Overall Picture of Tectonic Past

The rock record of New York State tectonic history begins with Grenville rocks. They are so named after the Grenville orogeny (mountain building episode), which took place approximately 1 billion years ago, and represents a continent to continent collision. At this time, configuration of continents on the planet formed Rodinia, or proto-Pangea, a composite of Laurentia (North America) and Gondwanaland (the Southern continents). In Grenville orogeny, older rocks were metamorphosed, and their age was reset to about 1 billion years. Prior to Grenville, this continent edge was most likely a passive continental margin, i.e. experienced a time of tectonic quiescence.

Drilling shows that Pre-Cambrian Grenville rocks are present underneath Paleozoic in nearly all of New York State, but are exposed in Adirondacks, due to later uplift of Adirondack dome. The High Peaks are underlain by intensely deformed olivy-green anorthosites, granitic gneisses, quartz, feldspar, biotite (meta-igneous and igneous rocks). However, the Adirondack dome is a very young geologic feature which is in no way related to any of the earlier orogenies, and is still being uplifted at the present moment.

(Photography by Andrew Vakhutinsky. High Peaks, Adirondacks region)

After some time of erosional activity, a new tectonic cycle began. About 600 million years ago, a rift developed in this area. The splitting of the continent created ocean floor for the proto-Atlantic ocean (called Iapetus ocean) with Laurentia (North America) on its North-West side. Early Paleozoic sediments and volcanic material (basalts) were deposited. Transgression (sea level rise) began as the sea-floor spreading rate increased; by the end of Cambrian, the sea covered almost all of this region, developing a continental shelf, slope and rise.

In mid-Ordovician, the tectonic cycle was coming to a completion. The ocean closed, and as our continent collided with an island arc, a new orogenic event took place. In the Taconic orogeny, accretionary wedge (low density material scraped off the incoming subducting plate) was thrusted onto the continent. This affected Northern Maine, Western New England, adjacent New York, Northern New Jersey, and South-Eastern Pennsylvania. Mountains were produced, and a Queenston delta was built. As the mountains wore down with time, the sea readvanced over them once more.

Acadian orogeny, which started in Mid-Silurian and lasted until Mid-Devonian, was caused by collision of three continents, as Avalonia collided with the Eastern side of Laurentia in the South, and Baltica - in the North. This produced a new mountain chain. The Catskill delta was built; however, none of the deltaic deposits of that time are preserved in New York state. The swamps on this delta resulted in widespread coals (Carboniferous), which are still abundant in Pennsylvania.

In Permian, the Alleghanian orogeny produced the "typical Appalachian" folds. Although Alleghanian orogeny is often called Appalachian, the present day Appalachian belt is a result of three orogenies - Taconic, Acadian, and Alleghanian. The Appalachian belt is still moderately high after millions of years of erosion, which probably means that it was rejuvenated at some point.

In late Triassic - early Jurassic, a new rifting episode began, resulting in arkosic deposits and basalts in the ocean-producing rift as well as in failed rifts. The modern Atlantic ocean was developing as continents drifted apart once more. In a transgressional environment, the present day continental shelf, slope and rise were built.

The last major event in this region is the Pleistocene glaciation.

Stratigraphic Column

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