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Format
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Section
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Africa
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East Africa
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Ethiopia (1)
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Ethiopian Rift (1)
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North Africa
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Morocco (1)
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Southern Africa
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Karoo Basin (1)
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South Africa (1)
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Altiplano (1)
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Arctic Ocean
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Barents Sea (1)
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Asia
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Arabian Peninsula
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United Arab Emirates
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Abu Dhabi (1)
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Far East
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China (1)
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Japan (1)
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Korea
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South Korea
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Ulsan South Korea (1)
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Indian Peninsula
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India
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Singhbhum shear zone (1)
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Indian Shield (1)
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Kemerovo Russian Federation (1)
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Krasnoyarsk Russian Federation
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Taymyr Dolgan-Nenets Russian Federation
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Middle East
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Turkey
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Pontic Mountains (2)
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Siberia (1)
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West Siberia (1)
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Atlantic Ocean
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North Atlantic
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Gulf of Mexico (1)
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Atlantic Ocean Islands
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Australasia
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Australia
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Western Australia
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Bass River (1)
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Buckskin Mountains (3)
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Canada
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Ontario
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Sudbury Structure (2)
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Quebec
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Hudson Bay (1)
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Western Canada
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Caribbean region
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West Indies
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Central America (2)
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Commonwealth of Independent States
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Georgian Republic (1)
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Russian Federation
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Kemerovo Russian Federation (1)
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Krasnoyarsk Russian Federation
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Taymyr Dolgan-Nenets Russian Federation
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Norilsk region (1)
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Siberian Platform (1)
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Transcaucasia (1)
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West Siberia (1)
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Espanola Basin (4)
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Europe
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Alps
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Central Europe
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Poland
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Georgian Republic (1)
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Southern Europe
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Italy
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Apennines
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Southern Apennines (1)
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Apulia Italy
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Murge (1)
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Campania Italy
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Romania
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Scotland
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Indian Ocean
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North America
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Appalachian Basin (1)
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Basin and Range Province
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Great Basin (2)
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Canadian Shield
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Superior Province
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Gulf Coastal Plain (1)
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Lake Superior region (2)
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North American Cordillera (2)
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Rio Grande Rift (5)
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Rocky Mountains
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U. S. Rocky Mountains
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San Juan Mountains (1)
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Williston Basin (1)
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North Slope (1)
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Oceania
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Micronesia
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Mariana Islands
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Guam (1)
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Pacific Ocean
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South Pacific
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Southwest Pacific
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Gulf of Carpentaria (1)
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West Pacific
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Southwest Pacific
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Gulf of Carpentaria (1)
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Permian Basin (1)
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South America
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Peru (1)
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United States
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Alaska (1)
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Arizona
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La Paz County Arizona (4)
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California
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Channel Islands (1)
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Colusa County California (1)
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Inyo County California
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Mono County California (1)
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San Luis Obispo County California
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San Luis Obispo California (1)
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Santa Barbara Channel (1)
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Santa Barbara County California (1)
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Sierra Nevada Batholith (2)
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Southern California (2)
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Transverse Ranges (3)
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Tuolumne County California (1)
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Ventura Basin (1)
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Ventura County California
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Simi Hills (1)
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Yolo County California (1)
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Chesapeake Bay (1)
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Clark's Fork Basin (1)
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Colorado
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Mineral County Colorado
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Creede mining district (1)
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San Juan County Colorado (1)
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Colorado Plateau (5)
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Columbia Plateau (1)
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Georgia
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Camden County Georgia (1)
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Great Basin (2)
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Idaho
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Custer County Idaho
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Borah Peak (1)
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Elmore County Idaho (1)
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Lemhi Range (1)
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Lost River Range
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Borah Peak (1)
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Snake River plain (1)
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-
Iowa
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Johnson County Iowa (1)
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-
Maryland
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Dorchester County Maryland (1)
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Talbot County Maryland (1)
-
-
Michigan
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Michigan Upper Peninsula
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Gogebic County Michigan (1)
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-
-
Midcontinent (1)
-
Minnesota
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Cook County Minnesota (1)
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Mesabi Range (1)
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-
Montana
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Teton County Montana (1)
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-
Nevada
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Eureka County Nevada
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Eureka Nevada (1)
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-
Lincoln County Nevada (8)
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Nye County Nevada
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Grant Canyon Field (1)
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Yucca Mountain (2)
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White Pine County Nevada (1)
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New Jersey
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Burlington County New Jersey (1)
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New Mexico
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Dona Ana County New Mexico (1)
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Jemez Lineament (1)
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Jemez Mountains (2)
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Los Alamos County New Mexico
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Los Alamos National Laboratory (6)
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-
Luna County New Mexico (1)
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Pajarito Plateau (6)
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Santa Fe County New Mexico (1)
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Valles Caldera (2)
-
-
New York
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Adirondack Mountains (1)
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Herkimer County New York (1)
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-
Oregon (2)
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Sevier orogenic belt (1)
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Southwestern U.S. (1)
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Texas
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Brazos River (1)
-
Brewster County Texas
-
Big Bend National Park (3)
-
-
Crane County Texas (1)
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Pecos County Texas (1)
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Ward County Texas (1)
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West Texas (3)
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Winkler County Texas (1)
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-
Trans-Pecos (1)
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U. S. Rocky Mountains
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San Juan Mountains (1)
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Utah
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Tooele County Utah (1)
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Virginia
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Mathews County Virginia (1)
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Northampton County Virginia (1)
-
-
Wyoming
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Albany County Wyoming (1)
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Converse County Wyoming (1)
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Heart Mountain Fault (1)
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Park County Wyoming (1)
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Yucatan Peninsula (1)
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commodities
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aggregate (1)
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brines (1)
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energy sources (3)
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geothermal energy (2)
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metal ores
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base metals (1)
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copper ores (9)
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gold ores (10)
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IOCG deposits (1)
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iron ores (1)
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lead ores (2)
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lead-zinc deposits (2)
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molybdenum ores (2)
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nickel ores (1)
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silver ores (3)
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uranium ores (1)
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vanadium ores (1)
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zinc ores (2)
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mineral deposits, genesis (13)
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mineral exploration (3)
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mineral resources (3)
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oil and gas fields (4)
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petroleum
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natural gas
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shale gas (1)
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water resources (1)
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zeolite deposits (1)
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elements, isotopes
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boron (1)
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carbon
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C-13/C-12 (2)
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C-14 (2)
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organic carbon (1)
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chemical elements (1)
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halogens
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chlorine (1)
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isotope ratios (6)
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isotopes
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radioactive isotopes
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Be-10 (1)
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C-14 (2)
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Pb-206/Pb-204 (1)
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Pb-207/Pb-204 (1)
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Pb-208/Pb-204 (1)
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stable isotopes
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C-13/C-12 (2)
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Cr-53/Cr-52 (1)
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Nd-144/Nd-143 (1)
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O-18/O-16 (3)
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Pb-206/Pb-204 (1)
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Pb-207/Pb-204 (1)
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Pb-208/Pb-204 (1)
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Sr-87/Sr-86 (2)
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metals
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alkali metals
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potassium (2)
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rubidium (1)
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sodium (2)
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alkaline earth metals
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beryllium
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Be-10 (1)
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calcium (2)
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magnesium (1)
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strontium
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Sr-87/Sr-86 (2)
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aluminum (2)
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chromium
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Cr-53/Cr-52 (1)
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iron
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ferric iron (2)
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ferrous iron (1)
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lead
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Pb-206/Pb-204 (1)
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manganese (1)
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precious metals (1)
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rare earths
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Nd-144/Nd-143 (1)
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titanium (1)
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noble gases (2)
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O-18/O-16 (3)
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silicon (1)
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fossils
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Chordata
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Vertebrata
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Tetrapoda
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Reptilia
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Archosauria
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Invertebrata
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Brachiopoda (3)
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Echinodermata
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Crinozoa
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Porifera
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Protista
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microfossils
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Conodonta (7)
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Plantae
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geochronology methods
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fission-track dating (1)
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geologic age
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Cenozoic
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Quaternary
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Bishop Tuff (1)
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lower Pleistocene (1)
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upper Pleistocene (2)
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upper Quaternary (1)
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Saugus Formation (1)
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Tertiary
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John Day Formation (1)
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lower Tertiary (1)
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middle Tertiary
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Soda Lake Shale Member (1)
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Neogene
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Miocene
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lower Miocene (2)
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middle Miocene (1)
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Paintbrush Tuff (1)
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Tiva Canyon Member (1)
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Topopah Spring Member (1)
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upper Miocene
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Modelo Formation (1)
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-
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Pliocene
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upper Pliocene (1)
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Tesuque Formation (1)
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Paleogene
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Eocene
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Absaroka Supergroup (1)
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upper Eocene (1)
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Oligocene
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Creede Formation (1)
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Paleocene
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lower Paleocene
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K-T boundary (2)
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Paleocene-Eocene Thermal Maximum (1)
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White River Group (1)
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Vaqueros Formation (1)
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upper Cenozoic (3)
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Mesozoic
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Cretaceous
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Lower Cretaceous (1)
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Middle Cretaceous (1)
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Upper Cretaceous
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Campanian (1)
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Gulfian
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Aguja Formation (1)
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K-T boundary (2)
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Maestrichtian
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lower Maestrichtian (1)
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Prince Creek Formation (1)
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Franciscan Complex (1)
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Great Valley Sequence (1)
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Jurassic
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Coast Range Ophiolite (2)
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Middle Jurassic
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Bathonian (1)
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Upper Jurassic
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Buckner Formation (1)
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Kimmeridgian (1)
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Smackover Formation (1)
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Orocopia Schist (1)
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Triassic
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Upper Triassic
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Carnian (1)
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-
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Paleozoic
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Carboniferous
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Lower Carboniferous (1)
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Mississippian
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Lower Mississippian
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Tournaisian (1)
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Madison Group (1)
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Pennsylvanian (1)
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Casper Formation (1)
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Devonian
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Guilmette Formation (8)
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Lower Devonian (1)
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Middle Devonian
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Cedar Valley Formation (1)
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Givetian (1)
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Thirtyone Formation (1)
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Upper Devonian
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Famennian
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lower Famennian (1)
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Frasnian
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upper Frasnian (2)
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Jefferson Group (2)
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Nisku Formation (1)
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Ordovician
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Trenton Group (1)
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Upper Ordovician
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Red River Formation (1)
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Yeoman Formation (1)
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Utica Shale (1)
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Permian
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Ecca Group (1)
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Lower Permian
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Cisuralian
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Kungurian (1)
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Whitehill Formation (1)
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Silurian
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Upper Silurian
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Wristen Formation (1)
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upper Paleozoic (1)
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upper Precambrian
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Paleoproterozoic (3)
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granites (6)
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pyroclastics
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tuff (5)
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welded tuff (2)
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oxides
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phosphates
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whitlockite (1)
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Primary terms
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GeoRef Categories
Era and Period
Epoch and Age
Book Series
Date
Availability
Alamo Breccia
Remagnetization of the Alamo Breccia, Nevada Available to Purchase
Abstract The Devonian Alamo Breccia is a thick (<30–130 m) unit, interpreted as a bolide impact deposit, which is bracketed by marine carbonates. Samples were collected within the breccia and above/below the breccia for a contact test to determine if the breccia acted as a conduit for fluids that could have caused the widespread chemical remanent magnetizations (CRMs) present in Palaeozoic Era rocks in Nevada. The carbonates above, below and in the breccia contain a Cretaceous Period syn-tilting CRM that resides in pyrrhotite and a pre-tilting late Palaeozoic Era CRM that resides in magnetite. The contact test is negative. Despite these results, diagenetic alteration by externally derived fluids is interpreted as the most likely mechanism of remagnetization. This hypothesis is supported by 87 Sr/ 86 Sr values in the breccia and surrounding rocks that suggest alteration by fluids with a radiogenic signature. The fluids were not localized in the breccia but are interpreted to have moved pervasively through the rocks. The results differ from some other studies that found that fluids caused localized CRMs around fluid conduits.
Impact-generated carbonate accretionary lapilli in the Late Devonian Alamo Breccia Available to Purchase
Full article available in PDF version.
Shocked quartz in the Alamo breccia, southern Nevada: Evidence for a Devonian impact event Available to Purchase
Alamo Event, Nevada: Crater stratigraphy and impact breccia Realms Available to Purchase
Based on evaluation of past results and new research, we have partitioned the distribution of the Alamo Breccia in southeastern Nevada and western Utah into six genetic Realms that provide a working model for the marine Late Devonian Alamo Impact Event. Each Realm exhibits discrete impact processes and stratigraphic products that are enumerated here. The first five form roughly concentric semicircular bands across the Devonian shallow-water carbonate platform. These are: (1) Rim Realm, where a newly defined impact stratigraphy includes both autogenic and allogenic breccias associated with the crater rim; (2) Ring Realm, where breccias are now interpreted to have formed sequentially by seismic shock, passage of the ejecta curtain, tsunami waves or surge, and runoff that accumulated over tilted terrace(s) bounded by syn-Event, ring-forming, listric faults; (3) Runup Realm, where graded breccias were stranded by tsunami surge or waves; (4) Runoff Realm, where sheet-floods carried traces of impact debris across the distal platform beds and channels filled with impact debris; (5) Seismite Realm, where near-surface beds far across the platform were uniquely deformed; and (6) Runout/Resurge Realm, where offshore channels of thick off-platform Alamo Breccia, together with large-scale olistolith(s), signal contemporaneous massive collapse of the platform margin, possibly into the central crater. Five breccia Units characterize the newly interpreted Rim Realm, in ascending order: (1) deformed target rocks, (2) injected dikes and sills, (3) chaotic fallback, (4) smeared fallback, and (5) resurge. This succession is covered by deepwater limestones deposited inside the crater rim, or across a new slope created after platform margin collapse. Unit 1 exhibits shatter-cone-like structures interpreted as impact products. Newly discovered Ordovician and probable older meter-scale clasts in Unit 3 confirm a minimum excavation depth of 1.5 km. Microscopic components in Units 3 and 4 indicate high pressures (>10 GPa), probable quenched carbonate melt, and accreted particles that may be new kinds of impact products. Postimpact tectonics and other factors obscure the full panorama, including the location and character of the missing central crater, but the assemblage of Realms offers a working model to compare with expected impact paradigms.
SEQUENCE STRATIGRAPHY ACROSS AN EVENT DEPOSIT: PRE-, SYN-, AND POSTIMPACT ACCOMMODATION TRENDS AND SEQUENCE DEVELOPMENT SURROUNDING THE ALAMO IMPACT BRECCIA Available to Purchase
ABSTRACT The effects of bolide impacts on carbonate platform sedimentation and stacking patterns are poorly understood, partly because the geological evidence for marine impact sites is typically unavailable. Givetian–Frasnian carbonates in southern Nevada contain a continuous record of sedimentation before, during, and after the Devonian (Frasnian) Alamo impact event (382 Ma), evidenced mainly by the regional Alamo Breccia Member of the Guilmette Formation. Two transects arranged from seven stratigraphic sections measured through the lower ~300 m of the Guilmette Formation record environmental lithofacies deposited from peritidal to deep subtidal zones. Stacking patterns of peritidal and subtidal cycles indicate four relatively high-frequency sequences superimposed on the larger-magnitude eustatic Taghanic onlap of the Kaskaskia sequence. Sequences are interpreted based on facies proportions and cycle stacking trends because of a lack of prominent erosional surfaces developed on the Frasnian greenhouse shelf. Lateral correlation of facies and cycle stacking indicates that the Alamo impact took place during the late phase of sedimentation during deposition of “Sequence 3” in the Guilmette Formation. Underlying facies and surfaces were obliterated and excavated during the impact, resulting in truncated terminations of sequence boundary and maximum flooding zones. Eustatic sea-level rise during the late Frasnian resulted in an overarching shoreline backstep and deepening of vertical facies associations prior to the Alamo impact. Additional accommodation was gained instantaneously as a result of the Alamo impact, which formed a local, steep-sided basin and shifted the slope break of the platform margin. Postimpact sedimentation within the Alamo crater is characterized by condensed sections of continuously deposited thin-bedded mudstones with pelagic (tentaculites) fauna. Thick shoreface sandstones were deposited in a lowstand clastic wedge as the last phase of crater fill in the study area. While accommodation and depositional environment changed dramatically at the impact site, long-term sedimentation trends immediately outside of the impact site were unaffected by the Alamo event, demonstrating that the forces that control overall carbonate platform growth and evolution (tectonics, climate, oceanography, biology) are of far greater importance than even regional-scale physical perturbations such as meteor impacts.
Devonian carbonate platform of eastern Nevada: Facies, surfaces, cycles, sequences, reefs, and cataclysmic Alamo Impact Breccia Available to Purchase
Abstract Devonian limestone and dolostone formations are superbly exposed in numerous mountain ranges of southeastern Nevada. The Devonian is as thick as 1500 m there and reveals continuous exposures of a classic, long-lived, shallow-water carbonate platform. This field guide provides excursions to Devonian outcrops easily reached from the settlement of Alamo, Nevada, ~100 mi (~160 km) north of Las Vegas. Emphasis is on carbonate-platform lithostratigraphy, but includes overviews of the conodont biochronology that is crucial for regional and global correlations. Field stops include traverses in several local ranges to study these formations and some of their equivalents, in ascending order: Lower Devonian Sevy Dolostone and cherty argillaceous unit, Lower and Middle Devonian Oxyoke Canyon Sandstone, Middle Devonian Simonson Dolostone and Fox Mountain Formation, Middle and Upper Devonian Guilmette Formation, and Upper Devonian West Range Limestone. Together, these formations are mainly composed of hundreds of partial to complete shallowing-upward Milankovitch-scale cycles and are grouped into sequences bounded by regionally significant surfaces. Dolomitization in the Sevy and Simonson appears to be linked to exposure surfaces and related underlying karst intervals. The less-altered Guilmette exhibits characteristic shallowing-upward limestone-to-dolostone cycles that contain typical carbonate-platform fossil- and ichnofossil-assemblages, displays stacked biostromes and bioherms of flourishing stromatoporoids and sparse corals, and is punctuated by channeled quartzose sandstones. The Guilmette also contains a completely exposed ~50-m-thick buildup that is constructed mainly of stromatoporoids, with an exposed and karstified crest. This buildup exemplifies such Devonian structures known from surface and hydrocarbon-bearing subsurface locations worldwide. Of special interest is the stratigraphically anomalous Alamo Breccia that represents the middle member of the Guilmette. This spectacular cataclysmic megabreccia, produced by the Alamo Impact Event, is as thick as 100 m and may be the best exposed proven bolide impact breccia on Earth. It contains widespread intervals generated by the seismic shock, ejecta curtain, tsunami surge, and runoff generated by a major marine impact. Newly interpreted crater-rim impact stratigraphy at Tempiute Mountain contains an even thicker stack of impact breccias that are interpreted as parautochthonous, injected, fallback, partial melt, resurge, and possibly post-Event crater fill.
Post-impact depositional environments as a proxy for crater morphology, Late Devonian Alamo impact, Nevada Open Access
Alamo impact olistoliths in Antler orogenic foreland, Warm Springs–Milk Spring area, Hot Creek Range, central Nevada Available to Purchase
The 45 km 2 map area is situated at the south end of the Hot Creek Range in central Nevada, ~16 km east of the buried leading edge of the Mississippian Roberts Mountains thrust. Three eastward-trending left-slip faults divide the area into four structural blocks. The southernmost block is occupied solely by upper Oligocene volcanic rocks. The narrow northernmost block, now occupied surficially by valley fill and volcanic rocks, represents the south end of the main part of the Hot Creek Range, from which the study area is offset. The middle two blocks display different aspects of the eastward-traveled outer crater rim created by the ca. 382 Ma (early Late Devonian, middle Frasnian) Alamo impact. The Alamo impact was produced by a 5-km-diameter bolide, most likely a comet, which excavated a transient submarine crater 44–65 km in diameter. Comparison of thin (8–12 m) Alamo Breccia deposits in the northern of the middle two blocks with a more easterly, thick (35–42 m) Alamo deposit in the main Hot Creek Range, 4 km north of the map area, suggests that these blocks traveled many kilometers eastward. The northern of the middle two blocks contains a large olistolith capped by the thin breccia, whereas the southern block contains a larger olistolith lacking an Alamo Breccia cap. Three Devonian pulses of the Antler orogeny are better documented in the chapter on the Bisoni-McKay area. Here, the first Antler pulse in latest Middle Devonian time is obscured within an ~9 m.y. hiatus enlarged by excavation of the Alamo impact crater. The second Antler pulse is recorded by the ~4 m.y. hiatus produced by the regional unconformity between the lower and upper members of the Woodruff Formation. The third Antler pulse is documented by an ~8 m.y. regional hiatus between the Mississippian Webb Formation and Upper Devonian Woodruff Formation. In previous papers, we had interpreted this pulse to initiate the Antler orogeny.
Late Devonian Alamo Impact, southern Nevada, USA: Evidence of size, marine site, and widespread effects Available to Purchase
The early Late Devonian (early Frasnian) Alamo Impact targeted an oceanic, off-platform site in southern Nevada, excavating a crater with a final diameter of 44–65 km. The original crater is now dismembered and buried beneath younger rocks. Consequently, its size and site must be deduced through multiple converging lines of geological and paleontological evidence. Previous and new evidence includes the catastrophically emplaced Alamo Breccia, tsunamites, shock-metamorphosed quartz grains, carbonate accretionary lapilli, an iridium anomaly, sub-Breccia clastic injection, deep-water Breccia channels, and ejecta material. We now demonstrate, on the basis of conodont microfossils in carbonate ejecta clasts within lapillistone blocks and widely distributed shocked-quartz and lithic-clast ejecta within the upper part of the Breccia, that the Alamo Impact excavated down at least into Upper Cambrian strata, at a depth of 1.7 km, and possibly into the underlying Proterozoic–Lower Cambrian Prospect Mountain Quartzite, ∼2.5 km beneath the Late Devonian seafloor. Distal tsunamites and probable ejecta are now documented as far north as Devils Gate, northern Nevada, and as far northeast as the Confusion Range, western Utah. A charcoal-bearing, early Frasnian estuarine deposit in the Bighorn Mountains, Wyoming, may provide the first evidence of an Alamo Impact fallout-generated forest fire. Our new data further document the widespread effects and size of the Alamo Impact, and constrain the likely present position of the tectonically transported crater to an area between the Timpahute and Hot Creek Ranges, southern Nevada.