--> The Sequence Stratigraphic Significance of TOC and Carbonate Carbon Trends in a Mixed Carbonate/Siliciclastic System (Upper Devonian, Western Alberta, Canadian Rocky Mountains), by F. S. P. Van Buchem, G. P. Eberli, M. T. Whalen, E. W. Mountjoy, and P. Homewood; #90986 (1994).

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Abstract: The sequence stratigraphic significance of TOC and carbonate carbon trends in a mixed carbonate/siliciclastic system (Upper Devonian, Western Alberta, Canadian Rocky Mountains)

Frans S. P. Van Buchem, Gregor P. Eberli, Michael T. Whalen, Eric W. Mountjoy, Peter Homewood

Basinal sediments surrounding the isolated Upper Devonian Miette and Ancient Wall carbonate platforms consist of fine-grained siliciclastics, organic matter, carbonates and carbonate mass gravity deposits. Six depositional sequences were identified which form the framework for an analysis of trends of TOC and carbonate carbon in the slope and basin sections.

First results show:

1. On a meter scale (4-5 m) cycles show variations in carbonate carbon between 4-12%. Lateral tracing of these cycles document the decrease of carbonate content basinward. This cyclicity is interpreted to result from variations of the amount of carbonate mud shed from the isolated platforms. Highest amounts of carbonate muds are shed during (high frequency) relative sea level highstands when the platform is flooded. Within the meter scale cycles, variations of TOC are inversely related to trends in carbonate carbon. TOC is overmature (HI=0), but fine and large scale variations are preserved.

2. On a basin scale highest TOC values were encountered in lower and upper Perdrix and upper Mt. Hawk Formations, with the Perdrix values consistently higher then the Mt. Hawk. The three zones of maximum TOC coincide with the turnaround from the transgressive to the highstand system tracts, when both siliciclastic and carbonate basinal sedimentation are at a minimum. TOC variations coincide in general with stages of platform development with

higher values occurring during backstepping and aggradation (TST), and lower values during progradation (HST).

These results show that TOC and carbonate carbon vary within a sequence stratigraphic framework, which allows to quantitatively address organic and carbonate carbon productivity in platform and basin, and predict TOC enriched zones on seismic scale systems tracts.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994