Dedolomitization of the Cambrian Ledger and Kinzers Formations, York County, PA

Abstract

The Great American Bank, deposited off the coast of Laurentia in the Cambrian and Ordovician consists of over 3000 meters of carbonate deposits, and in these deposits the early history of the North American continent is preserved (Matter, 1966). These deposits provide us, 500 million years later, with an understanding of the natural processes that have occurred in the area. This paper builds upon previous studies conducted at the LWB Refractories in York, PA, on the Middle Cambrian Ledger Formation. This study analyses the dedolomitized facies through petrographic and geochemical studies. Dedolomitization is the calcitization of dolomite (Carozzi, 1993). Petrographic and geochemical data is used to understand the process of dedolomitization and the environment in which these deposits formed. Isotopic and trace element data supports field and petrographic observations of localized calcitization of Ledger dolomite deposits. By comparing the data from the dedolomitized samples to data from dolomite of the Ledger Formation (Dinterman, 1998) we are able to understand the process of dedolomitization in relation to other diagenetic processes the deposits have undergone. Geochemical data indicate that the diagenetic fluids responsible for the dedolomitization were primarily low temperature meteoric waters. Geochemical data of the dolomite suggest the formation occurred through deep burial and warm waters (Dinterman, 1998). The presence of the Triassic unconformity directly overlying the dedolomite deposits suggest they formed after regional rifting, allowing for the introduction of meteoric water along faults. This supports the near surface model for dedolomitization (Carozzi, 1993).