Sedimantoloji Karbonatlara Bakış ( İngilizce İçerik ) - 1 Professor Chris Kendall Professor Chris Kendall An Overview of Carbonates An Overview of CarbonatesKireçtaşları ve dolomitler Kireçtaşları ve dolomitler Lecture Series Overview Lecture Series Overview ? Sediment production ? Types of sediment and sedimentary rocks ? Sediment transport and deposition ? Depositional systems ? Stratigraphic architecture and basins ? Chrono-, bio-, chemo-, and sequence stratigraphy ? Earth history“Sedimentary rocks are the product of the creation, transport, deposition, and diagenesis of detritus and solutes derived from pre-existing rocks”.Sedimentary Rocks Sedimentary Rocks ? Detrital/Siliciclastic Sedimentary Rocks ? conglomerates & breccias ? sandstones ? mudstones ? Carbonate Sedimentary Rocks ? carbonates ? Other Sedimentary Rocks ? evaporites ? phosphates ? organic-rich sedimentary rocks ? cherts ? volcaniclastic rocksLecture Outline Lecture Outline ? How photosynthesis, warm temperatures & low pressures in shallow water control carbonate distribution ? How carbonate sediment types is tied to depositional setting ? How most mud lime mud has a bio-physico-chemical origin ? Origins of bio-physico-chemical grains:- ooids, intraclasts, pellets, pisoids ? Separation of bioclastic grains:- foram’s, brach’s, bryozoan, echinoids, red calc’ algae, corals, green calc’ algae, and molluscs by mineralogy & fabric ? How CCD controls deepwater carbonate ooze distribution ? How Folk & Dunham’s classifications are used for carbonate sediments ? How most diagenesis, dolomitization, & cementation of carbonates takes place in near surface & trace elements are used in this determination ? How Stylolites develop through burial & solution/compactionLimestones Form Limestones Form - - Where? Where? ? Shallow Marine ? Late Proterozoic to Modern ? Deep Marine ? Rare in Ancient & commoner in Modern ? Cave Travertine and Spring Tufa ? both Ancient & Modern ? Lakes ? Ancient to ModernCO CO 2 2 - - Temperature & Pressure Effect! Temperature & Pressure Effect! ? High temperatures, low pressure & breaking waves favor carbonate precipitation. ? CO 2 + 3H 2 O = HCO 3 -1 + H 3 O +1 + H 2 O = CO 3 -2 +2H 3 O +1 ? Carbon dioxide solubility decreases in shallow water and with rising in temperature.CO CO 2 2 - - Temperature & Pressure Effect! Temperature & Pressure Effect! ? At lower pressure CO 2 is released & at higher pressure dissolves. ? HCO 3 -1 and CO 3 -2 are less stable at lower pressure but more stable at higher pressure. ? HCO 3 -1 and CO 3 -2 have lower concentration in warm waters but higher concentrations in colder waters.Calcium Carbonate Calcium Carbonate - - Solubility Solubility ? Note calcium carbonate dissociation: CaCO 3 = Ca +2 + CO 3 -2 ? CaCO 3 is less soluble in warm waters than cool waters ? CaCO 3 precipitates in warm shallow waters but is increasingly soluble at depth in colder watersCalcium Carbonate Calcium Carbonate - - Solubility Solubility ? CO 2 in solution buffers concentration of carbonate ion (CO 3 -2 ) ? Increasing pressure elevates concentrations of HCO 3 -1 & CO 3 -2 (products of solubility reaction) in sea water ? CaCO 3 more soluble at higher pressures & with decreasing temperatureControls on Carbonate Accumulation Controls on Carbonate Accumulation ? T emperature (climate) ? Tropics & temperate regions favor carbonate production: true of ancient too! ? Light ? Photosynthesis drives carbonate production ? Pressure ? “CCD” dissolution increases with depthControls on Carbonate Accumulation Controls on Carbonate Accumulation ? Agitation of waves ? Oxygen source & remove CO 2 ? Organic activity ? CaCO 3 factories nutrient deserts ? Sea Level ? Yield high at SL that constantly changes ? Sediment masking ? Fallacious! Limestones Limestones – – Chemical Chemical or or B Bi iochemical ochemical ? Shallow sea water is commonly saturated with respect to calcium carbonate ? Dissolved ions expected to be precipitated as sea water warms, loses CO 2 & evaporates ? Organisms generate shells & skeletons from dissolved ions ? Metabolism of organisms cause carbonate precipitation Distinction between biochemical & physico Distinction between biochemical & physico- -chemical chemical blurred by ubiquitous cyanobacteria of biosphere! blurred by ubiquitous cyanobacteria of biosphere!Biological Carbon Pump Biological Carbon Pump ? Carbon from CO 2 incorporated in organisms through photosynthesis, heterotrophy & secretion of shells ? > 99% of atmospheric CO 2 from volcanism removed by biological pump is deposited as calcium carbonate & organic matter ? 5.3 gigatons of CO 2 added to atmosphere a year but only 2.1 gigatons/year remains; the rest is believed sequestered as aragonite & calciteCarbonate Mineralogy Carbonate Mineralogy ? Aragonite – high temperature mineral ? Calcite – stable in sea water & near surface crust ? Low Magnesium Calcite ? High Magnesium Calcite ? Imperforate foraminifera ? Echinoidea ? Dolomite – stable in sea water & near surface ? Carbonate mineralogy of oceans changes with time! TROPICS TEMPERATE OCEANSBasin Ramp Open ShelfBasin Rim Restricted Shelf Open ShelfCarbonate Components Carbonate Components – – The Key The Key ? Interpretation of depositional setting of carbonates is based on ? Grain types ? Grain packing or fabric ? Sedimentary structures ? Early diagenetic changes Carbonate Components Carbonate Components – – The Key The Key ? Identification of grain types commonly used in subsurface studies of depositional setting because, unlike particles in siliciclastic rocks, carbonate grains generally formed within basin of deposition NB: This rule of thumb doesn’t always applyCarbonate Particles Carbonate Particles ? Subdivided into micrite (lime mud) & sand-sized grains ? These grains are separated on basis of shape & internal structure ? They are subdivided into: ? skeletal & non-skeletal (bio-physico-chemical grains)Lime Mud or Micrite Lime Mud or MicriteLime Mud Lime Mud or or Micrite Micrite Lime Mud Lime Mud or or Micrite MicriteWHITING LIME MUD ACCUMULATES ON BANK, OFF BANK & TIDAL FLATSThree Creeks Tidal FlatsLime Mud - Ordovician Kentucky? ? Carbonate Bio Carbonate Bio- -physico physico- -chemical Grains chemical Grains ? Ooids ? Grapestones and other intraclasts ? Pellets ? Pisolites and OncolitesOoids Ooids Ooids OoidsAragonitic OoidsAfter Scholle, 2003 Aragonitic Ooids