ABSTRACT: Stratigraphy and Paleogeography of Coal-Bearing Strata, Mesaverde Formation, Southeast Piceance Creek Basin, Colorado

Henry C. Nowak

The Upper Cretaceous Mesaverde Formation in the southern Piceance Creek basin of western Colorado contains an estimated 36 tcf of natural gas in the form of coalbed methane. The intertonguing relationships of the coal-bearing rocks are extremely complex. In order to enhance the successful exploration of coalbed methane, an accurate delineation of the stratigraphic framework of the Mesaverde Formation is necessary. Such a framework is presented here using a detailed study of outcrops, cores, and well logs. The outcrop study covers an 8 mi outcrop belt in the North Fork Valley east of Paonia. Electric logs and cores provided the data necessary to project the results of the outcrop study northward into the subsurface area of high coalbed methane potential. Results indicate t at the lower part of the coalbearing Mesaverde Formation, the Bowie shale member, was formed in a wave-dominated lower delta plain setting. The upper part of the coal-bearing Mesaverde Formation, the Paonia shale member, was deposited in an upper delta plain. A paleogeographic reconstruction shows that the deltaic shoreline trends north and south. Furthermore, the thickest (maximum of 32 ft) coalbeds found in the lower part of the Bowie shale member are parallel to and extend 6 to 8 mi landward of the paleoshoreline. Coalbeds of the Paonia shale member are thinner and less persistent. Consequently, exploration for coalbed methane should focus on the Bowie shale member in a belt 6 to 8 mi wide and shoreward (west) of any pinchouts in thick coalbeds.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990