Clastic sedimentary rocks

Describe (using appropriate terminology) a sandstone that demonstrates both textural and mineralogical maturity and suggests a possible environment of deposition.

quartz arenite > 95% quartz. Well sorted, well-rounded grains.

ENV: deserts and beach deposit

Classify and interpret this rock and suggest one possible environment of deposition.

Polymict, clast supported conglomerate. Clasts are fairly well rounded.

ENV: shoreline beach deposit.

How can mudrocks be useful in correlating and dating sedimentary sequences?

Hemipelagic mudrocks commonly contain fossils (example, Graptolites).

bentonites (altered volcanic ash) with zircons.

3 Ways that rocks pores around grains (clasts) can be filled

oil/gas

cement (precipitated during diagenesis)

matrix (fine grains)

What will the 80% of other silicates (20% is quartz) in sedimentary rocks be in order of weathering (chemical maturity)

reverse bowen serie = order of maturity = order to more stability on earth surface

Conglomerate vs breccia

C: rounded clasts above 2mm with finer grained matrix

B: angular clasts with a mud matrix (less 30microns)

Name 6 depositional environments of conglomerates

* beach shoreline, transgression (basal conglomerate), fluvial/braided river deposits, mature rivers, alluvial fan, glacial till

Def imbrication of clasts

depositional fabric which shows a preferred orientation of clasts, overlap each other like dominoes

def pebble lags vs tillites

conglomerate found at the bottom of a mature meandering river channel as part of a channel fill deposit

* tillites: conglomerate found in glacial environments

polymict vs monomict conglomerate/breccias + what does it means ‘‘matrix/clast supported’’

Poly: >2 different clast types

oligomict: 1 clast type only

* matrix supported = more matrix than clast
* clast… inverse

dominant minerals in sandstone

quartz-feldspars (also most common in the earth’s crust)

3 main components of sandstones

grains, matrix, cement

What is the Pettijon 1973/ QFL classification for sandstones

based on % of matrix present

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arenites, greywackes, mudstones

what is the aeolian sandstones maturity and why is it that

describe the grains

very mature because of continual movement of sand by wind and gravity

(well rounded, thinly coated with iron oxide, and scratched)

What are iron pellicles seen in thin sections

thin coat of iron oxide around sand grains (usually very mature)

How much % of sedimentary rock on earth is mudstone and why

50% because it is the end product of erosion (siltstone, mudstone, claystone)

def fissility and how are mudstone with fissility called

‘‘cleavage’’ only parallel to deposition due to burial pressure which removed the 80% of pore space through water loss i.e.

shale

What does a grey-black mudstone significates + where can it be found

significant amounts (>1%) of organic carbon and pyrite

* higher input of organics relative to O2 available (anoxic conditions needed for pyrite formation)

ENV: swamp, continental basin deep lake, marine shelf, low energy/quiet conditions, reduced ocean circulation

What does a red-brown-yellow-green mudstone significates + where can it be found

red: oxidized mudrock, ferric oxide

brown: geothite, ferric hydroxide

yellow: limonite

green: absence of above, reflection of sheet silicates without oxidized iron components

def green reduction spots/horizon in mudrocks

reflects the reduction of ferric iron by an organic material (i.e. plant root) commonly in red mudrocks

extensive horizons: shallow organic rich pond

most important clay minerals in mudrocks

illite, kaolinite, smectite

def flocculation process + when does it occurs

where finely dispersed sediment in water starts to clump and form larger particles

occurs when freshwater with fine sediments mixes with a solution containing electrolytes (sea water)

3 big categories of environments for mudstones and description, some examples in each, & colors

(near shore, hemipelagic, non-marine)

Marine, near shore, non marine

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near shore: tidal flats, lagoons, deltas (grey, coarse clastic, reduced fossil diversity)

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hemipelagic: with pelagic fossils (graptolites), deep marine settings (dark grey usually)

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non-marine: fluvial/braided-meandering rivers, deltas, alluvial flood plains, overbank deposits (red)

What is the major mudrock deposition area on land

lakes

differences in mudstones glacial vs non-glacial lakes laminations

* non-glacial: mm sized rhythmic lamination = seasonal bloom (organic rich-organic poor), oil shales

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glacial lakes: lamination (silt-sand) coarser = spring, more organic deposits in mm = summer,

varves helped determine cyclic climate variation

how much organic matter is in organic rich mudrocks (sulfidic black shales)

3-10%

Describe the process of organic matter deposition in anoxic env

in slow sedimentation rates, anaerobic sulfate reduce sulfate ions into H2s = precipitation of sulfide minerals

when exposed back to O2 = sulfuric acid = acid mine drainage

def bentonites and loess deposits

volcanic ash altered to clays = mudrock

* loess: aeolian silt deposits, very well sorted wind blown material