This research involves an integrated geologic, geochemical, and isotopic study of platform dolomites in the Cambro- Ordovician of the U.S. Applachians in Virginia and adjacent states. Two sequences selected from the 3 to 4 km thick passive margin succession and considered representative of the dolomite types in the sequence are the Early Cambrian Shady Dolomite (1500 m thick) and the Early Ordovician Knox Dolomite (600 m thick). Possible dolomite types include hypersaline tidal-flat and possible shallow marine dolomite, shallow subsurface dolomite forming from brines or mixed fluids beneath flats, mixing zone dolomites (possibly associated with prograded flats or with unconformities that cap the two successions), marine dolomites associated with the steep Cambrian platform margin and various types of burial dolomite, locally associated with MVT ore mineralization. The studies will be integrated with regional geologic studies involving computer modelling of platform sequences (which provides information on sea-level behavior, duration of cycle formation, progradation rates of tidal flats and migration of early diagenetic zones, and duration of emergence of flats during regressive events). For each dolomite type, data will be obtained on major and trace element chemistry, stable isotopic composition, and radiogenic Sr composition of the dolomites, as well as fluid inclusion data. The effects of recrystallization or replacement of early dolomites in subsequent diagenetic environments will be determined. The likely hydrologic and chemical systems involved in dolomitization history will be integrated will burial history plots that will provide timing of fluid migration and likely P- T conditions during diagenesis.
