Which term does NOT describe a gap in geologic time?
a. unconformity
b.nonconformity
c.disconformity
d. key bed
To determine which term does NOT describe a gap in geologic time, let's define each term:
a. Unconformity: An unconformity is a gap in the geologic record that represents a period of erosion or non-deposition. It occurs when there is a time interval where sedimentation ceased, and the existing layers were exposed to erosion before new sedimentary layers were deposited on top.
b. Nonconformity: A nonconformity is a specific type of unconformity where sedimentary rocks overlay crystalline rocks (igneous or metamorphic) indicating a significant time gap between their formation.
c. Disconformity: A disconformity is another type of unconformity where the contact between sedimentary layers indicates a time gap, but the sedimentary rocks on either side of the gap are parallel to each other.
d. Key bed: A key bed refers to a specific layer of rock or sediment that is used as a marker to correlate different rock formations in different locations. It helps in establishing the relative age of different rock units.
Now, considering the definitions, the term that does NOT describe a gap in geologic time is option d. Key bed. Unlike the other options, a key bed does not represent a gap in time but is used to correlate and determine the relative ages of different rock formations.