ERTH2003 Notes

Sediments uses

topography, climatologists, resource sector, mining, builders, environmentalists, hydrogeologists, farmers, geomorphology, planners, engineers, archaeologists,

Information from Seds

Provenance- where did the rock come from?

Process- how was it transported and deposited?

Product- compostion, properties, uses

Seds over time

weathering, erosion, despoition, burial, diagenesis

mineral vs rock

mineral- inorganic element or compound, naturally occuring, regular crustal structure, solid

rock- naturally occuring, solid, aggregate of minerals or non-minerals

bowens reaction series

rules of relative time

principle of original horizontality, superposition, cross-cutting relationships, inclusions

uncomformities

disconformity- time break with parallel strata above and below uncomformable contact

angular - time break with older strata dipping at an angle, relative to the overlying younger strata, which are parallel to the uncomformable contact

nonconformity- time break between igneous rock and overlying sediment

conformable deposited without a major breakdown in deposition, unconformable deposited with major breakdown, (with or without erosion)

cycles to note

atmospheric, hydrological, geologic rock cycle, plate tectonics

stability of minerals

clay, quartz, al hydroxides and fe oxides are the most resistant to weathering

erosion vs weathering

erosion- removing of material through a transport such as water, wind, ice

weathering- alteration of material (mechanical (disintergration) or chemical (alteration))

mass wasting

transfer of rock down slope due to gravity (land slide)

newtonian- water like

non-newtonian- viscosity changes with stress

bingham plastic- resists movement

mechanical weathering

root wedging, stress relief joints, frost wedging, quartz to sand

as the grain size decreases, surface to volume ratio increases, which can make chemical weathering faster

chemical weathering

• minerals chemically react or dissolve

• solvents or reactants (water and acids like carbonic and sulfuric)

climate and rate effect weatheing extent

dissolution vs dissociation

dissolution- quartz (sio2 + 2h2o—> h4sio4), calcite (caco3 + h2o + co2 —> ca2+ + 2hco3-)

dissociation- halite (nacl—> na + cl)

orthoclase

kaolinite + silica + ions

occurs through hydrolysis

clay

oxidation

iron pyroxene

olivine

these form hematite (rust)

oxyhydroxides can also form because of the water presence

oxyhydroxides and fe oxides are solids

common mineral weathering types

feldspar- hydrolysis

muscovite- hydrolosis

olivine- oxidation

quartz- dissolution

pyroxene- oxidation

solids vs ions

solids- form clasitc (detritus) sediments like sandstone

ions in solution- form oceanic salts and chemical sediments

dissolved silica—> chert

dissolved carbonate—> limestone

different cl and na in ocean vs rivers particularly

detrital/siliclastic sediment

clay, quartz, feldspar, rock fragments, muscovite

regolith

detritus that covers surface that is not removed by erosion or mass wasting, not soil as soil is water and organic matter with regolith

soil profile

o is organic layer, also varies by climate

granite vs basalt

granite- quartz, feldspar, mica, hornblende, lithic fragments, clay, minor fe oxides (na and k in solution rich)

basalt- plagioclase, olivine, pyroxine, clay, fe oxides (mg and ca solution rich), hematite

phi

a larger grain size will result in a smaller phi

the higher the peak, the better the sorting

grain size distribution doesn’t necessarily indicate a particular depositional environment

clastic sediment transport

fluid flow and sediment gravity flow

fluid flow examples

runoff, sheet flow, rills, channels

fluid density

mass per unit volume for water = approx. 1g/cm3

viscosity

relative ability of fluids to flow, rate dependent when carrying sediment loads

laminar vs turbulant flow

laminar- ray paths of fluid particles are parallel

turbulent- ray paths are irregular

channel characteristics

stream flow velocity

velocity of stream flow is influenced by the gradient, roughness and cross-sectional form of the channel

manning equation

estimate flow velocity

reynolds number

laminar or turbulent flow equation

500 or less- less velocity

2000 or more- high velocity

bernoulli lift

higher velocity over convex side leads to lower pressure there relative to underside producing lift

sediment flow transport types

traction- rolling or sliding

saltation- jumping

suspension- floating in liquid

dissolved- ions in water

settling velocity

Steady rate of fall after grains are lifted and decelerated = ‘terminal fall velocity’

Settling Velocity < flow velocity (= f shear velocity) Then → transported in suspension.

Settling Velocity > flow velocity Then → deposition or bed load transport.

saltation at boundary

grains hydrualic equivalent if deposited at same time

competence vs capacity

competence- largest size of particle carried by flow

capacity- total amount of sediment that can be carried by flow

flow regime types

depth and grain size essential

increasing: ripples, dunes, plane, antidunes, chutes and pools

ripples and wave structure

trough vs planar stratification

wave diagram

air transport

bed load- traction saltation

suspended load- dust load

ice transport

plastic behaviour- suspended, deposition on melting, some bed load

rafting- dropstones

turbidity current/bed

large amounts of water, clasts are fluid supported, sediment deposited by flow wanes

sole marks at bottom, scoured base, fining up, waning flow

flow and their stratigraphy

sedimentary structures

large-scale internal and surficial features of sedimentary rocks generated by depositional, erosional or diagenetic processes, fabrics and geometries visible at outcrop and hand sample scale

use:

• interpretation of depositional environment

• determination of younging direction (which is up)

• palaeocurrent analysis

PRIMARY (at deposition) AND DIAGENETIC (after deposition)

bedding features

• change of composition

• change of size

• change of shape

• change of orientation

• change of packing

lamination- smaller scale phenomenon within a bed

flow types in bedforms

unidirectional- leads predominantly to asymmetric bedforms (two- or three-dimensional) or plane beds ● Current ripples ● Dunes ● Plane beds ● Antidunes

oscillatory- waves, symmetrical

combined- both, low mounds

cross stratification

laminae not parallel to bedding, caused by ripples and dunes

has to scour downwards, it will swoop down

transport vs younging

transport= current direction

younging= which way is up (tangential only)

planar vs trough stratification

herringbone cross stratification

changes direction

climbing ripples

crest migrates down current, indicated waning flow, bed and suspension load

climbing ripple types

traction, traction and suspension, suspension

hummocky cross-stratification

storm waves, younging direction very hard, shallow marine to continental shelf

sand and clay bedding (intertidal)

flaser- sand with clay in troughs

wavy- alternation with sand and clay

lenticular- mostly shale with some sand

ripple marks

currents- asymmetrical

waves- symmetrical

concave surface up

interference ripples

multiple wave sets, includes ladder ripples

bedding plane erosion

current and tool formed

groove casts

infilling of trough left behind by dragged object, tool marks

flute casts

infilling of current generated scours, underside of bed

post depostional sedimentry structures

load, ball and pillow, flame

mudcracks

Polygonal cracks generated by subaerial desiccation of muds – cracks commonly filled by sandy material of succeeding flood or of eolian origin. caused by loss of water, wedge out downwards (protrude out)

syneresis cracks

Similar to mudcracks but discontinuous & variable in shape. Subaqueous shrinkage cracks formed in clayey sediment by loss of pore water from loosely compacted clays or by shrinkage of swelling-clay minerals due to changes in salinity of the surrounding water.

clay mineral that is underground and dries out, doesn’t protrude out

convolute bedding

soft sediment deformation, disturbed before lithification but after deposition

trace fossils

Traces of organisms or the activities of organisms not the organisms themselves. Uses: • Depositional environment • Oxygen levels, above & below sediment water interface • Traces of life where no organic matter preservation • Younging direction • Sedimentation rates • Biostratigraphy

they accumulate overtime which causes bioturbation

invertebrae trace fossils

locomotion traces, feeding, dwelling, resting, helps determine the location (bathymetric zonation)

meandering feeding trails and resting traces

low energy

skolithos burrows

high energy

tiering

depth to which different organisms burrow may be preserved, help determine sedimentation events

relationship between carbon, oxygen and bioturbation

more carbon means better preservation, less bioturbation and more fine sediments.

bioturbation stages

there is more likely to be bioturbation in a rock that has no new sediment depositon

regular, irregular, mottles, deposits

diagenetic sedimentary structures

concretions- mineral precipitation within the sediment

pseudofossils

cone in cone structures- mineral growth in shales during compaction during deeper burial

geopetal structures- sediment will fill in a structure at deposition angle, help determine younging direction

siliclastic rocks

mudrocks (50-60%) clay + silt grain sizes, non-laminated

Shale – laminated mudrock; clay and/or silt sized sediment. determined by oxygen and organic content

Siltstone – silt-size sediment.

Claystone – clay-size sediment.

siliclastic mudrocks

small grains

Textural classifications - proportions of silt and clay - relative hardness or induration - internal laminations – fissility

clay from chemical, silt from mechanical

current veolcities are low (deltas, deep sea, estuary) (lakes,rivers)

important for:

• quarries (brocks, ceramics, fossils)

• seal for petroleum

mudrocks colour meaning

black= high organic content, low oxygen

red= oxidising environment, terrestrial setting most likely

green=reducing environment, marine settings

sandstone (arenite)

lithified sediment, mostly sand sized, 25% of sedimentry rocks

transported grains: framework of large grains and matrix of small grains filling interstitial spaces

cement: chemical precipitation in pore spaces

formed in rivers, deltas, beaches, deserts

high perosity and permeability, good reservoir, good for silica and sand mining

matrix= over 10% is conscidered wacke

wacke (arenite)

sediment contains more that 10% mud sized particles between the sand grains

cement

- chemical precipitation in pore spaces - may be different or same composition to transported grains - if same composition may form overgrowths - may form very small (cryptocrystalline) to quite large crystals - usually

well-developed crystal faces

in position, while matrix is transported

pores

space between grains, commonly filled with a fluid or substance

QFL Diagram classification

practice with this

monocrystaline vs polycrystaline quartz

mono- straight extinction, quartz

poly- counted as lithic clast in sandstone classification, includes chert and quartzite

feldspar

plagioclase and orthoclase, clear cleavage,

lithic fragments

conglomerates and breccias

Epiclastic – breakdown of older rocks (normal type) Volcanic – pyroclastic or shattered volcanic rocks (breccia) Cataclastic – from faulting or land slide (breccia)

Solution – left after solution of surrounding rocks (breccia) Impact – shattered by meteorite (breccia)

Classified on combination of texture & composition of clasts.

- Angularity of clasts. - Proportions of gravel versus sand- and mud-sized material. - Whether clasts are derived from local reworking of underlying sediments or transported long-distance. - Whether clasts are of uniform or multiple lithologies

found in alluvial fans, mass wasting, rivers, beaches

orthoconglomerate

clasts in contact (clast/framework supported).

paraconglomerate

clasts “floating” in matrix (matrix-supported).

diamictite

Paraconglomerates where there are two distinct size fractions.

oligomict

single clast type

polymict

more than one clast type

quartzrose vs petromict

quartzrose if more than 90% quartz and chert

quartzrose orthoconglomerate/paraconglomerate…

petromict if less than 90% quartz and chert

sedimentry texture

grain size, grain sorting, rounding, grain shape, grain orientation

tells history and source of sediment, textural and mineralogical maturity

sphericity

degree to which a grain approaches a spherical shape (how compact a shape is)

may reflect source as micas and foliated metamorphic rocks are flat

roundness

degree to which corners of a grain have been rounded off, how smooth or angular a shape is

controls

• original sediment shape

• length of time in transport (longer=more rounding)

• hardness of material (softer=quicker rounding)

• sediment size relative to transport mode (traction loads round fastest, wash not at all)

silt and clay generally dont round

fabric

orientation of grains relative to eachother

textural vs mineralogical sediment maturity

textural- sorting, rounding, transport history

mineralogical- mineral stability, source of sediment/time/climate (hot and wet is best erosion)

mineralogical maturtiy

immature is feldspar and biotite and lithic fragments, lithic are being formed in the active tectonic movements, more stable environments have quartz so are more mature, cube has high sphericity, cobbles round faster, grains with high angularity are not necessarily immature

diagenesis

processes that bring about physical/chemical changes to sediments between deposition and metamorphism or exhumation/erosion.

everything between deposition and metamorphism/erosion

final rock

lithification processes

Changes in sediment occur owing to: 1. Increasing pressure with burial 2. Increasing temperature with depth (geothermal gradient) 3. Changes in pore fluid chemistry 4. Changes in mineral stability as conditions change

3 stages of diageneis

eodiagenesis- shallow burial

mesodiagenesis- deeper burial

telodiagenesis- erosional

eodiagenesis

bioturbation, compaction (most important in muds and organic sediments), precipitation/dissolution of new minerals

clay has weak attractive forces so when they compact they cause grains to adhere and form shale