Mtn Geog SG 3

Mtn Geog SG 3 - Mtn Geog Mid-term III Study Guide...

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Unformatted text preview: Mtn Geog Mid-term III Study Guide 13/11/2007 21:40:00 BASEMENT ROCK Emplaced 1.4-1.7 Gy Crystalline rock Black Canyon of the Gunnison: 1.7 Gy dark gneiss cut through by lighter 1.4 Gy granite and pegmatite Underlies most of present day Colorado Rockies GREAT UNCOMFORMITY An uncomformity is when formations of different ages lay on top of each other Another way to say this is that part of the geologic record is missing From 1.2 Gy to 500 My the geologic record is missing FRONTRANGIA: 300 My Ancestral mountain range 35 miles west of Boulder. Streams carried eroded sand and pebbles from the Ancestral Rockies, dumping the material in wide deposits of gravel. These debris would later become the Flatirons! FOUNTAIN FORMATION: 270 My Arkose sandstone, gravel deposits Sharp, angular points Iron oxidiation, red color Good climbing Remnants of FrontRangia Little transport Flatirons, Red Rocks park, Roxborough State Park LYONS FORMATION: 250 My 220 thick Well-sorted, fine sand Old sand dunes Main building material for CU-Boulder Sea began to creep in from the east Arid to west MORRISON FORMATION: 140 My Broad, swampy lowlands, floodplains Lake and stream deposits, mostly clays, Volcanic ash, Wild colors Massive amounts of dinosaur fossils; has been described as a bone yard. PIERRE SHALE Up to 9,000 thick Deposited by an inland sea Lots of dinosaurs, such as this pterodactyl City of Boulder built on Pierre Shale 70 My 70 million years ago, the sea slowly withdrew to the northeast. It left behind vast swamps, from which the coals of the Laramie Formation formed. Explains natural gas deposits in Denver Basin The withdrawal of the sea took about 10 to 15 million years. LARAMIDE OROGENY 70-40 My ago High angle thrust faults, Reverse fault Uplift of Precambrian basement Deformation of overlying Paleozoic & Mesozoic sedimentary rocks, eg Fountain Formation, Lyons Formation Colorado Mineral Belt Emplaced during Laramide Orogeny and during volcanism immediately afterward Hydrothermal emplacements caused formations of mineral veins Almost all mineral at high elevation SAN JUAN VOLCANICS Ash-flow eruptions in the SW corner of state about 30 My Silverton Caldera Formation of San Juan mountains EPIEROGENIC UPLIFT 28 My to present Broad, regional uplift with little tilting 10 My really kicked into gear Still continuing THE BIG DOME Uplifted all of western and central Colorado...
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Mtn Geog SG 3 - Mtn Geog Mid-term III Study Guide...

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