Geology Unconformity Quiz & Flashcards: Examples

Questions and Answers

What is an unconformity?

A process of erosion

A layer of sedimentary rock

A break in the rock record (correct)

A type of rock formation

What are the three main types of unconformities?

Disconformity, Angular Unconformity, Nonconformity

What is a disconformity?

A minor irregular surface separating parallel strata

What is an angular unconformity?

A tilted or folded sedimentary rocks overlain by younger strata Signup and view all the answers

What is a nonconformity?

When igneous or metamorphic rocks are exposed and younger sedimentary rocks are deposited above Signup and view all the answers

How can an unconformity be identified in cross-section?

By a wavy, eroded layer Signup and view all the answers

What is a fault?

A fracture in the rock where the rocks have moved Signup and view all the answers

What causes a fault?

Tension or compression Signup and view all the answers

What evidence must there be for a fault?

Movement of rocks on both sides, polished surfaces, and evidence of displacement Signup and view all the answers

What is a joint?

A fracture in the rock where the rocks do not move Signup and view all the answers

What causes a joint?

Compression, tension, or shear stress Signup and view all the answers

How do joints occur?

In sets, usually parallel Signup and view all the answers

What is the definition of unconformities?

Breaks in the geological record due to erosion Signup and view all the answers

Study Notes

Unconformities

Unconformity refers to a surface indicating a break in the rock record, often due to erosion or non-deposition.
Represents a significant gap in geological time, suggesting changes in environmental conditions.

Types of Unconformities

Angular Unconformity:
- Characterized by tilted or folded sedimentary rocks overlain by younger, horizontally deposited strata.
- Indicates previous rock formations were subjected to tilting or deformation before new layers were deposited.
Disconformity:
- Present when sedimentary rock layers remain parallel but are separated by an erosional surface.
- Represents periods of erosion followed by renewed sediment deposition.
Nonconformity:
- Occurs when younger sedimentary rocks are deposited over older igneous or metamorphic rocks that have been exposed to erosion.
- Shows a different geological history compared to surrounding sedimentary layers.

Identification of Unconformities

In geological cross-sections, unconformities can be recognized by their wavy, eroded surfaces.

Joints and Faults

Fault:
- Defined as a fracture in rock where movement has occurred on either side.
- Caused by tectonic forces such as tension or compression.
Evidence of Faults:
- Movement of rock on either side of the fault.
- Presence of crushed rock, polished surfaces with striations due to friction, and displacement of surface features.
Joint:
- A crack or fracture in rock where no movement occurs on either side.
- Typically formed due to stresses such as compression, tension, or shear.
Occurrence of Joints:
- Joints usually appear in parallel sets, indicating the response of rock to stress.

Summary of Definitions

Unconformity: A break in the rock layer caused by erosion or periods of non-deposition.
Disconformity: A surface separating parallel sedimentary layers with evidence of erosion.
Angular Unconformity: Overlapping younger layers on tilted or folded older strata.
Nonconformity: Sedimentary rocks deposited over eroded igneous or metamorphic rocks.

Description

Explore the fascinating world of unconformities in geology. This quiz covers the definitions, types, and significance of angular, disconformity, and nonconformity. Test your understanding of how these concepts reflect geological history and changes in environmental conditions.