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The AAPG/Datapages Combined Publications Database

North Dakota Geological Society

Abstract

NDGS-AAPG

Symposium on the Geology of Rocky Mountain Coal, October 2-4, 1984

Pages 137 - 151

ASH-FALL SEQUENCES IN A PALEOCENE COAL—POTENTIAL INDICATOR OF SYNCHRONEITY BETWEEN MONTANA AND WYOMING BASINS

Carol Waite Connor, U.S. Geological Survey, Denver, Colorado 80225

ABSTRACT

Numerous crystal tuff and altered volcanic ash partings in the Paleocene Big Dirty coal bed of the Fort Union Formation in south-central Montana's Bull Mountain coal field indicate a period of intense volcanism not recorded elsewhere in the area. These time-synchronous layers have been correlated 80 miles along the outcrop. The correlations were statistically tested and found to be significant. Because of its distinctive striped appearance imposed by the many light-colored ash layers, the Big Dirty is easily recognized in the field. Beds of similar general description in the same stratigraphic interval in widely scattered areas of Montana and Wyoming have been mentioned in the literature. The methods developed to describe and correlate the Big Dirty in the Bull Mountain basin can be used to determine whether those similar beds in other basins are equivalent.

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