Significance of Cyclic Pennsylvanian-Permian Coral/Algal Buildups, Snaky Canyon

CANTER, K. L., Coyote Geological Services, Boulder, CO, and P. E. ISAACSON, University of Idaho, Moscow, ID

Five cyclic algal, hydrozoan, and coral buildups occur within a thick sequence of Pennsylvanian-Permian (Virgilian through Wolfcampian) carbonates in south-central Idaho. The Juniper Gulch Member of the Snaky Canyon Formation, as described by Skipp and coworkers, is approximately 600 m thick and contains four depositional facies, including: (1) open circulation outer(?) platform, (2) hydrozoan and phylloid algal mound-dominated carbonate buildup, (3) backmound, restricted platform/lagoon, and (4) restricted inner platform facies. Several microlithofacies, including lime mud-rich bafflestone, diversely fossiliferous packstone and grainstone, bryozoan lime floatstone, and phylloid algal and hydrozoan (Palaeoaplysina) lime bindstone are described within the phylloid algal mounds. Collect vely, these microlithofacies represent sedimentation on or in proximity to phylloid algal and Palaeoaplysina-dominated carbonate buildups. These biostromes appear to be composed principally of the phylloid codiacean algae Eugonophyllum, associated skeletal debris, lime mud, and sparry calcite. The mounds (or biostromes) vary in thickness from 2-20 m. The lateral dimensions of a particular buildup cycle may be as many as 10 km, thereby giving the sense of laterally equivalent buildups, or perhaps stratigraphic reef complexes.

Successional faunal assemblage stages are recognized within the buildups. Colonial rugose corals comprise a stabilization stage. When the algal communities of the diversification stage reached wave base, because of their rapid upward growth, cross-bedded oolitic grainstone and occasional cross-bedded dolomite shoals developed. Supratidal to high intertidal platform sedimentation is represented by dolomitic Palaeoaplysina bindstone, algal mat bindstone, and vuggy dolomite. Five vertical sequences of buildup development, each terminated by intertidal, supratidal, or erosional events, are seen in the Juniper Gulch Member in the North Howe stratigraphic section of the southern Lost River Range. The carbonate platform was constructed within a depositional basin that includes an eroded high and to the west, and a mixed siliciclastic-carbonate inner platform with craton uplifts to the east.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)