--> ABSTRACT: Productivity Versus Preservational Controls on Carbonate Source Beds, Devonian of the Alberta Basin, by Jack Wendte, Nancy Chow, Stasiuk, Vern; #91020 (1995).

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Productivity Versus Preservational Controls on Carbonate Source Beds, Devonian of the Alberta Basin

Jack Wendte, Nancy Chow, Stasiuk, Vern

Integrated sedimentological and organic petrographic studies of two organic-rich successions, from basin to shallow-water settings, have provided new insights into depositional controls of carbonate source beds, especially the role of organic productivity versus preservation.

The Upper Devonian Duvernay Formation occurs as an areally widespread basin-floor deposit, several meters thick, and was examined along the margin of the Leduc reef complex at Redwater in east-central Alberta. organic matter was produced at normal rates by shallow-water planktonic algal growth in off-reef settings and was preserved due to bottom anoxic conditions at depths greater than 40 to 50 meters. Variations in organic concentration mainly correspond with the amount of reef-shed carbonate sediment and to intermittent storm-induced aerobic bottom conditions.

The Middle Devonian Lower Keg River succession occurs as a widespread carbonate ramp and was examined in the transition from the Senex Platform to the La Crete Basin in north-central Alberta. The source bed occurs as a meter-thick carbonate laminite within this succession in the La Crete Basin and was deposited in water depths of only 20 to 30 meters. Organic petrography shows that abnormally high rates of organic productivity, due to algal blooms, occurred in shallow water and triggered periods of anoxia. High concentrations of organic matter also correspond to only minor carbonate sediment dilution, mainly of planktonic origin.

Collectively, our studies demonstrate the utility of integrating organic petrography with sedimentology in assessing depositional controls on organic-rich successions.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995