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Depositional Depositional Environments, Environments, Facies, Facies Facies, Facies Models and Models and
PaleogeograpyPaleogeograpyGeologic History in Three Geologic History in Three
DimensionsDimensions
Depositional Depositional EnvironmentsEnvironments
Sediments accumulate in some environment of Sediments accumulate in some environment of deposition or deposition or depositional environmentsdepositional environments
These areas receive net depositionThese areas receive net deposition Erosion may occur, but deposition dominatesErosion may occur, but deposition dominates Features of these depositional environments are Features of these depositional environments are
preserved in the rock recordpreserved in the rock record Examples:Examples:
Sediment textureSediment texture Sedimentary structures (formed by processes in the Sedimentary structures (formed by processes in the
environment)environment) Fossils of organisms that lived in the environmentFossils of organisms that lived in the environment
Ancient environments can be reconstructed from the clues that are preserved in the sedimentary rocks
Depositional Depositional EnvironmentsEnvironments
FaciesFacies All the properties of a body of rock that allow us All the properties of a body of rock that allow us
to differentiate it from those above, below or to differentiate it from those above, below or laterally adjacent to itlaterally adjacent to it
Properties includeProperties include Lithology – rock type, including color, etc.Lithology – rock type, including color, etc. Composition – mineral content Composition – mineral content Texture – grain size, sorting, roundnessTexture – grain size, sorting, roundness Sedimentary structuresSedimentary structures FossilsFossils
Facies means aspect – same Latin root as “face” Facies means aspect – same Latin root as “face” Overall appearance of a rock bodyOverall appearance of a rock body Facies are the products of depositional Facies are the products of depositional
environmentsenvironments Examples:Examples:
Planar laminated fine quartz arenite faciesPlanar laminated fine quartz arenite facies Bioturbated, poorly sorted muddy skeletal limestone faciesBioturbated, poorly sorted muddy skeletal limestone facies Cross-stratified arkosic conglomerate faciesCross-stratified arkosic conglomerate facies Stromatoporoid-tabulate coral reef faciesStromatoporoid-tabulate coral reef facies
Facies ModelFacies Model
An idealized description of a faciesAn idealized description of a facies Constructed from modern Constructed from modern
environments and ancient rocksenvironments and ancient rocks Serves as a Serves as a
Norm for comparisonNorm for comparison Framework for observationFramework for observation Predictor of patternsPredictor of patterns
Facies PatternsFacies Patterns
Groups of facies commonly show patternsGroups of facies commonly show patterns ProximalProximal Facies (near the source) tend Facies (near the source) tend
to be coarse grainedto be coarse grained DistalDistal Facies (far from source) tend to be Facies (far from source) tend to be
finer grainedfiner grained This pattern is displayed upstream and This pattern is displayed upstream and
down in rivers and onshore to offshore in down in rivers and onshore to offshore in coastal areascoastal areas
Facies are arranged according to Facies are arranged according to distribution of depositional environmentsdistribution of depositional environments
Facies MigrationFacies Migration
Facies migrate through space and timeFacies migrate through space and time Migration is in response to Migration is in response to
environmental factorsenvironmental factors Sediment supplySediment supply Sea level changeSea level change SubsidenceSubsidence
Facies become stacked during Facies become stacked during migrationmigration
A single facies is likely to be different A single facies is likely to be different ages in different locationsages in different locations
Walther’s LawWalther’s Lawof the Correlation of Faciesof the Correlation of Facies
Only works where there are no unconformitiesOnly works where there are no unconformities Only facies that were laterally adjacent during Only facies that were laterally adjacent during
deposition (result of laterally adjacent deposition (result of laterally adjacent environments) can be stacked verticallyenvironments) can be stacked vertically
Vertical arrangement of facies gives us Vertical arrangement of facies gives us information oninformation on Distribution of environmentsDistribution of environments How environments migrated through space and timeHow environments migrated through space and time
Used as a basis to build Used as a basis to build facies mapsfacies maps or or paleogeographic mapspaleogeographic maps
Accurate time Accurate time correlationcorrelation of facies is essential of facies is essential Time lines provide framework for correlationTime lines provide framework for correlation
Bio-eventsBio-events Volcanic ashesVolcanic ashes Other thin, unique lithologies or marker bedsOther thin, unique lithologies or marker beds
Representing Facies:Representing Facies:Stratigraphic SectionsStratigraphic Sections
DeltasDeltas
Marginal Marine DepositionMarginal Marine Deposition
Ganges Delta, IndiaGanges Delta, India
Mississippi Delta Mississippi Delta (partial), USA(partial), USA
Mississippi Delta (partial), Mississippi Delta (partial), USAUSA
Drowning!Drowning!
Niger Delta 3D ModelNiger Delta 3D Model
Modern Delta Modern Delta SubenvironmentsSubenvironments