Geologic Mapping:Vocab – Flashcards
Unlock all answers in this set
Unlock answersquestion
What are geologic maps?
answer
Geologic maps show the distribution of rocks at the Earth's surface. Usually, the rocks are divided into mappable units that can be easily recognized and traced across an area. The divisions (contacts between units) are based on color, texture, or rock composition. Geologic maps only show what is exposed at the surface of the Earth.
question
What are geologic cross sections?
answer
Geologic cross sections are drawings of a vertical slice through the Earth.
question
What is superposition?
answer
Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest at the top. Steno's law.
question
What is original horizontality?
answer
Layers of sediment are originally deposited horizontally. The principle is important to the analysis of folded and tilted strata. Steno's law.
question
What is lateral continuity?
answer
Layers of sediment initially extend laterally in all directions, in other words, they are laterally continuous. Steno's law.
question
What is a cross-cutting relationship?
answer
A rock or fault is younger than any rock or fault through which it cuts. Hutton's law.
question
What is faunal succession?
answer
Sedimentary rock strata contain fossilized flora and fauna which succeed each other vertically in a specific order that can be identified over wide horizontal distances. Smith's law.
question
LAB
answer
LAB
question
To know the order of the layers in a cross section...
answer
**********SEE DIAGRAM**********
question
What color is the rock unit that USC is located on?
answer
Tan/beige
question
What is the abbreviation and the formal name of the formation that we are located on?
answer
QIs - Surficial sediments
question
What age are the rocks?
answer
Holocene
question
What kind of rocks are they?
answer
Sedimentary
question
Now find the North Branch of the San Gabriel Fault. What are the colors, names, and abbreviations of the rock units on either side of the fault?
answer
Qg = light blue = Surficial sediments/landslide Qog = light grey = Surficial sediments Qoa = beige = Surficial sediments Qd = purple = Quartz Diorite
question
How old are the rocks that the fault is cutting through?
answer
Cutting through Mesozoic age rocks, not cutting through Quaternary age rocks.
question
What can you tell about the age of the fault from the rock unit it cuts through?
answer
Has to be at least Mesozoic age.
question
Find the Devonshire Fault on the cross-section labeled A-B. Is this fault a normal, reverse, or strike-slip fault?
answer
Reverse fault
question
On cross-section A-A' find the fault below the Cheops Pyramid. This fault formed between the depositions of two rock units. Name these two rock units.
answer
Bright Angel Formation and Dox Formation
question
To draw syncline and anticline rock diagrams...
answer
**********SEE DIAGRAM**********
question
Anticline
answer
A fold in the form of an arch, with the rock strata convex upward and the older rock in the core
question
Brittle deformation
answer
A permanent change in shape or volume, in which a material breaks or cracks
question
Compression
answer
A stress that acts in a direction perpendicular to and toward a service
question
Craton
answer
A region of continental crust that has remained tectonically stable for a long time
question
Dip
answer
The angle between a tilted surface and a horizontal plane
question
Ductile deformation
answer
A permanent but gradual change in shape or volume of the material, caused by flowing or bending. Also known as plastic deformation
question
Elastic deformation
answer
A temporary change in shape or volume from which material rebounds after the deforming stress is removed
question
Fold
answer
A bend or warp in layered rock
question
Geologic cross section
answer
A diagram that shows geologic features that occur underground
question
Geologic map
answer
A map that shows the locations, kinds, and orientations of rock units, as well as structural features such as faults and folds.
question
Isostasy
answer
The flotational balance of the lithosphere on the asthenosphere. ie. the Appalachians (inactive mountain chain displaying topographic relief)
question
Normal fault
answer
A fault in which the block of rock above the fault surface (hanging wall) moves downward relative to the block below (foot wall)
question
Orogen
answer
An elongated region of crust that has been deformed and metamorphosed through a continental collision. ie. The Alps, Himalayas, and inactive Appalachians
question
Pressure
answer
A particular kind of stress in which the forces acting on a body are the same in all directions
question
Reverse fault
answer
A fault in which the block on top of the fault surface (hanging wall) moves up and over the block on the bottom (foot wall)
question
Shear
answer
A stress that acts in a direction parallel to a surface
question
Strain
answer
A change in shape or volume of rock in response to stress
question
Strike
answer
The compass orientation of the line of intersection between horizontal plane and a planar feature, such as a rock layer or fault
question
Strike slip fault
answer
A fault in which the direction of movement is mostly horizontal and parallel to the strike of the fault
question
Stress
answer
A force acting on the surface, per-unit area, which may be greater in certain directions than others
question
Structural geology
answer
The study of stress and strain, the processes that cause them, and the deformation and rock structures that result from them
question
Syncline
answer
A fold in the form of a trough, with the rock strata concave upward and the younger rock in the core
question
Tension
answer
A stress that acts in a direction perpendicular to and away from the surface
question
Thrust fault
answer
A reverse fault with a shallow angle of dip (less than 45). Common in mountain chains along convergent plate boundaries. ie. the Canadian Rockies. This type of fault represents a disturbance of the original stratigraphic sequence
question
Topographic map
answer
A map that shows the shape of the ground surface, as well as the location and elevation of surface features, usually by means of contour lines
question
Differential stress
answer
When the force is greater in one direction then in the other
question
Uniform stress/confining stress
answer
Also known as pressure, the forces on a body of rock are uniform in all directions
question
Elastic limit
answer
The degree of stress beyond which the material is permanently deformed
question
Strain rate
answer
The rate at which rock is forced to change its shape or volume
question
Brittle - ductile transition
answer
The depth below which ductile properties predominate
question
Hydrolytic weakening
answer
Trace amounts of water entering strong minerals such as quartz and olivine and significantly weakening them
question
Temperature
answer
When exposed to this in a higher degree rock becomes less brittle and more ductile; this is seen deep inside the planet. Rock is like glass in this respect
question
Confining pressure
answer
A high amount of this reduces the brittleness of rock because it hinders the formation of fractures. Near the earth's surface this is low and rock exhibits brittle behaviour, at great depth this is hot and rock tends to be ductile and deforms.
question
Rates of deformation
answer
The rate at which stress is applied to a solid. If stress is applied quickly the rock may have a brittle manner but if the stress is applied over a long period of time the rock maybe behave in a ductile manner
question
Composition
answer
Determines exact point at which it's brittle - ductile transition will occur
question
Overturned rock layers
answer
When rock layers are tilted even further than the vertical orientation
question
Microfracture
answer
Fractures that are so tiny that they can only be viewed under a microscope
question
Fault
answer
A fractured rock along which movement has occurred along the fracture surface
question
Left lateral
answer
A strike slip fault that appears to be moving to the left to an observer standing on either block.
question
Right lateral
answer
A strike slip fault that appears to be moving to the right tune observer standing on either block. ie. The San Andreas Fault
question
Monocline
answer
Simplest type of fold, a local steeping in otherwise uniformly dipping strata. ie. a tablecloth draped over a table
question
Axial plane
answer
Imaginary plane dividing the fold in half, as asymmetrically as possible
question
Flanks or limbs
answer
The two halves of the fold, on either side of the axial plane
question
Axis or hinge
answer
The line where the axial plane intersects the fold. This may be simple and horizontal or tilted and plunge
question
Axial trace
answer
The projection of the fold axis or an axial plane onto a horizontal plane (A map). A map needs to show a line representing the axial line and axial plane, a symbol to indicate the type of fold, an arrow to show the direction in which the axis is plunging and a number to show the plunge angle
question
Domes
answer
The structure caused by the up warping of strata
question
Basins
answer
The structure caused by the downwarping of strata
question
Asymmetrical fold
answer
A fold with one limb dipping more steeply than the other
question
Overturned fold
answer
A fold with one limb tilted so far over that it is upside down
question
Recumbent
answer
A fold that is so strongly overturned that it is almost lying flat
question
Outcrop
answer
Places where bedrock is exposed at the surface. Use for geologic mapping
question
Geologic contacts
answer
Boundaries between rocks on a map of the area
question
Topographic profile
answer
Using the height information from a topographic map to produce this type of profile
question
Relief
answer
The difference between the lowest and highest elevations in an area
question
Contour lines
answer
Lines of equal elevation used on topographic maps
question
Formation
answer
A rock unit that can be distinguished from units above and below it on the basis of rock type and recognizable boundaries
