SEA-FLOOR CHARACTER AND SEDIMENTRAY PROCESSES OFFSHORE OF ROCKY POINT, NEW YORK

The USGS, in cooperation with NOAA and the CT DEP, produces detailed maps of the sea floor in Long Island Sound. The current phase of this research focuses on studies of sea-floor topography and its effect on the distributions of sedimentary environments and benthic communities within a 28.7 square kilometer area offshore of Rocky Point, NY. Exposed boulder lag deposits, sand-wave fields, and scour features, which reflect the strength of the oscillating tidal currents, are visible in the digital terrain model and on the sidescan-sonar mosaic. Boulders and gravel are prevalent off Rocky Point and in the shallow water along the Long Island shoreline in the western part of the study area. These are high-energy areas characterized by sedimentary processes associated with erosion and nondeposition that have winnowed the submerged northern flank of the Harbor Hill – Roanoke Point – Orient Point moraine, leaving coarse lag deposits. Beds of shell debris and seaweed are common in and adjacent to rockier parts of the study area. These beds are ecologically important because they add considerably to the overall benthic compositional complexity. Sand is the dominant sediment offshore in the western part of the study area, on top of Orient Shoal, and in the protected area between Rocky and Terry Points. Much of the sea floor in the offshore sandy areas is covered with sand waves and megaripples, and the stoss slopes of these bedforms are covered in current ripples. These bedforms reflect sedimentary environments characterized by ongoing processes associated with coarse bedload transport. Bedform and scour asymmetry indicates that nearshore transport is predominantly eastward, but offshore transport is primarily westward in the northern and western parts of the study area. Sand-wave asymmetry adjacent to Orient Shoal indicates clockwise sediment transport is important to shoal morphology and maintenance.