Primary sedimentary structures are features formed during deposition of sedimentary rocks that provide information about the depositional environment. Some key primary sedimentary structures mentioned in the document include stratification, cross-bedding, ripples, graded bedding, sole marks, fossils, rip-up clasts, rainprints, desiccation cracks, imbrication, flute casts, soft-sediment deformation structures like slump folds, flame structures and clastic dikes. These structures can be used to determine paleocurrent direction, relative age, top vs bottom of strata, and the environmental conditions during deposition.

1. Prepared by
Azhar Mahmood

2. Structures acquired during
deposition of
sedimentary rock unit are
called as primary
sedimentary structures.

3.  These are useful for maping purpose.
 These are useful to mark paleocurrent
direction.
 These are also use for marking of top and
bottom of strata.
 Environment of deposition can also have
been marked by primary sedimentary
structures.
 Relative age is also marked by them.

4. Stratification - horizontal bedding is most common
structure in sedimentary rocks

5. Cross-bedding - inclined stratification recording
migration of sand ripples or dunes

6. Ripples - undulating bedforms produced by
unidirectional or oscillating (wave) currents

8.  Asymmetrical ripple marks describe the past
flow direction
 Symmetrical marks top and bottum

9. Graded bedding - progressive decrease in grain size
upward in bed
• indicator of upwards direction in deposit
• common feature of turbidites

10.  It,s useful for maping purpose.
 These are also use for marking of top and
bottom of strata.

11. Sole marks - erosional grooves and marks formed by
scouring of bed by unidirectional flows
• good indicators of current flow direction

12. Fossils – preserved remains of organisms, casts or moulds
• good strain indicators
• determine strain from change in shape of fossil
• relative change in length of lines/angle between lines

13. are pieces
of shale or mudstone created
when an erosive current
containing suspended
sediment flows over a shale
bed, tears up pieces of it, and
carries these "rip ups" some
distance

14.  Use for top and bottum
 Use for determine relative age

15.  are a geological feature
characterized by small
craterlike pits with slightly
raised edges that are the
result of the impact of rain
on soft sediment surfaces

16. are polygonal cracks that form
when
mud shrinks as it dries.They
indicate that the
mud accumulated in shallow
water that periodically dried
up.

17.  It,s tell us
 Top and bottum
 Environment [Arid,Semi Arid]
 Condition

18.  Imbrication is the
orderly, overlapping
arrangement of
flattened or sub-
spheroidal grains in
the direction of flow.
Flow in this case is
usually water flow,
but it can be other
types of fluid flow

19.  To determine paleo-path of rivers and
channel
 Current direction {which is always opposite to
dip direction}

20.  When a river flow in the center of riverV type
structure formed by loose material are called
flute cast

21.  In it deformation as well as
sedimentation carried out side
by side
 S.S.D = Deformation +
Sedimentation
 Types
 1: Slump fold
 2: Flame structures
 3: Clastic Dikes

22.  A slump is a form of mass wasting that occurs
when a coherent mass of loosely
consolidated materials or rock layers moves a
short distance down a slope Movement is
characterized by sliding along a concave-
upward or planar surface. Causes of slumping
include earthquake shocks, thorough
wetting, freezing and thawing, undercutting,
and loading of a slope

23.  A term introduced byWalton
(1956, p. 267) for a
sedimentary structure
consisting of sharp-crested
wave- or flame-shaped
plumes of mud that have
risen irregularly upward into
an overlying layer, generally
a rapidly deposited sand

24.  A clastic dike is a seam
of sedimentary material
that fills an open fracture in
and cuts across sedimentary
rock strata or layering in
other rock types. Clastic
dikes form rapidly by
fluidized injection
(mobilization of pressurized
pore fluids) or passively by
water, wind, and gravity

26.  They extend parallel
to passive
margins that have
high sediment supply
.Their fault plane
dips mostly toward
the basin and has
long-term
continuous
displacement