Abstract: Vitrinite Reflectance and Coal Maceral Composition of the Upper Cretaceous Blackhawk Formation in the Book Cliffs Coal Field

Steve Sommer, Brigitte Hucka

The coals of four Upper Cretaceous Blackhawk Formation members in the Book Cliffs coal field show significant variations in the maceral composition related to changes in depositional and tectonic setting, whereas the beds within each member show compositional similarities. These variations were determined from 165 characterizations of coal samples from the Spring Canyon, Aberdeen, Kenilworth, and Sunnyside Sandstone Members of the Blackhawk Formation, the entire coal-bearing section of the formation. This study is part of an effort to understand the paleo-environmental conditions which influenced coal formation, composition and quality. The results may also help to understand the influence of coal composition on the formation and retention of coalbed methane.

Vitrinite reflectance analyses show a high volatile bituminous B rank for most of the coal beds with increase in rank to high bituminous A for the easternmost coal beds. Relatively high percentages of exinite (8-10 percent) characterize the coal beds of the Aberdeen Member whereas the coal beds of the Sunnyside Member have the lowest percentages (3-6). Coal beds of the Kenilworth and Spring Canyon Members have exinite percentages ranging from 4-6 and 5-8 respectively. Inertinite percentages are highest for the coal beds of the Kenilworth Member (17-21), with generally lower inertinite percentages for the coal beds of the Aberdeen (16-18) Sunnyside (11-15), and Spring Canyon Members (9-15). Vitrinite percentages are highest for the Sunnyside Member (80-84) and the Spring Canyon Member 80-83), and lowest for the Kenilworth (73-79) and Aberdeen Members (73-78). Maps of vitrinite reflectance (% Rm oil) are used to assess the regional variations in coal rank and their correlation with coal maceral composition.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994