New Jersey Geologic History

satillite viewNew Jersey Coastal Composition

The New Jersey Atlantic Ocean coastline is roughly 130 miles in length and can be classified into three different shoreline types depending on the purpose of the classification scheme (Figure 1). The New Jersey upland along the coast is composed of gravel, sand and silt deposits whose geological origins are derived from both marine and non-marine sedimentary episodes. None of the sediments exposed at the surface in Monmouth, Ocean, Atlantic or Cape May Counties are cemented to form bedrock like that found along the New England coast. Since the geologic layers are not lithified, they erode easily under marine processes like wave action or tidal currents. These sediments are the source of all modern New Jersey beaches by erosion or by the reworking of other deposits formed from these older sediments prior to the present sea level rise. The rise in global sea level has been transpiring for the past 20,000 years at a variable rate, following the melting of the last great ice sheet covering northern North America. The local change has been in the range of 350 feet to 400 feet vertically, which has produced a long-term westward migration of the shoreline. The "New Jersey" shoreline lay at the edge of the continental shelf 20,000 years ago, 80 to 90 miles to the east of the present coast. As the ice sheets melted and retreated into Canada, the ocean marched across the relatively flat continental shelf constantly changing the position and configuration of the New Jersey shoreline. A review of property records from the 17th Century in Monmouth County has demonstrated up to 2,000 feet of shoreline retreat since about 1650. Concerns about surveying accuracy were answered by reviewing property records from the same era, inland near Colts Neck, NJ. Comparative calculations resulted in less than 50 feet of difference in dimensions of large land parcels originally surveyed in the Seventeenth Century. Lands mentioned in 17th Century records are now ocean, having vanished as the ocean continued its march westward in position and upward in elevation. The pattern followed stream channels back up the valley, flooding low areas first allowing the growth of white cedar trees, then salt marsh grass as tide water reached any particular point. Cores of the seafloor penetrate thin layers of beach sand and then enter dark brown salt marsh deposits that cover cedar peat deposits that can be found only a few hundred feet off the beach opposite the location of fresh water lakes present along the Monmouth County coastline.

The ancient coastal plain sediments are directly exposed to wave erosion from Long Branch, south to Bay Head. This part of the coast has been termed the headlands by Fisher (1965) and by Nordstrom, et al (1977). Along this stretch, the modern beach lies directly in front of a bluff that rises from several feet to 26 feet high. The exposed bluff was often buried by dune sand that blew up over the bluff a short distance inland. Excavations along the bluff margin in Deal show a contact between clean, well-sorted sand from dunes lying over the mixed silts and sands of the older deposits comprising the bluff. Major storms eroded the beach/dune cover and cut into the bluff sediments. The "new" gravel, sand, and silt were sorted by the waves with the sand extracted to supply the beaches. Thus as the bluff retreated, the beach out in front remained well supplied with sand. 

The littoral movement of sand distributed it to other segments of the New Jersey shoreline. This created the modern barrier beaches presently existing between Monmouth Beach and Sea Bright. North of Sea Bright is Sandy Hook, a feature marking the temporary end point of sand deposition by littoral processes. Coastal experts refer to these features as spits. Starting in Long Branch, the spit, which is attached to the mainland bluff, extended north across the mouths of the Navesink and Shrewsbury Rivers to create Sandy Hook. Historical records indicate that Sandy Hook has existed at various times as an island separated from the remaining spit by inlets or was attached to Atlantic Highlands directly with an inlet just south of Atlantic Highlands into the Navesink River. Presently, Sandy Hook is at the end of a long peninsula attached to the uplands at Long Branch. There is little doubt that in the absence of the Sea Bright sea wall, these large-scale alterations to the configuration of this sand barrier would have continued to the present. 

The Nordstrom classification scheme calls the sediment that moved to the