by
Dr. Alan I. Benimoff revised 10/04/12
Location 1 : Staten Island Serpentimite
Location 2. Graniteville Quarry(research by Alan I. Benimoff Ph.D.
Location 3 Cross bedded strata
Location 4: Terminal Moraine
Geologic Map of Staten Island, New York
The Geology of Staten Island
The borough of Staten Island in NYC exhibits a unique suite of rocks. These rocks reflect an interesting episode of earth history. Situated between the Newark Basin to the west, and the coastal plain to the east, is the Staten Island Serpentinite, which underlies the "highlands" of Staten Island. The Manhattan Prong, a geologic province northeast of Staten Island, contains metamorphosed rocks belonging to the New York City group. The geologic map(above) shows the different rock types that make up the bedrock of Staten Island. This map shows the rock type that lies under the soil and loose earth material. How and when did these rocks form? In an attempt to answer these questions, geoscientists have come up with the following scenario.
THE PALEOZOIC HISTORY OF STATEN ISLAND
500 million years ago, Staten Island as we know it, did not exist. What existed were some continental masses and some ocean basins. One of these continental masses was ancient North America, named Laurentia. At this particular time in earth history Laurentia was at the equator. Other major continental masses that existed at this time are Baltica - ancient Europe; Gondwanaland containing ancient Africa, South America, Australia, Antarctica, and India; fragments of Asia; and some microcontinents. During the last 500 million years these continental masses moved around to their present geographic positions.
The theory of plate tectonics explains how these continents moved. The outer shell(60 miles thick) of the earth, the lithosphere, is made up of rigid shifting plates. These rigid lithospheric plates move on top of the less rigid material of the earth's asthenosphere. Continents and ocean basins ride on these plates. Continents move because they are on plates that move. Presently, there are about 12 major plates. Plate tectonic theory calls for three types of plate boundaries. These are, (1) divergent plate boundaries, where plates move away from each other; (2) convergent plate boundaries, where plates move towards each other; and (3) transform plate boundaries, where plates "side-swipe" each other. As continents on different converging plates approach each other, the ocean between them gradually closes. Subduction is the process where one of these plates "dives" under the other converging plate. The reader is referred to any recent Physical Geology textbook for more on the theory of Plate Tectonics.
During much of the Paleozoic Era , the plate containing the continent of Laurentia(Ancient N.A.) and the plate containing the continent of Gondwanaland were converging. The proto-atlantic ocean that separated the two continental masses gradually closed. The resulting continental collisions formed the Appalachian Mountains. During the early stages of this mountain building event, a piece of ocean crust from the proto-atlantic ocean broke off and became incorporated into the collision zone. The altered remnant of this broken off piece is now the oldest bedrock unit of Staten Island, namely the serpentinite. This unit is lower paleozoic (approximately 430 million years old) in age, and consists predominately of the serpentine minerals, antigorite, chrysotile, and lizardite. This green rock is visible at the I-278 Sunnyside road cut, and at other localities. By the end of the Paleozoic era (248 million years ago) all major continental masses collided and were sutured into the supercontinent of Pangaea.
THE MESOZOIC HISTORY OF STATEN ISLAND
As Pangaea split apart in the early mesozoic era (approximately 225 million years ago) the Newark Basin began to form. The Newark Basin, which extends from Rockland County New York to southeastern Pennsylvania, is one of 16 such ENA(Eastern North America) basins that formed as the supercontinent of Pangaea split apart. The basins formed as a result of tensional stresses acting on the crust. These tensional stresses were associated with the newly formed divergent plate boundary. During this time the present day Atlantic Ocean began opening. Since the plate break occurred in a different area than the plate suture, pieces of ancestral africa remained attached to eastern North America. Earth material eroded from the adjacent highland regions was deposited in these newly formed basins during the late triassic to early jurassic periods(230-198 million years ago) of the early mesozoic era.
The sediment was subsequently lithified into hard Sedimentary rocks. The sedimentary rock units of the Newark Basin that appear as bedrock on Staten Island are (1) the Stockton Formation consisting of sandstones and arkoses; (2) the Lockatong Formation consisting of siltstones and shales; (3) the Passaic Formation consisting of shale, siltstone, sandstone, and conglomerate. In the early jurassic (192-186 million years ago) molten rock from the earth's mantle(below the crust) intruded between layers of sedimentary rock in the Newark Basin and crystallized into the igneous rock diabase that consists predominantly of the feldspar labradorite and the pyroxene augite. In other parts of the Newark Basin lava flowed on the surface during the same time.
During the cretaceous period of the late Mesozoic era( approximately 80 million years ago) material eroded from adjacent highland areas was deposited as coastal plain sediments such as the Raritan and Magothy formations.
THE CENOZOIC HISTORY OF STATEN ISLAND
During the last 2 million years four major glacial ages are recorded in earth history. The most recent glacial age, namely the Wisconsin, began approximately 90,000 years ago, and by 22,000 years ago the ice reached its maximum southern extent, covering all of what is now New York City.
The southern boundary of the Wisconsin glacier is now represented by the terminal moraine which crosses Staten Island. As the ice retreated, and the region became deglaciated, a blanket of loose unconsolidated, poorly sorted material referred to as glacial till was deposited. Glacial meltwater deposited outwash plain sediments south of the terminal moraine.
A gradual rise in sea level during deglaciation resulted in the flooding of former stream and glacial valleys. Drainage patterns of streams and rivers were altered during deglaciation.The surficial map of Staten Island is shown below.
Suggested reading:
Continental Collisions and Ancient Volcanoes: The Geology of Southeastern New York by Yngvar W. Isachsen, Educational Leaflet No. 24 published by The New York State Educational Department.