Abstract

Two linear sand ridges from the nearshore and middle parts of the New Jersey continental shelf were sampled using vibracores and box cores. Lithological descriptions were made of the cores, based on epoxy peels, X-ray radiographs, and impregnated core slabs and grain size analysis. Vibracores obtained for the study have an average penetration of 6 m and 95% recovery. Box core samples revealed lithologies and relative abundance of physical and biogenic structures found in the upper 25 to 46 cm of the sediment. Bottom topography was established on the basis of 3.5 kHz seismic data.

The nearshore sand ridge that was sampled (74°22′W, 39°19′N) exceeds 5 km in length and ranges up to 2 km in width and has a relief of 6 to 10 m. The mid-shelf ridge (74°08′W, 39°09′N) is nearly 4 km long, up to 1 km wide, and has a relief of 10 to 11 m.

Three to four general lithological units were recognized; these may be common to both ridges. At the base of many of the cores, nonskeletal mud and poorly sorted sands are present; some of the interlayered sands and muds contain laminations and abundant pebbles. Overlying this unit in the nearshore ridge is a shell-rich mud and sand interval that is relatively massive (bioturbated). This lithology was also recovered in one core from the middle shelf ridge. C-14 dates taken from the shell rich units indicate that the middle and nearshore ridges differ in age by more than 6000 years.

The top unit in all the cores is a fine- to medium-grained sand, here termed the upper ridge sand. This unit is similar in both ridges and consists of laminated, stacked beds ranging from 3 to 71 cm in thickness, and generally coarsens upward. This unit in the near shore ridge system has a slightly coarser mean grain-size range (150 to 400μ.) than the mid-shelf ridge (130 to 350μ). Both ridges contain alternating laminated- and non-laminated bed sequences.