Taconic orogeny


Taconic orogeny

The Taconic orogeny was a great mountain building period that perhaps had the greatest overall effect on the geologic structure of basement rocks within the New York Bight region. The effects of this orogeny are most apparent throughout New England, but the sediments derived from mountainous areas formed in the northeast can be traced throughout the Appalachians and midcontinental North America.

Beginning in Cambrian time, about 550 million years ago, the Iapetus Ocean began to grow progressively narrower. The weight of accumulating sediments, in addition to compressional forces in the crust, forced the eastern edge of the North American continent to fold gradually downward. In this manner, shallow-water carbonate deposition that had persisted on the continental shelf margin through Late Cambrian into Early Ordovician time, gave way to fine-grained clastic deposition and deeper water conditions during the Middle Ordovician. Sometime during this period a convergent plate boundary developed along the eastern edge of a small island chain. Crustal material beneath the Iapetus Ocean sank into the mantle along a subduction zone with an eastward-dipping orientation. Partial melting of the down-going plate produced magma that returned to the surface to form the offshore Taconic island arc. By the Late Ordovician, this island arc had collided with the North American continent. The sedimentary and igneous rock between the land masses were intensely folded and faulted, and were subjected to varying degrees of intense metamorphism. This was the final episode of the long-lasting mountain-building period referred to as the Taconic Orogeny.

When the Taconic Orogeny subsided in the New York Bight region during Late Ordovician time (about 440 million years ago), subduction ended, culminating in the accretion of the Iapetus Terrane onto the eastern margin of the continent. This resulted in the formation of a great mountain range throughout New England and eastern Canada, and perhaps to a lesser degree, southward along the region that is now the Piedmont of eastern North America. The newly expanded continental margin gradually stabilized. Erosion continued to strip away sediments from upland areas. Inland seas covering the Midcontinent gradually expanded eastward into the New York Bight region and became the site of shallow clastic and carbonate deposition. This tectonically-quiet period persisted until the Late Devonian time (about 360 million years ago) when the next period of mountain-building began, the Acadian orogeny.

Aftermath of the Taconic Orogeny

As the Taconic Orogeny subsided in early Silurian time, uplifts and folds in the Hudson Valley region were beveled by erosion. Upon this surface sediments began to accumulate, derived from remaining uplifts in the New England region. The evidence for this is the Silurian Shawangunk Conglomerate, a massive, ridge-forming quartz sandstone and conglomerate formation, which rests unconformably on a surface of older gently- to steeply-dipping pre-Silurian age strata throughout the region. This ridge of Shawangunk Conglomerate extends southward from the Hudson Valley along the eastern front of the Catskills. It forms the impressive caprock ridge of the Shawangunk Mountains west of New Paltz (town), New York. To the south and west it becomes the prominent ridge-forming unit that crops out along the crest of Kittatinny Mountain in New Jersey.

Through Silurian time, the deposition of coarse alluvial sediments gave way to shallow marine fine-grained muds, and eventually to clear-water carbonate sediment accumulation with reefs formed from the accumulation of calcareous algae and the skeletal remains of coral, stromatoporoids, brachiopods, and other ancient marine fauna. The episodic eustatic rise and fall of sea level caused depositional environments to change or to shift laterally. As a result, the preserved faunal remains, and the character and composition of the sedimentary layers deposited in any particular location varied through time. The textural or compositional variations of the strata, as well as the changing fossil fauna preserved, are used to define the numerous sedimentary formations of Silurian through Devonian age preserved throughout the region.

ee also

* Ebenezer Emmons, the geologist who first described the Taconic system

External links

*http://3dparks.wr.usgs.gov/nyc/valleyandridge/valleyandridge.htm (public domain source)
* http://3dparks.wr.usgs.gov/nyc/highlands/highlands.html (public domain source)


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Taconic Orogeny — Mountain building event that affected the Appalachian Geosyncline along the eastern coast of the U.S. Evidence for the orogeny is most pronounced in the northern Appalachian Mountains, but its effects can be noted as far away as Tennessee and… …   Universalium

  • Taconic — can refer to:*Taconic Mountains, part of the Appalachian Mountains, running through eastern New York State, western Connecticut, and Massachusetts, as well as southwestern Vermont in the United States *Taconic orogeny, a great mountain building… …   Wikipedia

  • orogeny — orogenic /awr euh jen ik, or euh /, orogenetic, adj. /aw roj euh nee, oh roj /, n. Geol. the process of mountain making or upheaval. Also called orogenesis /awr euh jen euh sis, or euh /. [1885 90; ORO 1 + GENY] * * * I Mountain building event,… …   Universalium

  • Taconic Mountains — The Taconic Mountains are a physiographic section of the larger New England province and part of the Appalachian Mountains, running along the eastern border of New York State, United States and adjacent New England from northwest Connecticut to… …   Wikipedia

  • Orogeny — Geologic provinces of the world (USGS)   Shield …   Wikipedia

  • Acadian orogeny — The Acadian orogeny is a middle Paleozoic deformation, especially in the northern Appalachians, between New York and Newfoundland. In Gaspé and adjacent areas, its climax is dated as early in the Late Devonian, but deformational, plutonic, and… …   Wikipedia

  • Iapetus Ocean — The Iapetus Ocean was an ocean that existed in the Southern Hemisphere between Laurentia (Scotland and North America) and Baltica (Scandinavia) between 400 and 600 million years ago. As a sort of precursor of the Atlantic Ocean, it was named for… …   Wikipedia

  • Geology of Pennsylvania — The Geology of Pennsylvania consists of six distinct physiographic provinces, three of which are subdivided into different sections. Each province has its own economic advantages and geologic hazards and play an important role in shaping every… …   Wikipedia

  • Ordovician Period — Interval of geologic time, 490–443 million years ago, the second oldest period of the Paleozoic Era. It follows the Cambrian and precedes the Silurian. During the Ordovician, many of the landmasses were aligned in the tropics. Life was dominated… …   Universalium

  • Geologic time scale — This clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga.[1] Other… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.