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 graded bedding in a turbidite sequence. In which direction does grain size increase within a single graded bed?
Answer: Grain size increases downward toward the base
Graded bedding in turbidites shows coarser grains at the base and progressively finer grains toward the top of each bed.
During reconnaissance mapping of a volcanic terrane, a geologist should use which feature FIRST to distinguish lava flows from pyroclastic deposits?
Answer: Vesicularity, welding texture, and presence of lithic fragments
Field textures such as vesicles in flows, welding and eutaxitic texture in ignimbrites, and abundant lithic fragments in fall deposits allow rapid discrimination.
On a geologic cross-section, the geologist must project a contact from the surface to depth. Which information is MOST critical for this projection?
Answer: The true dip and dip direction of the contact
True dip and dip direction are the geometric data needed to accurately project a planar contact from surface to subsurface depth.
A geologist recognizes a set of parallel joints in an outcrop. To determine if the joints are systematic (tectonic), which observation is MOST diagnostic?
Answer: Joints cut through multiple lithologies and maintain consistent orientation
Systematic joints are planar, parallel, and persistent across multiple rock types, reflecting a regional stress field rather than local effects.
Which field method best determines the thickness of a steeply dipping stratigraphic unit in the absence of a drill hole?
Answer: Measuring the map width and applying a dip correction using t = w × sin(dip)
True thickness is calculated from map width (w) and dip angle using the formula t = w × sin(dip), corrected for topographic slope if needed.
A geologist maps a series of en echelon fractures oriented obliquely to a fault zone. These are most consistent with which stress condition?
Answer: Right-lateral or left-lateral shear along the fault zone
En echelon fractures form at an angle to a shear zone and are classic kinematic indicators of strike-slip (right-lateral or left-lateral) faulting.
When preparing a final geologic map for submission, which element is considered MANDATORY for professional standards?
Answer: A north arrow, scale bar, legend, and correlation of map units
Professional geologic maps require a north arrow, graphic scale bar, legend defining all symbols and map units, and a correlation chart showing relative age.