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Presentation on theme: "Mudrocks."— Presentation transcript:

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. 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.

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 Mudrock compositions

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
Description Fissile Rock Nonfissile Rock >2/3 silt Abundant silt sized grains visible with a hand lens Silt-shale Siltstone >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 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. 


9 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 mm

10 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 Structureless Mudstone

11 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 sedex/tom/index_e.php

12 Laminated Phospatic Mudstone, Monterey Fm, Mussel Roc

13 Cross laminated mudrock, Brazil

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

15 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

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

17 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 Raymond Wiggers

18 Dropstone in laminated mudstone, Brazil

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-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?

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

22 Sediment Accumulation Rates Cm/1000yrs
Continental Margin Shelf Slope 20 Fraser River Delta 700,000 Deep Sea Coccolith Ooze Clays

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

24 Lithogenous Sediments
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 Composed mostly of quartz sand and clay

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

26 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

27 Lithogenous Sediment - Examples
Mt. Pinatubo Mississippi River Sahara Desert 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

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

31 Biogenous – Calcareous Examples
Foraminifera Composed of CaCO3 Foraminifera Widespread in relatively shallow areas Coccolithophore

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

33 Sediment Distribution – Calcareous/Siliceous

34 Biogenous – Siliceous Ooze
Distribution - areas of high productivity (zones of upwelling) Covers 15% of ocean floor 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

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

36 Biogenous – Calcareous oozes
Cover greater than 50% of ocean floor 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 Cold bottom waters undersaturated with respect to CaCO3 slightly 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 zone Depth of CCD depends on degree of undersaturation, productiviy, & flux

38 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

39 sedex/tom/index_e.php

40 Laminated Monterey Formation

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