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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 540

Last Page: 541

Title: Lithologic Comparison of Two Linear Sand Ridges from Nearshore and Middle Portions of New Jersey Continental Shelf, U.S.A.: ABSTRACT

Author(s): J. M. Rine, R. W. Tillman, W. L. Stubblefield

Article Type: Meeting abstract


Two linear sand ridges from the nearshore and middle portions of the New Jersey continental shelf were sampled using a vibracore system and box corer. Lithologic descriptions were made of the cores based on epoxy peels, X-ray radiographs, and impregnated core slabs. The cores were sampled for grain-size analysis. Box cores sampled lithologies and relative abundance of physical and biogenic structures found in the upper 25 to 46 cm (9.8 to 18.1 in.) of the sediment. Bottom topographies were established using 3.5 kHz data.

The nearshore sand ridge sampled (74°22^primeW, 39°19^primeN) exceeded 5 km (3 mi) in length and ranged up to 2 km (1.2 mi) in width and had a relief of 6 to 10 m (20 to 33 ft). A mid-shelf ridge (74°08^primeW, 39°09^primeN), nearly 4 km (2.5 mi) long and up to 1 km (0.6 mi) wide, with a relief of 10 to 11 m (33 to 36 ft) was also studied.

The vibracores averaged 6 m (20 ft) of penetration and in excess of 95% recovery, and although partially deformed as a result of the coring procedure, revealed three general lithologic units which may be common to both ridges.

At the base of many of the cores, nonskeletal mud and poorly sorted sand 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 for the most part 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 are of different ages.

The top unit in all the cores is a fine to medium-grained sand, here termed the upper ridge sand. This unit, similar in both ridges, consists of stacked beds ranging from 3 to 71 cm (1.2 to 28 in.) in thickness, and generally coarsens upward. This unit in the nearshore ridge system has a slightly coarser mean grain-size range (150 to 400 µ) than the mid-shelf ridge (130 to 350 µ). Both ridges contain some alternating laminated and nonlaminated bed sequences. C-14 dates from the upper ridge sand units are indecisive in establishing whether the upper units in the nearshore and middle shelf are time equivalent. Nearshore box cores which only penetrate the upper ridge sand from 25 to 46 cm (9.8 to 18.1 in.) contain well-developed ripples and cross-bedding; physical structures do inate. The middle shelf box cores are dominantly burrowed sand and are muddier than nearshore box cores.

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Major observations from this study are: (1) what is interpreted as the base of the nearshore ridge directly overlies skeletal rich sediments, whereas what is interpreted as the base of the middle shelf ridge directly overlies sediments without skeletal remains; (2) skeletal rich and nonskeletal lithologies are present in the relief-forming portions of the ridges; and (3) the upper unit, the "upper ridge sand," is generally similar in character on both ridges.

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