Geological History of the Colorado Plateau and of NA
Colorado Plateau Province

Ancient Precambrian rocks, exposed only in the deepest canyons, make up the basement of the Colorado Plateau. Most are metamorphic rocks formed deep within the Earth while continental collision on a grand scale produced the nucleus of the North American continent well over a billion years ago. Igneous rocks injected millions of years later form a marbled network through parts of the Colorado Plateau's darker metamorphic basement.

These deeply-formed rocks were uplifted, eroded, and exposed for eons. By 600 million years ago North America had been beveled off to a remarkably smooth surface. It is on this crystalline rock surface that the younger, more familiar layered rocks of the Colorado Plateau were deposited.

Throughout the Paleozoic Era, the Colorado Plateau region was periodically inundated by tropical seas. Thick layers of limestone, sandstone, siltstone, and shale were laid down in the shallow marine waters. During times when the seas retreated, stream deposits and dune sands were deposited or older layers were removed by erosion. Over 300 million years passed as layer upon layer of sediment accumulated.
It was not until the upheavals that coincided with the formation of the supercontinent Pangea began about 250 million years ago that deposits of marine sediment waned and terrestrial deposits dominate. Eruptions from volcanic mountain ranges to the west buried vast regions beneath ashy debris. Short-lived rivers, lakes, and inland seas left sedimentary records of their passage.

Beginning about 20 million years ago, during the Miocene Epoch both the Basin and Range and Colorado Plateau regions were uplifted as much as 3 kilometers. Great tension developed in the crust, probably related to changing plate motions far to the west. As the crust stretched, the Basin and Range Province broke up into a multitude of down-dropped valleys and elongate mountains. Yet for some reason not fully understood, the neighboring Colorado Plateau was able to preserve its structural integrity and remained a single tectonic block. Eventually, the great block of Colorado Plateau crust rose a kilometer higher than the Basin and Range.
As the land rose, the streams responded by cutting ever deeper stream channels. The most well-known of these streams, the Colorado River, began to carve the Grand Canyon less than 6 million years ago. The forces of erosion have exposed the rock layers .

Age of snails, bivalve molluscs, brachipods, primitive corals, sponges and other sea creatures.Over 150 families evolved. first land plants evolved also. A colliding microcontinent pushed up the east coast Taconic Orogney). erosion of these mts lead to a layer of sediment along the continents edge. Large extinction at the end of the period. Sea levels remained high. First jawed fish, large reef communities, movement of aquatic organisms into fresh water. First land animals millponds, mites insects. FIrst vascular land plants. Large reefs in center restricted water flow: Water evaporated forming thick deposits of slat and gypsum. Sea level dropped as continents clustered. Baltica rammed Laurentia and the collision initiated the pulse of Appalachian region mt building.
Fish developed quickly: primitive sharks, bony fish, lung fish, primitive amphibians, Large barrier reefs to the west formed. Seedless vascular plants evolved and land plants covered most of the continent. NEar the end forests spread : early insects spiders, snails. Global cooling at the end of this period. Reefs hit hard. Greats mt building period in the east created the Appalachian region. lots of erosion lead to the build of sediments to the west of the Appalachians. Ramming out west lead to Franklin & Antler mts. The continents were closely clustered now. Sea levels rose and a shallow carbonate sea spread. Shallow but widespread reefs with faster moving sharks and dish. Debris from all these animals left a layer of limestone rock. On land, new spore bearing plant arose ( ferns and larger pre-angiosperm types). Amphibians as large as 20 ft. long. At end seas dropped, many species with them. Lots of erosion of mts both east and west.
Pennsylvanian: Sea levels rose and fell with glaciation of Gondwanaland. Gymnosperms appeared. Earlier plants in swampy areas died to form massive coal deposits. First reptiles appeared. When the 2 continents came together, the Alleghian Orogeny resulted, which extended the Appalachians further south, built up the Ouachita Mt belt and formed the ancestral rocky mts. Permian Siberia join with e Europe, almost completing Pangea which drifted northward.Seas restricted to the west covered less of the continent. Gymnosperms dominated. Reptiles took over the amphibians with eggs, speed. jaws. Mammal like reptiles therapsids. The climate dried.Dune built up. Basins dried up leaving salt behind . A microcontinent hit the west edge and crumpled it. THe climate cooled down and 80% of the species disappeared.
Triassic: Pangea was complete. Large reptiles joined fish as top predators in the reefs. Large crocodiles emerged. The land mass was so large, that most of the land was far from the sea, and become arid. Gymnosperms & ferns dominated the land. Thecodonts differentiated into dinosaurs. Mammals arose from reptile but were small.. Late in the period first flying vertebrates, frog & turtles appeared. by the end 20% of specie were eliminated. W. NA hit a subduction zone resulting in mts. In the e. erosion almost eliminated the Appalachians. NA moved apart from Pangea, Applachians block and faulted. Jurassic: FIsh became modernized. On land forest of cycads, gymnosperms, ginkgo common. Dinosaurs diversified. First birds crossed skies. Pangea continued to fall apart. Gulf of Mexico formed a rift zone which lead to seawater filling basins with alternating evaporations = Louann Salt deposits.As sea levels rose several times, interior flooding lead to the Sundance Sea.At the end of the period the sea was expelled.

Cretaceous: Seas were high mostly. Temperature arose early on. ( GW due to volcanoes and CO2 increase from the Pangea split). In water teleost fish, on land first angiosperms.Insects developed relationship with flowering plants. Dinosaurs still dominated though. Formation of widening Atlantic Ocean forced Greenland and Eurasia to move apart from NA. Along W. Canada a microcontinent tagged along causing a major seaway formation in interior. Laramide Orogeny out west . Major extermination after massive extraterrestrial body struck earth .Dinosaurs died out.

Cenozoic (not pictured) with loss of dinosaurs, mammals filled niches. Mt building out west formed the Rockies. Glaciers sculpted northern sections. Humans appeared.

Palogene (above): Carnivorous mammals took to the sea to form whales.Also evolved penguins, walruses seals etc. First grasses evolved. New mammal species. ungulates, elephants, rodents, rabbits, bats dogs, cats primates.. Earths poles cooled down and new ice caps caused seas to drop worldwide. Cold dense seawater sunk to bottom and flowed N. CLimates cooled and dried. forests declined and grasslands spread.TO the west a bridge of land connecting Alaska to Siberia was above sea level and erosion cut down the mt out west.

Neogene ( 23 M to present) Climates grew cooler, drier, and more seasonal. Herbs beat out trees. Animals that ate such prospered including elephants & ungulates.WIth the west mts eroded, the continent rebounded raising the modern Rockies and Colorado Plateau. Sierra Nevada range rose. Lava poured across Columbia river.> The climate fluctuated creating periods of glaciation, which formed the Great Lakes.

Modern Ice Age: 3-2.5 MYA: Major period of glaciations, sometimes covering as much as 1/3 of the continent. Why these periods and general cooling?

  • Drop in Greenhouse gases
  • Uplifting of mountains changed climate. Existing alpine glaciers reflected back light cooling trend expand glaciers.
  • Isthmus of Panama strengthened the Gulf Stream which increased snowfall in the Arctic which enlarged the ice cap.
  • Cycles may be due by changes in earths axis tilt.
 

Each colored layer reflects a different era:

Jurassic

Evolution of flowering plants

First mammals

Age of giant dinosaurs

Morrison Brushy Basin Dark green rocks contain minerals which contain reduced (ferrous) iron, and were deposited in stagnant marine basins, swamps, bogs, and lakes. Greenish gray & maroon gray mudstones Dinosaur remains
Saltwash Channel sandstones and siltstones: petrified wood may contain uranium Contain dinosaurs
Tidwell Thin dark red sandstone Stream deposited laid down on lakes on swampy plains

Entrada

Sandstone

Moab Tongue Bright white rocks may consist of the mineral gypsum (CaSO4 2H2O) which is an evaporite mineral found in some rock layers White sandstone: dune deposits  
Slickrock Resistant marine sandstone; most arches eroded from this in Arches or hoodoos  
Dewey Bridge/ Carmel Deposited in shallow sea ( red-gray)  

Triassic

First dinosaurs appear

At the end many marine lifeforms disappear

Navajo Sandstone Deposited in dunes: white well rounded sand grains; cliff-former Desert sands overspread the land for million of years; dinosaur tracks
Kayenta Sandstone Deposited by streams and in lakes: slabby fragments- interbedded redshale and sand clams, reptile tracks, dinosaurs and tritylodonts ( crocodile-like animals)
Wingate Sandstone Red Sandstone accumulated in dunes, cliff former - orange sandstone from migrating sand dunes  
Chinle Stream, beach and lake deposits- soft red-pink shales weather into rounded hills  
Moenkopi Red to reddish brown to purplish rocks contain hematite (ocher) which is simply rust or iron oxide (Fe2O3). Less than half of a percent by weight of hematite is enough to color a rock brilliantly red. Red rocks were deposited under oxidizing conditions Accumulated on tidal flat-reddish brown  
Permian
first woody plants
Kaibab Limestone   Dolomitic sandstone  
21 = Colarado Plateau 22. Basin and Range

 

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