Depositional Environment & Facies Analysis

Vocabulary flashcards covering key terms from the lecture on depositional environments and facies analysis.

Depositional Environment

A portion of the Earth’s surface with characteristic physical, chemical and biological conditions where sediments accumulate.

Clastic Sediments

Fragments of pre-existing rocks that are transported and deposited in various settings such as mountains, plains, coasts and deep marine basins.

Continental Environment

Depositional setting located on land; includes fluvial, desert, lacustrine, glacial and alluvial systems.

Transitional Environment

Zone between land and sea (e.g., deltas, tidal flats, lagoons, barrier islands) where both marine and continental processes interact.

Marine Environment

Depositional realm below normal wave base; ranges from continental shelf to deep-ocean floor and includes neritic, oceanic and deep-marine settings.

Fluvial Environment

River-related depositional system composed of channels, point bars, floodplains and swamps.

Alluvial Fan

Fan-shaped, high-energy deposit at the base of mountains produced by stream and debris-flow processes.

Braided Stream

River system with multiple, shifting channels separated by bars, depositing coarse gravel and sand.

Meandering Stream

Single-channel river that migrates laterally, producing point-bar sands and floodplain muds.

Deltaic Environment

Marginal-marine system where a river enters standing water, forming delta plain, delta front and prodelta subenvironments.

Delta Plain

Uppermost, subaerial part of a delta dominated by distributary channels, levees and swamps.

Delta Front

Subaqueous, coarse-grained slope of a delta situated seaward of the delta plain.

Prodelta

Finest-grained, deepest part of a delta where clay and silt settle from suspension.

Tidal Flat

Low-relief, intertidal surface that alternately floods and drains, producing wavy, flaser and lenticular bedding.

Neritic Zone

Shallow-marine area on the continental shelf, generally above 200 m water depth.

Continental Shelf

Submerged, gently sloping extension of a continent seaward of the shoreline.

Continental Slope

Steep slope connecting the continental shelf to the deep-ocean floor; site of gravity-flow deposits.

Deep-Ocean Floor

Abyssal plain environment characterized by fine pelagic sediments and turbidites.

Facies

Body of rock with a distinctive combination of lithology, structures and fossils that differentiates it from adjacent units.

Facies Model

Three-dimensional conceptual diagram summarizing the spatial distribution of facies within a depositional system.

Facies Analysis

Method of interpreting sedimentary rocks by examining facies, facies associations and their successions.

Facies Association

Predictable assemblage of genetically related facies that collectively indicates a specific depositional environment.

Facies Succession

Vertical stacking pattern of facies reflecting temporal changes in depositional conditions.

Sedimentary Facies

Observable response element of a sedimentary environment, including geometry, texture, structures and fossils.

Process-Response Model

Concept linking dynamic environmental processes (waves, currents, biology) to the resulting sedimentary facies.

Sedimentary Structure

Physical feature formed during or shortly after deposition (e.g., bedding, cross-lamination, ripples).

Planar Lamination

Thin, horizontal layers produced by low-relief plane-bed flow or suspension settling.

Ripple Cross-Lamination

Inclined, small-scale laminae generated by migration of ripples under unidirectional flow.

Cross-Bedding

Tabular or trough-shaped sets of inclined strata produced by migration of dunes or bars.

Hummocky Cross-Stratification (HCS)

Undulating cross-strata formed by storm-generated combined flows in shallow marine settings.

Bouma Sequence

Ideal vertical succession (Ta–Te) describing graded turbidite deposits generated by gravity flows.

Bedform

Morphological feature (ripples, dunes, plane beds) created by fluid flow over a sediment surface.

Bioturbation

Disruption of sediments by organisms, producing burrows and mottled textures.

Ichnofabric Index

Semi-quantitative scale describing the intensity of bioturbation in a sediment or rock.

Grain Size

Diameter of sediment particles; key parameter for facies description and flow interpretation.

Sorting

Degree of uniformity of grain sizes within a sediment, reflecting transport energy and duration.

Heterolith

Interbedded sandstone and mudstone displaying rhythmic or irregular alternations (flaser, wavy, lenticular).

Lenticular Bedding

Heterolithic structure with isolated sand lenses in a muddy matrix, typical of slack-water tidal flats.

Flaser Bedding

Thin mud drapes within sandy ripple cross-lamination, indicating alternating currents and suspension fallout.

Sedimentary Log

Vertical graphical record of lithology, grain size, structures and thickness used to document facies successions.

Uniformitarianism

Principle expressed as “the present is the key to the past,” stating that ancient deposits formed by processes observable today.

Environmental Analysis

Study of rock properties (textures, structures, fossils) that possess environmental significance to deduce depositional settings.

Process Element

Dynamic aspect of a sedimentary environment, including physical, chemical and biological processes acting during deposition.

Response Element

Resulting sedimentary facies and properties produced by the operation of environmental processes.