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
When measuring strike using the right-hand rule, the geologist holds their right hand along the strike line with fingers pointing in which direction?
Answer: So the thumb points in the dip direction
The right-hand rule states that when you align your right hand along the strike with the thumb pointing in the dip direction, fingers curl in the direction of dip.
A geologist records a fold whose axial plane dips 30° and whose hinge line plunges 20°. This fold is best described as:
Answer: Inclined plunging
An inclined plunging fold has an axial plane that dips at an intermediate angle and a hinge line that plunges in the same vertical plane.
On a geologic map, a contact that is concentric with topographic contours and closes on itself typically represents:
Answer: An intrusive body or dome
Circular to elliptical contacts that parallel topographic contours indicate an intrusive body such as a pluton or a structural dome.
Which approach is MOST appropriate when mapping in areas with poor outcrop exposure?
Answer: Use float, soil color, and vegetation patterns to infer lithology
Indirect evidence such as float, soil characteristics, and vegetation changes helps infer subsurface geology where outcrops are absent.
The apparent dip of a bed is always _____ the true dip, except when the cross-section is cut perpendicular to strike.
Answer: Less than
Apparent dip is always less than true dip because you are measuring across an oblique section rather than perpendicular to strike.
A reverse fault in map view typically displays which relationship between hanging wall and footwall contacts?
Answer: Older rocks are thrust over younger rocks
Reverse and thrust faults place older (deeper) rocks over younger rocks because the hanging wall moves up relative to the footwall.
When sketching a stratigraphic column in the field, the geologist should record which of the following for each bed?
Answer: Lithology, thickness, grain size, sedimentary structures, and contacts
A complete stratigraphic column requires lithology, thickness, grain size, sedimentary structures, and contact types to allow later interpretation.