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Mudrocks. Introduction Mudrks mostly silt & clay Mudrks mostly silt & clay Sometimes called argillites Sometimes called argillites Make up 65% of sed.

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Presentation on theme: "Mudrocks. Introduction Mudrks mostly silt & clay Mudrks mostly silt & clay Sometimes called argillites Sometimes called argillites Make up 65% of sed."— Presentation transcript:

1 Mudrocks

2 Introduction Mudrks mostly silt & clay Mudrks mostly silt & clay Sometimes called argillites Sometimes called argillites Make up 65% of sed rks Make up 65% of sed rks Difficulties studying mudrocks Difficulties studying mudrocks RecessiveRecessive F. grainedF. grained Clay alterationClay alteration Hard to get to modern analogHard to get to modern analog Mineral i.d. difficult (qtz vs. felds)Mineral i.d. difficult (qtz vs. felds) Sed structure not common as in sandstoneSed structure not common as in sandstone Thus problem w/ strat. columnThus problem w/ strat. column Organic rich mudrocks -- economically imp. Organic rich mudrocks -- economically imp. Thin section of mudrock. Hard to distinguish grains

3 Recessive Mudstone Overturned 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) Overturned 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. 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/.../ www.nwtgeoscience.ca

5 Mudrock compositions Clays most abundant Clays most abundant Kaolinites [Al 2 Si 2 O 5 (OH) 4 ]Kaolinites [Al 2 Si 2 O 5 (OH) 4 ] formed in warm moist climates where Ca, Na, and K ions leached and removed by weathering. 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. kaolinite clays indicates a source in a humid tropical climate. Smectites -Smectites - Are expanding clays. Are expanding clays. Expand by taking in water between layers. Expand by taking in water between layers. Montmorillinite- (½Ca,Na) 0.7 (Al,Fe,Mg) 4 Si,Al) 8 O 20 (OH) 4.n H 2 O is a good example. Montmorillinite- (½Ca,Na) 0.7 (Al,Fe,Mg) 4 Si,Al) 8 O 20 (OH) 4.n H 2 O is a good example. Form from weathering of Fe -Mg rich ign & meta rocks in temperate climates Form from weathering of Fe -Mg rich ign & meta rocks in temperate climates Most abundant clays in modern sediment. Most abundant clays in modern sediment. Illites - K 1-1.5 Al 4 Si 7-6.5 Al 1-1.5 O 20 (OH) 4Illites - K 1-1.5 Al 4 Si 7-6.5 Al 1-1.5 O 20 (OH) 4 Formed by weathering of feldspars in temperate climates and by alteration of smectite clays during diagenesis. Formed by weathering of feldspars in temperate climates and by alteration of smectite clays during diagenesis. Have structure similar to muscovite. Have structure similar to muscovite. Mixed layer claysMixed layer clays Interlayering between smectites like layers and illite like layers in same crystal Interlayering between smectites like layers and illite like layers in same crystal Common in modern sediment. Common in modern sediment. More illite w/timeMore illite w/time i. 80% clay minerals in Paleozoic rks is illite i. 80% clay minerals in Paleozoic rks is illite ii. Reasons: ii. Reasons: increased volcanism; increased plant life,., climatic changes, diagenetic processes increased volcanism; increased plant life,., climatic changes, diagenetic processeshttp://soils.missouri.edu/tutorial/page8.asp

6 Mudstone Composition Continued Qtz Qtz Mostly silt-size, angularMostly silt-size, angular Feldspars Feldspars Low concentrationsLow concentrations Other Other Muscovite, calcite (skeletal & diagenetic), pyrite, glauconite, hematite, etc.Muscovite, calcite (skeletal & diagenetic), pyrite, glauconite, hematite, etc.

7 Classification Grain Size Description Fissile Rock Nonfissile Rock >2/3 silt Abundant silt sized grains visible with a hand lens Silt-shaleSiltstone >1/3, 1/3, <2/3 silt Feels gritty when chewed Mud- shale Mudstone >2/3 clay Feels smooth when chewed Clay- shale Claystone Depends on grain size & if rk fissile or not Depends on grain size & if rk fissile or not Fissile rock tends to break along sheet-like planes nearly parallel to bedding planes Fissile rock tends to break along sheet-like planes nearly parallel to bedding planes Fissility caused by clay minerals deposited with sheet structures parallel to depositional surface. Fissility caused by clay minerals deposited with sheet structures parallel to depositional surface.

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9 Texture Grain Shape Grain Shape Clays and quartz usually angularClays and quartz usually angular Not much rounding because grains small & carried in suspension Not much rounding because grains small & carried in suspension Thin section; cross polarized. Scale: each tick mark = 1 mm Thin section; cross polarized. Scale: each tick mark = 1 mm geohistory.valdosta.edu

10 Texture Continued FissilityDepends on FissilityDepends on Abundance of clay-more clay more fissileAbundance of clay-more clay more fissile Orientation of claysOrientation of clays Clay grains adhere to one another Clay grains adhere to one another Adhesion of grains called flocculation Adhesion of grains called flocculation Also depends on salinity & organic matter=more = more flocculationAlso depends on salinity & organic matter=more = more flocculation Bioturbation Bioturbation Destroys orientation of claysDestroys orientation of clays Diagenesis Diagenesis Aligns grains perpendicular to max stress directionAligns grains perpendicular to max stress direction Get slaty cleavage and foliation in metamorphic rocks Get slaty cleavage and foliation in metamorphic rocks geology.uprm.edu Structureless Mudstone geology.about.com

11 Describing Mudrocks Fissility--part parallel to bedding Fissility--part parallel to bedding Bioturbation-- massiveness? Bioturbation-- massiveness? Flocculation inhibits fissility Flocculation inhibits fissility Laminations Laminations Lamination vs bed? Lamination vs bed? 1 cm1 cm Origin of lamina Origin of lamina a. productivity variationa. productivity variation b. grain sizeb. grain size c.compositionc.composition d. biochemicald. biochemical No laminations = massive (bioturbation/redeposition) No laminations = massive (bioturbation/redeposition) Laminations due to textural differences Sand- laminated dark grey mudstone from unit MMa, Tom ore deposit, Paleozoic, Northern Canada 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

12 Laminated Phospatic Mudstone, Monterey Fm, Mussel Roc

13 Cross laminated mudrock, Brazil

14 Describing Mudrocks Concretions Concretions Nodular or stratiformNodular or stratiform Some Form immediately after deposition; Evidence?Some Form immediately after deposition; Evidence? Cannonball Concretions, New Zealand More Concretions, North Dakota

15 Describing Mudrocks Colors Colors Gray to black, generally > 1% o.m.Gray to black, generally > 1% o.m. Conditions favorable for o.m. preservationConditions favorable for o.m. preservation Little oxygen Little oxygen Rapid sedimentation Rapid sedimentation Low temperatures of water Low temperatures of water Low permeability Low permeability Oxygen present, o.m. goes to water & carbon dioxide Oxygen present, o.m. goes to water & carbon dioxide 3. Red, brown, yellow, green--iron present3. Red, brown, yellow, green--iron present Reflect oxidation state of Fe Reflect oxidation state of Fe Oxidizing conditions the most Fe = Fe +3 Oxidizing conditions the most Fe = Fe +3 Give rock red, brown, orange colorsGive rock red, brown, orange colors Hematite (Fe2O3) = red colorHematite (Fe2O3) = red color Iron hydroxide [FeO(OH)] (geothite) = brown colorIron hydroxide [FeO(OH)] (geothite) = brown color Limonite gives sediment yellow colorLimonite gives sediment yellow color Lack of iron then green (illite, chlorite, & biotite)Lack of iron then green (illite, chlorite, & biotite) Use color for descriptive purposesUse color for descriptive purposes

16 Color of Mudrocks: Green-oygenated environment Black-Organic-rich, low oxygen

17 Depositional Environments A. Major mudrock types A. Major mudrock types Residual--weathering & soil formation on pre-existing rockResidual--weathering & soil formation on pre-existing rock i. Preservation potential? i. Preservation potential? Detrital--erosion, transportation & depositionDetrital--erosion, transportation & deposition Weathering & alteration of volcanic depositesWeathering & alteration of volcanic deposites B. Residual B. Residual Calcretes (caliche)--common where evap>precipCalcretes (caliche)--common where evap>precip C. Detrital C. Detrital Marine/non-marineMarine/non-marine Distinguishing features:Distinguishing features: Fossils, bioturbation to laminated Fossils, bioturbation to laminated Deposition below active wave base Deposition below active wave base May pass shoreward to sandstones May pass shoreward to sandstones May be organic rich May be organic rich Local example is Monterey Fm. Local example is Monterey Fm. Residual Soil http://blass.com.au/definitions/resid ual%20soil Raymond Wiggers

18 Dropstone in laminated mudstone, Brazil

19 Mudcracks in red-brown mudstone, Watahomigi Formation. Red from hematite. Courtesy USGS

20 Depositional Environments Continued Non-marine Non-marine Common in river floodplains, assoc. w/s.s.Common in river floodplains, assoc. w/s.s. Lacustrine environments--varvedLacustrine environments--varved Glacial lakes = coarse = spring melting, winter= fines Glacial lakes = coarse = spring melting, winter= fines Non-glacial lakes--opposite- why? Non-glacial lakes--opposite- why? Volcaniclastic derived mudrocks Volcaniclastic derived mudrocks Volcanic material alters to clayVolcanic material alters to clay If alteration is to montmorillonite then mudrock known as bentoniteIf alteration is to montmorillonite then mudrock known as bentonite How identify volcaniclastic origin of mudrock?How identify volcaniclastic origin of mudrock?

21 Marine Sediments Most ocean floor covered by marine sediments Most ocean floor covered by marine sediments Sediment thickness is thinnest at mid-ocean ridge and thickest at continental marginsSediment thickness is thinnest at mid-ocean ridge and thickest at continental margins

22 Sediment Accumulation Rates Cm/1000yrs Continental Margin Continental Margin Shelf-15-40Shelf-15-40 Slope20Slope20 Fraser River Delta700,000Fraser River Delta700,000 Deep Sea Deep Sea Coccolith Ooze0.2-3.0Coccolith Ooze0.2-3.0 Clays0.03-0.8Clays0.03-0.8

23 Types of Ocean Sediments Terrigenous – rock-derived Terrigenous – rock-derived Biogenous – life-derivedBiogenous – life-derived Cosmogenous – cosmic-derived Cosmogenous – cosmic-derived Hydrogenous – water-derived Hydrogenous – water-derived

24 Lithogenous Sediments Composed mostly of quartz sand and clay Composed mostly of quartz sand and clay Derived from the weathering of rocks – continents or volcanic islandsDerived from the weathering of rocks – continents or volcanic islands Most deposited on continental marginsMost deposited on continental margins Transported by rivers, glaciers or windTransported by rivers, glaciers or wind Covers about 45% of ocean floor Covers about 45% of ocean floor

25 Lithogenous Sediments - Deltas Lithogenous sediments added to marine environment by deltas Lithogenous sediments added to marine environment by deltas Delta common features Delta common features

26 Pelagic and Neritic Defined Pelagic sediments deposited in deep ocean away from shelf processes influences Pelagic sediments deposited in deep ocean away from shelf processes influences Usually clays, unless turbidites – other gravity flows, ice raftingUsually clays, unless turbidites – other gravity flows, ice rafting Neritic sediments deposited in shallow water over shelves. Neritic sediments deposited in shallow water over shelves. Pelagic sediments in abyssal plains most red clays Pelagic sediments in abyssal plains most red clays Growing anthropogenic contribution –factory dust, plastic (PCBs), time markers Growing anthropogenic contribution –factory dust, plastic (PCBs), time markers

27 Lithogenous Sediment - Examples Red Clays Red Clays – Terrigenous from rivers, dust, and volcanic ash – Transported to deep ocean by winds and surface currents – Common in deep oceans, clays most common – Accumulates 2 mm (1/8) every 1,000 years Mt. Pinatubo Mississippi River Sahara Desert

28 Red Clays--Pacific Lacks calcium carbonate material Lacks calcium carbonate material Note siliceous materials Diatoms & sponge spicules Note siliceous materials Diatoms & sponge spicules Paula Worstell

29 Sediment Distribution Calcareous and Siliceous Oozes Calcareous and Siliceous Oozes

30 Biogenous Sediment Biogenic ooze – greater than 30% biogenous sediment Biogenic ooze – greater than 30% biogenous sediment Composed mostly of hard skeletal parts of once-living organismsComposed mostly of hard skeletal parts of once-living organisms Two main compositions of hard parts: Two main compositions of hard parts: 1. Calcium Carbonate (CaCO 3 ) a)Coccolithophore (phytoplankton) b)Foraminifera (zooplankton) c)Pteropod--molluscs 2. Silica (SiO 2 ) a) Diatoms (phytoplankton) a) Diatoms (phytoplankton) b) Radiolarian (zooplankton) b) Radiolarian (zooplankton) Distribution depends on chemistry, ocean productivity Distribution depends on chemistry, ocean productivity

31 Biogenous – Calcareous Examples Composed of CaCO 3 Composed of CaCO 3 Widespread in relatively shallow areasWidespread in relatively shallow areas Coccolithophore Foraminifera www.noc.soton.ac.uk

32 Biogenous – Siliceous Examples Diatoms Radiolarians Composed of SiO 2 Composed of SiO 2 Base of food chain Base of food chain Like forams Benthic ones better survive Like forams Benthic ones better survive

33 Sediment Distribution – Calcareous/Siliceous

34 Biogenous – Siliceous Ooze Covers 15% of ocean floor Covers 15% of ocean floor Diatoms common at higher latitudes Radiolarians common at equatorial regions Radiolarians common at equatorial regions Distribution - areas of high productivity (zones of upwelling) Distribution - areas of high productivity (zones of upwelling) Dissolve more slowly than calcareous particles Dissolve more slowly than calcareous particles Seawater undersaturated wrt silica, siliceous particles should dissolveSeawater undersaturated wrt silica, siliceous particles should dissolve Surface waters more depletedSurface waters more depleted Bottom waters colder, most dissolution on seafloorBottom waters colder, most dissolution on seafloor

35 Siliceous Oozes How do planktonic organisms get to bottom? How do planktonic organisms get to bottom? Lightweight, drift Lightweight, drift Biopackagingmarine snow, feacal pellets Biopackagingmarine snow, feacal pellets

36 Biogenous – Calcareous oozes Cover greater than 50% of ocean floor Cover greater than 50% of ocean floor Distribution controlled by dissolution processes Distribution controlled by dissolution processes Cold bottom waters undersaturated with respect to CaCO 3 Cold bottom waters undersaturated with respect to CaCO 3 – slightly acidic ( CO 2 ) – readily dissolves CaCO 3 Calcium Carbonate Compensation Depth (CCD) – the depth at which the rate of accumulation of calcareous sediments equals the rate of dissolutionCalcium Carbonate Compensation Depth (CCD) – the depth at which the rate of accumulation of calcareous sediments equals the rate of dissolution

37 Lysocline = depth at which dissolution of carbonate material begins Lysocline = depth at which dissolution of carbonate material begins Most dissolution takes place on seafloor, only pass short distance through corrosive zone Most dissolution takes place on seafloor, only pass short distance through corrosive zone Depth of CCD depends on degree of undersaturation, productiviy, & flux Depth of CCD depends on degree of undersaturation, productiviy, & flux faculty.uaeu.ac.ae/

38 Paleoclimatology/Productivity Paleoclimatology/Productivity A. Diatomaceous RocksA. Diatomaceous Rocks 1. Monterey, Sisquoc Fm 1. Monterey, Sisquoc Fm 2. Increased Miocene Oceanic Productivity 2. Increased Miocene Oceanic Productivity 3. Miocene sealevel changes 3. Miocene sealevel changes B. Phosphatic RocksB. Phosphatic Rocks 1. o.m. content 4-30 1. o.m. content 4-30 2. high productivity 2. high productivity 3. low oxygen levels in oceans 3. low oxygen levels in oceans C Oxygen Isotopes & MudrocksC Oxygen Isotopes & Mudrocks 1.O2 isotopes in shells in deep marine rocks 1.O2 isotopes in shells in deep marine rocks 2. Construct isotope curves 2. Construct isotope curves 3. Show changes in ocean temp. 3. Show changes in ocean temp. 4. Tie to sea level curve 4. Tie to sea level curve D. Carbon Isotopes & MudrocksD. Carbon Isotopes & Mudrocks 1. Reflect changes in productivity, continental runoff, ocean circulation, atmospheric 1. Reflect changes in productivity, continental runoff, ocean circulation, atmospheric

39 gsc.nrcan.gc.ca/.../ sedex/tom/index_e.php

40 Laminated Monterey Formation


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