DATING ROCK LAYERS
RELATIVE DATING
Law of Original Horizontality
Law of Superposition
Extrusions
Intrusions
Index Fossils
ROCK LAYER DISTURBANCES
FAULTS
Hanging Wall and Foot Wall
A = Hanging wall
B = Foot wall
Disturbances to rock layers
Faults: Dip slip, Strike Slip and Oblique
DIP SLIP FAULTS
Normal Fault
In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion
is caused by tensional forces and results in extension. [Other names: normal-slip fault, tensional fault or
gravity fault] EX., Sierra Nevada/Owens Valley; Basin & Range faults
Dip Slip Fault
Reverse Fault
In a reverse fault, the block above the fault moves up relative to the block below the fault. This fault motion is
caused by compressional forces and results in shortening. A reverse fault is called a thrust fault if the dip of
the fault plane is small. [Other names: thrust fault, reverse-slip fault or compressional fault] EX., Rocky
Mountains, Himalayas
STRIKE SLIP FAULTS
• Strike Slip
In a strike-slip fault, the movement of blocks along a fault is horizontal. If the block on the far side
of the fault moves to the left, as shown in this animation, the fault is called left-lateral. If the
block on the far side moves to the right, the fault is called right-lateral. The fault motion of a
strike-slip fault is caused by shearing forces. Examples: San Andreas Fault, California;
Anatolian Fault, Turkey [Other names: transcurrent fault, lateral fault, tear fault or wrench
fault.]
Transform Fault
A transform fault is a type of strike-slip fault wherein the relative horizontal slip is accommodating the
movement between two ocean ridges or other tectonic boundaries
Oblique Fault
Oblique-slip faulting suggests both dip-slip faulting and strike-slip faulting. It is caused by a combination of
shearing and tension or compressional forces. Nearly all faults will have some component of both dip-slip
(normal or reverse) and strike-slip, so defining a fault as oblique requires both dip and strike components
to be measurable and significant.
FOLDING
MONOCLINE FOLD
The simplest type of fold is called a monocline This fold involves
a slight bend in otherwise parallel layers of rock.
Anticline Fold
An anticline is a convex up fold in rock that resembles an archlike structure with the rock beds (or limbs) dipping way from
the center of the structure.
SYNCLINE FOLD
A syncline is a fold where the rock layers are warped downward (Figure 4 and 5). Both
anticlines and synclines are the result of compressional stress.
Folding
Relative Age
Disturbances
Tilting - Geologic tilting, also known as tectonic
tilting, occurs when the earth’s surface layers
begin to tilt or slant irregularly.
UNCONFORMITY – A SURFACE THAT REPRESENTS A
MISSING PART OF THE GEOLOGIC COLUMN
ANGULAR UNCONFORMITY – found between horizontal layers of
sedimentary rock and layers of rock that had been tilted or folded
UNCONFORMITY – A SURFACE THAT REPRESENTS A
MISSING PART OF THE GEOLOGIC COLUMN
Disconformity is an erosion surface between two packages of sediment, but the
lower package of sediments was not tilted prior to deposition of the upper sediment
package. Part of a sequence of parallel rock is missing ( represented by the black line)
UNCONFORMITY – A SURFACE THAT REPRESENTS A
MISSING PART OF THE GEOLOGIC COLUMN
NONCONFORMITY - are unconformities that separate igneous or metamorphic
rocks from overlying horizontal layers of sedimentary rocks. They usually indicate
that a long period of erosion occurred creating an eroded surface prior to
deposition of the sediments (several km of erosion necessary). In the diagram at
left, the igneous/metamorphic rocks below the nonconformity are colored in red.
STRATIGRAPHY
Stratigraphy refers to geological and
archaeological layers that make up an
archaeological deposit. Archaeologists
use stratigraphy to better understand
the processes that created the site.
STRATIGRAPHY
EXAMPLES