GEOCHEMICAL SIGNIFICANCE OF THE INWOOD MARBLE, MANHATTAN, NY

The Cambro-Ordovician Inwood Marble outcrops in Manhattan, NY and comprises much of the northern end of the island. It varies from pure white calcitic to dolomitic coarse grained marble, which is very siliceous, in places. In outcrops it typically displays buff colored weathering and a saccharoidal surface texture. Prominent solution features ranging from a few millimeters to several centimeters in diameter are quite evident in the field. There are occurrences of large-scale void spaces in the subsurface (from test borings), often filled with residual silicates such as chlorite and phlogopite. Significant heterogeneity in marble composition, observed in the field, may be attributed to facies variations in the protolith. In places, highly pyritiferous zones, suggesting alteration of the parent rock due to subsequent mineral-rich fluid flow, are observed. Silicate components, observed in the marble, are tremolite, diopside, phlogopite, chlorite, garnet, and quartz. Preliminary bulk chemical analysis indicates a magnesium rich (dolomitic) marble with variable concentrations of silicates. The overall chemical differences between the calcitic and dolomitic marble in terms of trace elements are noted in the analyzed samples, and may reflect the existence of mixed carbonate and siliciclastic deposition associated with the Iapetus Ocean environment.