Geology of New York (state)
The geology of the
Stratigraphy, Tectonics & Geologic History
The igneous and metamorphic crystalline basement rock of New York formed in the
The Avalonian mountain building event 575 million years ago in the Neoproterozoic is poorly understood but deformed and metamorphosed the Hudson Highlands and Manhattan Prong.
Paleozoic (539-251 million years ago)
New York constituted a continental margin in the Paleozoic as multi-cellular life became common. As the proto-Atlantic Ocean opened, a marine transgression in the Cambrian and Ordovician flooded much of the region, with the Potsdam Sea transgressing westward.
A reversal in mantle convection currents around 445 million years ago, in the
The current day Taconic Mountains are the stubs of towering ancient mountains, as evidenced by high-pressure metamorphism indicating that extant rocks were buried under miles of overburden, which subsequently eroded. The sedimentation pattern changed from gradual deposition toward the east to much more rapid sedimentation to the west, filling in the Queenston Delta from the late Ordovician onward into a shallow sea. At the end of the Taconic orogeny, an unconformity appears with the uplift and erosion of the massive delta.
In the Silurian and Devonian, new sediments covered the erosional surface, beginning with the white quartz pebbles of the Shawangunk conglomerate. Crustal stretching created a series horst and graben features, which remain in the Adirondacks as well as in the Mohawk, Hudson and Champlain areas. Down-dropped grabens preserved Ordovician rock from erosion.
Between 375 and 335 million years ago, the proto-Atlantic Ocean closed, forming the supercontinent Pangaea. The Acadian orogeny formed a massive range, much taller than the heavily eroded Taconics further to the east. Rocks in what is now eastern New York as far west as the Adirondacks was "overprinted" with new mineral assemblages forming due to deformation that had begun in the Taconic orogeny.
The newly formed mountains rapidly eroded and shed sediments, even as uplift continued. A massive apron of sediment formed the Catskill Delta to the westward, burying much of the Taconics and filling in a shallow sea. The Catskill Mountains formed through erosion of the debris field from the Acadian mountains.
The Peekskill granite intruded after the orogeny, in Westchester County, between 335 and 320 million years ago. Around 250 million years ago, the final Appalachian mountain orogeny, the Alleghanian orogeny occurred. Geologists debate whether gentle east–west folds in the Alleghany Plateau are remnants of this orogeny.[2]
Mesozoic (251-66 million years ago)
The Newark Lowlands of the
Offshore of New York is the Fall Zone Peneplain, an area of much more ancient crystalline rocks that forms the slowly sinking continental shelf of eastern North America. Eroded nearly flat, this surface began to be covered by the current sediments of the
A research well, COST B-3 drilled 130 kilometers off of Long Island in the Baltimore Canyon Trough, encountering two-kilometer thick rocks from the Cretaceous. Most rocks offshore are marl with some clay and limestone. The green mineral glauconite is particularly common.[4]
Cenozoic (66 million years ago-present)
Aside from sediments produced or moved by glaciers, rivers and streams during the last 2.5 million years of the Quaternary, Cenozoic rocks are extremely rare in New York. A small Oligocene lignite deposit near Brandon, Vermont may extend into New York. Several kilometers of rock eroded and deposited offshore in the Atlantic coastal plain and eastern North American continental shelf.
Drilling offshore of New Jersey and Long Island indicates Cenozoic sediments 130 meters thick reaching up to 1.5 kilometers thick near the edge of the continental shelf. The biggest increase in thickness took place during the Miocene. Deeply weathered saprolite soils formed throughout the region, with small remnants found in New York City, the Adirondacks, and Catskills during highway construction.
Rivers responsible for transporting sediment out of the region were significantly rechanneled or filled with sediments during the Pleistocene glaciations. The Erian River once downcut Middle Devonian shales, feeding into the Erie Basin while the Ontarian River eroded Ordovician shales into the Ontario Basin. The Sound River has been inferred as an eastward flowing river replaced by Long Island Sound.[5]
References
- ISBN 978-0-87842-180-0.
- ^ Van Diver 1985, p. 22-28.
- ^ Isachsen, Y.W.; Lauber, J.M.; Landing, Ed; Rickard, L.V.; Rogers, W.B. (2000). Geology of New York: A Simplified Edition. New York State Education Department. pp. 270–280.
- ^ Isachsen et al. 2000, p. 285-289.
- ^ Isachsen et al. 2000, p. 295-299.