Geol 285 - Petrology, Dr. Helen M. Lang, West Virginia University, Spring 2009Sedimentary RocksRocks resulting from the consolidation of loose sediment or chemical precipitation from solution at or near the Earth’s surface; or organic rocks consisting of the secretions or remains of plants and animalsSedimentary Rocks are mostly marine. Why?Sediments are deposited in Basins (low places on the Earth’s surface)There are several common Sedimentary Basin Types related to different Plate Tectonic SettingsSix Major types of Sedimentary Basins- Oceanic basins - Arc-trench system basins - Continental-collision basins - Grabens along continental margins - Intracratonic basinsPlate Tectonic SettingsOceanic Basins- On oceanic lithosphere - Atlantic and Pacific Ocean basins - Terrestrial muds near continents - Away from continents, sediments are the remains of planktonic (floating, usually within light-penetration distance) organisms that "rain" down from the surface - Some planktonic organisms have carbonate remains, some have siliceous remainsCarbonate Compensation Depth (CCD) - see handoutArc-trench System Basins- Trench sediments - in trench above subduction zone - Fore-arc basins - in front of (relative to the trench) the volcanic arc - Intra-arc basins - within the volcanic arc (between the volcanoes)- Retro-arc or Back-arc basins - behind the volcanic arcArc-Trench System Basins - see handoutTrench Sediments- Turbidites - deposits from submarine flows of sediment water mixture; they commonly develop from submarine landslides and are transported along the trench - Mélanges - chaotic tectonic mixtures of very large fragments of older sedimentaryand crystalline rocks in a muddy matrixThe Aleutian TrenchFore-arc Basin Sediments- Sediment from volcanic arc: mainly volcanic and plutonic source rocks - Lithic sandstones and wackes common - Sandstones rich in volcanic rock fragments and calcic plagioclase grainsContinental Collision Basins- Low places where sediments accumulate when two continental blocks collide - Convergence of the southeastern part of North America and the northeastern part of South America in the Caribbean - Convergence of Africa and Europe in the Alps/Mediterranean - Convergence of the Indian plate with the Eurasian plate in the HimalayasHimalayan Collision Zone: high erosion rate, enormous quantities of sediment, many sites for sediment accumulationGrabens along Rifted Continental Margins like east coast of U.S.Intracontinental Basins- Epicontinental seas - upon the continent - Covered the interior of North America during most of the Paleozoic - Relatively shallow water sediments - Many unconformities - Preponderance of nearshore sediments - Abundant carbonates and evaporites - e.g., the Michigan BasinMichigan
View Full Document
Unlocking...