chapter 17 GEO 100
Popular in Physical Geology
Popular in Geology
This 7 page Class Notes was uploaded by samantha Flavell on Monday March 14, 2016. The Class Notes belongs to GEO 100 at State University of New York at Oswego taught by Rachel Lee (P) in Fall 2015. Since its upload, it has received 20 views. For similar materials see Physical Geology in Geology at State University of New York at Oswego.
Reviews for chapter 17
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 03/14/16
Ch.17 Sedimentary rocks why do we care? sedimentary rocks record what the Earth’s surface was like in the past Types chemical/biochemical: formed partly or entirely of material form organic or inorganic chemical precipitation. classic :( physical) made up of broken fragments later cemented together Clastic: made from weathering or preexisting rock Nonclastic: chemical: precipitated from seawater biochemical: from shells of organisms organic: from plant material Clastic sedimentary rock result of several processes weathering: generation of sediment by rock disintegration erosion: removal of sediment grains from rock by gravity, water, wind or ice Transport: dispersal of sediment by wind, water and/or ice Deposition: accumulation after transport steps Energy and depositional environment sedimentary particles require Energy to move high energy depositional environments have sediments with largest grain sizes; as transport energy drops. The size of the smallest particle carried drops proportionally higher energy environments: steep mountain streams, beaches low energy environments: slow moving streams lakes Deep Ocean lithification: transformation into solid rock burial: more sediment is added on to a previous layer compaction: overburden weight reduces pore space sand; 1020% clay: 5080% cement: minerals from ground water that "glue" sediments together Cements *After chemical weathering there is a lot of leftover dissolved ions (Si, K, Ca are among the most important and widespread) these are generally carried away in groundwater *Evaporating solutions such as these creates the cement in many sedimentary rocks *Carbonate (Calcite) Silicate (quartz) or clay minerals are the most common cementing agents *Characteristics of the rock can be used to infer the environment in which the sediment accumulated (depositional environment) *A sequence of sedimentary rocks (clastic or nonclastic) record the history of environmental change in an area. *classified on the basis of texture and composition clast (grain) size Clast composition Roundness (angularity) Sorting *characteristics influenced by transport and conditions in depositional environment Grain Size *The average diameter of clasts *With increasing transport, average grain size decreases KINDS OF CLASTIC ROCKS *course conglomerate and breccia’s *Medium sandstones *Fine shales and mudstones CLAST COMPOSITION *Stable end: products of weathering (quartz, iron oxides, clay) indicate conditions in which weathering is complete *Sediment exposed to weathering for a long time (slow burial; slow sedimentation rate) *Humid environments *Waves or currents reworking the sediment after it’s deposited *Unstable minerals (feldspar, biotite, amphiboles) signify special conditions where not much weathering occurred *Rapid burial (rapid sedimentation rate) *dry environment Rounding (Angularity) *Only water transport can round grains *grain roundness increases with transport wellrounded: long transport distance Angular: deposited near source OR not transported by water Sorting *Uniformity of grain size *wellsorted: uniform grain size *poorly sorted: wide variety of grain sizes *indicates transport medium wind very well sorted Water: waves well sorted Currents moderately sorted Ice poorly sorted *Sorting indicates the constancy of environment energy well sorted: uniform energy (i.e. a beach) Poorly sorted: Variable energy (i.e. an alluvial fan) Maturity *a measure of the degree of “processing” or reworking of sediment Textural maturity: degree of roundness of sorting Mineral maturity: degree of unstable mineral removal *reflects the amount of weathering that the sediment has undergone *sediments become progressively more modified as they’re acted on by weathering processes, wither during transport or after deposition *Stable area: sediments mineralogically and texturally mature Slow sedimentation rates mean that sediment is acted on by weathering for a long time *Tectonically active area: sediments mineralogically and texturally immature Rapid sedimentation rate buries sediment before weathering can break it down Nonclastic Sedimentary Rock *Biochemical limestone: made from CaCO3 shell remains Warm (tropical and subtropical) Normal salinity marine water Oxygenated Shallow *Rarely distinguishable from precipitated limestone *Organic rocks: made from organic carbon *Coal: altered remains of fossil vegetation Accumulates in lush tropical wetland/swamp settings Requires deposition in the absence of oxygen Coal *Immature petroleum products Biochemically organic sedimentary rocksformed through different degrees of diagenesis of organicrich (carbon rich plant) material *Different types of coal release different amounts of energy when burned *Peat (least productive) *Lignite (soft coal) *Bituminous (moderately hard) *Anthracite (highest grade coal) *Chemical rocks precipitated from sea water *Limestone: warm (tropical and subtropical) Normal salinity marine water Oxygenated Shallow *Dolostone: usually limestone that’s been altered by Mg rich fluids after burial *Chemical rocks precipitated from sea water *Evaporties (halite, gypsum, other salts) Restricted circulation High evaporation rates (characteristic of the subtropics) *Chemical rocks precipitated from groundwater Travertine (calcite) Limestone *Principle chemical/biochemical sedimentary rock (may also be bioclastic) *All limestone is made of calcite. It’s a common rock because so many invertibrated animals have calcite shells *Bioclastic limestone: rock formed from brokem shell material in a nearshore (relatively high energy environment) *Crystalline limestone: either reefframework or deep sea varieties *Inorganic limestone: desert, cave and hot spring deposits (travertine, tufa) formed by evaporation Fine Grained Limestone *deep sea limestone will not have visible fossils, because they’re made up of the densely cemented shells of little bugs Chert *Not to be outdone, there are marine microorganisms that secrete silica shells too *When these pile up on the deep ocean floor, they lithify to become a microcrystalline quartz rock called Chert (same stuff as the substance flint) Banded Iron Formation *BIF is a finely laminated deep sea chemical sedimentary rock typically containing 15% or more of iron and abundant silica. Iron oxides include both hematite and magnetite *BIF is our most important source of iron for the iron industry.
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'