ACCUMULATION OF ORGANIC-MATTER IN THE ROME TROUGH OF THE APPALACHIAN BASIN AND ITS SUBSEQUENT THERMAL HISTORY

We used geochemical data to examine the origin and preservation of org anic matter contained in the lower part of the Huron Member of the Ohi o Shale formation and the Rhinestreet Shale Member of the West Falls F ormation (Devonian) in Kentucky Ohio, West Virginia, and Virginia. The thermal history of the organic matter was determined by relating rela tive temperatures experienced by the organic matter to the geologic se tting. The organic matter in these formations is predominantly marine in origin and was most probably derived largely from algal organisms, Although the rate of production of marine organic matter may have been uniform within the basin, its preservation apparently was controlled by the existence of a set of fault-bounded anoxic subbasins associated with the Rome trough, a Cambrian structural complex, These subbasins apparently were anoxic because they limited oxygen recharge by circula ting waters, Preservation of organic matter was also enhanced by perio dic blooms of the alga Tasmanites and similar organisms in the waters above the subbasins during both early Huron and Rhinestreet deposition . A significant negative correlation was identified between the vitrin ite reflectance peak temperature, an integrated measure of the thermal history of a rock, and the hydrogen index, a measure of the remaining hydrocarbon-generation potential of kerogen. Although peak temperatur es were controlled by burial depth, excess heating occurred perhaps by hot brines rising from depth through fractures associated with major structures in the study area.