Sequence Stratigraphy of Upper Pleistocene-Holocene Sediment, Middle U.S. Atlantic Shelf

Robert D. Winn Jr., William J. Schweller, Roderick W. Tillman, Steven J. Culver

Vibracores, seismic-reflection data, boxcores, grab samples, foraminiferal biostratigraphy, and ¹⁴C isotopic dates from the middle U.S. Atlantic shelf indicate a complicated stacking of facies in the shallow subsurface. The site investigated is 35 km from the New Jersey shore in 22-36 m of water in an area of sand ridges. The upper 25 m of sediment from bottom to top consists of: (1) a mostly shallow-marine sand and mud; (2) a discontinuous, non-fossiliferous, cross-bedded and ripple-laminated sand and gravel of probable valley-fill origin; (3) a transgressive, shell-rich gravel and gravely sand; (4) a complexly interstratified sand, gravel, and mud; and (5) surficial ridge sand. Radiocarbon isotopic dates of the lower sand and mud regionally range from >36. -22.035 ka indicating deposition across the middle Wisconsinan-late Wisconsinan boundary probably during falling sea level. The cross-cutting erosional lower contact of the valley is interpreted as the late Wisconsinan maximum glacial lowstand sequence boundary. The valley fill and overlying gravel and gravely sand were deposited during early stages of the late Wisconsinan-Holocene sea level rise. Radiocarbon dates of the overlying sand, gravel, and mud, in turn, are from 13.24-10.95 ka indicating continued deposition during the late Wisconsinan transgression, although sedimentation may have continued into the Holocene. Sedimentary structures and foraminiferal paleoecology of the unit indicate sedimentation in low-energy back barrier, tidal channel, and possibly tidal delta, tidal inlet, and upper-shoreface environments. A dominantly inner to middle shelf foraminiferal assemblage and ¹⁴C dates of 7.5-<0.5 ka indicate deposition of the ridge sand during the Holocene beyond inner-shelf water depths. The sand ridges probably were reworked from shallow-water precursors. Ripple cross lamination recovered in boxcores indicate episodic present-day sand movement during storms.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995