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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 785

Last Page: 785

Title: Stratigraphy and Diagenesis of Niagaran Pinnacle Reefs (Silurian) in Northern Michigan Basin: ABSTRACT

Author(s): John M. Huh, Louis I. Briggs

Article Type: Meeting abstract


In the Michigan basin, the Middle Silurian Niagaran reef facies directly underlies the Upper Silurian Salina evaporite facies. The basal Salina Formation includes the A1-evaporite, subjacent to the A1-carbonate and the A2-evaporite in successive order. Subsurface study of 40 drill cores disclosed that most of the Niagaran pinnacle reefs in the inner-basin slope environment ceased growth by A1-evaporite time and were regenerated during deposition of the A1-carbonate.

The uppermost section of the algal stromatolite and algal boundstone facies at the top of the pinnacle reefs was deposited contemporaneously with the A1-carbonate of the off-reef section. The algal-stromatolite facies of the A1-carbonate overlies the A1-evaporite on the reef flanks and extends laterally to the off-reef facies in the vicinity of the pinnacle reefs. The general lithology of the A1-carbonate in the off-reef sections differs greatly from the lithology of the A1-carbonate reef facies.

Some of the pinnacle reefs apparently continued to grow during the early formation of the A2-evaporite. There is no significant erosional contact between the A2-evaporite and the algal stromatolite at the top of the reef. Furthermore, LLH- and SH-type algal stromatolites show repeated stages of growth in situ, within the lowermost few feet of the A2-evaporite section.

A vadose zone representing subaerial exposure is present in the pinnacle reefs at the top of the organic reef facies, which overlies the basal biohermal facies. This zone is characterized by a more complex sequence of diagenesis than either the basal biohermal facies or the uppermost algal stromatolite facies.

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Copyright 1997 American Association of Petroleum Geologists