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.
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
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 geohistory.valdosta.edu

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
geology.uprm.edu
Structureless Mudstone geology.about.com

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 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 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
faculty.uaeu.ac.ae/

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

40. Laminated Monterey Formation