2 Introduction Mudrks mostly silt & clay Sometimes called argillites Make up 65% of sed rksDifficulties studying mudrocksRecessiveF. grainedClay alterationHard to get to modern analogMineral i.d. difficult (qtz vs. felds)Sed structure not common as in sandstoneThus problem w/ strat. columnOrganic rich mudrocks --economically imp.Thin section of mudrock. Hard to distinguish grains
3 Recessive MudstoneOverturned Mississippian Lisburne Formation (resistant carbonate) in depositional contact with overturned Permian Echooka Formation (recessive mudstone), on the south face of Atigun gorge, Alaska. (photo: Alan Carroll)
4 More Recessive Mudstone Contact between lower, light brown sandstone and dark brown silty mudstone within Imperial Formation on a tributary to the Arctic Red River, Northwest Territories.photo shows the character of bedding at a scale of a few meters. The thicker sand beds are typically a little coarser-grained and tend to be more resistant and stick out of the cliff. The finer-grained material is commonly in thinner beds and more recessive.clasticdetritus.com/.../
5 Mudrock compositions Clays most abundant Kaolinites [Al2Si2O5(OH)4] formed in warm moist climates where Ca, Na, and K ions leached and removed by weathering. kaolinite clays indicates a source in a humid tropical climate.Smectites -Are expanding clays. Expand by taking in water between layers.Montmorillinite-(½Ca,Na)0.7(Al,Fe,Mg)4Si,Al)8O20(OH)4.nH2O is a good example. Form from weathering of Fe -Mg rich ign & meta rocks in temperate climatesMost abundant clays in modern sediment.Illites - K1-1.5Al4Si7-6.5Al1-1.5O20(OH)4Formed by weathering of feldspars in temperate climates and by alteration of smectite clays during diagenesis.Have structure similar to muscovite.Mixed layer claysInterlayering between smectites like layers and illite like layers in same crystalCommon in modern sediment.More illite w/timei. 80% clay minerals in Paleozoic rks is illiteii. Reasons:increased volcanism; increased plant life,., climatic changes, diagenetic processesMudrock compositions
6 Mudstone Composition Continued QtzMostly silt-size, angularFeldsparsLow concentrationsOtherMuscovite, calcite (skeletal & diagenetic), pyrite, glauconite, hematite, etc.
7 Classification Depends on grain size & if rk fissile or not DescriptionFissile RockNonfissile Rock>2/3 siltAbundant silt sized grains visible with a hand lensSilt-shaleSiltstone>1/3, <2/3 siltFeels gritty when chewedMud-shaleMudstone>2/3 clayFeels smooth when chewedClay-shaleClaystoneDepends on grain size & if rk fissile or notFissile rock tends to break along sheet-like planes nearly parallel to bedding planesFissility caused by clay minerals deposited with sheet structures parallel to depositional surface.
9 Texture Grain Shape Clays and quartz usually angular Not much rounding because grains small & carried in suspensionThin section; cross polarized. Scale: each tick mark = 1 mm geohistory.valdosta.edu
10 Texture Continued Fissility—Depends on Abundance of clay-more clay more fissileOrientation of claysClay grains adhere to one anotherAdhesion of grains called flocculationAlso depends on salinity & organic matter=more = more flocculationBioturbationDestroys orientation of claysDiagenesisAligns grains perpendicular to max stress directionGet slaty cleavage and foliation in metamorphic rocksgeology.uprm.eduStructureless Mudstone geology.about.com
11 Describing Mudrocks Fissility--part parallel to bedding Bioturbation--massiveness?Flocculation inhibits fissilityLaminationsLamination vs bed?1 cmOrigin of laminaa. productivity variationb. grain sizec.compositiond. biochemicalNo laminations = massive (bioturbation/redeposition)Laminations due to textural differences Sand-laminated dark grey mudstone from unit MMa, Tom ore deposit, Paleozoic, Northern Canada gsc.nrcan.gc.ca/.../ sedex/tom/index_e.php
14 Describing Mudrocks Concretions Nodular or stratiform Some Form immediately after deposition; Evidence?Cannonball Concretions, New ZealandMore Concretions, North Dakota
15 Describing Mudrocks Colors Gray to black, generally > 1% o.m. Conditions favorable for o.m. preservationLittle oxygenRapid sedimentationLow temperatures of waterLow permeabilityOxygen present, o.m. goes to water & carbon dioxide3. Red, brown, yellow, green--iron presentReflect oxidation state of FeOxidizing conditions the most Fe = Fe+3Give rock red, brown, orange colorsHematite (Fe2O3) = red colorIron hydroxide [FeO(OH)] (geothite) = brown colorLimonite gives sediment yellow colorLack of iron then green (illite, chlorite, & biotite)Use color for descriptive purposes
16 Color of Mudrocks: Green-oygenated environment Black-Organic-rich, low oxygen
17 Depositional Environments A. Major mudrock typesResidual--weathering & soil formation on pre-existing rocki. Preservation potential?Detrital--erosion, transportation & depositionWeathering & alteration of volcanic depositesB. ResidualCalcretes (caliche)--common where evap>precipC. DetritalMarine/non-marineDistinguishing features:Fossils, bioturbation to laminatedDeposition below active wave baseMay pass shoreward to sandstonesMay be organic richLocal example is Monterey Fm.Residual SoilRaymond Wiggers
19 Mudcracks in red-brown mudstone, Watahomigi Formation Mudcracks in red-brown mudstone, Watahomigi Formation. Red from hematite. Courtesy USGS
20 Depositional Environments Continued Non-marineCommon in river floodplains, assoc. w/s.s.Lacustrine environments--varvedGlacial lakes = coarse = spring melting, winter= finesNon-glacial lakes--opposite- why?Volcaniclastic derived mudrocksVolcanic material alters to clayIf alteration is to montmorillonite then mudrock known as bentoniteHow identify volcaniclastic origin of mudrock?
21 Marine Sediments Most ocean floor covered by marine sediments Sediment thickness is thinnest at mid-ocean ridge and thickest at continental margins
24 Lithogenous Sediments Derived from the weathering of rocks – continents or volcanic islandsTransported by rivers, glaciers or windMost deposited on continental marginsCovers about 45% of ocean floorComposed mostly of quartz sand and clay
25 Lithogenous Sediments - Deltas Lithogenous sediments added to marine environment by deltasDelta common features
26 Pelagic and Neritic Defined Pelagic sediments deposited in deep ocean away from shelf processes influencesUsually clays, unless turbidites – other gravity flows, ice raftingNeritic sediments deposited in shallow water over shelves.Pelagic sediments in abyssal plains most red claysGrowing anthropogenic contribution –factory dust, plastic (PCBs), time markers
27 Lithogenous Sediment - Examples Mt. PinatuboMississippi RiverSahara DesertRed ClaysTerrigenous from rivers, dust, and volcanic ashTransported to deep ocean by winds and surface currentsCommon in deep oceans, clays most commonAccumulates 2 mm (1/8”) every 1,000 years
28 Red Clays--Pacific Lacks calcium carbonate material Note siliceous materials—Diatoms & sponge spiculesPaula Worstell
29 Sediment Distribution Calcareous and Siliceous Oozes
30 Biogenous Sediment Biogenic ooze – greater than 30% biogenous sediment Composed mostly of hard skeletal parts of once-living organismsTwo main compositions of hard parts:Calcium Carbonate (CaCO3)Coccolithophore (phytoplankton)Foraminifera (zooplankton)Pteropod--molluscs2. Silica (SiO2)a) Diatoms (phytoplankton)b) Radiolarian (zooplankton)Distribution depends on chemistry, ocean productivity
31 Biogenous – Calcareous Examples ForaminiferaComposed of CaCO3ForaminiferaWidespread in relatively shallow areasCoccolithophore
32 Biogenous – Siliceous Examples RadiolariansComposed of SiO2Base of food chainLike forams Benthic ones better surviveDiatoms
34 Biogenous – Siliceous Ooze Distribution - areas of high productivity (zones of upwelling)Covers 15% of ocean floorDissolve more slowly than calcareous particlesSeawater undersaturated wrt silica, siliceous particles should dissolveSurface waters more depletedBottom waters colder, most dissolution on seafloorDiatoms common at higher latitudesRadiolarians common at equatorial regions
35 Siliceous Oozes How do planktonic organisms get to bottom? Lightweight, driftBiopackaging—marine snow, feacal pellets
36 Biogenous – Calcareous oozes Cover greater than 50% of ocean floorDistribution controlled by dissolution processesCalcium Carbonate Compensation Depth (CCD) – the depth at which the rate of accumulation of calcareous sediments equals the rate of dissolutionCold bottom waters undersaturated with respect to CaCO3slightly acidic ( CO2)readily dissolves CaCO3
37 Lysocline = depth at which dissolution of carbonate material begins Most dissolution takes place on seafloor, only pass short distance through corrosive zoneDepth of CCD depends on degree of undersaturation, productiviy, & fluxfaculty.uaeu.ac.ae/
38 Paleoclimatology/Productivity A. Diatomaceous Rocks1. Monterey, Sisquoc Fm2. Increased Miocene Oceanic Productivity3. Miocene sealevel changesB. Phosphatic Rocks1. o.m. content 4-302. high productivity3. low oxygen levels in oceansC Oxygen Isotopes & Mudrocks1.O2 isotopes in shells in deep marine rocks2. Construct isotope curves3. Show changes in ocean temp.4. Tie to sea level curveD. Carbon Isotopes & Mudrocks1. Reflect changes in productivity, continental runoff, ocean circulation, atmospheric
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