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ABSTRACT: Cement Stratigraphy of the Wahoo Formation, Sadlerochit Mountains, Alaska

Randall C. Carlson

A number of generations of calcite cement are present in the intergranular and moldic pore space in the Wahoo Formation. The most common sequence of cements is (1) nonferroan calcite with a complex, cathodoluminescent zonation of several nonluminescent, bright and dull bands, (2) dull, nonferroan calcite, (3) very dull, ferroan calcite accompanied by fractures filled with ferroan calcite, and (4) dull, nonferroan calcite.

Complexly zoned, nonferroan calcite is most abundant in uncompacted fabrics and occurs within discrete stratigraphic intervals (6-100 m thick). The tops of these intervals commonly coincides with the tops of shallowing-upward sequences. Upward pinch-outs of complexly zoned cement also occur at the Mississippian-Pennsylvanian boundary, the Morrowan-Atokan boundary, and at the top of the Wahoo. These relationships suggest that these cements were precipitated from meteoric waters during subaerial exposure.

Dull, nonferroan calcite is the second generation of cement in the lower two-thirds of the Wahoo. The dull, nonferroan calcite predates and postdates minor compactional features and appears to be of shallow burial origin.

Ferroan calcite cements can be traced for 297 m throughout the Wahoo. In the lower two-thirds of the Wahoo, precipitation during deep burial is indicated by cements in overcompacted fabrics, broken grains, fractures, and stylolites. The upper one-third of the formation has small amounts of ferroan calcite that predate complexly zoned calcite and greater amounts of ferroan calcite that postdate compaction. Remaining pores are filled by dull, nonferroan calcite.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990