Beekmantown Formation-Middle Ordovician limestone unconformity on the northwest limb of the Green Ridge anticline near Fincastle, Virginia
Campbell, Joseph Kent
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The depositional and erosional history can be summarized as follows: 1) Subtidal carbonate shelf sedimentation through Early Ordovician (and including early Middle Ordovician White Rock?) time represented by the Beekmantown Formation. 2) Emergence of a Beekmantown terrain due to eustatic lowering of sea level and inception of gentle folding in late Early Ordovician (or early Middle Ordovician White Rock?) time. Subsequent erosion of the Beekmantown Formation and development of drainage and topographic relief. Development and filling of the paleodolinen on the topographic high. 3) Transgression of the sea. Previously developed drainage was drowned, evidenced by fining upward of the Cahoon Conglomerate Member into dolomite. Continued development and filling of the paleodolinen on the still exposed topographic high. 4) Development of tidal flats with numerous shoaling episodes as evidenced by fenestral fabrics and crystal silt in the New Market Limestone. Fresh meteoric waters available for crystal silt to fill voids throughout much of New Market time. Continued development and filling of the paleodolinen on the still exposed topographic high. Topographic high exposed until end of New Market time. 5) Beginning of Lincolnshire sedimentation marks complete submergence of topographic high. Deeper water, lower energy environment with abundant argillaceous material being brought into the basin and abundance of mud producing organisms. 6) Development of offshore biostromes as represented by Effna Limestone. Lack of mud may reflect high energy or the absence of mud-producing organisms.
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