SedStrat

sedimentology vs. stratigraphy

Sedimentology:

• Classification, origin, and interpretation of sedimentary rocks

• Concerned with physical (textures, structures, minerology), chemical, and

biological properties of the rocks

Stratigraphy:

• Science of rock strata

• Age relationships and chronological arrangement of strata, successions

(stacking patterns), correlation and stratigraphic order of beds

3 types of sedimentary rocks

siliciclastic

chemical/biochemical

carbonaceous

weathering

the in situ decomposition of rocks and minerals at the Earth’s surface

6 components of physical weathering

 freeze-thaw

 thermal expansion

 salt weathering

 wetting and drying

 release of overburden (unloading)

 other processes (biological activity, etc.)

Processes of Chemical Weathering (6)

hydrolysis

hydration and dehydration

oxidation

solution

ion exchange

chelation

3 products of weathering

1. Source rock residuals

2. Secondary minerals

3. Soluble minerals

humus

decayed remains of animal and plant life (organic matter in soil)

Controls of Soil Formation (5)

climate

time

parent material

plants and animals

slope

soil profile: O zone, A zone, E zone, B zone, c zone

O zone: loose and partly decayed organic matter

A zone: mineral matter and humus

E zone: zone of eluviation and leaching

B zone: accumulation of clay transported from above

c zone: partially altered parent material

paleosols and how to recognize them

paleosol: buried, fossilized soil

diagnostic features: root traces, soil horizons, peds and cutans

peds and cutans

network of irregular planes formed by clay skins (cutans) that surround more stable aggregates of soil (peds).

glaebules

hard chemical concentrations of minerals in a soil

flow type depends on (3 things)

-Roughness of the bed

– Velocity of the fluid

– Viscosity of the fluid

Reynolds number tells you…what two values?

less than 500=laminar

greater than 2400=turbulent

unknown between the two values

viscous sublayer

Molecular adhesion causes particles of the flow to remain stationary right above the boundary. Successive layers of the fluid slide over lower layers.

boundary layer

the region of the flow that is slowed due to frictional resistance from the bed/sides of the flow

-Most sediment transport occurs within this zone

transport (erosion) requires two things:

entrainment

sustained movement

4 sediment transport pathways

Bedload (water):

• Constant or intermittent contact with the bed

Suspended Load (water):

• High above the bed

• Settling velocity < shear velocity

Dustload (wind)

Ice- coarse poorly sorted material

Hjulstrom diagram assumes (3 things)

Spherical quartz grain

• 1 m depth of water

• Flow over a smooth bed

4 major dispersive forces in gravity flows

1. Turbulence

2. Upward escape of fluid

3. Grain-to-grain interactions

4. Support by a cohesive matrix

turbidity current sediment concentrations

Low Sediment Concentration-(~ < 1 % sediment by volume)

High Sediment Concentration-(~1 - 10 % sediment by volume)

bouma sequence

low to high:

graded sand and gravel

Parallel laminated sands

ripple laminated sands

parallel laminated muds

bioturbated mud

Debris flow

cohesive matrix provides dispersive force

• Cohesive strength of matrix prevents larger grains from settling out

Poorly sorted, Matrix supported deposits

sediment gravity flow (2 ways)

Grain-to-grain interactions (fronts of dunes)

Upward escape of fluid (quicksand example)

cutoff between clay, silt, sand, and gravel

clay to silt: .0039 mm

silt to sand: .0625 mm

sand to gravel: 2 mm

grain form

Gross overall configuration or outline

• E.g. sphere, platy, rodlike, etc.

zing classification

grain roundness

Sharpness of the corners

• Weddell’s roundness, Powers roundness

grain surface texture

Microrelief and pits, scratches, ridges, etc.

2 components of grain fabrics

Orientation

• Alignment of grains

• Imbrication

Grain packing

• Spacing or density patterns of grains

• Important for porosity and permeability of materials

Imbricated flow

when rocks are aligned in the direction of flow

Processes that Create Primary Sedimentary Structures (4)

Depositional

Erosional

Deformational

Biogenic

lamina

less than 1 cm thick beds

amalgamation surfaces

erosional surfaces that merge two sedimentary beds

3 ways beds laterally terminate

pinch out

lateral gradation into another bed

cross cut by other features

Ball and pillow

weight of sand on top of mud makes the sand sink into the mud causing ball like structures

flame structures/slumps

weight of sand on mud makes flame like contacts/slumps that look like folds

pillar and dish structures

can see water being “squeezed” out of the sediment

load casts

weight of overlying sediment makes depressions in the underlying sediment and makes the rock look bumpy when lithified

flute class

“nose” of the cast points up stream

form by eddies in the flow

chevron casts

point in the direction of flow

parallel laminations

long wavelength

fallout from suspension

graded bedding

normal-fining up

reverse-coarsing up

bedforms: definition and examples

Any deviation from a flat bed, generated by the flow

on the bed.

ripples, dunes, anti dunes, panar bedding ect.

ribs and furrows

small scale troughs that form from ripples migrating downstream

climbing ripples

form as ripples migrate downstream as a result of fast flow and fast deposition

tabular vs. trough cross bedding

tabular-cross beds are sandwiched between planter beds

trough-all over the place

convolute bedding

complex, folded, and crumpled laminations as a result of loading or slope slumping

hummocky cross stratification

form as a result of major storms in shallow marine environments below the wave base

looks like a wave

herringbone cross bedding

looks like arrows that point in the direction of flow

two erosional structures

channels

scour and fills

groove casts

flow drags debris across beds and makes tube looking casts. shows flow direction

trace fossil

Sedimentary structures created by the boring, feeding, and locomotion activities of organisms

Ichnogenera:

ichnospecies:

ichnofacies:

1. classification system (or group) of trace fossils based on animal behavior

2. particular trace

association of trace fossils that recur in space and time and

reflect a set of environmental conditions such as water depth, salinity, and nature of the substrate.

how do sedimentary dikes and sills form

sediment rich fluid injection into layers below as a result of overburden weight

siliciclastic rocks (general)

Composed of particles derived by the weathering and breakdown of

older rocks and by pyroclastic volcanism.

• Classified on the basis of grain size

• Conglomerates

• Sandstones

• Mudrocks (shales)

• ¾ of all sedimentary rocks

• ~75% all oil and gas

sandstone

0-25% of all sedimentary rocks

Composition:

Framework gains: silicate grains 1/16-2 mm (sand size)

Mineral cements

Matrix minerals

3 most common framework grains in a sandstone

quartz

feldspar

rock fragments

most common framework MINERALS in sandstone

quartz

feldspar

micas

sandstone cements (commonality)

most common-quartz

second most-carbonate

third-others: hematite feldspar, etc

most common matrix mineral in sandstone and size

clays

grains less than .03 mm

sinurysis cracks vs. mud cracks

siniurysis are a result of salinity while mud cracks are purely from wetting and drying

stromatolite vs. strombolite

stromatolites have laminations strombolites to not.

they are both algae beds

Sandstone classification percentages: arenite vs. wacke

true sandstone- >50% sand sized grains

Arenite: <10% matrix

• Wacke: 10%<x<50% matrix

lithic vs. feldspathic arenite

lithic: < 90% Q, F < L

feldspathic arenite: < 90% Q, F > L

lithic vs. feldspathic wacky

lithic wacke: < 90% Q, F < L

feldspathic wacke: < 90% Q, F > L

arkose sandstone definition:

feldspathic arenite >~25% feldspar

greywacke sandstone

Matrix-rich sandstone that has usually gone deep burial, has a chlorite matrix

and dark-grey, green color. Very hard and dense.

conglomerate definition and where they are found

>30% of the grains >2 mm

Usually have a matrix of clay and micas, or sand-sized quartz,

feldspar, rock fragments, and heavy minerals

found in areas of tectonic uplift

conglomerate class types (3)

Oligomict: single kind of clast

Polymict: assortment of different types of clasts

Petromict: polymict with large portion of unstable or metastable clasts (e.g. basalt, limestone)

diamicton/diamictite

Poorly sorted or unsorted matrix-supported conglomerate

• Strictly a descriptive term but very common within glacial deposits and debris flows

olistostrome

sedimentary deposit consisting of a mass of intimately mixed

heterogenous materials such as blocks and muds that accumulated by submarine gravity sliding or slumping

cataclastic conglomerates

Formed from the breakup of rocks by sliding, slumping, or tectonic action like

along faults, or the collapse of a cave

olistolith

Large exotic block transported by sediment gravity flows into a basin or other sedimentary deposit

clinker

red-orange rocks that form when coal seems ignite Mudrock or shales around them

mud rocks and shales definition

>50% grains <0.0625 mm

Mudstone versus Shale:

• Fissility: property of fine-grained rocks to break into thinly spaced planes or

sheets parallel to bedding planes

• Shales: laminated or fissile

• Mudstones: non-laminated or fissile, massive

clay minerals through time-which are lost which are gained

Smectite and kaolinite are lost

through time

• Illite and chlorite are gained

through time

diagenesis definition

all changes to a rock after deposition below 250 degrees celsius

four components of lithification

Cementation

• Compaction

• Desiccation

• Crystallization

what are the three stages of diagenesis?

eogenesis

mesodiagenesis

telogenesis

eogenesis

Earliest stage of diagenesis

• Very shallow (< 10’s of meters)

• Largely reflects environmental conditions

Bioturbation

• Minor compaction and repacking

• Some mineralogical changes

mesodiagenesis and the 4 processes causing changes during this stage

second stage of diagenesis

Deep burial

Decrease in porosity and permeability

Processes causing changes:

• Cementation

• Dissolution

• Replacement

• Clay-mineral authigenesis

porosity __ with compaction

decreases

cementation (what it is and two main cement types)

Precipitation of new minerals into pore space

• Decrease porosity and permeability

silica and carbonate are the two common types

dissolution

dissolve minerals

includes pressure solution which dissolves silicate minerals for cementation

replacement

One mineral dissolves at

the same time as new

mineral precipitates

Clay-mineral authigenesis

One clay alters to another

Telogenesis

Deeply buried rocks come back to the surface

• Unloading

• Cements dissolve, others precipitate

• Grades into weathering at the Earth’s surface

5 types of chemical/biochemical sed rocks

Carbonates – the most common

• Evaporites

• Silicious sedimentary rocks

• Iron-rich sedimentary rocks

• Phosphorites

two main types of carbonates

limestone and dolomites

4 major minerals assemblages in carbonates

aragonite

low mg calcite (<4% mg)

high mg calcite (>4% mg)

dolomite (>50% mg)

Allochems (carbonate grains) (5 types)

1) carbonate clasts:

intraclasts-pieces of the depositional environement within the carbonate

extraclasts-peices of things not within the depositional environment caught in the carbonate bedding

2) skeletal grains-most common

3)Ooids

4) peloids-carbonate grains w/o internal structure

5) aggregate grains

3 major components of carbonate texture

allochems (carbonate grains)

microcrystalline calcite-matrix

sparry calcite-cement

sparry calcite

clear calcite that grows in empty space

forms in agitated water

microcrystalline calcite

fine grained calcite matrix between grains

planar vs. non planar dolomite

planar - a type of dolomite made of rhombic, euhedral to

anhedral crystals

nonplanar - dolomite dominated by anhedral crystals.

coquina

carbonate rock made almost entirely of shells

chalk

soft, Earthy, fine-textured limestone mainly from the calcite

tests (shells) of floating micro-organisms

marl

mixture of clays and fine-grained carbonates

what dissolves or precipitates carbonates (think environmental conditions and molecules)

more CO2→dissolves carbonates

less CO2→carbonates precipitate

magnesium inhibits calcite but not aragonite

warm temps + low pressure +lower salinity=more carbonate precipitation

whitings

spontaneous precipitation of aragonite