6. Facies & Basin Analysis

Lithostratigraphy

The geological sub-discipline of classifying and correlating rock layers based on their physical characteristics, such as composition, texture, and colour

Facies

A body of rock with distinctive characteristics, such as different faces/attributes/aspects; it helps us to understand the spatial and temporal reconstruction of sedimentary, environmental, climatic, and/or tectonic environment of a succession

Base

The facies of sedimentary units/descriptions

Lithofacies

Facies that helps us understand processes during transport/deposition

Biofacies

Facies that help us understand the paleoecology during & after deposition (fossils)

Ichnofacies

Facies that help us understand the paleoecology during & after deposition (trace fossils)

Seismic Facies

Facies that help us understand the shape and reflection characteristics

Facies Assemblages

Genetically-related facies that are group that represent a single type of depositional element

2D Facies Model

Gives a graphical summary of facies and processes typical for particular depositional environments; can also gives the synthesis of many local examples (stratigraphy logs, drill holes, cross sections, etc.)

3D Block Diagram

Constructed based on 2D diagrams such as stratigraphy logs from drill holes and allows us to see the transitions between the environments as well as temporal shifts in the erosion and deposition

Regional-Scale Facies Model

Shows us the facies on a regional level, is more detailed than a 3D block diagram, and forms interpretations based on observations, showing the number of spatially interrelated depositional environments

Walther's Law of Facies

States that the vertical succession of facies reflects lateral changes in environment; vertically = timeline from old to young and laterally = environments next to each other with respective to sea level

Borehole

A deep, narrow hole made in the ground, especially to locate water or oil; can be used to map stratigraphic structures

Fluvial Accommodation Space

Space between actual land surface and graded profile in which sediment can accumulate

Marine Accommodation Space

Base between the seafloor and the base sea level at 0 m where sediment can accumulate

Accommodation Space

The volume available for sediment to accumulate which can be created or destroyed; it decreases as a basin fills, decreases when sea level lowers, increases when a basin subsides, and increases when sea level rises

Base Level

The lowest elevation level of a specific geographical location

Local Fluvial System

A network of waterways in a limited geographical area

Eustasy

A change of sea level throughout the world, caused typically by movements of parts of the earth's crust or melting of glaciers

Eustatic Sea Level

The distance from the center of the Earth to the sea surface

Subsidence

The downward movement (relative to sea level) of earth surface due to loading, mining or dissolution

Uplift

The upward movement (relative to sea level) of earth surface due to erosional, tectonic, or thermal processes

Transgression

Where the sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding which can be caused by land sinking, ocean basins filling, ocean basins decreasing in capacity, tectonic events, and climate change

Regression

A geological process occurring when areas of submerged seafloor are exposed during a drop in sea level

Unconformity

A buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous

Disconformity

An unconformity that occurs between parallel layers of strata indicating either a period of no deposition or a period of erosion

Nonconformity

A type of unconformity that develops where sediments are deposited on top of an eroded surface of igneous or metamorphic rocks

Angular Unconformity

An unconformity where older, tilted or folded rock layers are overlain by younger, horizontal layers, representing a significant gap in the rock record

Basin

A large, low-lying depression in the Earth's surface

Basin Analysis

Structural analysis of the tectonic setting can tell us about deformation during deposition, sedimentological analysis tells us the sources of sediment and environment of deposition, geological history analysis tells us about subsidence/uplift history, and stratigraphic analysis tells us about the age of rock units, correlation of the basin

Continental Basins

Intercontinental/-cratonic sag, continental rift basins, river floodplains, terraces, bars

Marine Basins

Proto-oceanic trough, oceanic basin (rise, abyssal plain), passive continental margin (shelf, slope)

Subduction Zone Related Basins

Back-arc basins, fore-arc basin, subduction zone trench

Continental-Orogeny Related Basins

Peripheral foreland basin (retro-arc), intramontane basin

Depositional Intracratonic/Continental Sag Basins

May be structurally controlled, containing pre-existing structures such as old faults/joint systems, or grabens; during ongoing deposition it undergoes subsidence meaning that the center gets deeper with added weight, and deposits include continental, marginal marine and/or marine (epicontinental sea)

Michigan Basin

This basin is formed due to deformation structures with a circular pattern of lithologies as evidence with sediments deposited on basement rocks shows evidence of great unconformity; subsidence continuously increases the accommodation space of the basin

Continental Rift Basin

Elongate, narrow depressions with symmetrical grabens in accumulation space which may be filled with water with coarse to fine continental sediments present; basin is structurally controlled with normal faults dipping toward each other which formed due to tensile forces with continental rifts caused by crust movement

Graben

A structure bounded by conjugate normal faults

Horst

A structure bounded by outward dipping normal faults

Half-Graben

Fault blocks slide of along curved detachment fault, blocks fall over like dominos; is asymmetrical

Symmetrical Graben

Normal faults on the two sides of the system are opposing, stretching of crust lets central portion sink down along normal faults

Margin

Where the horst is the original surface elevation

Listric Fault

A normal fault that is concave upwards; may appear steep on the surface outcrop but it is horizontal at depth

Synthetic Fault

A fault that is parallel and same relative movement as master fault

Antithetic Fault

A fault that is the opposite direction to master fault

Proto-Ocean Troughs

Includes continuation of rifting via graben systems where the stepped normal fault controlled causing an elongated depression which fills with ocean water; deposits are continental to marine

Marine Sag Basins

Formed in transition region with older part of continental and oceanic crust on the passive continental margin with normal faults which are covered by shelf sediments (continental to shallow marine)

Atlantic Basins

Remnants of normal faults (passive continental margins) that formed the initial graben system on both sides of ocean are still preserved under later marine sediment cover

Ocean Island Arc Basins

It is subduction related and caused by ocean-ocean collision forming a stretching of crust behind a volcanic island arc/subduction zone due to magma rise from mantle wedge or along the subduction zone trench

Continental Volcanic/Magmatic Arcs

Includes back-arc basins, fore-arc basins, and subduction zone trenches

Orogen

The mountain belt above subduction zone which is formed due to compression, plate collision,and tension

Orogen Basins

Fore-arc basins are intramontane basins, retro-arc peripheral foreland basin may be covered by epicontinental sea water, fresh water, or dry water with mostly continental sediments; are subduction zone related

Appalachian Foreland Basin

It is foreland basin containing Paleozoic sedimentary rocks of early Cambrian through early Permian age; located in East to Northeast USA

Arch

It is a topographic high which may be exposed to erosion and can be related to plate tectonics

Molasse

Sandstones, shales and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains, accumulating in a foreland basin

Flysch

A sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstone, deposited among deep marine environments

Intermontane

Includes normal faults, reverse faults, thrust faults, strike-slip faults or a similar combination, mountain ranges, and alluvial fans in basins

Death Valley

Located in California, it is the lowest point in North America at 86 metres below sea level, is an example of an endorheic basin, which are basins that collect water but have no outlet to the ocean

Pull-Apart Basins

A geological depression formed where two parallel strike-slip faults move apart, causing crustal stretching and sinking

Fluvial Systems

A natural system of a river and its associated landscape, including streams, valleys, floodplains, and terraces, where water flows across a landscape and carves it, transports sediment, and deposits it where deposition only possible if enough accommodation space; it is affected by tectonics, climate & amount of sediment supply