Chapter 8 – FROM SEDIMENT INTO SEDIMENTARY ROCK

Sediments and Sedimentation Deposition Laying down of sediment Separated into 3 broad categories Clastic (Detrital) Chemical Biogenic (Biochemical)

Sediments and Sedimentation Clastic sediment Fragmented rock & mineral debris from weathering & erosion Described by particle shape, angularity, & size Volcani-clastic sediments Pyroclasts Distinguished by size (bombs, lapilli, ash)

Sediments and Sedimentation Chemical sediment Precipitation of minerals dissolved in lake, river, or sea water Limestone Shallow sea water evaporation causes dissolved salts to precipitate

Sediments and Sedimentation Biogenic sediment Primarily composed of plant or animal remains Shells, bones, teeth Wood, roots, leaves

Sedimentary Rocks Lithification Processes where loose sediment transforms into sedimentary rock Bedding Layers of strata in sediment/sedimentary rock Bedding surface Top or bottom of rock bed Graded bed Bed with large clasts at bottom, fining toward top Cross bedding Beds are inclined relative to layer they occur in

Lithification Processes Compaction Reduced pore space due to weight of sediments above Cementation Dissolved substances precipitate out & act as glue Recrystallization Form new crystalline mineral grains from old ones Diagenesis Low temperature/pressure changes

Types of Sedimentary Rocks Clastic sedimentary rock Conglomerate or breccia Large fragments in fine grained matrix Sandstones Medium grained (sand sized) Arkose or Quartz Sandstone Mudstones Very fine grained rock Same composition as shale but lacks fissility Shale Very fine grained fissile rock Fissile = breaks into layers Particle Sizes in Clastic Sedimentary Rocks Diameter (mm) Particle Type Sediment Name Sedimentary Rock More than 256 Boulder Gravel Conglomerate or Breccia 64 to 256 Cobble 4 to 64 Pebble 2 to 4 Granule 1/16 to 2 Sand Sandstone 1/256 to 1/16 Silt Mud Siltstone, Shale or Mudstone Less than 1/256 Clay

Types of Sedimentary Rocks Chemical sedimentary rocks Classified mainly by composition Evaporite Formed by lake or sea water evaporation Rock salt; rock gypsum Limestone & related Oolitic Dolostone Chert

Types of Sedimentary Rocks Biogenic sedimentary rocks Limestone Mostly made of calcite Coquina Chalk Peat Formed by accumulation & compaction of plant remains Coal Formed by lithification of plant-rich sediment Bituminous coal

Depositional Environments Interpreting environmental clues Patterns made by air & water that moved over sediments Ripple marks Fossils Mud cracks

Depositional Environments on Land Streams Alluvial fan Forms where stream is not constrained by valley walls Fan-shaped Lakes Delta Forms where stream enters standing body of water Usually triangle-shaped Playa Seasonal lake

Depositional Environments on Land Glacier Till Mixed particles sizes & shapes Wind Eolian sediment Sediments carried & deposited by wind Loess Wind-blown silt & clay sediment

Depositional environments in & near the ocean Delta Estutary Semi-enclosed body of coastal water Fresh water mixes with sea water Beaches Mixed material; quartz common Shelves Silt or sand sediment; numerous fossils Carbonate platforms and reefs Reef: wave-resistant structure built of marine invertebrate skeletons

Depositional environments in & near the ocean Turbidites & turbidity currents Turbulent, gravity driven flow of sediment & water Moves sediment from continental shelf to deep sea Seafloor Nutrient-rich Calcareous ooze Siliceous ooze

Depositional environments in and near the ocean Sedimentary facies Changes in the character of sediment from one environment to another

How Plate Tectonics Affect Sedimentation Divergent plate boundaries Rift valleys Convergent plate boundaries Collisional type Subduction type Back-arc basin Accretionary wedges