COASTAL AND ESTUARINE SEDIMENTARY ENVIRONMENTS OF EASTERN LONG ISLAND SOUND

The fluvial-estuarine to marine coastal system of Long Island Sound (LIS) and its tributary rivers along New York and Connecticut is dynamic with distinct sedimentary environments representative of a wide range of processes. Detailed studies of these facies permit to characterize recent sedimentation processes and evaluate how coastal LIS may be modified by sea-level rise and storms. Long Island Sound is a tidal dominated estuary with tidal velocities decreasing from E to W from 60 to 10 m/s. Sediment grain size also decreases from E to W from coarse to fine. We focus on eastern LIS that was mapped and sampled as part of The Long Island Sound Cable Fund Habitat Mapping. We acquired multibeam bathymetry, acoustic backscatter, subbottom profiles, 31 gravity cores <2 m in length and 300 grabs from eastern LIS. Based on core photos and X-rays, grain size variability, lithological descriptions, and physical properties (bulk density and magnetic susceptibility) we distinguish different sedimentary environments in the cores: 1) low energy environments where the sediments are composed of clayey silts and silty clays, have been homogenized by bioturbation and not much change has occurred through time. 2) Moderate-energy, with episodic sedimentation characterized by coarser grained beds and clayey silt and silty clay intervals. The more energetic sand-rich intervals have sharp lower and upper contacts, laminae and lenses, and are reworked as evidenced by floating lithic clasts, shell fragments and wood. Potential hiatuses are revealed by truncated strata, sharp contacts and dramatic changes in sedimentation. 3) High energy facies dominate the central part of the estuary and the southern shore of Fisher’s Island. Offshore the facies are composed of medium to coarse sand, low bioturbation and fossil species are marine.