GEOCHEMICAL EVIDENCE FOR DOLOMITIZATION ALONG THE CLARENDON LINDEN FAULT IN WESTERN NEW YORK

Dolomitization after initial lithification of carbonate rocks is achieved through fluid flow and a replacement of pre-existing carbonate components producing saddle dolomite. This geochemical process has been documented in the Western Canadian Sedimentary Basin with the dolomitization product occuring among Devonian carbonate reservoir rocks as a result of fluid migration along preferential pathways. The resulting dolomite are typically lower in Mg than pure dolomite.

In this study, dolomitization is described along the Clarendon Linden Fault (CLF) system in western New York. The CLF is the expression of tectonic crustal adjustment in the Paleozoic rock above the boundary of two basement megablocks of differing petrological provinces. The fault system is a series of east dipping listric normal faults that morphologically look like thrusting reverse faults. Samples of Onondaga limestone were collected at 6 locations east and west of the apparent fault zone, and at 4 locations along the fault zone. Samples were powdered and dissolved in concentrated HNO3. Solutions were analyzed by ICP to determine the concentration of Ca, Mg and selected trace elements to evaluate the dolomitization process and impact of brines on the limestone. Result show a distinct geochemical boundary along the fault zone. Samples collected west of the CLF have Mg concentrations of 0.1 to 0.14% of the sum of Ca + Mg. Along the fault zone and east of the CLF, Mg concentrations rise to 43.8 to 46.8%. These results are indicative of the formation of a saddle dolomite. Trace elements show supportive patterns. The percent Al in the carbonates doubles from west of the fault zone to within the CLF, and shows a 740% increase from west to east of the CLF. These data suggest that the CLF may have extensive associated fracture zones from the CLF to the east, and that deep brines have migrated along these fractures producing alteration of the original limestone.