Presentation on theme: "COASTAL PLAIN CRETACEOUS TO RECENT. Cretaceous History of North America The Cretaceous was a time of high sea level and vast epicontinental seas. The."— Presentation transcript:
Cretaceous History of North America The Cretaceous was a time of high sea level and vast epicontinental seas. The most prominent feature in North America during the Cretaceous, was the shallow epicontinental sea that flooded much of the western interior of the continent, from the Gulf of Mexico to the Arctic Ocean, as well as the Atlantic and Gulf Coastal Plains.
Cretaceous Chalk Chalk, a white, fine-grained variety of limestone composed of microscopic shells (called coccoliths) of golden-brown algae, was deposited in many places around the world during the Cretaceous. The word Cretaceous is derived from the Latin word for chalk, creta.
Atlantic Coastal Plain The Atlantic Coastal Plain began to subside (or sink) early in Cretaceous time. Marine and deltaic sediments accumulated, gradually building a wedge of sediments that thickened seaward. Most of the Cretaceous sediment in this area was deposited on the present-day continental shelf.
Late Cretaceous Units POTOMAC FORMATION - (early and late Cretaceous) - A moderately well sorted and cross-bedded, quartz sand with quartz and quartzite pebbles deposited in fluvial environments. The Potomac Formation is the basal sequence of the Cretaceous system in southern and central New Jersey (it is not recognized beneath the lower Raritan Formation in the bay area). The thickness is reported in the range of 250 to 800 feet.
Late Cretaceous Units RARITAN FORMATION - (Cenomanian, Cretaceous) - In the Raritan Bay region the Raritan Formation unconformably overlies Newark Basin and older rocks, representing the beginning of a series of major transgressions and regressions of the seas during Cretaceous time. The Raritan consists of clay, sand, lignite, and gravels representing progradational alluvial plain, coastal and neashore marine environments. Very well exposed in unglaciated regions around the western end of Raritan Bay. Subdivided units include the Raritan Fire Clay, Farrington Sand Member, Woodbridge Clay Member, Sayreville Sand Member, and South Amboy Fire Clay Member (oldest to youngest, respectively). The Sayerville Sand Member is famous for its amber- bearing lignite lenses, insect remains, fossil wood and leaves, and pyrite nodules.amber The Sayreville fossil beds have yielded an astonishing amount of information about life in the Late Cretaceous.
Amber in the Raritan Formation The Sayreville Clay Member of the Raritan Formation yields amber form scattered lignite horizons. The amber is not of consistently high quality like other amber-bearing regions of the world. However, it is one of the older amber-bearing deposits, and the amber frequently contains insects (mostly gnat-like insects).
Late Cretaceous Units MAGOTHY FORMATION - (Coniacian and Santonian, Cretaceous) - Unconformably overlies the Raritan Formation. The Magothy Formation is beneath Quaternary glacial cover throughout most of Long Island, the south shore of Staten Island, and is fairly well exposed in small outcrops and excavations around Raritan Bay. The Magothy is subdivided into units: the Oldbridge Sand Member, the Amboy Stoneware Clay Member, and Cliffwood Beach Member (oldest to youngest, respectively). The Magothy represents nearshore and alluvial depositional environments, similar to the Raritan Formation. The thickness ranges between 10 and 200 feet.
Late Cretaceous Units MERCHANTVILLE FORMATION - (late Santonian to early Campanian, Cretaceous) - Conformably overlies the Magothy Formation and consists of mixed sand and clay units representing nearshore and shallow marine depositional environments. It is poorly exposed around the southern side of Raritan Bay. It interfingers with the overlying Woodbury Clay. The thickness of the unit measures between 20 and 100 feet.
Late Cretaceous Units WOODBURY SHALE - (early Campanian, Cretaceous) - Dark gray clay mud of the Woodbury Clay is exposed in excavations and along the shore of Raritan Bay near Cheesequake State Park, NJ. The gray carbonaceous shale contains pyrite and bioturbation features of a marine or lagoonal environment.
Late Cretaceous Units ENGLISHTOWN FORMATION - (early Campanian, Cretaceous) - The Englishtown consists of clay, slit and sand which locally displays lamination, thin- to thick- bedding, and cross stratification. Fossils are generally scarce. Locally the unit contains lignite beach-type sand deposits. The upper-most bed display bioturbation with burrows locally filled with glauconitic quartz sand from the unconformable overlying Marshalltown Formation. The formation ranges from 20 to 150 feet in thickness.
Late Cretaceous Units MARSHALLTOWN FORMATION - (middle Campanian, Cretaceous) - The Marshalltown consists of greenish-gray massive quartz-rich, glauconitic sand, silt and dark, micaceous clay. Pyrite and siderite concretions, some displaying evidence of boring and reworking, are abundant at the base of the unit. Other than traces of lignite and bioturbation, fossils are scarce in the unit. The thickness of the formation is between 15 to 20 feet.
Late Cretaceous Units WENONAH FORMATION - (late Campanian, Cretaceous) - The Wenonah consists of micaceous quartz and silt and is rich in organic material (mostly silt-sized lignite fragments) and pyrite (in very fresh exposures). The unit ranges in thickness from 35 to 55 feet along Raritan Bay, inland the upper part of the unit is exposed intermittently along creek banks. Phosphatic nodules, siderite concretions filling bioturbation structures, and thin sand beds are common near the top of the unit. Sharks teeth and fossil shell molds are common along with bone fragments and teeth of fish, reptiles, and swimming dinosaurs near the top of the unit. Sedimentation patterns reflect storm-dominated depositional patterns on a shallow shelf environment. The thickness of the formation measures in the range of 70 to 100 feet.
Fossils of the Wenonah Formation A - D. sharks teeth (an excellent guide to identifying sharks teeth is: Bretton W. Kent, (1994), Fossil Sharks of the Chesapeake Bay Region. Columbia, MD: Egan Rees & Boyer, Inc., 146 p.); E. sawfish teeth; F. large fish scales; G. vertebrae, probably shark; H. molds of pelecypods (Cardium wenonah) and gastropods (Lunatia halli; I. Coral. (An exceptional publication of fossil descriptions with plates is: Horace G. Richards, etal., The Cretaceous Fossils of New Jersey, Part 1 (1958) and Part 2 (1962); Trenton, NJ: Department of Conservation and Economic Development.)
Late Cretaceous Units MT. LAUREL FORMATION - (latest Campanian, Cretaceous) - The Mt. Laural is very similar in appearance and composition to the underlying Wenonah with the exception that it contains abundant micaceous, glauconitic sand which is locally cross- bedded. The unit contains an abundance of phosphatic peletal material and bioturbation features; siderite concretions commonly fill burrows. The unit is about 25 feet thick near Sandy Hook but pinches out landward over a distance of several miles beneath an unconformity beneath the overlying Navesink Formation. The boundary between the underlying Wenonah is undifferentiated in most areas east of the coastal area. Common Mt. Laurel and Wenonah fossils include sharks teeth and bone, shell molds, etc.Mt. Laurel and Wenonah fossils
Late Cretaceous Units NAVESINK FORMATION - (early Maastrichtian, Cretaceous) - The Navesink consists of peloidal glauconitic marl and sand that is locally thick bedded or crossbedded, and is locally clay-rich. Fossils are very abundant in some areas. Carbonaceous matter and phosphatic material, especially at the base. Mollusk fossils are abundant in the lower and middle portions of the unit. Common Navesink fossils include Belemnitella americana, Expgyra costata, Expgyra cancellata, Pyncnodont sp., Ostrea falcata, Ostrea mesenterica, Choristothyris plicata, and many others. (An small collection of Navesink fossils is on diplay at the visitor's center at Poricy Park, Monmouth County, NJ).Navesink fossils The fossils occur in concentrated horizons within the unit. The fauna suggest a marine shelf environment. It ranges in thickness between 65 to 45 feet throughout the Atlantic Highlands region.
Fossils of the Navesink Formation Mollusks: A-B:Exogyra cancellata, C: Pyncnodont mutabilis, D: Belemnitella americana, E: Spondylus gregalis, F: Ostrea mesenterica, G: Ostrea falcata; Braciopod: H. Choristothyris pilcata
Late Cretaceous Units REDBANK FORMATION - (Maastrichtian, Cretaceous) - The Redbank Formation consists of gray to red sand deposited in nearshore environments. Subaerial exposure at the end of "Redbank time" resulted in the leaching of shell material and the alteration of glauconite to limonite (hence the red color). A lower brownish- black micaceous sand unit is called the Sandy Hook Member and displays abundant concretions in bioturbated horizons and has been described as locally fossiliferous. The upper Shrewsbury Member is yellow to orange-gray sand. The unit is a approximately 120 feet thick near Sandy Hook along the valley of the Navesink and Shrewsbury rivers, but grows progressively thinner until it eventually pinches out landward.
Late Cretaceous Units TILTON FORMATION - (late Maastrichtian, Cretaceous) - The Tilton is a massive "olive to evergreen" green glauconitic quartz sand which is locally clay-rich and silty. The unit displays an abundance of iron-staining and locally bears limonite and hematite crusts and concretions. Locally glauconite constitutes as much as 80% (or more) of the sand, making portions of the formation an economic greensand in the central Coastal Plain. Fossils, mostly poorly preserved molds and casts of pelecypods, Camptonectes, are common, whereas a richer marine fauna occurs further southward in central New Jersey. The unit displays heavy bioturbation. The formation is in the range of 20 to 25 feet thick.
The Cenozoic Era 65.5 million years ago to the present Name "Cenozoic" = "new life" or "recent life"
Periods of the Cenozoic Era The Cenozoic Era consists of two periods – Older Paleogene Period – Younger Neogene Period The Paris Basin is the type area for most of the epochs of the Cenozoic. There is a major unconformity in the basin that was chosen as the boundary between the Paleogene and the Neogene.
Periods of the Cenozoic Era Until 2003, the two periods in the Cenozoic Era were the Tertiary and Quaternary Periods. You will see these terms on older maps and in older publications. In 2003, the International Commission on Stratigraphy revised the nomenclature, dropping the terms Tertiary and Quaternary. The two periods of the Cenozoic Era are officially recognized as the Paleogene and the Neogene.
Paleogeography and Plate Tectonics During the Cenozoic, the Atlantic and Indian Oceans widened, and the continents moved to their current positions. Half of the present ocean crust has formed at the mid-ocean ridges since the beginning of the Cenozoic.
Tectonic and Paleographic Changes and Their Effects on Climate The Panama land bridge blocked the westward flow of the North Atlantic Current. The current was deflected to the north (turning to the right, as a result of the Coriolis Effect), and formed the Gulf Stream. The Gulf Stream transported warm water northward and resulted in bringing warmer climates to northwestern Europe. Gulf Stream also supplied warm, moist air toward the North Pole, which would ultimately result in precipitation which helped build the glacial ice sheets.
Important continental breakups: 1.North Atlantic rift separated Greenland from Scandinavia 2.Australia separated from Antarctica. Circumpolar currents isolated Antarctica from warmer waters. Led to cooling of Antarctica. 3.Cold, dense ocean waters around Antarctica drifted northward along ocean floor, contributing to global cooling and the Ice Age. 4.Rifting occurred between Africa and Arabia, forming the Red Sea and the Gulf of Aden.
North America During the Paleogene The Paleogene is dominated by: –The deposition of marine sediments in eastern and southeastern North America
Eastern and Southeastern North America Ridges and valleys of the Appalachian Mountains were carved by erosion. As erosion proceeded, gentle isostatic uplift occurred. This stimulated more erosion, as streams cut downward.
Eastern and Southeastern North America Uplift in the eroding Appalachians was coupled with downward tilting and deposition of sediments on the Atlantic Coastal Plain and continental shelf. Sediments thicken seaward forming a clastic wedge.
Eastern and Southeastern North America Eight marine transgressions and regressions are recorded in Cenozoic sediments on the Atlantic and Gulf Coastal Plains. Carbonate sediments accumulated in Florida where less terrigenous clastic sediment was available.
Tertiary Units HORNERSTOWN FORMATION - (Danian, early Paleocene) - A drastic change in fauna is represent at the base of the Hornerstown in New Jersey. This is a reflection of both a mass extinction even as well as a hiatus in deposition. The formation is lithologically similar to the Tilton consisting of a green glauconitic quartz sand. Cretaceous fossils have been noted reworked upward into the basal units. Fossil in the Hornerstown include gastropods, pelecypods, and other vertebrate bone material. The unit displays heavy bioturbation.
Tertiary Units VINCETOWN FORMATION - (Paleocene to Eocene) - The Vincetown consists of quartz sand with phosphatic pellets and glauconite ranging form nearly trace to nearly 100% in some beds (glauconite being most abundant at the base of the unit where it appears gradational with the underlying Hornerstown). Near the shore fossils are absent, however, the unit displays bioturbation structures. Elsewhere on the Coastal Plain it is extremely fossiliferous containing abundant foraminifera, bryozoa, and a prominent basal shell bed containing Oleneothyris harlani, Gryphaea dissimilaris, and bone fragments. Thickness is in the range of 50 to 100 feet.
Tertiary Units MANASQUAN FORMATION - (Eocene) - This unit is missing in the Atlantic Highlands region, however, it crops out along creek bottoms southward along the Jersey Shore. It consists of a mixed shaley and sandy marl with abundant apatite pellets and siderite concretions, with fossils rare or absent. Thickness (including Shark River) in the range of 50 to 200 feet.
Tertiary Units SHARK RIVER FORMATION - (Eocene) - This unit is also missing beneath the Cohansey Sand in the Atlantic Highlands region, however, it crops out along the creek banks of the Shark River (as the name applies) and contains sharks teeth. The unit consist of a sandy, carbonaceous glauconitic marl and quartz sand. It lies conformably on the Manasquan below. Some researchers do not differentiate Shark River from the underlying Manasquan Formation.
Tertiary Units KIRKWOOD FORMATION - (middle Miocene) - The Kirkwood Formation is missing from the Atlantic Highlands section beneath the Cohansey Sand. Further south the formation consists of a clayey to silty mudrock, massive sand, and thin pebble lenses deposited in a sublittoral to nearshore environments. The unit is equivalent to the Calvert, Choptank, and St. Marys River formations in Maryland and Virginia. The sparse occurrence of Calvert cliffs fauna in beach pebbles suggest that the Kirkwood-equivalent strata on the continental shelf is fossiliferous. (This unit has been suggested as time equivalent to the formation of the late Tertiary Schooley Peneplane throughout the mountainous Appalachian region.) The bottom of the Kirkwood sits unconformably in top of older Tertiary units. The thickness is in the range of 100 to 300 feet in the Pine Barrens region.
Tertiary Units COHANSEY SAND - (late Miocene to early Pliocene) - The formation consists of medium to coarse-grained arkosic quartz sand (well stratified and cross-bedded), with thin clay lenses and quartz and quartzite pebble conglomerate. The unit represents a range of sedimentary environments ranging from fluvial to transitional marine environments (swamps, deltas, lagoons, beach sand, and shallow open marine shelf). Sediments at the base of the Cohansey appear to fill broad fluvial channels carved downward into the underlying formations (down to the Tilton in the Atlantic Highlands region).
Tertiary Units COHANSEY SAND Many beds within the unit are heavily cemented by iron; these ironstone sand and gravel depositons form a resistant hilltop caprock in the Highlands region. The Cohansey represents most of the surface deposits throughout the New Jersey Coastal Plain and is well exposed on hills and roadcut and sand pits throughout the Pine Barrens region. All fossil material appears to be leached out of the Cohansey (possibly by processes similar to the acid waters and bog-iron formation currently active in the Pine Barrens region. The unit ranges in thickness from a several meters on hilltops to more than 150 feet on the western side of the coastal plain.
Tertiary Units BEACON HILL FORMATION - (Pliocene?) - An iron-stained sandy quartz and quartzite-rich gravel deposit on top of the highest hill in Monmouth County, NJ (373 feet) probably represents a Pliocene fluvial gravel equivalent to late deposition the Cohansey Formation. The Beacon Hill caps Apple Pie Hill and other small hills in the Pine Barrens region.
Quaternary and Holocene Deposits BRIDGETOWN FORMATION - (early Pleistocene?) - The precise age of the Bridgetown Formation is unclear, however, it consists of a deeply weathered mix of silt, sand, and gravel and represents fluvial environments. The Bridgetown probably represents sedimentation during an earlier, pre- Wisconsin interglacial stage. (Isphording & Lodding, (1969) state that the Bridgetown and Pensauken formations are virtually indistinguishable along the coastal areas. Both units lack fossils.)
Quaternary and Holocene Deposits PENSAUKEN FORMATION - (Late Pleistocene) - Wisconsin till unconformably overlies this unit that crops out along a trend from Staten Island to Trenton, NJ and southward along the Delaware River valley. The unit consist of mixed detritus (eroded from older glacial material and exposed Coastal Plain formations) that was deposited in fluvial flood plain environments. The existence of the Pensauken formation suggest that, for a time, the major drainage from the pre-Wisconsin glaciers was southward from the New York area toward Trenton into the Delaware River drainage. Pedogenic weathering of the sediments suggest that it was deposited during a warm interglacial period.
Quaternary and Holocene Deposits CAPE MAY FORMATION - (Late Pleistocene to Holocene) - The Cape May formation consists of surficial silts, sands and quartz-rich gravels along the coastal region of New Jersey and represents coastal beach and barrier sand deposits and back bay estuarine deposits. The source of the sand is mostly from the Delaware River drainage supplemented by shelf sands and longshore drift sand from the Mid- Atlantic region. The progessive reworking of Cape May deposits is the source of much sand on the New Jersey coast.
Quaternary and Holocene Deposits COLUMBIANA GROUP (early to late Quaternary) consists of three named units - the Pensauken, Bridgetown, and Cape May formations (oldest to youngest, respectively) - each represents different depositional environments throughout the region. The Gardeners Clay is probably a marine equivalent to the Pensauken Formation. Active research in the region will no doubt refine the correlation problems between Pleistocene and Holocene sedimentary deposits as investigations proceed on glacial deposits, and lacustrine, swamp, terrestrial, fluvial, estuary, nearshore and marine shelf deposits in the Bight region.
Quaternary and Holocene Deposits GARDENERS CLAY - This poorly consolidated clay underlies Wisconsin Age glacial deposits throughout southern Long Island and has been interpreted as occurring beneath the modern barrier spit of Sandy Hook. The Gardeners Clay contains a rich estuarine fauna with abundant foraminifera. The unit probably represents high-standing seas between advances of the latest Pleistocene (Wisconsin) glacier.
Quaternary and Holocene Deposits WISCONSIN GLACIAL TILL - Wisconsin glacial deposits are apparent everywhere throughout Long Island, across northern Staten Island and in northern New Jersey. Glacial till consists of unstratified mix of clay, silt and sand with a mix of rock material ranging from pebbles to giant boulders (derived from all rock source areas ranging from Manhattan to Central Quebec). The terminal moraine extends across central New Jersey along a sinuous line from the vicinity of Perth Amboy to around the Delaware Water Gap on the western side of the state. Outwash sand and gravel deposits (altered by soil- forming processes) cover much of southern Long Island, southern Staten Island and areas south of the terminal moraine in New Jersey. Varved lake clays and swamp peat cover areas flooded by lakes.
Quaternary and Holocene Deposits HOLOCENE DEPOSITS - The modern beach and barrier islands around the New York Bight represent reworked sand material that began accumulating during a slow-down in sea level rise that began about 3-4,000 years ago. These modern coastal deposits overly older Holocene estuarine and fluvial sediments deposited behind barriers that developed during a period ranging from 12,000 to about 7,000 years ago. (These old barrier deposits are partially eroded and/or buried by younger sediments. These barriers existed anywhere from 2 to 20 kilometers seaward of the current shoreline when sea level was approximately 20 to 40 meters lower. On the continental shelf these ancient barriers are currently supplying sediment to offshore sand ridges. Sand along the Hudson River and on Staten Island displays an abundance of angular feldspar and lithic fragments indicative of fluvial sedimentation in the harbor region when sea level was lower. Modern anthropogenic sediments and human activity has modified nearly all coastal and nearshore marine sedimentary environments.
Global Surface Cooling There was a 10 o C (18 o F) temperature drop at end of Cretaceous Period. Several warming trends occurred in the late Paleocene and Eocene, as indicated by: –Fossils of palm trees and crocodiles in Minnesota, Germany, and near London. –Fossils of trees from temperate zones in Alaska, Norway and Greenland. –Coral reefs in latitudes 10-20 o closer to the poles than at present.
Antarctica in the Paleogene The climate was semitropical and mild in Antarctica during the Paleogene, as indicated by fossil spores and pollen, despite the fact that it sat on the South Pole. Before Antarctica separated from Australia, it was warmed by currents moving southward from more equatorial latitudes.
Australia began to separate from Antarctica in the early Eocene, about 55 m.y. ago. After separation, circumpolar currents developed around Antarctica, cutting it off from equatorial currents. This resulted in temperature decrease and glacial conditions over Antarctica.
Global Surface Cooling Temperatures dropped by about 8-13 o C (roughly 22 o F) near the Eocene-Oligocene boundary, as indicated by isotope data from brachiopods from New Zealand. Antarctic sea ice began to form by 38 m.y. ago. Greenhouse conditions were replaced by icehouse conditions.
Worldwide cooling resulted in: 1.First Cenozoic widespread growth of glaciers in Antarctica about 38-22 m.y. ago. 2.Global sea level dropped by about 50 m in the Early Oligocene, as glaciers formed. 3.Cold, dense polar water flowed northward across ocean bottom. 4.Upwelling of cold bottom waters affected world climate.
5.Decrease in diversity and extinctions of many: –marine molluscs –planktonic and benthonic foraminifera –ostracodes 6.Extinctions were earlier and more severe at higher latitudes. 7.Reefs shifted toward the equator. 8.Calcarous biogenic deep sea sediments (foraminiferal ooze) shifted toward the equator and were replaced by siliceous biogenic sediments (diatom and/or radiolarian ooze) at higher latitudes.
9.Changes in pollen indicate long term cooling and drying. –Temperate and tropical forests shifted toward the equator. –Grasslands expanded. –Rainforests became confined to tropical, equatorial areas. 10.Glaciation occurred in other areas in Pliocene (and younger) deposits - Sierra Nevada, Iceland, South America, and Russia.
Antarctic Bottom Waters The cold waters around Antarctica were dense, and sank to the ocean floor around Antarctica. (Cold water is denser than warmer water.) Cold, dense ocean-floor waters moved downward and outward, away from Antarctica. The northward movement of cold dense waters contributed to cool conditions during the late Eocene and early Oligocene, and ultimately led to the Pleistocene Ice Age.
The Pleistocene The Pleistocene began 1.8 m.y. ago. The most extensive glaciations began about 1 m.y. ago. The end of the Pleistocene is when the ice sheets melted to approximately their current extent. The Pleistocene-Holocene boundary is placed between about 12,000 and 11,000 years ago, at the midpoint of the warming of the oceans. This coincides with a rise in sea level.
The Pleistocene Ice Age The Pleistocene is significant as the time in which humans evolved. More than 40 million km 3 of snow and ice covered about 1/3 of Earth's land area. Continental glaciers covered much of North America and Europe. Alpine glaciers covered parts of the Cordilleran Mountain range in western North America, the Alps, and other mountain ranges of Europe.
Pleistocene continental glaciers in the Northern Hemisphere
As a result of the Ice Age: 1.Climatic zones in the Northern Hemisphere were shifted southward. 2.Arctic conditions prevailed across Europe and the U.S. 3.Sea level dropped as much as 75 m (225 ft) and the shoreline shifted seaward, exposing the continental shelves as dry land. 4.Streams cut deep canyons into the continental shelves and on land.
5.Land bridges existed and led to migrations of mammals, including humans –Across the Bering Sea between Siberia and Alaska –Between Australia and Indonesia –British Isles were attached to Europe 6.The land was sculpted by glaciers in Europe and North America. 7.U-shaped valleys formed in mountainous areas
8.Rainfall increased at lower latitudes. 9.Large lakes formed in the Basin and Range Province. –Lake Bonneville in Utah covered more than 50,000 km 2 and was about 1000 ft deep in places. –The Great Salt Lake is a small remnant of Pleistocene Lake Bonneville. –The Bonneville salt flats were formed as the lake evaporated.
10.Winds coming off glaciers blew sediment southward forming löess deposits (Missouri River area, central Europe, northern China) 11.Parts of northern and eastern Africa that are currently arid had abundant water and were fertile and populated by nomadic tribes. 12.Nomadic tribes hunted along the edges of the continental glaciers. Wild game was abundant, furs provided warm clothing, and there were less problems with spoiled meat in the cold temperatures.
13.Formation of the Great Lakes (depressions scoured by glaciers and flanked by moraines) 14.Formation of Cape Cod, MA - a moraine 15.Formation of Long Island, NY - a terminal moraine 16.Formation of Niagara Falls 17.Formation of large ice-dammed lakes, including Lake Missoula which drained catastrophically, forming the channeled scablands 18.Formation of hummocky topography and Pleistocene sand dunes
19.Weight of the ice depressed the continental crust to as much as 200-300 m downward. 20.Uplift (isostatic rebound) after ice melted. Coastal features are now elevated high above sea level. Map illustrating post-glacial uplift in North America.
Names of the "traditional" glacial and interglacial stages in North America