ASBOG Flashcards
Offset
The horizontal component of displacement measured perpendicular to the strike of the disrupted unit.
Reverse Fault
A dip-slip fault in which the hanging wall has moved up relative to the footwall. The dip of the fault is between 45 and 90 degrees.
Rule of V’s
The outcrop pattern of a formation as it crosses a valley forms a V shape (as viewed on a map). The V points in the direction that the formation underlies the valley.
Strike Separation
The horizontal distance between a stratigraphic unit offset by a fault, measured along the strike of the fault. It is an apparent displacement.
Strike-slip Fault
The horizontal distance between a stratigraphic unit offset by a fault, measured along the strike of the fault. It is an apparent displacement.
Throw
The amount of vertical displacement on a fault, also, the vertical component of net slip.
Thrust Fault
A reverse fault in which the fault plane dips less than 45 degrees.
Type Locality
The place where a geologic feature (such as a fossil species) was first recognized and described. It contains the type section.
Type Section
The originally described strata that constitutes a stratigraphic unit to which other parts of the unit may be compared. It is preferable to describe the location where the unit attains its maximum thickness and where the top and bottom unit are exposed.
Unconformity
A gap in the geologic record; an interruption in the depositional sequence that implies uplift and erosion have removed part of the geologic record or non-deposition has occurred.
Cenozoic
Present - 65 m.y.a | Quaternary (Age of Man) & Tertiary (Age of Mammals)
Mesozoic
65 - 248 m.y.a | Cretaceous, Jurassic & Triassic (Age of Reptiles)
Paleozoic
248 - 543 m.y.a | Permian - Mississippian (Age of Amphibians), Devonian & Silurian (Age of Fish), Ordovician & Cambrian (Age of Invertebrates)
Precambrian
543 - 4200? m.y.a
Law of Superposition
The oldest layer is on the bottom and the youngest layer is on the top. Assumes that the layers have not been overturned during deformation. Applies to any layered rock sequence.
Yardang
A long, jagged, sharp-edged ridge between troughs, oriented with the direction of the prevailing winds, in an arid region which is underlain by relatively weak materials
Ventifacts
Stones that have been abraded by the wind on at least one side so they are polished or faceted. They are usually only found in a unique environment of no vegetation, strong wind and plentiful sand.
Pedestal Rocks
Commonly called balanced rocks, these formations are a results of a combination of wind and water erosion (deflation) in an area where there are resistant rocks capping weaker more easily eroded rocks.
Blowout
A depression caused by deflation in an area where either migrating dunes exist or a small break develops in the surficial integrity of a stabilized windblown deposit or in some cases the underlying material is composed of a poorly to non-indurated material.
Desert Pavement
Sometimes called desert armor, is a name applied to the relatively flat residual surface of closely-packed, wind polished stones. This type of condition is the result of the removal of the fine-grained particles by wind and sheetwash. Often these remaining stones are somewhat cemented in place.
Ripples and ridges
Small-scale features that are usually found on the surfaces of sand deposits resulting from the flow of wind or water over the surface. The shape of the ripple mark can be an indicator of the direction of flow of the wind or water or of the depositional environment.
Sand shadows and sand drifts
These two features are similar in that both form as a result of an obstruction in the path of migrating sands. The sand shadow forms behind the obstruction where the velocity of the wind declines causing the sand to drop. Sand drifts develop in the lee (downward side) of a gap where the velocity of the wind declines after passing through the gap.
Dunes
Sand that is piled up as a result of transportation by the wind of sand sized particles. Often found in back beach areas or desert climates where the topography is relatively flat and the surface sand is dry. Most dunes are composed of a well-sorted sand.
Barchan Dune
Crescent-shaped, tails to leeward, rarely vegetated
Parabolic Dune
Crescent-shaped, tails to windward often associated with some vegetative cover.
Transverse Dune
perpendicular to the wind, exhibits the traditional gentle windward slope and the steep slip face nearing the angle of repose. Both the Barchan and Parabolic dunes are a variety of transverse dune.
longitudinal or Seif Dune
Parallel to the wind, thought to develop in area in which the prevailing wind caused the dunes to lengthen in the direction of the wind but the dune height increases due to the cross winds during periods of irregular wind flow.
Whaleback or sand levees
Very large hill or ridge of sand elongated parallel to the prevailing wind. In general whalebacks do not migrate and can be over 100 miles long, a couple of miles wide and 150 feet high.
Undulations
similar to a whaleback but smaller
Sandsheets
extensive flat areas covered with a coarse-grained sand that does not form dunes, but typically are covered with ripple marks
Alpine Glaciation
Found in the mountainous areas particularly in the Rockies and the Cordilleran Ranges
Continental Glaciation
What covered much of the central and northern U.S. during the Ice Ages
Conditions for a Glacier
- Large accumulation or mass of ice and snow
- Must be located principally on land
- Must be formed by the compaction and recrystalization of snow
- Must be evidence of past or present movement
- Remains from year to year
Cirque
Horseshoe-shaped hollow high on a mountainside that was created by the erosive action at the head of a glacier
Tarn
Small deep lake formed in a cirque basin
Glacial Polish
Smooth surface produced on bedrock by abrasion by the movement of a glacier
Striations
Lines scraped into the bedrock by rocks being carried along at the base of the glacier. Lines generally indicate the direction of glacier movement. Larger rocks create grooves or grooved rock that can be as big as a valley.
Glacial Trough (U-shaped Valley)
Steep-sided valley that extends down from the cirque in which glacial action has widened and deepened an existing valley
Glacial Steps or Stairway
Series of cross-valley steps extending down from the cirque which are characterized by a relatively flat floor or with a slight up-valley slope broken by steeper sections steepening down valley.
Paternoster Lakes
A series or chains of lakes occupying the glacial steps.
Hanging Valley
U-shaped glacial tributary valley truncated by a deeper U-Shaped glacial main valley leaving a valley whose mouth is relatively high on the main valley wall. The discordance is due to the greater erosive power of the main glacier
Arete
Jagged sharp sawtooth-like ridge that results form the growth of cirques on opposite sides of a mountain ridge by alpine glaciation.
Col
Narrow sharp-edged pass or sag between cirque head and side walls along an arete.
Horn
A jagged sharp peak at the high point in an arete which has been sculpted by the erosional action of three or more cirques. This pyramidal feature is the remainder of the original mountain summit in a region modified by alpine glaciation.
Monuments (tinds)
A horn that has been isolated by the lateral intersection of cirques.
Truncated or faceted Spur
Ridge, which once protruded into a pre-glacial valley, that has been truncated by the abrasion of glacial action as it straightened the valley. This feature characteristically has an inverted V-shaped face.
Fjords, fiards (fjards)
Submerged glacial trough or valley at its seaward end resulting from the raising of sea level as the glaciers melted. The fiard is a shallower and shorter, but often broader, feature than the fjord.
Trough Lakes
Similar to fjords in that they consist of a long glacial trough and contain water but are found above sea level.
Moraine
Mound or ridge composed of accumulated glacial drift or till deposited directly by the glacier. Moraines are composed of a heterogeneous collection of unsorted and unstratified clay, silt, sand, gravel and boulders.
End (terminal) Moraine
An arcuate moraine that has been deposited at the terminus of the glacier, marking the furthest progression of the glaciation. Older terminal moraines that are not the maximum extent of glaciation are typically destroyed by the subsequent glacial advances incorporation the older moraine material with the younger. Younger glaciations which do not exceed the maximum extent will deposit a series of moraine deposits called recessional moraines which are created during a temporary hiatus in the retreat of the glaciers.
Lateral Moraine
Linear moraine located along the edge of a valley glacier and composed of materials deposited on the glacier from the valley walls.
Medial Moraine
Linear moraine paralleling the valley walls which occurs when two valley glaciers merge joining the two inside lateral moraines from the two or more tributaries as they flow into the more major drainage.
Valley Train
Long, narrow deposit of outwash (sand and gravel), deposited by glacial meltwater, which begins at the end moraine and extends downvalley.