Geology of the New York City Region

Quaternary and Holocene Deposits of the Coastal Plain

HOLOCENE DEPOSITS - The modern beach and barrier islands around the New York Bight represent reworked sand material that began accumulating during a slow-down in sea level rise that began about 3-4,000 years ago. These modern coastal deposits overlie older Holocene estuary and fluvial sediments deposited behind barriers during a period ranging from 12,000 to about 7,000 years ago when sea level was lower. (These old barrier deposits are partially eroded and/or buried by younger sediments and exist anywhere from 2 to 20 kilometers seaward of the current shoreline). These ancient barriers are currently supplying sediment to offshore sand ridges on the continental shelf. Sand along the Hudson River and on Staten Island displays an abundance of angular feldspar and lithic fragments indicative of fluvial sedimentation in the harbor region when sea level was lower. Modern anthropogenic sediments and human activity has modified nearly all coastal and nearshore marine sedimentary environments.

WISCONSIN GLACIAL TILL - Wisconsin glacial deposits are apparent everywhere on Long Island, across northern Staten Island and throughout northern New Jersey. Glacial till consists of an unstratified mix of clay, silt and sand within a mix of rock material ranging from pebbles to giant boulders (derived from all rock source areas all the way from Manhattan to Central Quebec). On Long Island the terminal moraine is represented by two ridges that extend the length of the island: the southern, older Ronconcoma moraine and the northern, younger Harbor Hill moraine along the Sound. The terminal moraine extends across central New Jersey along a sinuous line from the vicinity of Perth Amboy to just south of the Delaware Water Gap on the western side of the state. Outwash sand and gravel deposits (altered by soil-forming processes) cover much of southern Long Island, southern Staten Island and areas south of the terminal moraine in New Jersey, particularly along the lower Delaware River Valley. Varved lake clays and swamp peat cover areas flooded by lakes that formed in lowland regions north of the terminal moraines shortly after the glaciers receded.

GARDENERS CLAY - This poorly consolidated clay underlies Wisconsin Age glacial deposits throughout southern Long Island, and it has been interpreted as occurring beneath the modern barrier spit of Sandy Hook. The Gardeners Clay contains a rich estuarine fauna with abundant foraminifera. Many of the fossils found on area beaches are probably derived from the Gardeners Clay or equivalent strata. The unit probably represents high-standing seas between advances of the latest Pleistocene (Wisconsin) glacier.

COLUMBIANA GROUP (early to late Quaternary) consists of three named units: the Pensauken; Bridgetown; and Cape May formations (oldest to youngest, respectively). Each represents different depositional environments throughout the region: the Pensauken and Bridgetown Formations are the result of glacial outwash and interglacial stade fluvial sediments preserved in stream terrace deposits (primarily along the "saddle" west of the Atlantic Highlands between Raritan Bay and the Delaware River Valley). The Cape May represents coastal plain deposits along the southern and eastern shores of New Jersey. The correlation of these terrestrial deposits with offshore areas are poorly resolved..

CAPE MAY FORMATION - (Late Pleistocene to Holocene) - The Cape May formation consists of surficial silts, sand and quartz-rich gravels along the coastal region of New Jersey; it represents coastal barrier and beach ridge sand and back bay estuarine deposits. The source of the clastic material is mostly from the Delaware River drainage supplemented by shelf sands and longshore drift from the Mid-Atlantic region. The progressive reworking of Cape May deposits is the source of much sand on beaches along the New Jersey coast.

PENSAUKEN FORMATION - (Late Pleistocene) - Wisconsin till unconformably overlies this unit that crops out along a trend from Staten Island to Trenton, NJ and southward along the Delaware River Valley. The unit consist of mixed detritus (eroded from older glacial material and exposed Coastal Plain formations), deposited in fluvial flood plain environments. The existence of the Pensauken Formation suggests that, for a time, the major drainage from the pre-Wisconsin glaciers was southward from the New York area toward Trenton into the lower Delaware River basin. Pedogenic weathering of the sediments suggests that it was deposited, in part, during a warm interglacial period. In the Raritan Bay area, the Pensauken Formation is equivalent to terrace gravel deposits between around 30 to about 60 feet above modern sea level. These terrace deposits contain an abundance of orange-to-brown iron-stained quartz pebbles in heavily weathered sediments that have endured long-term subaerial weathering.

BRIDGETOWN FORMATION - (Early Pleistocene) - This formation is limited to the terrace deposits along the Delaware River Valley. The precise age of the Bridgetown Formation is unclear, however, it consists of a deeply weathered mix of silt, sand, and gravel, representing fluvial environments. The Bridgetown probably signifies sedimentation during an earlier, pre-Wisconsin interglacial stade.

Return to Geology of the Coastal Plain Province.
Continue to the next page. Return to Main Page
The URL is:
Last modified: 3/11/2019