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2-Sedimentary Rocks Jarðsaga 1 - Saga lífs og lands – Ólafur Ingólfsson Sedimentary Rocks and Sedimentary Environments Sedimentary Rocks are the Principal Repository for Information About the Earth’s Past Environment Earth’s history largely read from sedimentary strata And C e em ssur en re tat P ion Erosion Sedimentary Sediment Rocks P H n r n e o o e si i s o s a r s E o ur t r e E Heat and Pressure Metamorphic Igneous Rocks Rocks He g lin at o Co Magma Sedimentary Rocks Clastic Rocks (molaberg) • Made of Fragmentary Material • Deposited by – Water (Most Common) –Wind Chemical-Biological –Glacial Action Sedimentary Rocks –Gravity •Evaporation •Precipitation • Biogenic Sediments Sedimentary Rocks Clastic Rock – composed of fragments of preexisting rocks. Nonclastic Rock – composed of chemical precipitates or biogenic matter. Sediment Sizes and Clastic Rock Types Rock Type Sediment Grain Size Shale Clay less than 0.001 mm Siltstone Silt .001-0.1 mm Sandstone Sand .01-1 mm Conglomerate Gravel 1mm + Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks. Clastic Sediment Size Some Special Clastic Rock Types • Arkose Feldspar-Rich • Breccia Angular Fragments • Graywacke Angular, Immature Sandstone Classification of Clastic Sedimentary Rocks Major types of sandstone based on mineral/rock content Quartzite Arkose Lithic Sandstone Greywacke Chemical-Biological Sediments Evaporites -Water Alteration After Soluble Deposition •Halite • Limestone ⇨ Dolomite •Gypsum Biogenic Sediments • Calcite • Limestone - Shells, Precipitates Reefs, Etc. •Gypsum Organic Remains • Limestone •Coal • Iron Formations • Petroleum Biogenic Sediments Terestrial Sediments - mainly plant matter Marine Sediments -mainly carbonates Corals - Large components of reefs. Bivalves, Gastropods (sníglar), Foraminifers (götungar) - Whole or partial skeletons form sand and gravels. Algae, Crinoids (sælilja), Echinoderms (skrápdýr), Bryozoans (mosadýr) - disintergrate to form some sand particles and lime mud. Diatoms (kísilþörungar), Radiolaria (geislungar) – Bedded chert SiO2 Conglomerate (völuberg) Sandstone Coal Shale (leirskífur) Limestone (kalksteinn) Arkose Some major types of sedimentary rocks Limestone Gypsum Environmental Clues in Sedimentary Rocks • Grain Size - Power of Transport Medium • Grading - Often Due to Floods • Rounding } Transport, Reworking • Sorting • Cross-bedding - Wind, Wave or Current Action Features in sedimentary rocks Sand grains show evidence of transport fossil fish ripple marks formed by Mud cracks wind or wave action Bedding or Stratification • Almost Always Present in Sedimentary Rocks • Originally Horizontal • Tilting by Earth Forces Later • Variations in Conditions of Deposition • Size of Beds (Thickness) – Usually 1-100 cm – Can Range From Microscopic to 50m • Sedimentary rocks commonly show layering that form as sediment is deposited Sedimentary – Stratification (lagskifting) structures – cross bedding (skálögun) – graded bedding (lóðgreining) Cross bedding is wind wind Migration of the dune formed by the migration of windward leeward sand waves (ripple marks or dunes) by sand particles travelling up the windward face and depositing down the leeward face Graded bedding • Graded bedding can be produced by turbidity currents, which can travel up to 100 As the current slows km/hr the coarse grains are – currents can be started by deposited first,followed landslide or earthquake down the by successively finer- continental slope grained sediments – deposition based on density (gravity) and settling velocity Environmental Clues in Sedimentary Rocks • Fossils – Salt Water - Corals, Echinoderms (skrápdýr) – Fresh Water - Insects, Amphibians – Terrestrial - Leaves, Land Animals • Color And Chemistry – Red Beds - Often Terrestrial – Black Shale - Oxygen Poor, Often Deep Water – Evaporites – Arid Climates Each kind of sedimentary environment on Earth’s surface is characterized by particular kinds of sediment and patterns of bedding • Sediments are deposited in a variety of places. • Each is characterized by a combination of the kind and amount of water, the local topography, and the biological activity. • These in turn are related to plate tectonic setting and climate. • Although sediment can be deposited anywhere, large accumulations of sediment are not, being found in only a handful of environments. Common Sedimentary Environments: Non-marine environments Stream sediments, Lake sediments, Glacial (ice deposited) sediments, Eolian (wind deposited) sediments Continental Shelf sediments Estuarine sediments, Deltaic sediments, Beach sediments, Carbonate shelf sediments, Marine evaporite sediments Continental slope and rise sediments Turbidites, Deep Sea Fans, Sediment drifts Deep Sea Sediments Deep -Sea oozes, Land-derived sediments Major sedimentary environments fluvial alluvial tidal • Sedimentary fan beach flat environments dunes glacier delta barrier lake island encompass the physical, chemical, and biological Shallow marine conditions in areas deep marine organic reef where sediment is organic deposited. These reef comprise three distinct groups: 1) continental, • weathering - physical and chemical • transportation - wind, water, and ice 2) shoreline –sorting (transitional), • deposition 3) marine Sedimentary Environments Shoreline Environments Deltaic Continental (land-based) Tidal flat Environments Beach Alluvial Marine Environments Desert Continental shelf Lake Continental slope Glacial Organic reefs Deep-sea Continental sedimentary environments – Classification Chart Alluvial Fan Fluvial Lacustrine Dunes Rock type Breccia, Conglomerate, Siltstone, Quartz arenite conglomerate, sandstone, shale,limestone (sandstone) or arkose siltstone, shale or evaporites gypsum Composition Terrigenous Terrigenous Terrigenous, Terrigenous or carbonate, or evaporite evaporite Grain Size Clay to gravel Clay to gravel Clay to silt or Sand (Fining upward) sand (Coarsening upward) Grain Shape Angular Rounded to ----- Rounded angular Sorting Poor Variable Variable Good Sedimentary Cross-bedding Asymmetrical Symmetrical Cross-bedding and graded ripples,cross- ripples, Structures bedding bedding,graded lamination, bedding,tool cross-bedding, marks graded bedding (http://www.dc.peachnet.edu/~pgore/geology/historical_lab/environmentchart.htm) Transitional sedimentary environments BARRIER LAGOON TIDAL FLAT DELTA BEACH Rock Type Sandstone, Quartz Siltstone, Siltstone, shale, calcilutite, siltstone, arenite, shale, dolostone or gypsum shale, coal coquina limestone Composition Terrigenous Terrigenous Terrigenousc Terrigenous, carbonate, or or carbonate arbonate, or evaporite evaporite Grain Size Clay to sand Sand Clay to silt Clay to silt Grain Shape --- Rounded to --- --- angular Sorting Poor Good Poor Variable Inorganic Cross- Cross- Lamination, Lamination, mudcracks, ripples, Sedimentary bedding, bedding, ripples, cross-bedding Structures graded symmetrical cross- bedding ripples bedding Organic or Trails, Tracks, Trails, Stromatolites, trails, tracks, Biogenic burrows trails, burrows burrows Sedimentary burrows Structures Fossils Plant Marine shells Marine shells Marine shells fragments, shells Marine sedimentary environments CONTINENTAL CONTINENTAL SLOPE AND REEF SHELF RISE Rock Type Fossiliferous Sandstone, shale, Litharenite, siltstone, and shale limestone siltstone, (or limestone) fossiliferous limestone, oolitic limestone Composition Carbonate Terrigenous or Terrigenous or carbonate carbonate Grain Size Variable, Clay to sand Clay to sand framework, few to no grains Grain Shape --- --- --- Sorting --- Poor to good Poor Inorganic --- Lamination, cross- Graded bedding, cross-bedding, Sedimentary bedding lamination, flute marks, tool Structures marks (turbidites) Organic or --- Trails, burrows Trails, burrows Biogenic Sedimentary Structures Fossils Corals, marine Marine shells Marine shells, rare plant shells fragments • Continental glaciers greatly modify the entire landscape they cover. Flowing ice Continental removes and transports soil and bedrock, glacier and transports it long distances. Supraglacial debris system outwash proglacial plain subglacial till lake plucking abrasion moraine iceberg Surface tilts towards glacier dropstones Isostatic subsidence Glacial landforms and sediments Glacial till Glacial varves •Geological fingerprinting of continental scale glaciations is very important in Moraine terrain Esker paleogeographical reconstructions – •Distribution of glacial tills used early on to argue for Continental Drift drumlin outwash plain The glacial environment • Glaciers generally create poorly sorted Margins of a valley Ancient glacial sediments sedimentary glacier in Canada (diamictite) in Utah rocks The delta environment • Deltas (óseyri) form a variety of rock types, depending on the environment of Minor delta in the Ancient delta deposit Great Bear Lake, Canada in the Colorado Plateau deposition. Deltas • The history of the Mississippi delta involves repeated switching of the main channel. Previous deltas are numbered (1-6) by age from oldest to youngest. River systems and tectonics • The evolution of the major rivers of the world is influenced directly and indirectly by plate tectonics. The fluvial environment • Rivers are the major channels by which erosional debris is transported from the continents to the oceans. • River deposits are characterized by channels of sand or gravel. • River deposits are typically graded due to channel migration and a decrease in flow energy Point
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