Geologic Cross Section Quiz

The geologic cross section below shows an unconformity in New York State bedrock layers that have not been overturned. Index fossils found throughout some rock layers are shown. Which New York State index fossil may have been present in a rock layer that is missing due to the unconformity?

• A) Condor

• B) Bothriolepis

• C) Lichenaria

• D) Maclurites

Base your answer to the following question on the Earth Science Reference Tables, the core section below, and your knowledge of Earth Science. The core section shows the subsurface bedrock geology for a location north of Buffalo, New York. What do the unconformities shown near the base of the drill core indicate?

• The continental plates were separated for a long period of time.

• Part of the geologic rock record has been destroyed.

• This area was covered by a warm, shallow sea.

• Extinction of many kinds of living things was widespread.

Many parts of the rock record in New York State are missing. These parts are most likely missing because of

• A) uplift and erosion

• B) earthquakes and volcanic activity

• C) subsidence and deposition

• D) folding and faulting

Pleistocene deposits of gravel are found lying directly on Precambrian bedrock. The interface between the gravel and the bedrock indicates

• A) a zone of contact metamorphism

• B) an area of volcanic activity that resulted in extruded gravels

• C) a period of continuous deposition

• D) a major time gap in the geologic record

Bedrock outcrops A and B are located at two different locations along the Mississippi River. Rock layers 1, 2, and 4 are the same in both outcrops. Which statement best explains why rock layer 3 is missing from outcrop B?

• A) A fault exists between outcrops A and B

• B) Erosion created an unconformity between rock layers 2 and 4 in outcrop B

• C) A volcanic eruption destroyed rock layer 3 in outcrop B

• D) Metamorphism of outcrop A created rock layer 3.

Which evidence would lead scientists to suspect that a tide or storm had washed up these jellyfish on a beach?

• Primitive life existed on land 500 million years ago.

• The rock containing the jellyfish fossils has distorted crystal structure.

• Treeroot fossils appear to have been pitted and folded.

• Large ripple marks were found in the fossil-containing rock layers.

The diagrams below show the sequence of events that formed sedimentary rock layers A, B, C, and D. This sequence of events best illustrates the

• formation of a buried erosional surface (unconformity)

• movement of rock layers along a fault between layers B and D

• overturning of rock layers

• metamorphism of sandstone (layer B) into quartzite

Base your answer to the following question on the geologic cross section below of the Grand Canyon. The numbers 1 through 10 represent Paleozoic sedimentary rock layers. The unconformity between the Paleozoic sedimentary rocks and the Precambrian sedimentary rocks represents:

• a gap in the geologic time record

• an intrusion of igneous rock

• an abundance of fossils

• a region of metamorphic rock

The geologic cross section below shows the geologic age of two rock layers separated by an unconformity. The unconformity at the bottom of the Silurian rock layer indicates a gap in the geologic time record. What is the minimum time, in millions of years, shown by the gap?

• 13

• 47

• 101

• 126

The diagram below shows a cross-sectional view of part of the Earth's crust. What does the unconformity (buried erosional surface) at line XY represent?

• an area of contact metamorphism

• a time gap in the rock record of the area

• proof that no deposition occurred between the Cambrian and Carboniferous periods

• overturning of the Cambrian and Carboniferous rock layers