Microfacies of the Middle Ordovician New Market limestone in Rockbridge County, Virginia

Abstract

Two� sections were measured and their microfacies defined macroscopically at two locations in Rockbridge County, Virginia. Nineteen microfacies are defined on the basis of detailed petrographic study of one section. Most microfacies are crystalline limestones of Type II (Microcrystalline Allochernical) and III (Microcrystalline), but rnicrofacies of shale, conglomerate (or clastic limestone), and dolomite also occur. Chert (in beds and nodules) and authigenic pyrite grains are intermixed in the carbonate microfacies. Significant sedimentary structures are laminations and cross-lamination. Intrepretatian of the depositional environments of individual microfacies indicates 4 periods of transgression and regression during which the basin changed from a normal, shallow, open type basin ta a restricted or semi-restricted, relatively deep basin.