence facies compositions. The m-scale cycles are probably an autocyclic channel-related feature, although their distribution, plus the rarity of carbonate strata in the Windermere, suggests eustasy and tectonics ultimately controlled the distribution of grainsizes and compositions on the shelf. Common photic-zone carbonate clasts further suggest the LIC calciturbidites may represent late highstand to early regressive times, when progradation-aggradation had produced shallow outer shelf waters, but prior to a probable lowstand restriction of this carbonate factory by low relative sealevel, and an abundant siliciclastic mud flux.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California