THE LOWER DOLOMITE MEMBER OF THE ORDOVICIAN CHAZY LIMESTONE AND THE ST. PETER SANDSTONE

Until recently little was known of the exact disposition of the Lower Dolomite Member of the Chazy Limestone and the St. Peter Sandstone in the area of study. This study has been done to illustrate their relationship to the underlying erosional topography on the Knox Dolomite Group. The Lower Dolomite Member of the Chazy Limestone varies in thickness from a maximum of 100 feet to zero. The greater thicknesses are deposited in erosional valleys developed in the Knox Dolomite and the thinner sections are found deposited over the higher remnants, or hills, of Knox Dolomite. The use of geophysical well logs for placing the upper contact of this unit is very helpful. The sandstone pinches out in the area of study in an easterly direction. A local depression or basin was formed in northern Kentucky where in excess of 60 feet of sand accumulated. The sands were probably from two sources: 1) sand from the St. Peter source area as erosion progressed landward, and 2) local erosion of Knox Dolomite "hills"