Class Note for GEOS 195K at UA
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Date Created: 02/06/15
GEOLOGIC HIGHLIGHTS OF SOUTHEASTERN ARIZONA AND VICINITY YEARS AGO GEOLOGIC TIME SCALE GEOLOGIC AND LIFE HISTORY QUATERNARY PERIOD 07100 years 7 Holocene 10000 years 7 Holocene 10000716 my 7 Pleistocene TERTIARY PERIOD 16753 my 7 Pliocene 537150 my 7 Miocene 1507237 my 7 Miocene 2377366 my 7 Oligocene Industrialized society develops mineral and water resources Today39s Sonoran Desert appears Many mammals go extinct Glacialinterglacial climate uctuations occur with associated changes in lakes rivers ora and fauna Large mammals like mammoths mastodons and giant ground sloths roam across southern Arizona Hunters and gatherers arrive in Southern Arizona about 11000 years ago eg Curry Springs mammoth kill site Episodes of basaltic volcanism occur in the Pinacates San Francisco Peaks White Mountains and San Bernardino Valley The presentday Basin and Range landscape of the Sonoran Desert begins to take shape 15 my ago Deep pervasive fracturing of the crust and earthquake activity break up a high mountainous southern Arizona into blocks Some of these crustal blocks drop down to form the Basins while others tilt but remain high to be mountains Present stream systems evolve The initially closed basins ll up with sediments washed off the surrounding mountains and slowly integrate into regional drainage systems eg Gila Salt and Colorado Rivers The climate becomes semiarid The Gulf of California and the San Andreas fault develop as southwestern North America begins to get torn apart by plate tectonic processes With the opening of the Gulf of California the Colorado River drains south and excavates the Grand Canyon Subduction of ocean crust along the western margin of North America continues until the East Paci c Rise interacts with the continental crust resulting in the activation of the San Andreas fault and Basin and Range faults Rivers carry sediments off the high mountains in southern Arizona and deposit gravels to the north onto what is now the edge of the Colorado Plateau The horse evolves in North America and other modern mammals diversify Between 20730 my tremendously explosive volcanic eruptions rip across the Southwest and northern Mexico The landscape is built up higher by layers of volcanic rocks eg tuffs ash and rhyolite These volcanic rocks now make up the Chiricahua Tucson Galiuro Superstition Ajo and Atascosa Mountains in southern Arizona and the Sierra Madre Occidental in Mexico During this volcanism plutons are emplaced into the upper crust eg Kitt Peak and Stronghold Dragoon Mountains granites 3667518 myi Eocene 5787664 my 7 Paleocene CRETACEOUS PERIOD 664P800 my CRETACEOUS PERIOD continued 807144 my JURASSIC PERIOD 1447208 my TRIASSIC PERIOD 2087245 my PERMIAN PERIOD 2457286 my PENNSYLVANIAN PERIOD 2867320 my MISSISSIPPIAN PERIOD 3207360 my DEVONIAN PERIOD 360408 my SILURIAN PERIOD 4087438 my ORDOVICIAN PERIOD 4387505 my CAMBRIAN PERIOD 5057570 my Volcanic mountains exist in southern Arizona A tremendous geologic upheaval occurs in western North America called the Laramide Orogeny Intrusions of molten rock into the crust and associated volcanism form new continental crust enlarging the North American continent These plutonic rocks are now exposed in Texas Canyon The CatalinaRincon Graham Tucson Sierra Nevada and many other mountains are intruded metamorphosing large portions of the upper crust As the Paci c Ocean crust rapidly subducts under colliding North America the continental crust is deformed and folded buckling like an accordion Beneath some volcanoes most copper and molybdenum deposits now being mined in Arizona are forming by hydrothermal interactions Dinosaurs go extinct around 66 my ago Mountains called the Mogollon Highlands begin to build up in southern Arizona as great quantities of granitic magma intrude the crust of western North America Some molten rock erupts onto the Earth s surface eg 20000 feet of volcanic rock in the Santa Rita Mountains These high volcanic peaks form a mountain chain stretching from Alaska to Mexico The Bisbee copper deposit forms beneath one of these volcanoes Other parts of Arizona are covered by an extensive swampy mud at across which meander rivers jammed with logs now the Petrified Forest Volcanic ash blown in from the south and west occasionally falls on these swamps Later a great sand desert extends across Northern Arizona and into Utah and Colorado Fossilized sand dunes from this desert are now exposed in the cliffs of Zion and Arches National Parks A shallow sea covers southeastern and northeastern Arizona about 100 my ago Abundant plant growth along the swampy margins of that seaway accumulates to form coal now being mined on Black Mesa Flowering plants and birds evolve in Jurassic time Dinosaurs and insects become abundant in Triassic and Jurassic time North America is part of a supercontinent called Pangea Reptiles become abundant Tropical shallow sea and coastal environments exist in Arizona for a few 100 million years There are at least three cycles of shallow sea inundation transgressions followed by uplift and emergence of land regression Coral reefs fishes and marine invertebrates are abundant in the warm shallow waters that cover the continental crust Thick deposits of limestone mudstone shale and sandstone form in these marine and tidalbeach environments Paleozoic marine sedimentary rocks from this time are now exposed throughout Arizona notably in the Grand Canyon and Whetstone Mountains The first abundant fossils of marine life with hard parts appear in Cambrian rocks
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