Geology of New York (state)
The Adirondack Mountains, Thousand Islands, Hudson Highlands, and Fordham gneiss, along with outcrops in the Berkshires just over the state line in Massachusetts, are part of the Grenville Province, a large piece of continental crust which accreted to the Canadian Shield and underlies much of Quebec, Ontario as far west as Lake Huron and as far east as Labrador.
These rocks date to 1.3 to 1.1 billion years ago in the Proterozoic and formed from lime mud, sand and clay on coastal barrier islands as well as evaporites in intervening lagoons.
[1] 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.
A reversal in mantle convection currents around 445 million years ago, in the Middle Ordovician, launched the Taconic orogeny and closed the Iapetus Ocean.
This complex tectonic situation produced intense folding, fracturing, thrust faults and large landslides which are now preserved in the Taconic Mountains.
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.
A rift valley lake deposited the mudstone and black shale of the middle unit—the Lockatong Formation—which holds extremely well preserved fossilized freshwater fish.
Because rifting thinned the crust, magma upwelled and intruded the basin, producing the feldspar and pyroxene dominant diabase of the Palisades Sill and an almost pure layer olivine up to six meters thick.
[3] 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.
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.
Deeply weathered saprolite soils formed throughout the region, with small remnants found in New York City, the Adirondacks, and Catskills during highway construction.
