The document discusses various types of sedimentary structures classified based on their formation process. Primary structures form during deposition without external forces, while secondary structures form after deposition due to forces. Examples of primary structures include ripple marks, cross-bedding and flaser bedding. Secondary structures include sole marks, tool marks and groove marks formed by erosion. Chemical structures also form via processes like dissolution and precipitation. Sedimentary structures provide clues about depositional environments and sediment transport directions.

1. Presented by: Salman Naseer and
Ali Asghar Shahid
Bahria University Karachi

2.  Definition: These are the structures that are formed by the
sediment layers in the way they are deposited over each
other.
 Classified on two approaches, one is morphologic, the other
genetic.
 A purely morphologic classification is rather artificial and leads
to grouping of unrelated structures.
 Genetic classification group’s structures according to the
process involved in their formation, such as, biogenetic,
hydrodynamic or rheologic.

3.  Importance of Sedimentary Structure:
 Study of sedimentary structures is important
because they are the most valuable features
for interpreting depositional environment.
 We know a lot about how most structures are
formed, so finding them in the rocks can tell
you a lot about the conditions of deposition.
 They are much more useful than textural
things like grain-size distribution and grain
shape.

4. Primary structures
Secondary structures

5. Definition:
They are also known as Pre-
depositional structures.
The structures formed during deposition
without any forces applied.

6. Definition:
They are also known as Post-
depositional structures.
The structures formed after deposition with
some forces applied.

7. Physical
Chemical
Biogenic

8. Massive bedding: A thick bed which is
structure less.

11. Progradation is an example of it’s
depositional environment

12. Massive bedding Uses:
Shows the depositional environment
changed from a regularly repeating
depositional system to one with very little
change over time.

13. Graded bedding: It is bedding in which the
particles are sorted according to density,
size and shape.

14. Graded bedding types:
Normal Grading: If the particle size
decreases upward, the bed is said to be
normally graded.
Reversely Graded: If the particle size
increases upward, the bed is said to be
reversely graded or inversely graded.

16. fluvial:Diagram illustrating the formation of
a graded bed (turbidite). Slope failure
produces turbulent suspension that
moves/accelerates downslope. Once it
reaches the flat deep sea regions, it slows
down due to friction, and gradually the
sediment settles out of suspension. Larger
grain sizes settle out first, and then
successively smaller ones.

18. Use:indicator of upward and downward
direction in deposition
Can be useful for mapping purpose
Can also be useful for marking top and
bottom of strata.

19. Ripple Marks: Wavy feature formed by
wind, wave or current. Streamlines lie
parallel to a flat bed but where there is an
irregularity such as a step in the bed
caused by an accumulation of grains, the
streamlines converge and there is an
increased transport rate.

21.  Ripple Marks types:
 Asymmetrical definition: These are created a one
way current( e.g. river) or the wind ( e.g.
desert).This create ripple with still pointed crests
and rounded troughs, it inclined in the direction of
the current.
 Current ripples do not form in sediment coarser
than 0.6 mm in diameter (coarse sand).
 Current ripples can develop in almost any
environment river, delta, shoreline, offshore shelf
and deep sea. • On the basis of shape, three types
of current ripple are common: straight-crested,
sinuous or undulatory, and linguoid ripples

24. Wind ripples and dunes: These are
asymmetric structures like current ripples.
Wind ripples typically have long, straight,
parallel crests with bifurcations like
waveformed ripples.

26. Ripple Marks types:
Symmetric definition: They are formed by
two way current, often found on beaches.
They are wave dominating. Nearly pointed
crest and rounded trough and it doesn’t
inclined in the direction of the wave. non-
cohesive sediment, medium silt to coarse
sand grades, and they are typically
symmetrical in shape.

29. Tidal environment and eolin environment.
Use: direction of the flow of air or water
Moreover it also tells the stregnth of wind
or water.

30.  Cross bedding: It is formed on inclined surface during
deposition by crossing a bed to another bed. The set
height is generally greater than 6 cm and the individual
cross-beds are many millimeters to 1 cm or more in
thickness.
 Most cross-stratification arises from the down current
migration of ripples, dunes and sand-waves when
sediment is moved up the stoss side and then
avalanches down the lee-side of the structure.
 Foresets- steeply dipping parts of the cross-strata,
have either angular or tangential contacts with
horizontal.
 Bottom sets- The lower less steeply dipping parts.

34. Cross bedding: Common two types are,
Tabular and wedge cross-bedding consists
of mostly planar cross-beds which have an
angular contact with the basal surface of
the set. On the bedding surface, planar
cross-beds are seen as straight lines.
Trough cross-beds usually have tangential
bases, and in bedding-plane view the
cross-beds have a nested, curved
appearance.

36. Use: The inclination of the cross-beds
indicates the transport direction and the
current flow (from left to right in our
diagram).The style and size of cross
bedding can be used to estimate current
velocity, and orientation of cross-beds
allows determination direction of paleoflow.

38. Flaser bedding: It is a bedding in which
high energy environment is involved which
forms a bedding pattern in which sand is a
dominating layer which is later infilled by a
mud layer.
These structures often are considered to
form mostly in tidally influenced
environments.

40.  Lenticular: the bedding which is opposite to flaser bedding in
which mud is the dominating layer and a thin layer of sand
deposited at trough. Its bedding display is a 'lens-like' shape.
 Formed during periods of slack water, mud suspended in the
water is deposited on top of small formations of sand once the
water's velocity has reached zero.
 They are commonly found in high-energy environments such
as the intertidal and supratidal zones.
 Geologists use lenticular bedding to show evidence of tidal
rhythm, tidal currents and tidal slack, in a particular
environment.

42.  Convolute: Convolute bedding forms when
complex folding and crumpling of beds or
laminations occur.
 Beds of fine sand, up to a meter thick,
deposited rapidly by such events as turbidity
currents.
 The beds have planar lower and also upper
contacts, but the bed is internally folded into
broad synclines and sharp to dome-shaped or
even mushroom-shaped anti-clines, which
usually die out upward to planarity at the
upper contact.

44.  The most common places for Convolute
bedding to materialize are in deep water
basins with turbidity currents, rivers,
deltas, and shallow-marine areas with
storm impacted conditions. This is because
these environments have high deposition
rates, which allows the sediments to pack
loosely

45. Sole marks : Erosional marks formed by
scouring of bed by unidirectional flows.
Forms in marine environment, This is
usually a sediment gravity flow in a
moderately deep marine environment but
strong currents in other situations can
make sole marks as well. Used for paleo
flow direction.

47.  Sole Marks types:
 Flute Casts: Geometrical features produced
on a sediment bed by erosion by a strong
current. Flutes are heel-shaped hollows,
scoured into mud bottoms. Each hollow is
generally infilled by sand, contiguous with the
overlying bed.
 As the current velocity declines, flute erosion
ceases and the hollows are buried beneath a
bed of sand.
 Formed in shallow marine environments.

48. Uses of Flute Casts:
Indicators of turbidites, shallow marine and
non-marine environments.

49. Tool Marks: By mechanical disruption of
the bed by large objects carried by a
strong current. Tool marks are erosional
bottom structures.
They are irregular in shape, both in plan
and cross-section, though they are roughly
oriented parallel with the paleocurrent

51. fluvial deposits and marine storm deposits
They are valuable indicators of
paleocurrent direction and also give some
information about the nature of the clay
bottom and the sediment transport
mechanism operating in the flow that
deposited the overlying sand.


52. Groove Marks:
They are long, thin, and straight erosional
marks.
Contains mud and overlain by sand.
Few millimeters deep or wide, but they
may continue uninterrupted for a meter of
more.
They are developed in downcurrent
situation than flutes.

54. groove mark A linear groove, cut in a
muddy substrate by the dragging of an
object through the sediment by flowing
water. The orientation of the groove will be
parallel to the current direction.
Subsequent infilling of the groove by
sediment will result in a groove cast being
preserved on the base of the overlying
bed.

55. Balls and Pillows: In more extreme
loading, whole masses of the overlying
bed sink down into the underlying material.
Masses end up with concave-up
stratification that is terminated abruptly
around the margins of the sunken mass.
This called ball-and-pillow structure
 earthquakes, erupting volcanoes,
or meteoric impacts can create these
formations.

57. Definition: These structures are formed by the chemical
disruption of the sediments.
Types: Solution Structures:
 Stylolites
 Mud cracks
 Vugs
Accretionary Structures:
 Nodules
 Concretions
 Crystal aggregates
 Veinlets
 Color Banding

58.  Stylolites: Consisting of a series of relatively small,
alternating, interlocked, tooth like columns of stone; it
is common in limestone, marble, and similar rock.
 Insoluble minerals, such as clays, pyrite and oxides,
remain within the stylolites and make them visible.
 They occur most commonly in homogeneous rocks,
carbonates, cherts, sandstones, but they can be found
in certain igneous rocks and ice.
 Their size vary from microscopic contacts between two
grains (microstylolites) to large structures up to 20 m in
length and up to 10 m in amplitude in ice.
 Stylolites usually form parallel to bedding, because of
overburden pressure.

59. Formed by the result of chemical solution
by groundwater circulating through semi-
consolidated or consolidated, hardened
rock.

61. Mud cracks: These structures form when
the clay-rich sediments found in muds dry
and shrink. As the sediment shrinks crack
begin to form in the sediment creating
polygonal patterns called mud cracks.
Mud cracks form in any environment that
allows for the wetting and subsequent
drying of sediment such as marshes,
seasonal rivers, or lake shores.

63. Use: They indicate that the mud
accumulated in shallow water that
periodically dried up.
Also tells us about the environment
whether it is arid or semi arid.

64.  Vugs: They are small to medium-sized cavities
inside rock that may be formed through a variety of
processes.
 Most commonly cracks and fissures opened by
tectonic activity (folding and faulting) are partially filled
by quartz, calcite, and other secondary minerals.
 Vugs may also result when mineral crystals or fossils
inside a rock matrix are later removed through erosion
or dissolution processes, leaving behind irregular
voids.
 Fine crystals are often found in vugs where the open
space allows the free development of external crystal
form.

66.  Nodules: In sedimentology and geology, a
nodule is small, irregularly rounded knot,
mass, or lump of a mineral or mineral
aggregate that typically has a contrasting
composition, such as a pyrite nodule in coal,
a chert nodule in limestone, or a phosphorite
nodule in marine shale, from the enclosing
sediment or sedimentary rock.
 Minerals that typically form nodules include
calcite, chert, apatite (phosphorite), anhydrite,
and pyrite.

68.  Concretions: A concretion is a hard, compact
mass of matter formed by the precipitation of
mineral cement within the spaces between
particles, and is found in sedimentary rock or
soil. Concretions are often ovoid or spherical
in shape, although irregular shapes also
occur.
 There is an important distinction to draw
between concretions and nodules.
Concretions are formed from mineral
precipitation around some kind of nucleus
while a nodule is a replacement body.

70.  Color Banding: They are formed in sedimentary rocks
when some variation occur in the mineral composition
or due to the cementing material present in the rock.
 Liesegang bands are colored bands of cement
observed in sedimentary rocks that typically cut-across
bedding.
 These secondary sedimentary structures exhibit bands
of minerals that are arranged in a regular repeating
pattern.
 Frequent occurrence in sedimentary rocks, rings
composed of iron oxide can also occur in permeable
igneous and metamorphic rocks that have been
chemically weathered.

72. Biogenic sedimentary structures: Biogenic
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.

73. Tracks and trails: These features result
from organisms moving across the
sediment as they walk, crawl, or drag their
body parts through the sediment.

75. Molds: Reproduction of the inside or
outside surface of a living thing.
Cast : Duplicate of the original organism;
usually formed by replacement of inside of
living thing

76.  Crawling traces: trails, uncomplicated pattern
linear
 Grazing traces: more complicated surface trails,
symmetrical or ordered pattern.
 Resting traces: impression of where animal rested
during life (but not a fossil mold).
 Dwelling structures: simple to complex burrow
systems, burrows can be lined or small ball of
mass.
 Feeding structures: simple to complex burrow
systems commonly with well organized and
defined branching pattern indicating systematic
reworking of sediment.

78. Burrow Marks:
Any organism that burrows into soft
sediment can disturb the sediment and
destroy many of the structures.
 If burrowing is not extensive, the holes
made by such organisms can later become
filled with water that deposits new
sediment in the holes.
 Such burrow marks can be excellent top
and bottom indicators.

80. Boring : A boring is any biogenic structure
that involves erosion of an already
consolidated substrate by an organism; the
process of forming a boring by an
organism is bioerosion.

82. Bioturbation: One of the agents of organic
weathering, bioturbation is the disturbance
of the soil or sediment by living things.
Bioturbation aids the penetration of air and
water and loosens sediment

84.  Stromatolites: They are organically formed,
laminated structures composed of fine silt or
clay-size sediment or, more rarely, sand-size
sediment. • Most ancient stromatolites occur
in limestones however, have also been
reported in siliciclastic sediments.
 They are organosedimentary structures
formed largely by the trapping and binding
activities of blue-green algae
 The laminated structure forms because fine
sediment is trapped in the very fine filaments
of algal mats.