Timing- and origin of dedolomite in upper Wappinger Group (Lower Ordovician) strata, southeastern New York

Abstract

Detailed petrographic-, geochemical-, and geologic (including surface- and subsurface) study of the massive regional-scale dolostones of the upper Wappinger Group (Lower Ordovician part of Sauk Sequence, southeastern New York) enables us to recognize the products of three stages of dolomitization and of one episode of dedolomitization. The three dolomite stages are: (1) earliest syndepositional dolomite, very fine crystalline dolomite (10 to 30 μm) and some tiny cores of coarser rhombs and displaying δ18O mean value of −7.2‰ and δ13C mean value of −1.2‰; (2) second-stage, shallow-burial dolomites including both replacement-type phases (fine- to coarsely crystalline dolomite), and some dolomite cement that was precipitated between crystals of replacement origin and displays δ18O mean value of −7.6‰ and δ13C mean value of −1.7‰; and (3) late-stage dolomite that fills fractures and crosscuts earlier-stage dolomites and that probably formed at intermediate depth of burial.