Lecture02

Lecture02 - Parks Formed by Stream Erosion and Weathering...

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Unformatted text preview: Parks Formed by Stream Erosion and Weathering (part 1) GRAND CANYON NATIONAL PARK ZION NATIONAL PARK Colorado Plateau relatively undeformed rocks surrounded by the highly deformed Rocky Mountains, and Basin and Range Provinces. The margins of the Colorado Plateau are marked by major volcanic accumulations The major structures of the plateau include: – – – – – broad flexures, monoclines, vertical faults, igneous laccoliths and volcanics Salt tectonic features. Stratigraphy of Colorado Plateau From Geology of the Colorado Plateau, 1999, Annabelle Foos, Geology Department, University of Akron Grand Canyon NP ­ Vital Statistics Northwest Arizona Western Colorado Plateau ~1,200,000 acres or 1,900 square miles Native American History ~1000 BC Evidence of Native American Hunters in caves, artifacts Basket Making Native Americans AD 1350 Pueblo culture (~500 sites) Up to today, still home of three tribes – – – Navajo (east) Hopi (east) Havasupai (west) Photo: NPS Human History (con’t) 1540, Don Lopez de Cardenas 1869, John Wesley Powell lead expedition of 4 wooden boats & 9 men down the Colorado River (again in 1871) 1893 protected as a Forest Reserve 1908 TR proclaimed the area a NM 1919 established as Park Geologic Features Stream Erosion Mass Wasting Differential Erosion Unconformities Colorado River is 2nd longest river in US Colorado River eroded Grand Canyon Canyon is 217 miles long, 1 mile deep, up to 18 miles wide Erosion began between ~5 million years ago PANORAMIC VIEW OF THE GRAND CANYON FROM PIMA POINT ON THE WEST RIM DRIVE, GRAND CANYON N.P. NPS PHOTO. Stream Erosion Stream Erosion Colorado River Erosion mainly vertical VIEW DOWN THE COLORADO RIVER IN GRAND CANYON N.P. FROM NANKOWEAP IN MARBLE CANYON. MIKE QUINN, NPS Movement of material downward due to gravity Main process involved in widening canyon Climate is arid; mechanical weathering; talus Mass Wasting Photo: Mirsky Differential Erosion Responsible for rugged nature of cliffs Caused by different degree of resistance to erosion Unconformity: Buried erosion surface – Resistant – cliffs – limestone, sandstone – Less resistant – slopes – shales Differential Erosion Kaibab SS Coconino SS Hermit Sh Supai Group Redwall Ls Bright Angel Sh Tapeats SS Photo: CD, HTT Unconformities – PC/C nonconformity Tapeats Sandstone Vishnu Schist Unconformities – PC/C angular unconf. Tapeats Sandstone C Grand erie yon S an s Geologic History ­ Stratigraphy Geologic History – Pre­ Cambrian 2,000 mya marine sediments and volcanic rocks (since metamorphosed into Vishnu Schist) and 1,700 mya folding, faulting, intrusions (Zoroaster Granite) 1,000 mya sea transgressed and deposited Grand Canyon Series Mountain building, then erosion to low hills Geologic History – Paleozoic Cambrian – Sea transgresses again Ordovician, Silurian – no rock record Devonian Temple Butte Limestone – Tapeats Sandstone – Bright Angel Shale Geologic History – Paleozoic Mississippian Pennsylvanian – Redwall limestone ­ marine – Supai formation – lower part marine upper part non marine, with reptile tracks – Hermit Shale – non­marine, more tracks – Coconino sandstone – dune sand, x­beds – Toroweap formation – marine – Kaibab limestone – top cliff, marine Permian near shore alternating Geologic History – Mesozoic Thousands of feet of sediment deposited, but mostly eroded away from GC area Rock of this age to north (Zion, Bryce), east (Painted Desert, Black Mesa) and remnants near Grand Canyon at Cedar Mt. Geologic History ­ Cenozoic Miocene – Ancestral Colorado River flowed over lowlands with little elevation Pliocene – beginning of uplift of Colorado Plateau (continues to present) Mid­Pliocene – Colorado River entrenchment begins ~4­6 mya Geologic History – Pleistocene to Today Colorado River cut quickly through Pz sed Inner Gorge cut more slowly River only removes material in its channel Mass wasting delivers sediment to river Faulted areas form tributary valleys Zion National Park Cliffs of Navajo Sandstone Vital Statistics Southwest Utah Western Colorado Plateau 1909 Monument (by TR) 1919 National Park 147,000 acres or 230 square miles Expanded in 1937 & 1956 Later Human History ~ AD 500 Basket Maker Culture Native Americans Later, Piute tribe 1776, Don Lopez de Cardenas 1872, John Wesley Powell lead expedition and named the area Mukuntuweap 1909 TR proclaimed the area a NM as Mukuntuweap NM 1918 name changed to Zion NM 1919 established as Park Geologic Features Stream Erosion & Mass Wasting Structural Control Weathering Arches Stream Erosion & Mass Wasting Virgin River has gradient of ~60 ft/mi Mass wasting widens Zion Canyon Sapping by springs creates overhangs Tributaries – less water, left hanging Rectangular stream pattern – fractures Columns and Pyramids Vertical fractures encourage vertical cliffs Rapid downcutting through soft sandstone leaves deep, narrow canyons Bedding planes also act as plane of weakness Structural Control Structural Control Rectangular stream pattern – fractures Columns and Pyramids Vertical fractures encourage vertical cliffs Rapid downcutting through soft sandstone leaves deep, narrow canyons Bedding planes also act as plane of weakness Structural Control ­ Columns and Pyramids Rectangular stream pattern – fractures Columns and Pyramids Vertical fractures encourage vertical cliffs Cliffs of Navajo Sandstone Rapid downcutting through soft sandstone leaves deep, narrow canyons Bedding planes also act as plane of weakness Great White Throne Structural Control Rectangular stream pattern – fractures Columns and Pyramids Vertical fractures encourage vertical cliffs Rapid downcutting through soft sandstone leaves deep, narrow canyons Bedding planes also act as plane of weakness Structural Control ­ Bedding planes also act as plane of weakness Rectangular stream pattern – fractures Columns and Pyramids Vertical fractures encourage vertical cliffs Checkerboard Mesa Navajo Sandstone Rapid downcutting through soft sandstone leaves deep, narrow canyons Bedding planes also act as plane of weakness Weathering Rock color from iron oxide Frost wedging Acid dissolves calcium carbonate cement Arches – example Kolab Arch Kolab Arch Stratigraphy of Colorado Plateau From Geology of the Colorado Plateau, 1999, Annabelle Foos, Geology Department, University of Akron Geologic History Permian – Kaibab limestone – shallow sea Triassic – – arid near­shore – Uplift and some volcanic ash – Fossils fresh water fish, clams, snails, amphibians, wood, dinosaur tracks Geologic History – Jurassic Navajo Sandstone – arid climate with sand dunes (up to 2000 ft thick) Navajo Sandstone Forms the White Cliffs Frosted, fine­grained, quartz sandstone Cross­bedded Capped by marine Carmel Formation Geologic History ­ Jurrasic Geologic History – Cretaceous and Cenezoic Cretaceous (End of Mz) – erosion Lt. Miocene (~13mya) block faulting – Tilted – Uplifted – increased river gradient, rejuvenated stream erosion, carved Zion Canyon ...
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This note was uploaded on 01/13/2011 for the course BUS A202 taught by Professor Tindall during the Spring '10 term at IUPUI.

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