Detailed geologic mapping and paleontological investigations in an area of about 500 square miles in north-central Arkansas have indicated that rock-stratigraphic units and faunal zones coincide for the most part. However, at least one important discrepancy has not been entirely resolved.

Field mapping indicates that the lowermost member of the Hale Formation, the Cane Hill, is bounded above and below by regional unconformities and that the member grades from nearshore marine deposits to the north and northwest into open marine deposits to the south. A brachiopod fauna is present in the northern facies and a goniatite fauna in the southern facies--locally within 5 miles of each other.

The theory now accepted by many paleontologists indicates a Pennsylvanian age for the northern brachiopod fauna and a Mississippian age for the southern goniatite fauna. This theory requires either that two discrete rock units of different ages have been lumped together by the field mappers or that the single rock unit mapped is transgressive.

End_Page 318------------------------

North-central Arkansas is 200 miles from the type Chester Series in southern Illinois. The Upper Mississippian and Lower Pennsylvanian sequences in those two areas are somewhat similar--the Lower Pennsylvanian of Arkansas does, however, contain more marine beds. In 1904 Adams and Ulrich placed the Mississippian-Pennsylvanian boundary in northern Arkansas at the unconformity at the top of the Pitkin Limestone, which marks the base of the Cane Hill Member. Ulrich considered the post-Pitkin regional unconformity to correspond with the unconformity at the top of the Chester sequence in its type area of southern Illinois. Most geologists have accepted Ulrich's theory and field evidence alone would still tend to support it; paleontological evidence apparently does not.

ERNEST E. GLICK

Ernest E. Glick is a geologist with the United States Geological Survey, Denver, Colorado. He received a B.A. degree in 1949 from the University of Southern California and attended the University of Illinois 1949-1951. He has been employed by the U.S. Geological Survey since 1951.

Mr. Glick, prior to being transferred to Denver, spent 8 years in Tulsa, Oklahoma where he was engaged in regional subsurface studies and quadrangle mapping in northern Arkansas. He is a member of the AAPG, GSA, and several local societies.

End_of_Record - Last_Page 319-------