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Mudrocks

Mudrocks. Introduction. Mudrks mostly silt & clay Sometimes called argillites Make up 65% of sed rks Difficulties studying mudrocks Recessive F. grained Clay alteration Hard to get to modern analog Mineral i.d. difficult (qtz vs. felds) Sed structure not common as in sandstone

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Mudrocks

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  1. Mudrocks

  2. Introduction • Mudrks mostly silt & clay • Sometimes called argillites • Make up 65% of sed rks • Difficulties studying mudrocks • Recessive • F. grained • Clay alteration • Hard to get to modern analog • Mineral i.d. difficult (qtz vs. felds) • Sed structure not common as in sandstone • Thus problem w/ strat. column • 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)

  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. www.nwtgeoscience.ca 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 climates • Most abundant clays in modern sediment. • Illites -  K1-1.5Al4Si7-6.5Al1-1.5O20(OH)4 • Formed by weathering of feldspars in temperate climates and by alteration of smectite clays during diagenesis. • Have structure similar to muscovite. • Mixed layer clays • Interlayering between smectites like layers and illite like layers in same crystal • Common in modern sediment. • More illite w/time • i. 80% clay minerals in Paleozoic rks is illite • ii. Reasons: • increased volcanism; increased plant life,., climatic changes, diagenetic processes http://soils.missouri.edu/tutorial/page8.asp

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

  7. Classification • Depends on grain size & if rk fissile or not • 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. 

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

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

  10. Describing Mudrocks • Fissility--part parallel to bedding • Bioturbation--massiveness? • Flocculation inhibits fissility • Laminations • Lamination vs bed? • 1 cm • Origin of lamina • a. productivity variation • b. grain size • c.composition • d. biochemical • No 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

  11. Laminated Phospatic Mudstone, Monterey Fm, Mussel Roc

  12. Cross laminated mudrock, Brazil

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

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

  15. Color of Mudrocks:Green-oygenated environmentBlack-Organic-rich, low oxygen

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

  17. Dropstone in laminated mudstone, Brazil

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

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

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

  21. Sediment Accumulation Rates Cm/1000yrs • Continental Margin • Shelf- 15-40 • Slope 20 • Fraser River Delta 700,000 • Deep Sea • Coccolith Ooze 0.2-3.0 • Clays 0.03-0.8

  22. Types of Ocean Sediments • Terrigenous – “rock-derived • Biogenous – “life-derived” • Hydrogenous – “water-derived” • Cosmogenous – “cosmic-derived”

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

  24. Lithogenous Sediments - Deltas • Lithogenous sediments added to marine environment by deltas • Delta common features

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

  26. Lithogenous Sediment - Examples Mississippi River Sahara Desert Mt. Pinatubo • 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

  27. Red Clays--Pacific • Lacks calcium carbonate material • Note siliceous materials—Diatoms & sponge spicules Paula Worstell

  28. Sediment Distribution • Calcareous and Siliceous Oozes

  29. Biogenous Sediment • Biogenic ooze – greater than 30% biogenous sediment • Composed mostly of hard skeletal parts of once-living organisms • Two main compositions of hard parts: • Calcium Carbonate (CaCO3) • Coccolithophore (phytoplankton) • Foraminifera (zooplankton) • Pteropod--molluscs 2. Silica (SiO2) a) Diatoms (phytoplankton) b) Radiolarian (zooplankton) • Distribution depends on chemistry, ocean productivity

  30. Biogenous – Calcareous Examples Foraminifera • Composed of CaCO3 Foraminifera www.noc.soton.ac.uk • Widespread in relatively shallow areas Coccolithophore

  31. Biogenous – Siliceous Examples Radiolarians • Composed of SiO2 • Base of food chain • Like forams Benthic ones better survive Diatoms

  32. Sediment Distribution – Calcareous/Siliceous

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

  34. Siliceous Oozes • How do planktonic organisms get to bottom? • Lightweight, drift • Biopackaging—marine snow, feacal pellets

  35. Cold bottom waters undersaturated with respect to CaCO3 • slightly acidic ( CO2) • readily dissolves CaCO3 Biogenous – Calcareous oozes • Distribution controlled by dissolution processes • Calcium Carbonate Compensation Depth (CCD) – the depth at which the rate of accumulation of calcareous sediments equals the rate of dissolution • Cover greater than 50% of ocean floor

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

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

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

  39. Laminated Monterey Formation

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