Download Structural Geology (Geol 305) Semester (071)

Structural Geology
(Geol 305)
Semester (071)
Dr. Mustafa M. Hariri
Non-Tectonic Structures
Objectives
By the end of this unit you will be able to know:
„ The Fundamental Concepts in Geology and their
importance
„ What is the Non-Tectonic Structures and how they
formed?
„ The difference between Tectonic and Non-Tectonic
Structures
„ The different types of Non-Tectonic Structures
FUNDAMENTAL CONCEPTS
These concepts are very important to study
structural geology and they help in solving the
structural problems
1) Doctrine of uniformitarianism:
The present is the key to the past (Processes are
taking place today within the earth are
similar to the ones took place in the past and
to that will take place in the future) example
sand bars and beaches
Can't be applied to: Iron to iron formation in lake superior
(different atmospheric composition)
Contrast in nature of Archean and proterozoic crusts (differences
in processes)
2) Law of superposition:
Within layered sequence oldest rocks occur at the
base of sequence and younger rocks toward
top unless the sequence is inverted
3) Law of original horizontally:
Sediments and Sedimentary rocks form in
horizontal to nearly horizontal orientation at
the time of deposition.
FUNDAMENTAL CONCEPTS
4) Law of crosscutting relationships
(structural relationships):
An igneous body or any structure (fold or
fault) must be younger than the rocks
it cuts ( the rocks contain the igneous
body or structure must have been
there before the structures or the
igneous body)
5) Law of faunal succession:
The fossil organisms should be
systematically changed, possibly more
advanced toward the top of the
sequence (Permits determination of
whether the sequences is upright or
overturned)
6) Multiple working hypotheses:
Consider more than one assumptions and
test them until you are sure from one
of them.
FUNDAMENTAL CONCEPTS
7) Outrageous hypothesis:
Consider the data to reach to
solution and illuminate
other hypothesis
8)Pumpelly’s rule:
Small structures are a key to
and mimic the styles and
orientation of larger
structures of the same
generation within a
particular area.
NONTECTONIC STRUCTURES
Those structures include the primary sedimentary
and volcanic structures. They are useful in
determining the facing direction in a sequence
of rocks
Examples of these structures are:
„ Bedding features
„ mud cracks
„ ripples marks
„ sole marks
„ vesicles
Bedding Planes
Nontectonic Structures can be distinguished from
Tectonic Structures by the following:
1)Nontectonic structures usually older than
the tectonic structures
2)Tectonic structures usually show a
parallel orientation over wide area
compare to the nontectonic ones.
3) Small structures in tectonic mimic large
size ones.
Non-Tectonic Structures
Primary Sedimentary Structures
BEDDING
Bedding planes represents
mechanical zones of weakness
and they form when there is a
compositional or textural
difference is exist between two
beds.
Examples are:
Different grain sizes
Different compaction
Discontinuity of deposition
.
Bedding Planes
Graded bedding contain a range of
particle sizes from large at the
base to small at the top.
(boulder…… to…….clay)
Graded bedding is important in
determining the facing direction
They are useful in determining the
facing direction.
Graded Bedding
Non-Tectonic Structures
Primary Sedimentary Structures
BEDDING
Cross bedding forms in sediments
transported by water or wind
Types:
tangential
planar
trough
Cross Bedding
festoon
For finer sediments and small scale
ripple
Hummocky
Mud cracks form by extensional
cracks due to drying of fine grain
sediments deposited by water.
Mud Cracks
Non-Tectonic Structures
Primary Sedimentary Structures
BEDDING
Ripple Marks form where sediments is
moved by a current. They are very
common along beaches and streams
as well as deeper water, where bottom
currents or surface waves interact with
bottom sediments.
Types:
1) current they are asymmetric, their
steep sides face downstream in the
direction of transport. They are not
useful in determining the facing
direction
2) oscillatory they are symmetrical and
consist of high and low crests
They form by back and forth motion of
water (such as lake)
Ripple Marks
They are useful in determining the facing direction
as the crests have sharp peaks separated by
rounded trough.
Non-Tectonic Structures
Primary Sedimentary Structures
BEDDING
Rain Imprints form where rain falls on fine
sediment and preserved in sedimentary
record by another layer of sediment.
They are used also to determine facing
direction.
Tracks and Trails left by organisms, used
also in determining the facing direction of
beds.
Sole Marks, Scour Marks, Flute Casts
Marks formed as an object moves across
a bedding surface or as currents scour a
bedding surface. Flute molds consist of
scoop-shaped structures formed when
the currents scour and erode a surface.
Flute casts form when these molds filled
with sediment.
All these features are used to determine
the top of the bed.
Rain-imprint
Fossils Track
Non-Tectonic Structures
Primary Sedimentary Structures
BEDDING
Dewatering Structures (Load Cast) form after
deposition and dewatering of sediments as a result
of gravitational instability at the interface between a
layer of water saturated sand and underlying mud.
The weight of the newly deposited overlying
sediment forces out the interstitial water.
They can also be used in determining the facing direction by using the
broadly convex bottom side of the cast that face the toward the bottom.
Fossils they are useful in determining the relative age
and facing direction by studying the relative position
in sequence.
They are also useful strain indicators.
Reduction Spots are sedimentary structures produced
by a small grain or fragment that is chemically
different from the surrounding.
They are useful as strain indicators.
Non-Tectonic Structures
Primary Sedimentary Structures
Sedimentary Facies
Sedimentary Facies
The vertical and lateral variation in sedimentary
rocks due to the paleoenvirnoments change.
Each sediment (rock) type is called a facies
or lithesome. One facies is separated from
others by particular characteristics
(composition, texture, sorting, physical
and biogenic sedimentary structures)
Non-Tectonic Structures
Primary Sedimentary Structures
Unconformities
Unconformities
A break in the sedimentary record, where
part of a stratigraphic succession and
history is missing. Unconformities are
produced by erosion or non-depostion
(or both).
Disconformity
Angular
Types of unconformities:
Disconformity:
Is produced by deposition of a sequences
followed by erosion without tilting or
deformation, then comes subsidence
and renewed deposition. Beds above
and below unconformity remain parallel.
Topographic relief along the
unconformity may be present.
Paraconformity is in places where there is
little relief on an unconformity.
Non-conformity
Non-Tectonic Structures
Primary Sedimentary Structures
Unconformities
Angular unconformity:
unconformity
Is produced where a sequence has
been tilted as a result of
slumming or tectonic
processes, and followed by
deposition of new sedimentary
strata.
Nonconformity:
Is an unconformity in which igneous
or metamorphic rocks (or both)
occur below the erosion surface,
and sedimentary rocks occur
above. It indicates that a long time
interval passed between formation
of the igneous and metamorphic
rocks at great depths in the Earth
and deposition of sediment.
The three types of unconformities may be
present in one area.
Non-conformity and Angular Unconformity
Non-Tectonic Structures
Primary Igneous Structures
Foliation and Lineation
„ Foliation,
„ Pillow
structures
„ Phenocrysts,
„ Cross-cutting,
Cross-cutting
Pillow Lava
Non-Tectonic Structures
Primary Igneous Structures
-Xenoliths,
- Pyroclastic rock
structures
-Compositional banding
- Contact metamorphic
zones
-Vesicles.
Some of these structures are useful
in determining the facing direction
and top position
Breccia
Non-Tectonic Structures
Gravity Related Features
Landslide and Submarine
Flows:
Flows
They form above and below
sea level and triggered by
„ earthquakes (tectonic)
„ overloading of slopes
„ high precipitation
„ oversteeping of slopes
„ human activities
Non-Tectonic Structures
Gravity Related Features
Turbidities are deposits by rapid
flow of sediments driven by
turbidity current down a slope
onto sea floor or lake floor.
floor They
consist of unsorted mass of
sediments called
BOUMA SEQUENCE
Non-Tectonic Structures
Gravity Related Features
BOUMA SEQUENCE OF
TURBIDITES
„ Shale (pelite)
„ Silt (pelite)
„ Rippled or cross-bedded
sandstone
„ Laminated sandstone
(well sorted)
„ Graded bedding of
poorly sorted sandstone
These are useful in determining the
facing direction and the top of
the sedimentary sequence.
Non-Tectonic Structures
Gravity Related Features
SALT STRUCTURES
Evaporite deposits occur in sedimentary sequences at
shallow crustal levels. Rock salt deposits formed by
evaporation of sea water and composed mostly of halite.
These rocks flow more readily than does any other rock
type.
Non-Tectonic Structures
Gravity Related Features
Salt flows at surface conditions by
the force of gravity. The salt
density contrasts with the greater
density and strength of the
sediments surrounding them.
This produces a variety of
structures ranging form glacier
on the surface to salt pillow and
stocks and domes at depth. The
internal structure of these salt
features indicates a plastic flow
“with folds, foliation, and other
structures similar to the ones
form under high pressure and
temperature in metamorphic
rocks.
Non-Tectonic Structures
Gravity Related Features
SALT STRUCTURES
Diapirs: are salt or other material that move upward and
gravitationally intrude the above sediments. They serve in many
places of the world as hydrocarbon traps.
Locations of diapirs and geometry of the structures produced within the
sediments are controlled by:
extensional process in cover sediments related to the flow of the
salt by gravity underneath.
Non-Tectonic Structures
Gravity Related Features
IMPACT STRUCTURES
These structures are formed by meteoritic impact and are
usually have a circular or elliptical outlines. They are
characterized by shatter cones structures (cone shape
fractures with epics at the point of force and the base is
away from it)