The Building of the NYC Region

The Building of the NYC Region

Definitions Fall Line marks the area where an upland region (continental bedrock) and a coastal plain meet Piedmont the plateau region of the eastern United States which lies between the coastal plain, from which it is divided by the fall line, and the eastern mountain ranges, the Appalachian Mountains Allochthonous A large block of rock moved from it s original location usually by a thrust fault Autochthonous a sediment or rock that can be found in situ at its site of formation or deposition

Subdivisions of physiographic provinces assigned to the NYC region Physiographic provinces are defined by contiguous physical geographic characteristics, such as flat sandy plains, mountainous areas, or rolling hills. Piedmont Fall Line

Map of continental arrangement at different times in the Phanerozoic

Generalized Geologic Map of NYC Region

The Grenville Orogeny Began roughly 1.3 billion years ago (Middle Proterozoic), and ended roughly around 800 million years ago (Late Proterozoic)

The Taconic Orogeny Ordovician 550-430 mya Beginning in Cambrian time, about 550 million years ago, the Iapetus Ocean began to grow progressively narrower. about 440 million years ago Taconic Orogeny subsided in the New York Bight region during Late Ordovician time subduction ended culminating in the accretion of the Iapetus Terrane onto the eastern margin of the continent.

The Taconic Orogeny had the greatest overall effect on the geologic structure of basement rocks within the New York Bight region The effects are most apparent throughout New England, but the sediments derived from mountainous areas can be traced throughout the Applachians and midcontinental North America.

The Acadian Orogeny Avalonia Collides with Proto North America Devonian Period (408 to 360 million years ago) Avalonia Volcanic island arc (J) Gwandanaland

The Appalachian (Alleghenian) Orogeny Permian ~280 to 245 mya The geology of the Appalachians dates back to more than 480 million years ago the combined continents of Europe and Africa Gondwana collided with North America to form the supercontinent of Pangaea This collision exerted massive stress on what is today the Eastern Seaboard of North America, resulting in a large-scale uplift of the entire region Closer to the boundary between the colliding plates, tectonic stresses contributed to the metamorphosizing of the rock These stresses concurrently caused faults as well as folding.

The Appalachian Mountains At the peak of the mountain-building process the Appalachians could have risen as high or perhaps even higher than the present-day Himalaya Evidence The immense region involved in the continental collision the vast temporal length of the orogeny and the thickness of the pile of sediments and igneous rocks known to have been involved

Middle Appalachians. USGS Northeast Appalachians. USGS

Major fault at the dividing line between the Allegheny Plateau and the true Appalachian Mountains, Williamsport, Pennsylvania. The rock layers on the left are metamorphic while the rock layers on the right are sedimentary

Subdivisions of the Appalachian Orogeny The Highlands Province - the ancient crystalline core of the Appalachian Mountains The Valley and Ridge Province - an extensive belt of folded sedimentary rocks extending from the Catskills region southwestward along the trend of the Appalachian Mountains.

The Highlands Province

Subdivisions of the Appalachian Orogeny The Mesozoic Rift Basins include the Newark and Connecticut River Basins in the New York City region The Atlantic Coastal Plain refers to the subaerially exposed landward extension of the Atlantic Continental Shelf The continental shelf is transitional with the Baltimore Trough, a deep, thick, submarine sedimentary basin far offshore from the New York Bight area

Piedmont Valley and Ridge

Newark Basin

The Palisades

Formed in multiple stages between about 192 to 186 million years ago (late Early Jurassic) The eroded cross-section of a large intrusive diabase sill Intruded between layers of sandstone and shale of the Late Triassic Stockton and Lockatong Formations in the Newark Basin Rises 600 feet above the Hudson The Palisades

Cenozoic Early Tertiary Many transgressions and regressions Miocene/Pliocene Global cooling begins Pleistocene Glacial advances

Map showing the location of the terminal moraine of the Wisconsin glacier (Stage 2) and the extent of morainedammed lakes in the New York City area (after Schubert, 1967).

Hypothetical map of the New York Bight during the maximum advance of the late Wisconsin glacier (Stage 2 - about 20,000 years BP).

Hypothetical map of the New York Bight during deposition of the Gardeners Clay in Early Holocene time (Stage 1 - about 8,000 year BP).

Pleistocene glacial deposits and features in the New York City region.

Ice Ages in the Bight For periods of time when sea level was lower, New York Harbor was probably a canyon for a very turbulent Hudson River when it wasn't buried by glaciers South of the terminal moraines of the great ice sheet meltwater carried gravel, sand, and silt away from the melting ice, and deposited it on a broad outwash plain Sea level fell each time the continental ice sheets grew, and rose when the ice melted. the ocean's surface elevation possibly dropped as much as 400 feet, causing regression to the outer fringes of the continental shelf.

Long Island s Glacial History Two terminal morainal ridges An older more southerly deposit is called the Ronkonkoma Moraine formed during the an early part of the Wisconsin Stage of the Pleistocene Epoch (Stage 4 - prior to about 55,000 years ago). forms most of the low rolling hills along an east-to-west transect generally on the south side of the LIE (Long Island Expressway).

Long Island s Glacial History The higher, younger, more northerly morainal ridge is called the Harbor Hill Moraine. represents the terminal moraine of the most recent advance of Wisconsin Stage glacier (Stage 2) reached its most southward advance about 18,000 years ago. This glacier probably completely melted in the New York City region in the range of 13,000 to 12,000 years ago.

Lignite in the Late Cretaceous Magothy Formation exposed at the base of the sea cliffs in Caumsett State Park. Note the large glacial erratics on the gravel beach. Caumsett State Park Stratified (outwash) and unstratified (till) deposits exposed in the sea cliffs along Long Island Sound in Caumsett State Park.

Present Day