--> ABSTRACT: Influence of Depositional Environment on Diagenesis in St. Peter Sandstone, Michigan Basin, by C. E. Lundgren, Jr. and David A. Barnes; #91022 (1989)
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Influence of Depositional Environment on Diagenesis in St. Previous HitPeterNext Hit Sandstone, Michigan Basin

C. E. Lundgren, Jr., David A. Barnes

The Middle Ordovician St. Previous HitPeterNext Hit Sandstone in the Michigan basin was deposited in marine peritidal to storm-dominated, outer shelf depositional environments that evolved in a regionally significant transgressive pattern. The formation is bounded by carbonate and shaly clastic strata of the Prairie du Chien Group below and is transitional to condensed sequence clastics and carbonates of the Glenwood Formation above.

Sedimentologic and petrographic analysis of conventional core from 25 wells suggests that reservoir quality in the formation is strongly dependent on a complex diagenetic history, especially the nature and subsequent dissolution of intergranular carbonate in the sandstone. Muddy sandstones in the upper storm-shelf facies contain primary carbonate mud matrix (now dolomitized) due to biogenic reworking of episodically deposited sand-carbonate mud beds. Well-sorted quartz sandstones deposited in higher energy, peritidal environments have little primary matrix. Burial dolomite pore fill is the common intergranular carbonate in these sandstones.

Petrographic evidence indicates that porosity in the formation formed by dissolution of precursor dolomite of various origins and, locally, the formation of pore-filling authigenic clay (chlorite-illite). Authigenic clay is the incongruent dissolution product of dolomite, detrital K-feldspar, and, possibly, muscovite and results in diminished reservoir quality where abundant in the St. Previous HitPeterNext Hit Sandstone.

Authigenic clay is volumetrically more significant in the upper portions of the formation and is associated with higher concentrations of detrital K-feldspar. Depositional facies controlled the distribution and types of intergranular carbonate (now dolomite) and detrital K-feldspar in the St. Previous HitPeterTop Sandstone and hence reservoir quality; both components were more significant in storm-shelf sandstone facies.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.