ASBOG Field Geology and Mapping 3

Question 1

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:

Accepted Answer

To the east, past the fold hinge

Answer

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.

Question 2

Which map symbol correctly represents a vertical contact?

Accepted Answer

A straight line without any dip tick

Answer

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.

Question 3

In a V-pattern on a geologic map, beds with a V pointing upstream that have dip values less than the stream gradient indicate:

Accepted Answer

Beds dipping downstream at less than the valley gradient

Answer

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.

Question 4

A geologist encounters a fault with slickenlines plunging 80° on the fault surface. This kinematic indicator suggests:

Accepted Answer

Predominantly dip-slip motion

Answer

Slickenlines plunging steeply (near 90°) on a fault surface indicate nearly pure dip-slip motion.

Question 5

Which property of a rock unit makes it most useful as a regional stratigraphic marker bed?

Accepted Answer

Lateral continuity and distinctive character

Answer

Marker beds are useful precisely because they can be traced over a wide area and are lithologically or biologically distinctive.

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG Field Geology and Mapping 3