SERPENTINITE BRECCIA ASSOCIATED WITH THE STATEN ISLAND SERPENTINITE: A PALEO-DEBRIS FLOW DEPOSIT

Associated with the Staten Island Serpentinite is a lithified, poorly sorted, unstratified serpentinite breccia containing angular clasts of serpentinite up to 0.35 m in size. The red colored matrix of the serpentinite breccia contains clasts of red sandstone and what appears to be grey shale. In addition, the matrix of the serpentinite breccia is calcareous and contains fine flakes of serpentinite. Structurally, there is no evidence of shearing or foliation in the matrix within the breccia. The presence of red clasts of sandstone suggests that this deposit is either Triassic or post Triassic in age.

Other documented occurrences of Serpentinite breccia can yield important clues into its petrogenesis. Carlson (1984) reported on the depositional facies of sedimentary serpentinite from the Coast Ranges in California and noted the ”Foliate Serpentine breccia of sedimentary but non-detrital origin”. Casey and Dickinson (1984) reported on serpentine - clast conglomerate and Breccia from the Big Blue formation in California. Bate (1984) shows schematic paleogeography and distribution of lithofacies including serpentinous debris flow deposits from the Big Blue formation in the central Joaquin valley of California. Furthermore, mass transport (slumps, slides and flows) can explain the origin of sedimentary serpentinites (Carlson, 1984).

Based on the above characteristics, it is therefore hypothesized that the serpentinite breccia of this study was formed by the transport and subsequent deposition of a debris flow that included angular particles of serpentinite. Petrologic evidence suggests that this deposit is either Triassic or post Triassic.