Generation of Late Holocene Sand Ridges on the Middle Continental Shelf of New Jersey, USA—Evidence for Formation in a Mid-Shelf Setting Based on Comparisons with a Nearshore Ridge
- D. J. P. Swift5,
- G. F. Oertel5,
- R. W. Tillman6 and
- J. A. Thorne7
Published Online: 14 APR 2009
Copyright © 1991 The International Association of Sedimentologists
Shelf Sand and Sandstone Bodies: Geometry, Facies and Sequence Stratigraphy
How to Cite
Rine, J. M., Tillman, R. W., Culver, S. J. and Swift, D. J. P. (1992) Generation of Late Holocene Sand Ridges on the Middle Continental Shelf of New Jersey, USA—Evidence for Formation in a Mid-Shelf Setting Based on Comparisons with a Nearshore Ridge, in Shelf Sand and Sandstone Bodies: Geometry, Facies and Sequence Stratigraphy (eds D. J. P. Swift, G. F. Oertel, R. W. Tillman and J. A. Thorne), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303933.ch12
Norfolk, Virginia, USA
Tulsa, Oklahoma, USA
Plano, Texas, USA
- Published Online: 14 APR 2009
- Published Print: 30 JAN 1992
Print ISBN: 9780632032372
Online ISBN: 9781444303933
- generation of late Holocene sand ridges on middle continental shelf of New Jersey, USA— evidence for formation in mid-shelf setting;
- coring procedures - Vibracores obtained with Alpine Vibracore;
- general lithostratigraphic units;
- shell-rich poorly sorted sand and mud unit;
- statistical discrimination of lithostratigraphic units;
- nearshore ridge 1a and mid-shelf ridge 2;
- mid-shelf ridge development scenario
Data from this study support a new theory that sand ridges on the middle continental shelf of the Middle Atlantic Bight were formed seaward of the nearshore, probably at or near present-day water depths. An implication of this theory is that more sediment transport and deposition is occurring seaward of the nearshore zone than previously hypothesized.
In 1979 a consortium of oil companies and the National Oceanographic and Atmospheric Administration (NOAA) conducted a geological investigation of two linear sand ridges, ridges 1A and 2, on the New Jersey continental shelf. Two separate ridge systems were studied because of differences in their characteristics and because of differences in published theories concerning their origins. Ridge 1A is a nearshore ridge within 4.8 km of the shoreline and in less than 20.3 m of water. Ridge 2 is a mid-shelf ridge, 40 km from shore and in 25–36 m of water.
Three general lithological units are in the sedimentary sequences recovered in vibracores from both ridges 1A and 2. The basal ‘non-fossiliferous’ mud and sand unit contains no macrofauna, traces of microfauna, and few burrows within its layers of sand, laminated muds and pebbly sand. The medial shell-rich poorly sorted sand and mud unit contains numerous shell fragments and is for the most part bioturbated. The upper ridge sand unit generally coarsens upward, is fine to medium-grained, and consists of stacked beds of sand (2.5–70 cm in thickness) that have alternating laminated and nonlaminated (bioturbated) layers. The upper ridge sand unit is interpreted to be the actively depositing portion of both ridge 1A and ridge 2.
Discriminant analysis of grain-size data and differences in the assemblages of benthic Foraminifera indicate that the upper ridge sand unit of ridge 2 was not deposited in the same setting as ridge 1A. Multiple discriminant analysis, utilizing 50 grain-size parameters, was used to test the validity of the lithostratigraphic units and to determine if the units could be distinguished according to ridges. Within the individual ridges, 97% of the samples in ridge 1A and 95% in ridge 2 were discriminated correctly into lithostratigraphic units. In a comparison of only the upper ridge sand samples from both ridges, 93% of the samples were correctly discriminated according to their respective ridge.
Foraminiferal faunas of the upper ridge sand units in ridges 1A and 2 show considerable differences both in species present and in relative abundances of species that the ridges contain in common. Although both ridges are located within an inner shelf foraminiferal biofacies (shallower than 60 m) the foraminiferal assemblages of ridge 1A are interpreted as representing an open inner shelf environment of normal marine salinity and the assemblages of ridge 2 are interpreted as representing open inner to middle shelf conditions.
The findings of this study support the following model. Time 1, during a period of slow sea-level rise or a stillstand, sand was concentrated by nearshore processes into a barrier/strandplain in the vicinity of the present-day mid-shelf. Time 2, as the rate of sea-level rise increased, the band of concentrated sands was reworked by inner shelf and eventually mid-shelf processes. Time 3 (present day), a majority of the sediment originally deposited in the nearshore has been reworked and redeposited by mid-shelf processes. This mid-shelf deposited sediment comprises the up-to-5.5-m-thick upper ridge sand unit of ridge 2.