SUBMARINE SAND RIDGES: GEOLOGY AND DEVELOPMENT, NEW JERSEY, U.S.A. (MARINE GEOLOGY, SHELF SEDIMENTATION)

Four areas with submarine sand ridges are studied on the New Jersey continental shelf. Two areas located on the nearshore, one on the mid-shelf and one on the outer shelf are studied through extensive use of high resolution seismic and vibracores. Despite their different orientations, the nearshore and the mid-shelf ridges are believed to have similar origins.; The ridges and underlying strata are subdivided into seismic units of distinct character. The upper unit of the ridges (Green seismic unit) lacks internal reflectors and is bounded by a horizontal reflector on its lower contact. The undelying seismic unit (Red Unit) has a variety of internal reflectors, including channel structures and inclined and irregular reflectors. In some cases, the Red unit, as well as the Green unit, are included in the ridge topography. Below the Red unit are other units which are mostly transparent to seismic (Brown in Area 1A, Blue in Areas 1B and 2, and Orange in Area 3).; Correlation of vibracore data with seismic indicates that the upper seismic unit (Green unit) is made of fine- to medium-grained sand and is deposited in the shoreface to shelf environment. The underlying seismic unit (Red unit) corresponds to a shell-rich, poorly-sorted sand and mud and represents inlet and backbarrier channel deposits. The deeper, mostly transparent units (Brown, Blue, and Orange), are inferred to be mud strata from a backbarrier or bay environments.; The upper unit (Green) is Holocene in age while the underlying unit (Red) can include Holocene and Pleistocene sediments. The deepest mapped units are inferred to be Pleistocene or older in age.; It is hypothesized that the nearshore submarine sand ridges begin forming at inlets and develop as sea level rises and shoreface retreats. The closing of inlets does not halt ridge development. The process of formation of the mid-shelf ridges is considered to be a variation of that of the nearshore ridges. It is suggested that the mid-shelf ridges are formed sub-parallel to the shore because of the large offset of the inlet downdrift margin.