Sediment/Rock Classification Sediments/rocks classified according to grain size & composition. Sediments/rocks classified according to grain size & composition.

Sediment/Rock ClassificationSediment/Rock Classification

• Sediments/rocks classified Sediments/rocks classified according to according to grain sizegrain size & & compositioncomposition..

• What is size?What is size?• Several scales proposedSeveral scales proposed

• Udden-Wentworth is Udden-Wentworth is geometric (1,2,4,8,16)geometric (1,2,4,8,16)

• Krumbein = phi scale; Krumbein = phi scale; phi=-log2Sphi=-log2S

• Present data Present data graphicallygraphically

• The greater the distance The greater the distance of transport the smaller of transport the smaller the grain size.the grain size.

• Caution. Grain size may Caution. Grain size may reflect what is available reflect what is available to be transportedto be transported

Gravel

Sand

Silt

Clay

Grain RoundingGrain Rounding

• Roundness = curvature of Roundness = curvature of corners of grainscorners of grains

• Have angular to well-roundedHave angular to well-rounded

• The rounder the grain, the The rounder the grain, the greater the distance of greater the distance of transport transport

• Rounded quartz grains imply Rounded quartz grains imply many cycles of uplift, erosion, many cycles of uplift, erosion, depositiondeposition

• Beach and desert better Beach and desert better rounded than river/glacial seds rounded than river/glacial seds

• Large grains round fastestLarge grains round fastest

Grain SortingGrain Sorting

• Measure of grain size distributionMeasure of grain size distributionIndicate effectiveness of depositional Indicate effectiveness of depositional

medium in separating grains of diff medium in separating grains of diff sizessizes

• Sorting depends on such factors as Sorting depends on such factors as depositional mechanism, rk typedepositional mechanism, rk type

• Poor sorting usually means limited Poor sorting usually means limited transporttransport

• Better sorting usually means Better sorting usually means greater distance of transportgreater distance of transport

• Rivers are good examplesRivers are good examples• Used to distinguish seds of dif. env.Used to distinguish seds of dif. env.

FabricFabric• Fabric/grain alignmentFabric/grain alignment

– may indicate beddingmay indicate bedding

• Results from grain transport--e.g. Results from grain transport--e.g. wind, waterwind, water

• Lack of grain alignment also Lack of grain alignment also important important

MatrixMatrix• Is finer material between grainsIs finer material between grains

• grains floating in matrix = matrix supportedgrains floating in matrix = matrix supported• grains in contact = framework/grain-grains in contact = framework/grain-

supportedsupported

• Lack of MatrixLack of Matrix• probably removed by wind/water currentsprobably removed by wind/water currents

• Presence of matrixPresence of matrix• reflects transport mediumreflects transport medium• e.g. debris flowe.g. debris flow

Textural MaturityTextural Maturity• Immature = lots of matrix, poor sorting, angular grainsImmature = lots of matrix, poor sorting, angular grains• Mature = little matrix, mod-good sorting, well roundedMature = little matrix, mod-good sorting, well rounded• Supermature = no matrix, v. good sorting, well roundedSupermature = no matrix, v. good sorting, well rounded• Provides clue to depositional processProvides clue to depositional process

• persistent currents = more mature sedspersistent currents = more mature seds• immature seds = fluvial and glacialimmature seds = fluvial and glacial• more mature = desert, beach, shallow marinemore mature = desert, beach, shallow marine

Compositional MaturityCompositional Maturity• Compositionally mature = predominantly quartzCompositionally mature = predominantly quartz

• Unstable minerals removed during transportUnstable minerals removed during transport

• B. Compositionally immature = labile constituents B. Compositionally immature = labile constituents and quartzand quartz

CementCement• Holds rock together--lithifiesHolds rock together--lithifies

• could be clay, silica, calcium could be clay, silica, calcium carbonatecarbonate

• clay looks like mudclay looks like mud• quartz usually clear to white, quartz usually clear to white,

harder than calciteharder than calcite• calcitecalcite

Depositional Environments and Grain SizeDepositional Environments and Grain Size

• Low energy environments Low energy environments such as lakes and deep such as lakes and deep oceans consist of oceans consist of muds/claymuds/clay

• High energy environments High energy environments such as rivers and such as rivers and beaches consist mostly of beaches consist mostly of gravel and sandgravel and sand

Sedimentary Environments & Sedimentary Environments & Transporting AgentsTransporting Agents

Color of Mudrocks:Color of Mudrocks:Green-oygenated environmentGreen-oygenated environmentBlack-Organic-rich, low oxygenBlack-Organic-rich, low oxygen

Southern California ShelfSouthern California Shelf

SEDIMENT DISTRIBUTIONSEDIMENT DISTRIBUTION