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4 Organic Geochemistry An important implication of the thin-skinned thrusting hy- pothesis is that Paleozoic platform sedimentary rocks beneath the sole of the overthrust may have hydrocarbon potential (Cook et al., 1979). The approximately 8-km depth and likely degree of deformation and metamorphism (chlorite zone of the greenschist facies) of these rocks beneath the drill site suggest that if hydro- carbons are present in significant quantities, they will be in the form of natural gas. More likely, hydrocarbons would be unsta- ble this far southeast of the Valley and Ridge province (Hatcher, 1982), although some methane might be present. Nevertheless, documentation of organic materials would have far-reaching im- plications for the hydrocarbon potential of correlative rocks to the west at shallower depths and for other overthrust terranes. Or- ganic constituents of fluids trapped in overlying crystalline rocks may be related to metamorphism of the platform rocks during and following thrusting. Coring would provide an opportunity to study organic constituents as a function of depth and metamorphism in pristine samples. Analysis of organic components and light stable isotopes of the elements that form them should be undertaken wherever possible in samples from the southern Appalachian drill hole. 17
18 Sampling for organic geochemical studies requires knowing the depth, temperature, and geologic history of the material. Core would allow these criteria to be satisfied. Migration of hydrocar- bons across interfaces between rock types can only be studied if samples are obtained at the very close intervals that cores provide. If light hydrocarbon gases are present, it will be necessary to use a high pressure coring device to ensure that none of the gases escapes during collection. After collection it would be highly desirable to freeze the cores to eliminate loss of volatile components prior to analysis. Contamination will be a major problem in samples from a southern Appalachian hole because organic content is likely to be low. Oil based drilling muds should be avoided, and care will be required to protect the core from contamination from pipe grease or other sources of organic material in the vicinity of the drilling rig-
