structural interpretation of aerial photographs Flashcards
6 aspects of bedding attitude
bed, bedding plane, dip, azimuth, strike, talus
sedimentary stratum greater than 10mm,
lesser than 10mm?
> 10mm = bed
< 10mm = laminae
surface that separates and represents the contact between two beds
bedding plane
angle between the horizontal surface and the bed
dip
angular distance from the magnetic north
azimuth
direction of the line formed by the intersection of a planar structure and the horizontal
strike
outward sloping and accumulated heap or mass of rock fragments of any size or shape (usually coarse and angular) derived from and lying at the base of a cliff or very steep, rocky slope, and formed chiefly by gravitational falling, rolling, or sliding
talus
important factors to classify a pile of sediments as talus
-usually coarse and angular
-at the base of a cliff or very steep rocky slope
-from gravitational falling, rolling or sliding
appear as linear features on aerial photographs
beds
how do beds occur as?
a group of persistent linear ridges
what orientation do beds follow?
parallelism
abrupt termination of beds indicate what
fault
3 groups of beds based on degree of dip
- horizontal and gently dipping beds
- medium dipping beds
- steep and vertical dipping beds
how are horizontal and gently dipping beds distinguished
by tonal contrast and different resistance to erosion
horizontal and gently dipping bed bands are parallel to what
to the topographic contours with loop like shapes
drainage pattern of horizontal and gently dipping beds
dendritic
can horizontal and gently dipping beds always be observed?
yes until obliterated by talus
how are bedding in medium dipping beds expressed?
by bands of differing photographic tone or topographic breaks in slope due to resistance of beds
compare how resistant beds and less resistant beds appear
resistant beds are thinner
what part of the attitude can you determine using beds
dip angle, direction and strike
a ridge with a gently dipping slope and a steeply dipping slope
cuesta
aka cuesta
dip-slop
an asymmetric ridge
cuesta
the longer gentler slope of a cuesta
face slope
the steeper slope of a cuesta
steep slope lol
what is the use of rule of V’s for medium dipping beds
used to determine the direction of dip where a stream valley intersects the trace of a bed. the V points to the dip direction
describe the relationship of the magnitude of the dip and the size of the outcrop in plan view
inversely proportional
what is the diagnostic landscape for steeply dipping beds
hogback ridges
sharp, straight or slightly curved ridges with the same high dipping opposing slopes
hogback
describe the presence of talus on hogback riges
it’s often covered with talus on both sides
describe the long axis in hogback ridges
parallel to the strike of the bedding
T or F: the true thickness of vertical or nearly vertical bed cannot be measured
F.
how to tell the direction of dip (criteria)
- V rule
- Drainage characteristics
are the V rule and drainage characteristics applicable to all surfaces
no, only those where the topographic surface coincides with the bedding surfaces
explain the rule of V, and how the V’s look like in steep vs gentle dips
- the apex of the V points to the dip direction
- the V is narrower and longer in gently dipping beds (less dip angle)
- the V is wider and shorter for medium and steep dipping beds
describe the V when the slope is following the face slope
when the slope is following the face slope, the apex of the V points downstream (and looks thinner)
describe the V when the slope is following the steep slope
when the slope is following the steep slope, the apex of the V points upstream (and looks thicker)
how do beds cut by streams in plan view look like if the beds are vertical
horizontal
what cuesta slopes are shown if the tributary system is relatively long
face slope (gentle)
what cuesta slope is shown if tributary systems are short
back slopes (steep slopes)
what type of slope characterize high drainage density
steep slopes/dips
why is drainage density higher in steeper slopes
because streams are usually parallel and do not combine, compared to gentler slopes that end up joining
form zig-zag shape of V shape patterns in aerial photos
folds
appears as V shaped outcrop pattern with the apex (or nose) pointing in the direction of plunge
plunging anticline
for plunging synclines, what part of the fold points to the direction of plunge
the opening of the limbs
in aerial photos how can you tell if the fold is a syncline or anticline
based on the drainage pattern
circular/elliptical outcrop with beds dipping away from the central area
dome
when a dome is eroded, describe the relative ages of beds you can see from the center outward
oldest at center, progressively younger outward
drainage pattern of domes
radial
if a dome is dissected by stream erosion describe the orientation of the Vs
outward from center
elliptical/circular outcrop pattern with beds dipping toward a central area
basin
describe the relative ages of the beds in basins
younger at center
if a dome is dissected by stream erosion, where does the V point to
to the center of basin
appear as lines or zones of displacement that abruptly offset structures and terminate contacts between formations
fault patterns
generally dip at low angle and appear as zigzag irregular trace
thrust faults
