Facies Concept

Definition
Facies is a body of rock characterized by a particular
combination of lithology, physical and biological
structures that bestow an aspect that different from
the bodies of rock above, below and laterally adjacent
The facies concept refers to the sum of
characteristics of a sedimentary unit, commonly at a
fairly small (cm-m) scale including:
 Lithology
 Grain size
 Sedimentary structures
 Color
 Composition
 Biogenic content

Facies associations/assemblage :
o constitute several facies that occur in combination, and
typically represent one depositional environment (note
that very few individual facies are diagnostic for one
specific setting)
o groups of facies genetically related to one another and
which have some environmental significance (Collinson,
1969)
Facies successions:
 a progressive change in certain facies properties in a
specific direction (vertically or laterally).

o Facies analysis is the interpretation of strata in
terms of depositional environments (or
depositional systems), commonly based on a
wide variety of observations
o Facies Model is a general summary of a
particular depositional system, involving many
individual examples from recent sediments and
ancient rocks

Why do we need to understand the
deposits of differing environments?
 Sedimentary & geological history (small-large scale)
 Economic importance -e.g. hydrocarbons, water
 Economic importance -minerals and metals (e.g. gold-diamonds-
gypsum-aggregates)
 Prediction/management of contemporary
environments

Every depositional environment puts its own distinctive imprint on the
sediment, making a particular facies. Thus, a facies is a distinct kind of
rock for that area or environment.
Sandstone facies (beach/shallow marine environment)
Shale facies (offshore marine environment)
Limestone facies (far from sources of terrigenous input/ deep sea)

Johannes Walther
(1860-1937)
Walther’s Law: ‘Facies
adjacent to one another
in a continuous vertical
sequence also
accumulated adjacent to
one another laterally’
Means that two different facies found superimposed on one
another and not separated by an unconformity, must have been
deposited adjacent to each other at a given point in time

 Generally, facies are distinguished by what aspect of the
rock or sediment is being studied.
Lithofacies
• Facies based on petrological characters such as
grain size and mineralogy
Biofacies
• Facies based on fossil content (flora & fauna)
Ichnology
• Facies based on trace fossil

o Presence of cross bedded sandstone can form during
deposition in deserts, rivers, deltas, lakes, beaches and
shallow marine
o In contrast, present of hermatypic corals indicate that the
sediments were deposited in shallow clear and warm
seawater

Ripples developed on surface of a sand body. This texture can be diagnostic of
depositional environment. These ripples are diagnostic of near-shore tidal
environment, but ripples also develop in fluvial (river) and aeolian (air, sandstorm)
environments.

Facies = Lithofacies (core log sample)

Facies associations/assemblage, facies sequences and facies codes

Facies Association
(combination few facies)

Facies Succession
(progressive change)
Beach environment
Tidal environment

Facies Succession
Beach Env.
Deltaic Env.

Sedimentary Facies :
1. Non-Marine Environment:
• Lacustrine
• Fluvial & Alluvial Fan
• Delta & Estuarine
2. Coastal and Shore face Environment:
• Estuarine
• Turbidite
3. Marine Environment:
• Turbidite

Braided Stream
Alluvial Fan & Fluvial System
Meandering

Delta & Estuary
Marine delta
(estuary)
River delta

Turbidite System
(Deep sea depositional)

Facies Concept

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Facies Concept