Evidence of Unconformity at Top of Trenton Limestone in Indiana and Adjacent States

Abstract

Subsurface data indicate that in Indiana and parts of adjacent states the Trenton Limestone was exposed to subaerial erosion before the deposition of the overlying shale, which generally is considered to be Cincinnatian in age. The subsurface data include: possible truncation of the Trenton Limestone in southern Indiana; knife-sharp contact between the Trenton Limestone and the overlying shale; concentration of pyrite, angular chert, phosphatic grains, and brecciated limestone and dolomite; solution pits on the surface of the Trenton Limestone and solution cavities within the Trenton Limestone; and local relief on the surface of the Trenton Limestone. East of a line, here called the hinge line, which extends from the Findlay arch to the eastern edge of the Ozark dome, the writer has not observed evidence of unconformity.