Effects of Sequence Stratigraphy on Distribution of Cambro-Ordovician Siliciclastic Hydrocarbon Reservoirs in Michigan Basin

John C. Horne, Christopher L. Reel, Gloria D. Cummins

The lateral and vertical distribution of Cambrian-Ordovician siliciclastic reservoir-potential rock types in the Michigan basin is governed by the sequence stratigraphy. The sequence stratigraphy is controlled primarily by the interaction of four variables: subsidence, eustasy, volume of sediments, and climate.

Seven sequential stratigraphic intervals can be defined in the pre-Utica, Cambrian-Ordovician deposits of the Michigan basin. Each of these unconformity-bounded sequences begins with a siliciclastic unit deposited over a lowstand surface of erosion. These lowstand surfaces developed during periods when eustatic sea level decline exceeded the rate of subsidence in the basin, and much or all of the basin became exposed.

Where the sedimentation rate was less than the sum of the rate of subsidence and sea level change, a transgressive sequence developed with more open-marine carbonates overlying shallower water and/or non-marine facies. Reservoir-potential siliciclastics accumulated in incised valley-fill and transgressive reworked deposits.

When the sedimentation rate approximately equaled the sum of the rate of subsidence and sea level change, stacked sequences of sedimentary facies evolved where only minor fluctuations of facies patterns are exhibited in the stratigraphic sequence. Reservoir-potential siliciclastics accumulated in peritidal coastal and nearshore marine deposits. Because of minor lateral fluctuations of facies patterns, multiple reservoir-potential pays are possible in this type of stratigraphic sequence.

Although interacting with sediment supply, subsidence, and eustasy, climate acts as a primary control on the nonmarine and marginal marine depositional settings. In the Cambrian-Ordovician deposits of the Michigan basin, eolian, braided stream, and fan delta reservoir-potential siliciclastic deposits accumulated in arid nonmarine to marginal-marine settings.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.