ABSTRACT

Dominantly carbonate rocks of Pennsylvanian and Lower Permian age thin eastward out of the Bird Spring Basin portion of the Cordilleran Miogeosyncline across the Callville Shelf. The lithostratigraphic subdivision used here is based upon detailed examination of four stratigraphic sections: Arrow Canyon on the west in the Bird Spring Basin, Frenchman Mountain on the line between basin and shelf, and Azure Ridge and Iceberg Canyon closest to the positive areas to the east. Four major subdivisions can be recognized at all four locations. These are the Illipah Formation, the lower and upper members of the Bird Spring-Callville Group, and the overlying Pakoon Formation. Nine lesser subdivisions can be correlated from Frenchman Mountain to Azure Ridge and Iceberg Canyon.

The lower member of the Bird Spring-Callville Group thins eastward by onlap of succesively younger strata onto a low relief, low gradient land-mass. The near-shore sediments are represented by the Illipah Formation and equivalents whereas offshore sediments are referred to the lower member of the Bird Spring-Callville Group. This latter sequence is characterized by low energy limestone facies to the west and higher energy facies in the east. The upper member of the Bird Spring-Callville also has more low energy limestone facies to the west but is distinguished from the lower member by an abundance of cross bedded sandstone units.

The upper member of the Bird Spring-Callville thins much less markedly than the lower and has somewhat more sandstone in the east. It represents a time of large scale transgressive and regressive fluctuations in which regressive phases coincided with an influx of quartz clastics. Lower energy environments persisted in the west.

The Pakoon Formation also thins eastward but Pleistocene (?) erosion has removed a portion of its original thickness at Arrow Canyon. It is dominantly dolostone with variable amounts of sandstone and micritic limestones also present. The Pakoon Formation formed during a major westward regression in which low energy, shallow water, conditions prevailed.