Field Geology and Mapping Flashcards
7 cards from real ASBOG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Field Geology and Mapping flashcards as text
A geologist observes that bedding planes in a sandstone dip 45° to the east, while cleavage planes dip 60° to the east. The fold that produced this geometry is most likely located:
Answer: To the east, past the fold hinge
When cleavage dips more steeply than bedding in the same direction, the outcrop is on the overturned limb and the fold hinge lies to the east.
Which map symbol correctly represents a vertical contact?
Answer: A straight line without any dip tick
A vertical contact or vertical fault is shown as a straight line with no dip tick because the feature is perpendicular to the map surface.
In a V-pattern on a geologic map, beds with a V pointing upstream that have dip values less than the stream gradient indicate:
Answer: Beds dipping downstream at less than the valley gradient
When beds dip in the same direction as the stream but at a gentler angle than the valley slope, the V-pattern points upstream but opens more gently than the contours.
A geologist encounters a fault with slickenlines plunging 80° on the fault surface. This kinematic indicator suggests:
Answer: Predominantly dip-slip motion
Slickenlines plunging steeply (near 90°) on a fault surface indicate nearly pure dip-slip motion.
Which property of a rock unit makes it most useful as a regional stratigraphic marker bed?
Answer: Lateral continuity and distinctive character
Marker beds are useful precisely because they can be traced over a wide area and are lithologically or biologically distinctive.
When mapping a contact between two units in rugged terrain, the geologist should prioritize which technique?
Answer: Walking the contact and noting its position relative to topography
Walking the contact and recording its position relative to topographic features provides the most accurate three-dimensional placement of the contact.
A geologist measures three strike-and-dip readings across a dome structure. The strikes diverge radially and the dips increase outward. This pattern best indicates:
Answer: A periclinal dome with a flat top
Radially diverging strikes with outward-increasing dips define a periclinal or doubly plunging dome structure.