The importance of sedimentary rocks

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Chapter Lecture Earth: An Introduction to Physical Geology Eleventh Edition Sedimentary Rocks Tarbuck and Lutgens © 2014 Pearson Education, Inc The Importance of Sedimentary Rocks • • • • Sedimentary rocks cover ~ 75% of Earth’s surface ~ % (by volume) of Earth’s outer 10 miles Contain evidence of past environments: Important resource – Coal, oil, and other fossil fuels – Groundwater resources © 2014 Pearson Education, Inc Origins of Sedimentary Rock • Products of mechanical & chemical weathering • Sediments & soluble constituents are transported down slope by gravity • Sediments are deposited & buried • Deposition causes lithification • Types of sedimentary rocks: – Detrital – Crystalline – Chemical/Organic sedimentary rocks © 2014 Pearson Education, Inc Detrital Sedimentary Rocks • Detrital Rocks – form from sediments that have been weathered and transported – Mostly clay minerals, quartz, feldspars, and micas – Particle size is used to distinguish among the various rock types © 2014 Pearson Education, Inc Detrital Sedimentary Rocks • Shale – Silt & clay-sized particles – Form from settling of sediments in quiet, nonturbulent environments – Sediments form in thin layers (laminae) – Has fissility (rock can be split into thin layers) – Most common sedimentary rock © 2014 Pearson Education, Inc Detrital Sedimentary Rocks • Sandstone – – – – Sand-sized particles Forms in many environments Common sedimentary rock Quartz is the most abundant mineral • Quartz sandstone (quartz) • Arkose sandstone (feldspar) • Graywacke contains rock fragments and matrix, in addition to quartz and sandstone © 2014 Pearson Education, Inc Detrital Sedimentary Rocks • Sandstone – Sorting is the degree of similarity in particle size in a sedimentary rock – If all the grains in a rock are of similar size, the rock is well sorted – If the grains in a rock are different sizes (both large and small grains), the rock is poorly sorted – Sorting can help decipher the depositional environment of the rock © 2014 Pearson Education, Inc Detrital Sedimentary Rocks • Sandstone – The particles in sandstone vary and are classified by their sorting and shape © 2014 Pearson Education, Inc Detrital Sedimentary Rocks • Conglomerate and Breccia – Conglomerate consists of rounded, gravel-sized sediments – Breccia consists of angular, gravel-sized sediments – Both types of rocks are poorly sorted © 2014 Pearson Education, Inc Chemical Sedimentary Rocks • Form from precipitated material that was once in solution • Precipitation of material occurs by: – Evaporation – Organic processes from water-dwelling organisms form biochemical sedimentary rocks © 2014 Pearson Education, Inc Turning Sediments into Sedimentary Rock: Diagenesis and Lithification Many changes occur to sediment after it is deposited Lithification—unconsolidated sediments are transformed into sedimentary rocks Compaction—as sediments are buried, the weight of the overlying material compresses the deeper sediments Cementation—involves the crystallization of minerals among the individual sediment grains © 2014 Pearson Education, Inc Classification of Sedimentary Rocks Sedimentary rocks are classified according to the type of material • Two major groups – • • © 2014 Pearson Education, Inc Detrital – Has clastic texture, composed of discrete fragments cemented together Chemical/Organic – Has nonclastic or crystalline texture, where the minerals form patterns of interlocked crystals Identification of Sedimentary Rocks © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments An environment of deposition or a sedimentary environment is a geographic setting where sediment is accumulating Determines the nature of the sediments that accumulate (grain size, grain shape, etc.) © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments Types of Sedimentary Environments Three broad categories Continental Marine Transition © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments Continental Environments Dominated by stream erosion and deposition Streams are the dominant agent of landscape alteration Glacial Deposits are typically unsorted mixtures of sediments that range from clay to boulder-sized Wind (eolian) Well-sorted, fine sediments © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments Marine Environments Shallow marine (to about 200 meters) Borders the world’s continents Receives huge quantities of terrestrial sediments Warm seas with minimal terrestrial sediments have carbonate-rich muds Deep marine (seaward of continental shelves) Primarily fine sediments that accumulate on the ocean floor Turbidity currents are the exception © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments Transitional Environments The shoreline is the transition zone between marine and continental environments Examples include: Beaches Tidal flats Lagoons Deltas © 2014 Pearson Education, Inc Sedimentary Environments © 2014 Pearson Education, Inc Sedimentary Structures • The layers of the sedimentary rocks are called strata or beds © 2014 Pearson Education, Inc Sedimentary Structures • Cross-bedding occurs when the layers in the sedimentary rocks are inclined • Characteristic of sand dunes, deltas, and some stream deposits © 2014 Pearson Education, Inc Sedimentary Structures • Graded beds - sediments in a strata gradually change from coarse at the bottom to fine at the top © 2014 Pearson Education, Inc Sedimentary Structures – Ripple marks are small waves that are lithified in the sedimentary rocks – Mud cracks indicate sediments form in an alternatively wet and dry environment – Fossils evidence of prehistoric life © 2014 Pearson Education, Inc The Carbon Cycle and Sedimentary Rocks • CO2 is one of the most active parts of the carbon cycle – Plants absorb CO2 through photosynthesis – When plants die, some of the CO2 is deposited in the sediments • Over geologic time, considerable amounts of plant biomass is converted into fossil fuels • When fossil fuels are burned, that CO2 is released back into the atmosphere © 2014 Pearson Education, Inc End of Chapter © 2014 Pearson Education, Inc [...]... buried, the weight of the overlying material compresses the deeper sediments Cementation—involves the crystallization of minerals among the individual sediment grains © 2014 Pearson Education, Inc Classification of Sedimentary Rocks Sedimentary rocks are classified according to the type of material • Two major groups – • • © 2014 Pearson Education, Inc Detrital – Has clastic texture, composed of discrete... that are lithified in the sedimentary rocks – Mud cracks indicate sediments form in an alternatively wet and dry environment – Fossils evidence of prehistoric life © 2014 Pearson Education, Inc The Carbon Cycle and Sedimentary Rocks • CO2 is one of the most active parts of the carbon cycle – Plants absorb CO2 through photosynthesis – When plants die, some of the CO2 is deposited in the sediments • Over... fragments cemented together Chemical/Organic – Has nonclastic or crystalline texture, where the minerals form patterns of interlocked crystals Identification of Sedimentary Rocks © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments An environment of deposition or a sedimentary environment is a geographic setting where sediment is accumulating Determines the nature of the sediments that... 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments Transitional Environments The shoreline is the transition zone between marine and continental environments Examples include: Beaches Tidal flats Lagoons Deltas © 2014 Pearson Education, Inc Sedimentary Environments © 2014 Pearson Education, Inc Sedimentary Structures • The layers of the sedimentary rocks are called strata or... 2014 Pearson Education, Inc Sedimentary Structures • Cross-bedding occurs when the layers in the sedimentary rocks are inclined • Characteristic of sand dunes, deltas, and some stream deposits © 2014 Pearson Education, Inc Sedimentary Structures • Graded beds - sediments in a strata gradually change from coarse at the bottom to fine at the top © 2014 Pearson Education, Inc Sedimentary Structures – Ripple... Organic Sedimentary Rocks • Stages of Coal Formation – Accumulation of plant remains – Formation of peat – Formation of lignite and bituminous coal – Formation of anthracite coal © 2014 Pearson Education, Inc Turning Sediments into Sedimentary Rock: Diagenesis and Lithification Many changes occur to sediment after it is deposited Lithification—unconsolidated sediments are transformed into sedimentary rocks. .. Education, Inc Sedimentary Rocks Represent Past Environments Types of Sedimentary Environments Three broad categories Continental Marine Transition © 2014 Pearson Education, Inc Sedimentary Rocks Represent Past Environments Continental Environments Dominated by stream erosion and deposition Streams are the dominant agent of landscape alteration Glacial Deposits are typically unsorted mixtures of sediments...Chemical Sedimentary Rocks • Limestone – Most abundant chemical sedimentary rock – Mainly composed of the mineral calcite – Can form from inorganic and biochemical origins © 2014 Pearson Education, Inc Chemical Sedimentary Rocks • Biochemical limestone forms from shells of marine organisms – Large quantities of marine limestone are formed from corals – Corals... Education, Inc Sedimentary Rocks Represent Past Environments Marine Environments Shallow marine (to about 200 meters) Borders the world’s continents Receives huge quantities of terrestrial sediments Warm seas with minimal terrestrial sediments have carbonate-rich muds Deep marine (seaward of continental shelves) Primarily fine sediments that accumulate on the ocean floor Turbidity currents are the exception... Australia’s Great Barrier Reef is the largest coral reef on Earth – Coquina is composed of cemented fragments of shell material – Chalk is composed of microscopic marine organisms © 2014 Pearson Education, Inc Carbonate Reefs © 2014 Pearson Education, Inc Coquina © 2014 Pearson Education, Inc The White Chalk Cliffs © 2014 Pearson Education, Inc Chemical Sedimentary Rocks • Evaporites – Form when restricted
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