Conclusion and Economic Importance
S E D I M E N T A R Y S T R U C T U R E S C L A S S I F I E D
Physical sedimentary structures
Physical (inorganic) structures are sedimentary features formed by physical
processes without the influence of organism.
Primary sedimentary structures are the most important.They are mechanical
structures formed during deposition of the sediments.
The simplest sedimentary structures is plane bedding.They form in practically all
sedimentary environments and under a variety of conditions.
Three basic mechanism can form plane bedding: sedimentation from suspension,
horizontal accretion from a moving bed load, and encroachment into the lee of
Bed forms Generated By Unidirectional Currents
As soon as flow attains a force sufficient to erode particles from the
bed, sediments are transported in a set of structures of the bed called
If they are latter buried and preserved, they will form sedimentary
Finer scale plane bedding (less than
1 cm thick).
It can be form by alteration of light
and dark layers such as glacial
Lamination in mud is usually the
result of slow steady deposition.
Absence of lamination in mud is due to flocculation (clumping of clays before they
settle) or to secondary bioturbation.
Laminated sands are the results of rapid deposition, often by a single
Lack of lamination may be the result of bioturbation.
Studies have shown that there is a
predictable sequence of bedforms that
depend on velocity, grain size, depth of
In Sand that is finer than 0.7 mm (coarse
or finer) the first feature to form is
Typically their spacing is 10 to 20 cm or less,
and their height is less than a few
As flow velocity increase the ripples enlarge
until they form sand waves, and finally
dunes, which have spacing from 0.5 to 10m
or more and heights of tens of cm to a
meter or more.
In deeper currents, greater flow velocity is
required to produce the large bedforms.
With increasing flow velocity, dunes are
destroyed and the turbulent flow which was
out of phase turns into sheetlike flow in
phase with the bedform. It forms plane beds.
At higher velocities plane beds are replaced
by antidunes of up to 5m spacing. Low dip
angles of 10 degrees or less, eventually
chutes and pool.
Ripples & dunes
Is produced by migrating
Terminology for the shape of the crests of ripples
and dunes formed by unidirectional currents.
Ripple types and variation with flow regime
Interference pattern form
In symmetrical ripples from
Two coexisting wave sets
In a modern tidal flat.
alternating tidal currents.
Bedform generated by
In tidal regions the most significant features are caused by the mixing of sand- and
mud-sized fractions from the asymetrical currents. Lenticular bedding occur when
sand is trapped in troughs in the mud as sand waves migrate across a muddy
substrate. If mixing produces minor mud layer in a sandy substrate the pattern is
called flaser bedding.
Lenticular bedding Flaser bedding
Small-scale erosional features on a bed surface are referred to as sole
marks.They are preserved in the rock record when another layer of
sediment is deposited on top leaving the feature on the bedding plane.
Sole marks may be divided into those that form as a result of turbulence in
the water causing erosion (scour marks) and impressions formed by
objects carried in the water flow (tool marks).They may be found in a very
wide range of depositional environments, but are particularly common
in successions of turbidites where the sole mark is preserved as a cast at
the base of the overlying turbidite.
Bio-genic Sedimentary Structures
Bio-genic structures result from bioturbation, the post-depositional
disturbance of sediments by living organisms.This can occur by the organisms
moving across the surface of sediment or burrowing into the first few
centimeters. It is usually contemporaneous with deposition.
The organisms that cause these alterations in the sediments have a dual
affect.They physically and chemically alter the original deposit, and they give
some useful information about the bottom conditions at the time of deposition.
Depending on the location, these animals can affect up to 90% of the
sediment surface. As a result, this biological action can completely destroy
primary laminations and the original orientation of sediment particles.
There are usually significant changes in the formations porosity and
permeability.This can help determine the origin and magnitude of any abnormal
pore pressures. It can also enhance the tendency for slumping and sliding on
steep continental margins, as the sediment shear strength is decreased.
Conclusion and Economic Importance:
Having gone through the study of sedimentary structures, it is necessary to
note that they can be used to determine depositional processes, being that
depositional processes occurs in several environments, and few structures are
immediately diagnostic of a specific environment.
Sedimentary structures can also indicate the direction of paleocurrent
flow, paleoslope, paleogeography and sand-body trend.
They record the processes that occur during deposition and so
help in interpreting sedimentary and post-depositioal processes
Help in defining geological history and surface processes .
Cross-beds within ancient rocks helps to tell the direction a stream flowed
millions of years ago or the direction of prevailing wind in the past.
Baker hughes INTEQ, Petroleum geology.
Principles of Sedimentation and Stratigraphy.
Sedimentary structures, Wikipedia.