Environments of Deposition on an Offshore Barrier Sand Bar, Moriches Inlet, Long Island, New York

Michael G. Mackenzie

Abstract


Environments of deposition associated with an offshore barrier sand bar system at Moriches Inlet, Long Island, New York, were studied by mechanical analysis and heavy mineral analysis. Samples collected from six traverses normal to the barrier trend were statistically defined by measurement of mean diameter (Mɸ) and standard deviation (σɸ). Variations in heavy mineral content in different parts of the sand bar are related to the concept of hydraulic equivalent size in sedimentation. By relating threshold velocity (Vt) to grain characteristics, the concept of hydraulic equivalent size, developed for water-transported sands, can be effectively extended to wind-blown particles. Two distinct sedimentary regimes are defined by the methods used in this study, namely, a forebar and a backbar. The small dimensions of the environments studied preclude further subdivision by these methods. Results are discussed with reference to fossil shoestring sand bodies found in the geologic record. It is concluded that lateral mineralogical and textural variations should be combined with gross geometric properties in studies involving the genesis of shoestring sands.


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