Abstract

This paper summarizes the results of a correlation and mapping project of Fort Union Formation coals in the eastern Powder River Basin completed for Devon Energy Corporation and Kerr McGee Corporation between 1996 and 1999. The project area covered over 4,400 square miles and included approximately 10,000 data points. The project consisted of six smaller study areas, which were integrated, and led to the following conclusions: (1) The major Fort Union coals in the eastern Powder River Basin are part of a single lithologic unit that was continuously deposited through Late Paleocene time in a migrating depocenter; (2) The size of the depocenter was controlled by climate, accommodation space, and sediment supply (because the size of the depocenter increased and decreased through time, multiple, thin coals were deposited along the edge of the basin, whereas thick coals accumulated near the basin center); and (3) The depocenter moved laterally through time, due primarily to tectonic activity within the basin (subsidence) and along the basin margins (uplift). This activity affected the local balance between peat accumulation and preservation space below the groundwater table. The development and application of these conclusions is the subject of this paper.