sedimentarystrucy\ture

1. Sedimentary Structures
PREPARED BY:
HAWKAR AGEEB
SARMAD DILSHAD
1
Soran University
Faculty of Science
Department of Petroleum Geosciences
Hawkargeology@gmail.com sarmadanesg@gmail.com

2. Introduction sedimentary structures
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Features within sedimentary rocks produced
during or just after sediment deposition.
Sedimentary structures are important attributes of
sedimentary rocks. They occur on the upper and
lower surfaces of beds as well as within beds.

3. Importance of sedimentary
structures
interpreting ancient depositional environments.
The direction of the currents that deposited the sediments.
Even the original way-up of the strata.
Direction of paleoslope.
 Ploting the paleoshore-line.
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4. Classification of sedimentary
structures
Sedimentary structures are divided into :-
-Primary structures are those generated in sediment during or shortly
after deposition. They result mainly from the physical processes,
Examples of primary structures include ripples, cross-bedding, and
slumps. Primary sedimentary structures are divisible into inorganic
structures, including those already mentioned and organic structures,
such as burrows, trails, and borings. Table.1
- Secondary sedimentary structures are those that formed sometime
after sedimentation. They result from essentially chemical processes,
such as those which lead to the diagenetic formation of concretions.
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5. Table.1 show Classification of Sedimentary Structure
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6. Primary inorganic sedimentary structures
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Three main groups can be defined by their morphology
and time of formation (Table 2).

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1- Predepositional (Erosional )Sedimentary Structures
These are some common erosional structures:
A-Flute Marks
B-Groove Marks
C-Tool Marks

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A- Flute Marks
Flute Marks : Flutes form when eddies in turbulent flow touch the
sedimentary surface .The deep narrow portion points upstream. Flute
casts are typical of sandstone turbidities. They also occur on the
underside of fluvial sandstones.

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B- Groove Marks
• Grooves form when objects such
as sticks or rocks are dragged
along the surface by the flow.

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C- Tool Marks
These form when an
object hits sediment
and bounces off or
skips. Impacts can
be meteor-size down
to pebble-size.

11. 2-Syndepositional sedimentary structure
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Syndepositional sedimentary structures are formed at the time of
deposition, in response to the flow characteristics of the
depositing fluid and the conditions of deposition.
A. Bedding and Lamination.
B. Ripples and Dunes.
C. Cross-Stratification.
D. Graded Beds.

12. A-Bedding and Lamination
Stratification is officially subdivided into bedding and lamination, depending upon the
thickness of the strata, and bedding and lamination are in turn subdivided according to
thickness.
Strata between 1 cm to 100 cm are known as beds
Strata less than 1 cm thick are known as laminations
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Beds
Lamination Lamination

13. B-Ripples and Dunes
Ripples Small ridges formed on
surface of sediment layer by
moving wind or water (shallow
water deposition).
Dunes form by the same processes
as ripples, only on a much larger
scale. Wind Formed Dunes.
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14. C- Cross-Stratification
Cross stratification is stratification that is
locally at some angle to the overall
stratification as a consequence of
changes in the geometry of the
depositional surface during deposition.
Cross stratification can be classified as
either cross bedding or cross lamination.
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15. cross-lamination and cross-bedding
If the bed form is a ripple the resulting structure is
referred to as cross-lamination.
Migration of dune bedforms produces cross-
bedding.
A single unit of cross-laminated, cross-bedded or
cross-stratified sediment is referred to as a bed-set.
Where a bed contains more than one set of the
same type of structure, the stack of sets is called a
co-set.
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16. cross-bedding
Basically, three main types of cross-
bedding can be defined by the
geometry of the foresetsand their
bounding surfaces:
A-Tabular planar cross-bedding
B-Wedge shaped cross-bedding
C-Trough cross-bedding
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17. D-Graded Beds.
The grain size in a bed is usually variable
and may show a pattern of an overall
decrease in grain size from base to top,
known as normal grading, or apattern of
increase in average size from base to
top, called reverse grading
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18. 3-Post depositional sedimentary structure
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A variety of structures are formed after deposition, some through
mass movement of sediment (slumping and sliding) and others
through internal reorganization by dewatering and loading.
A-slumping and sliding
B- Pseudo nodules
C- Loadcast Structure
D- Deformed Bedding

19. A-slumping and sliding
slump structure A sedimentary
structure consisting of
overturned folds, formed by the
mass sliding of the semi-
consolidated sediment downslop
e under the influence of gravity.
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Slump
Slide

20. B- Pseudo nodules
Nodules (also called concretions) commonly form in
sediments after deposition as a result of local cementation
in mud rocks, limestones and sandstones. Nodules may be
spherical through flattened and elongate to irregular in
shape.
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21. C- Load cast Structure
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• Load cast structures form by one bed
sinking into the one below it.
• Load casts are common on the soles of
sandstone beds overlying mud rock,
occurring as bulbous, rounded structures,
generally without any preferred elongation
or orientation

22. D- Deformed Bedding
Deformed bedding, and terms such as , convolute and contorted
bedding, can be applied where the bedding, cross-bedding and
cross lamination produced during sedimentation have been
subsequently deformed.

23. 4-Miscellaneous sedimentary structure
this kind is developed because of different reason.
Like (shirinkage cracks, syneresis cracks, rain print,
sand dike)
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A-Mud cracks(Shrinkage Cracks)
B-Rain-Spots

24. Mud cracks are polygonal cracks
that form when mud shrinks as it
dries.
They indicate that the mud
accumulated in shallow water
that periodically dried up.
Under-surface
0n-surface
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A-Mud cracks(Shrinkage Cracks)

25. B-Rain-Spots
Rain-spots are small depressions with rims, formed through the
impact of rain on the soft exposed surface of fine-grained
sediments.
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Top of the bed Bottom of the bed

26. - Primary organic sedimentary structures:
Biogenic sedimentary structures are formed through the activities of animals and
plants and vary widely from indistinct disruptions of bedding/laminations
(bioturbation) to discrete trace fossils (ichnofossils).
Biogenic structures include the following:
(1) Bioturbation structures (burrows, tracks, trails, root penetration structures).
(2) Biostratification structures (e.g. algal stromatolites).
(3) Bioerosion structures (borings, scrapings, bitings).
(4)Excrement (coprolites, such as fecal pellets or fecal castings).
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A- Bioturbation
B-Trace Fossils

27. A- Bioturbation
Bioturbation is the process of mixing sediment as organisms
crawl around feeding and burrowing in the sediment.
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28. B-Trace Fossils
Trace fossils are marks in the sediment that result
from organisms crawling, feeding, and
burrowing in or on the sediment. They can be
very helpful in determining age relations and
facies analysis.
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Recent Tracks of Gander Lasso Trail

29. Secondary sedimentary structures
They are structures formed by precipitation of mineral substances in the
pores of semi-consolidated or consolidated sedimentary rock or by
chemical replacement processes.
A-Nodules
B-Stylolites
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30. 30
Nodules of chert in chalk. Chert shows the typical conchoidal fractures, while the surrounding chalk show stylolites,
which are common diagenetic structures of carbonatic rocks. White Park Bay, Northern Ireland. Photo by Siim Sepp.

31. Reference:
-AN INTRODUCTION TO GEOLOGY, Chris Johnson, Matthew D. Affolter,
Paul Inkenbrandt, Cam Mosher ,Salt Lake Community College – 2017.
-PETROLOGY OF SEDIMENTARY ROCKS , SAM BOGGS, JR.
University of Oregon, 2009, SECOND EDITION
- (uomosul.edu.iq)
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