BSc 4 th Semester OPEN ELECTIVE Other than Geology Main students Dr Abdullah Khan Associate Professor Department of Geology AMU Aligarh FOLDS Folds are regular wavelike undulations of layers or surfaces present in the rocks ID: 934914
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Slide1
Introduction to Fold, Fault, Joint, Cleavage, Foliation, Lineation and Unconformities
BSc 4
th
Semester
(
OPEN ELECTIVE)
Other than Geology Main students
Dr Abdullah Khan
Associate Professor
Department of Geology, AMU, Aligarh
Slide2FOLDS
Folds are regular wavelike undulations of layers or surfaces present in the rocks.
They occur in scales ranging from very small up to microscopic level to extremely large covering 100’s of kms Force – Compressive
Slide3Hinge Point:
maximum curvature along fold
Hinge line: Formed by joining hinge points
Inflexion line:
The line having
zero or least curvature on a folded surface.
Crest and trough:
Crest and trough of a fold represent highest and lowest point respectively
Fold limb:
The surface region between inflexion line and hinge zone is known as limb of a fold. Fold limbs can be straight or curved.
Slide4Slide5Antiform
: Convex upward
Synform: Convex downward
Slide6FAULTS
Faults are brittle fractures along which shear displacement takes place.
Either side of rocks slide past each other In size, faults ranges from small to very large scale. Forces responsible – Tensile/compressional/shear
Slide7Slide8Slide9Slide10Slide11Slide12JOINTS
Joints are extensional fractures along which no shear displacement takes place.
NO MOVEMENT on either sideForce responsible: Tensile
Slide13Slide14Slide15Cleavage (Rock Cleavage and Mineral Cleavage)
Rock cleavage refers the ability of rock to split or cleave into more or less parallel surfaces.
Mainly cleavage develop due to parallel arrangement of platy/flaky minerals.e.g. Slaty cleavage
Slide16Mineral cleavage
describes how a crystal breaks when subjected to stress.
Cleavage is often measured by three factors:1) Quality of Cleavage2) Number of Sides Exhibiting Cleavage / No of sets3) Cleavage Habit/shape
Slide17Slide18Slide19Slide20FABRIC: Fabric means preferred orientation of grain or minerals
Fabric depends upon grain shape, grain size and arrangement in a rock
LINEATION: Lineation is linear fabric
FOLIATION: Foliation is planar fabric
LINEATION: Non-Penetrative structure
FOLIATION: Penetrative structure
Slide21UNCONFORMITY
Unconformity is the
surface of erosion and period of non-deposition. An unconformity is a contact between two rock units in which the upper unit is usually younger than the lower unit.Unconformities represent a break in sedimentation for millions of years
or even more.
Slide22Parallel
Angular relationship between
Older and younger sequence
Older sequence is Igneous
Or Metamorphic rock