MAPPING THE MARINE WANTAGH FORMATION, COMMONLY KNOWN AS THE 20 – FOOT CLAY, IN QUEENS AND BROOKLYN, NEW YORK

There are 2 inter-glacial/stadial marine strata of uncertain age in NYC, the Gardiners Clay and the Wantagh Fm. The Gardiners (pre-Illinoian – AAR dates or Sangamon – ¹⁴C) has been found in scattered locations in lower Manhattan and NY Harbor and is mapped in southern Brooklyn and Queens (Buxton & Shernoff 1999) and eastward to Quogue, NY. It is overlain by a layer of glacial outwash (Merrick Fm. – Rampino & Sanders 1981), which in turn is overlain by the Wantagh, a discontinuous unit (Sangamon or mid-Wisconsin age) mapped along the south shore of Long Island (Doriski & Wilde-Katz 1983) that continues westward into NYC.

New borings from Post-Sandy rebuilding projects, in addition to data in MRCE archives, allows for a more detailed mapping of the Wantagh in NYC. The northern edge of the Wantagh does not extend as far inland or as far to the east as the underlying Gardiners. It is unclear if this reflects deposition at a lower relative sea level or greater subsequent erosion. The stratum has not been identified in Manhattan, NY Harbor, or along the north shore of Jamaica Bay.

The Wantagh is a 20’ to over 40’ thick layer present below the western 1/3 of Coney Island. Its surface slopes westward from ~El. -40’ to -60’, then drops off steeply at the very western edge of Coney Island, as does the underlying sand. Both strata were likely scoured deeper by water flowing from the Hudson. Heading eastward, the Wantagh quickly lenses out and appears to be absent to around Broad Channel/Seaside where it reappears, initially lensing in and out eastward to Arverne, where it mostly fills depressions in the underlying sand. The unit appears to be missing along the barrier island between Arverne and Edgemere and becomes more continuous at the Far Rockaway mainland.

Heading northward at Broad Channel and the Rockaways the Wantagh shallows slightly. In general, where present it tends to be a 10’ to 20’ thick layer found somewhere between elevations -30’ to -60’ along the barriers and -20’ to -50’ at its northern edge. It appears to be scoured away in at least part, if not most, of Jamaica Bay between Broad Channel and the Rockaways.

The Wantagh often has shallow organic layers and lenses above it associated with more recent channel fill and marsh development. The Wantagh is often, but not always, a stiffer clay, so it may be difficult to differentiate from these younger sediments.