geology midterm
Terms
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- states that when reconstructing earth history, one must assume the basic laws have always operated as they do today
- principle of actualism
- states that in a stack of layered rocks, the oldest is on the bottom
- principle of superposition
- states that layers of sedimentary rock are originally laid down in a nearly horizontal orientation
- principle of original horizontality
- states that rock layers were originally continuous over considerable lateral distance
- principle of original lateral continuity
- states that if any rock layer contains inclusions of another rock type, then the rock represented by the inclusions must have existed before the rock in which it is included
- principle of inclusions
- sstates that because life on earht has evolved over time, there is an understandable succession of fossils that can be used to help determine relative time
- principle of biologic succession
- defined as a buried surface of erosion or non-deposition , and they represent a period with no geologic record
- unconformity
- unconformity where the layers above and below the unconformity
- disconformity
- unconformity where the layers below are at an angle to those above
- angular unconformity
- unconformity where the rlationship between the beds above and below cannot be determined, usually where the underlying rocks are igneous or metamorphic
- nonconformity
- gaps in the time-rock records, surfaces that represent non deposition or erosion
- unconformities
- results from contact metamorphism
- "baked" zone or aureole
- physical character of a rock or rock formation.
- lithology
- study of layered sedimentary rocks
- stratigraphy
- basic subdivision of a geologic sequence
- formation
- plane along which adjacent formations touch is referred to as
- contact
- A horizontal layer of material, especially one of several parallel layers arranged one on top of another
- strata
- the angle at which beds descent into the earth, measure perpendicular tot he strike direction, angle measure from the horizontal plane to the bedding plane
- dip
- type of fold characterized by the rocks dipping toward the fold axis, and the youngest rocks in the fold are found nearest the axis
- syncline
- 3 types of stress
- tension, shear stress, compressional
- layering of sedimentary rocks at a location os often drawn as a
- geologic column
- area where a rock unit is exposed at the earth's surface
- outcrop
- particularly recognizable beds like volcanic ash layers or thin black shales are called
- marker beds
- widely used method for correlating geologic units from one outcrop to another is by matching the
- sequence of beds
- when rocks change their shape or volume in response to specific pressures or forces they are
- deformed
- a bed , a layer of sedimentary rock that is distinguishable from the rocks above and below it, or layer that is no longer flat-lying(horizontal)
- dip
- describes how steeply the bed is dipping
- dip angle
- direction that a given bedding plane trends on teh surface of the earth
- strike
- a rock that has been bent is described as
- folded
- when the fold is arched up and the beds dip away from the center
- anticline
- when the fold is arched downward and the beds dip toward the center of the fold
- syncline
- where are the oldest rocks on a syncline
- outside
- a set of connected anticlines and synclines
- foldbelt
- deformation where all sides dip towards the center
- basin
- deformation where all sides dip away from the center
- dome
- bend subject to pressure
- ductily
- plane along which motion has occurred is called
- fault plane
- hanging wall moves up relative to the footwall due to compression or squeezing
- reverse faults
- low angle faults that result from compression, hanging wall moves up relative to the foot wall
- thrust faults
- faults that result from tension, hanging wall moves down relative to the foot wall
- normal fualts
- faults in which the motion along the fault plane is horizontal, rather than up or down
- strike slip faults