SEA-FLOOR CHARACTER AND SEDIMENTARY PROCESSES OFFSHORE OF THE CONNECTICUT RIVER, NORTHEASTERN LONG ISLAND SOUND

The USGS, in cooperation with NOAA and the CT DEEP, has produced detailed, interpretive maps of the Long Island Sound sea floor. The current phase of this research focuses on studies of sea-floor topography and on the distributions of sedimentary environments and benthic habitats within a 29.1 sq. km area off the mouth of the Connecticut River. The surficial-sediment distribution is a product of the Quaternary depositional history and modern environmental conditions. Bedrock outcrops, boulder lag deposits, gravelly pavements, and scour features, that together reflect the strength of the oscillating tidal currents, are prevalent off Hatchett Point and around Hatchett Reef. These are high-energy areas characterized by sedimentary processes associated with erosion and nondeposition. Outcrops, which are elongate and have trends similar to onshore glacially-smoothed ridges, and larger rocks are overgrown with sessile fauna and flora that add to the overall benthic complexity. Sand waves and megaripples cover more than 50% of the study area, reflecting moderate conditions characterized by processes associated with coarse bedload transport. Transverse bedform morphologies dominate on shoals where sand supply is abundant; barchanoid morphologies occur along the southern edge of the study area and east of Hatchett Reef where sand supply is more limited. Megaripples and current ripples, are typically present on the stoss slopes of sand waves, showing that transport is ongoing. Sand-wave, megaripple, and obstacle-mark asymmetry shows that net sediment transport is flood-tide dominated and to the west. Where protected, such as northeast of Hatchett Point, the sea floor is relatively flat, sediment mud content increases, infaunal communities are better developed, and lower energy sedimentary environments characterized by processes associated with sorting and reworking prevail. Shell beds have accumulated at the western end of the elongate depression between Hatchett Reef and the mainland and around some of the rocky areas, but these beds are generally thin and ephemeral.