Carbonate rocks of Cambrian and Ordovician age in the Lancaster quadrangle, Pennsylvania

Abstract

Detailed mapping has shown that the carbonate rocks of Cambrian and Ordovician age in the Lancaster quadrangle, Pennsylvania, can be divided into 14 rock-stratigraphic units. These units are defined primarily by their relative proportions of limestone and dolomite. The oldest units, the Vintage, Kinzers, and Ledger Formations of Cambrian age, and the Conestoga Limestone of Ordovician age are retained in this report. The Zooks Corner Formation, of Cambrian age, a dolomite unit overlying the Ledger Dolomite, is named here for exposures along Conestoga Creek near the village of Zooks Corner. The Conococheague (Cambrian) and Beekmantown (Ordovician) Limestones, as mapped by earlier workers, have been elevated to group rank and subdivided into formations that are correlated with and named for geologic units in Lebanon and Berks Counties, Pa. These formations, from oldest to youngest, are the Buffalo Springs, Snitz Creek, Millbach, and Richland Formations of the Conococheague Group, and the Stonehenge, Bpler, and Ontelaunee Formations of the Beekmantown Group. The Annville and Myerstown Limestones, which are named for lithologically similar units in Dauphin and Lebanon Counties, Pa., overlie the Beekmantown Group in one small area in the quadrangle. INTRODUCTION Carbonate rocks of Cambrian and Ordovician age underlie a lowland that occupies most of the Conestoga Valley in southeastern Pennsylvania. Detailed mapping by the authors of the Lancaster quadrangle in the Conestoga Valley (fig. 1) now allow carbonate rocks formerly assigned to the Conococheague and Beekmantown Limestones (Jonas and Stose, 1930) to be more closely subdivided into units defined primarily by their proportions of limestone and dolomite. Most of these units are herein correlated with units in the Great Valley in Lebanon, Berks, and Dauphin Counties, Pa. (Geyer and others, 1958, 1963; Hobson, 1957, 1963; Prouty, 1959). In addition, a newly defined dolomite unit is herein named the Zooks Corner Formation. Gl