Depositional Environments and Sedimentary Facies

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Depositional Environments and Sedimentary Facies

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Depositional Environments

• Areas of the Earths surface where distinct
  processes generate specific geological
  (sedimentary) products

-Physical -Biological -Chemical
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Sedimentary (litho) Facies and (litho) Facies
Analysis

• Sedimentary (litho) facies
• Lithostratigraphic Units (time independent)
• Defined by sum total of (relevant) rock
  properties
• Reflects processes during genesis and may include
• Lithology
• Sedimentary Structures
• Fossils
• Bedding style and geometry (on various scales)
• Paleo-sediment transport indicators

• e.g. hummocky cross stratified, Zoophycus
  burrowed, fine- to medium-grained, sandstone

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Facies Analysis, Facies Associations, Facies
Sequences, and Facies Models

• Otbo reoccurring associations of sedimentary
  facies
• (hummocky cross stratified, Zoophycus burrowed,
  fine- to medium-grained, sandstone Storm Shelf,
  Hummocky Sequence )

• It is possible to more precisely determine the
  sum total of processes active at the site of
  deposition and interpret depositional
  environment
• Facies sequences are recurring (in the geological
  record) facies associations which occur in a
  particular order due to the inherent temporal
  changes in depositional conditions in particular
  depositional environments

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Common Siliciclastic Stratigraphic Successions

• Vertical successions characterized by lithology,
  associations and vertical arrangement of
  sedimentary structures
• Indicative of particular sedimentary depositional
  environments
• Expression of Walthers Law
• Reflects Autocyclicity
• stratigraphic variability inherent to a
  particular depositional environment

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Distinctive and Common Sedimentary Facies
Associations

• High gradient, low sinuosity, sand and gravel
  dominated
• BRAIDED RIVER SYSTEM

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Distinctive and Common Sedimentary Facies
Associations

• Low Gradient, high sinuosity, mud to sand
  dominated
• MEANDERING RIVER SYSTEM

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Distinctive and Common Sedimentary Facies
Associations

• Sediment gravity flow-dominated (turbidity
  currents), deep water sediment dispersal
• SUBMARINE FAN SYSTEM

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Facies Analysis, Facies Associations, Facies
Sequences, and Facies Models

• Otbo reoccurring associations of sedimentary
  facies
• (hummocky cross stratified, Zoophycus burrowed,
  fine- to medium-grained, sandstone Storm Shelf,
  Hummocky Sequence )

• It is possible to more precisely determine the
  sum total of processes active at the site of
  deposition and interpret depositional
  environment
• Facies sequences are recurring (in the geological
  record) facies associations which occur in a
  particular order due to the inherent temporal
  changes in depositional conditions in particular
  depositional environments

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Common Sedimentary Facies Associations in
Carbonate Dominated Environments
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Common Sedimentary Facies Associations in
Carbonate Dominated Environments

• Carbonate sediment dominated, rimmed shallow
  marine shelf
• RIMMED CARBONATE SHELF SYSTEM

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Facies Analysis, Facies Associations, Facies
Sequences, and Facies Models

• Facies Models are a general summary of a given
  depositional environment or depositional system
• Lithostratigraphic unit representing depositional
  processes and geographic location

• The apparent existence of order in Nature suggest
  that there are (and have been through geological
  time) a limited number of different and
  recognizable depositional systems
• These depositional systems are identified
  through the use of
• Facies Models

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Facies Analysis and Walthers Law

• It is a basic statement of far reaching
  significance that only those facies and facies
  areas can be super imposed primarily that can be
  observed beside each other at the present time

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Facies Analysis and Walthers Law

• Gradational (vertical) transitions from one
  facies to another indicate original adjacency and
  genetic relationship during formation.
• Sharp/erosional (vertical) contacts between
  facies provides NO evidence of contemporaneous
  genetic relationship of depositional environments

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Depositional Systems Analysis

• Depositional Systems (lithostratigraphic units)
• Three dimensional assemblages of lithofacies,
  which are interpreted to be genetically linked
  by process and environment

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Actualism and "Genetic Stratigraphy"

• Recognition of Uniformitarianism
• the relationship between modern processes of
  sedimentation and the rock record

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Lithostratigraphy

• Formations, Members, Groups, etc.
• Material Units and "Classical Layer Cake
  Stratigraphy
• catastrophism continuous layering time
  equivalence
• NO!
• Further organization and subdivision of the rock
  record otbo
• Relative age
• Superposition, unconformities, cross cutting
  relationships, included fragments
• Original Horizontality
• Lateral Continuity

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Objective Subdivision of the Stratigraphic Record
Into Distinct Lithostratigraphic Units

• Formations
• with a type section, geographic or lithologic
  name, and definition based on
• limited and distinctive lithologic variability
• consistent stratigraphic context
• extensive map distribution in the surface or
  subsurface

• Groups and Supergroups
• Are formations lumped otbo stratigraphic
  association
• Members and beds
• Subdivisions of Formations
• lithostrat units with less areal extent defined
  as it is useful