Sed/Strat 1

Sed Strat exam 1

Quaternary

2.58Ma

Neogene

2.58-23.03 Ma

Paleogene

23.03-66Ma

Cenozoic

End 66 Ma (Quaternary, Neogene, Paleogene)

Cretaceous

66-145Ma

Jurassic

145-201.3 Ma

Triassic

201.3-251.9Ma

Mesozoic

66-251Ma (Cretaceous, Jurassic, Triassic

Paleozoic

251-541Ma (COSDMPP)

Ordovician

443.8-485.4Ma

Cambrian

485.4-541Ma

Precambrian

541-4600Ma (Proterozoic, Archean, Hadean)

Proterozoic

541-2500Ma

Hadean

4000-4600Ma

Sedmentology

Process oriented

Straitigraphy

Spatial and Temporal variations

Principals of Stratigraphy

Steno

1. Superposition

2. Original Horizontality

3. Original Lateral Continuity

Superposition

in anysequence of undisturbed strata, oldest layer at bottom, and successively younger layers are successively higher

Original Horizontality

states that sedimentary layers were deposited nearly horizontal and parallel to Earth’s surface

Original Lateral Continuity

At the time of depotion, strata extened cont in all directions until they termintated by thinning at the edge of the basin, ended abruptly at a barrier to sedimentation, or graded laterally into a different sediment type

Uniformitarianism

Principle that processes acting upon Earth today have also operated in the geologic past

Fossil (biotic succession

principle that body fossils occur in strata in a definite determinable order

cross cutting relationships

states that a rock unit, sediment body, or fault that cuts another geologic unit is younger than the unit it was cut

Walther’s Law

facies that are found today in vertical sequence are the product of a series of depositional environments which lay laterally adjacent to eachother

What is info is preserved in sedimentary rocks

Tectonics(internal)

Climate(external)

Sediment Routing System

tectonics+climate=erosions+deposition

Physical weathering

abrasion

insolition(thermal fatigue) and exfoliation

frost wedging and exfoliation

root-wedging

salt-wedging

transport

Chemical weathering

dissolution

hydrolysis

oxidation and reduction

Goldich Stability Series

What controls sedimentation?

amount of material available (erosion)

space available (accommodation space)

preservation potential

why is sed/strat important?

host most natural resources (oil,gas,water)

preserve Earth’s geological history

significant for energy resources, environment, economy

How much of Erath’s exposed rocks are sed

70%

Reynold’s Number

Froude Number

Fr<1

Subcritical

Fr>1

Supercritical

Re>>2000

Turbulent

Re<500

Laminar

Flow Regimine Diagram

Hjulstrom Diagram

How does a particle settle back down?

Function of viscosity, size, shape and density of particles

Stoke’s Law

a single solide sphere settling in a fluid has a terminal settling velocity which is uniquely related to the diameter

Implications of stoke’s law

high density minerals settle more rapidly than low density minerals

slow moving, high viscous fluids can transport courser grained materials more easily than less viscous materials

How do we describe sed rocks?

texture

composition

sed structures

Sandstones

classified according to grain size and composition

Conglomerate

classified according to clast size and composition

composed of ^{>30% of clasts}

Pebble size

4-64mm

Cobble size

64-264mm

Boulder size

264+mm

Granule size

2-4mm

Wentworth scale

Laminar flow

flows smooth and streamlined

Turbulent Flow

flows irregular and chaotically

Phi Scale

phi=-log2(d)

fine size: positive

course size : negative

What 3 things affect grain shape

form

roundness( angularity)

surface texture

sorting

measure of the range of grain sizes presnt and the magnitude of the spread around the mean size

Why is grain size and sorting important?

Give us info on physical processes and depositional environments

control oil and gas resivior quality (porosity and permeability)

control groundwater reservior volume

Grain orientation to determine flow direction

clasts supported

orthoconglomerate

when clasts are in contact with eachother and matrix is <20%

Matrix Supported

paraconglomerate

when matrix is >20%

polymictic conglomerate

made of clasts of different compositions

olimictic or monogenic

made of clasts of the same composition

conglomerate naming formula

support+clast type+avg size of clasts+conglomerate

Composition of sandstones

relative proportion of quartz, feldspars and lithics/rock fragments

imbrication

primary depositional fabric

QFL

l=lithics (<62micrometers

QFR

R=rock fragments include all polycrystalline lithic fragments (size bias)

Sediment gravity flows

sediment transported by the effect of gravity acting directly on the sediment or rock

Debris Flow

highly cohesice sediment water mixture drived by its own weight

initiate on slopes >10, flow on slopes <5

Debris flow deposit

poorly sorted

large range of grain size

mud matrix

lack internal layering

base may show evidence of shearing or scouring

either no grading, normal or reverse grading

Turbidity Currents

subaqueous

triggers: earthquake, storm, sediment failure, alignment slopes

turbulence causes sediment to become suspened

creates desnity contrast with surrounding water

flows stop when density contrast is reduced by settling

Turbiditty currents three main parts

head: concentration of courser particles, most intense turbulance, overhanging, velocity slower than body

body: uniform, steady velocity, velocity > haed velocity, feeds head, near uniform thickness, can be area of erosion or deposition

tail: thins rapidly away from body, becomes more dilute, area of deposition

What drives velocity on turbidity currents?

desnity contrast

Turbididte Bouma Sequence E

Massive Ungraded mudstone, possibel bioturbation, pelagic seds

Turbididte Bouma Sequence D

Lower flow regimes planar laminated siltstone

Turbididte Bouma Sequence C

Ripple laminated fine-grained sandstone, flame/convolute lamination

Turbididte Bouma Sequence B

Uper flow regime planar laminated medium grained sandstone

Turbididte Bouma Sequence A

Normally garded sandstone, course grains or rip-up clasts at the base scoured base

liquefied flows

concentarted dispersions of grains in which sedimenrt is supported by upward escape of flow of pore water or by injection of water from below

liquefied flow deposit

thick, poorly sorted sand

identified by fluid escape structures

Grain flow

occur on steep surfaces near angle of repose (30)

cohesion often causes cohesionless sediment to be piled up beyond angle of repose

grain-to-grain contact supports flow

most commonly observed in aeolian environments

deposits difficult to preserve

almost like billiards balls

Carbonate production

material for carbonate sediments is extracted from the dissovled load of the sea or other body of water

what controls carbonate production

light, pH, temperature and nutrients

main areas of carbonate production

carbonate platforms (non-reefs)

organic reef env

slope basin carbonates or carbonate ramps

mixed carbonate siliciclastic systems (non-reef)

light

most important control on skeletal carbonate precipitation because of the dominance of photo-autotrophic arganisms in carbonate productions

carbonate compensation depth

the water depth at which the rate of supply of calcium carbonate from the surface is equal to the rate of dissolution

What controls the CCD?

solubility of calcium carbonate is determined by temperature, pressure and dissolved CO2 in the water

in areas of high productivity, greater rates of supply makes the CCD deeper

increase pH

decrease CaCO3 solubility, deeper CCD, higher T, lower P

What does a Temp increase do to the CCD?

The CCD gets deeper

would you expect a shallower or deeper CCD in areas of upwelling

Deeper

Components of limestone

biogenic

non-biogenic

carbonate minerals (micrite and sparite)

Carbonate Minerals

calcite, aragonite, dolomite

carbonate grains: skeletal and plants

molluscs, stromatolites, nanoplanktos, cephalopods, corals, crinoids, coccoliths, oncoids

nonbiogenic constitients of limestone

ooids( speherical bodies of CaCO3 less than 2mm

poloids (fecal pellets) no cocentric structure

intraclasts- fragments of calcium carbonate material that has been partially lithified and then broken up and reworked to form clasts

carbonate mud- micrite

made of fine-grained calcium carbonate less then 4 micrometers across

they form by chemical precipitation of CaCO2 out of saturated wtaer

Sparry Calcite- sparite

course-grained calcite crystals that appear clear to translucent in plane light

Folk Sequence

relative abundance of 1. carbonate grains or allochems, 2. microcrystallline carbonate mud (micrite) and sparry calcite cement

Dunham Sequence

relative abundance of allochems and micrites or sparite, but does not consider ID of grain

How to decrease CO2

increase temp

decrease pressure

increase CO2 and lower solubility of CO2

photosynthetic organisms

inorganic precipitation

preference for calcite vs aragonite seas

Mg2+ rich seas favor aragonite