Sedimentary Processes and Sedimentary RocksImportant pointsFine-grained rocks – All tend to form fine bedsPowerPoint PresentationSlide 5Slide 62. Chemical sedimentary rocksTypes of Chemical Sed. RocksChemical Sedimentary Rock names you need to know:Solubility of Chemical Sed RocksCarbonates CaCO3Some limestone is formed on Carbonate “Banks” and “Platforms”Slide 13Slide 14Evaporites – retreating seas or isolated lakes (Salt Lake) where evaporation is greater than input of waterEvaporites in the Mediterranean basinSlide 17Silica precipitates – Silica will dissolve in high pH (High Basic) conditions. A few micro-organisms secrete silicaMicroorganisms – responsible for some Limestones (Chalk) and some Cherts (Almost all of these organisms are Marine)Sedimentary environmentsSlide 21Slide 22Slide 23What type of rock is more common?Slide 25Slide 26Slide 27Slide 28Controls of sedimentary environmentsSedimentary StructuresSlide 31Sedimentary featuresFossilsSlide 34Ripple marksSlide 36Cross beds (can occur at many scales)Slide 38Graded Beds (indicate a rapid event)Slide 40Slide 41MudcracksSlide 43Sedimentary Processes Sedimentary Processes and Sedimentary Rocksand Sedimentary RocksLecture 13Lecture 13Important points•What are the major chemical sed rocks•How do they form?•What are the chief minerals of chemical sedimentary rocks?•What are sedimentary structures and how are they important?•What are graded beds?Fine-grained rocks – All tend to form fine beds•All have clay-sized particles•SHALE – fine grained sediment with concetration of organic material•SILTSTONE –clay particles and very small quartz•CLAYSTONE clay minerals; lacks organicsVariation of Sandstones•Mature Sandstone – almost pure quartz grains cemented together (called quartz arenite)–Indicates a high degree of physical weathering, abrasion and transport–Usually well sorted•Immature Sandstone – other minerals or rock fragments indicate low to moderate weathering and transport–Orthoclase-rich – Arkose–Rock fragments – Lithic sandstone–Poorly sorted, small fragments - GraywackeGeneralized diagramshowing the Relationship ofsediment formation, transportation and sedimentary rock2. Chemical sedimentary rocks•Always occur in an aqueous or marine environment (they precipitate from water)•Mineral composition is low Temp. minerals, but these are generally soluble minerals•They can be direct precipitates from the water, or, can have bioclastic detrital•These are “self-cementing”, in that they either crystallize as a mass, or, the soluble minerals dissolve and re-precipitate around the grainsTypes of Chemical Sed. Rocks •Carbonates – can have crystalline texture, or have shell detrital–Limestone (CaCO3)–Dolostone (Mg,Ca)CO3–Most limestone is from biotic origins, though some precipitate from the water•Evaporites -form from evaporating seawater–Gypsum – CaSO4Halite - NaCl•Silica –sometimes silica can be precipitated from water or secreted by a few organisms–Chert, Flint, Jasper, Opal•Coal – organic remains from plants buried in conditions of little or no O2Chemical Sedimentary Rock names you need to know:Limestone and Dolostone (carbonates)(CaCO3)Gypsum and Halite (evaporites)Chert, Flint, Jasper & Opal (Silica)Solubility of Chemical Sed Rocks•Evaporites > very high solubility in aqueous environments•Carbonates > Limestone has moderate solubility; enhanced with low pH Dolostone has lower solubility than Limestone•Silica has very low solubility, except in high pH conditionsCarbonates CaCO3Primary mineral (Rock type):Calcite (Limestone)Dolomite (Dolostone)Some limestone is formed on Carbonate “Banks” and “Platforms”Florida was once submerged and organisms flourished.The Bahamas are an abiotic bank, With Ooids precipitated from the waterOoids carbonate spheres that abiotically precipitateOver time, a Carbonate Platformis built as sea level rises andreef building organisms try to remain in the lightEvaporites – retreating seas or isolated lakes (Salt Lake) where evaporation is greater than input of waterCaSO4 NaClEvaporites in the Mediterranean basinEvaporites up to 1 Mile thick (!!)were depositedSilica precipitates – Silica will dissolve in high pH (High Basic) conditions. A few micro-organisms secrete silicaSiO2Microorganisms – responsible for some Limestones (Chalk) and some Cherts (Almost all of these organisms are Marine)Sedimentary environments•Most (but certainly not all) sedimentary rocks form in aqueous or marine environments•Sedimentary rocks form in specific environments•Sedimentary rocks record information from where they formTransitionalWhat type of rock is more common?•Sandstone•Conglomerate•Limestone•Shale•Claystone•BrecciaLittle energy is necessary to keep fine-grained particles in suspensionMarine Sediments Calcareous ooze, which is composed primarily of minute shells and skeletons formed of calcite, covers ~48% of the world ocean's floorSiliceous ooze is composed of the debris of plankton having shells and covers ~15% of the ocean floor clay, a varied mix of clay minerals, only accumulates in the deepest and most remote areas of the ocean, but still covers ~38% of the ocean floorControls of sedimentary environments•Sea level–Sea Level Rise = TRANSGRESSION–Sea Level Fall = REGRESSION•Tectonic activity and boundaries–Uplifted “highs” and downwarped “lows”•The presence and effects of biota–Biota contributes to much of the chemical sediment–Biota can “churn” sedimentSedimentary Structures•Features in sedimentary rocks can tell you about–Biota–The depositional environment•Terrestrial v. Marine•Streams v. Lakes•Desert v Beach•And much more……….–Environmental processes–Which way is “up”Which way is Up? (The top of the stratigraphic sequence)?Sedimentary features•Fossils–Environment– how habitable an area may have been•Ripple marks–Symmetric v Assymetric–Direction of wind or water flow•Cross bedding•Graded Beds•Mud cracks•Rain drop impressions•And many others….FossilsRipple marksCross beds (can occur at many scales)From large Dunes to…Graded Beds (indicate a rapid event)Graywacke Sandstone often forms from deep sea turbidity currentsIn a single depositional bed, the grain size changes from coarse to fining