Chapter 9 geology

Formation

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Period

A basic unit of the geologic time scale that is a subdivision of an era. Periods may be divided into smaller units called epochs.

Index fossils

A fossil that is associated with a particular span of geological time

Era

A major division on the geological time scale; eras are divided into shorter units called periods

Inclusions

A piece of one rock unit that is contained within another. Inclusions are used in relative dating.the rock mass adjacent to the one containing the inclusion must have been there first in order to provide the fragment.

Cross cutting relationship

A principle of relative dating. A rock or fault is younger than any rock (or fault) through which it cuts

Principle of superposition

A principle which states that in any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below

Relative dating

A process of determining the chronological order of events by placing rocks and structures in their proper sequence or order

Unconformity

A surface that represents a break in the rock record, caused by erosion and non deposition

Mesozoic era

A time span on the geologic time scale between the Paleozoic and Cenozoic eras. From 248 to 65.5 million years ago

Paleozoic era

A time span on the geologic time scale between the Precambrian and Mesozoic eras-from about 542 million to 251 million years ago

Cenozoic era

A time span on the geological time scale beginning about 65.5 million years ago, following the Mesozoic era.

Disconformity

A type of unconformity In which the beds above and below are parallel

Epoch

A unit of geologic time scale that is subdivision of a period

Precambrian

All geologic time prior to the Phanerozoic eon. A term encompassing both the Archean and Proterozoic eons.

Non conformity

An unconformity in which older metamorphic or intrusive igneous rocks are overlaid by younger sedimentary strata.

Angular unconformity

An unconformity in which the older strata dip at a angle different from that of the younger beds

Define each of the following: Principle of Superposition, Principle of Original Horizontality, and Principle of Cross-cutting Relationships. How are each of these principles applied to relative dating?

Law of Superposition: In an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below (Figure 9.2). Principle of Original Horizontality: • Layers of sediment are generally deposited in a horizontal position • If resulting sedimentary rock is folded or faulted, then the deformation occurred after formation Principle of Cross-cutting Relationships (Figure 9.4): • If a fault cuts rocks or a magma intrudes rocks... - The fault/magma are younger than the rocks - Faulting and intrusion occurred after the sediments were deposited and lithified Inclusions (Figure 9.5) • Inclusions are fragments of a rock unit enclosed in another rock unit • The rock unit that supplied the inclusions must be older than the rock containing the inclusions

Original horizontality

Layers of sediment that are generally deposited in a horizontal position.

Carbon-14 dating

Look up

Radio activity

Picture in book

. Distinguish between relative and absolute (numerical) dating.

Relative dating - Determine sequence or order that geologic events and processes occurred - No actual dates attached, just the order • Absolute dating - Determine actual ages of rocks and events - Utilizes isotopes and radiometric dating

Comformable

Rock layers that were deposited without interruption

Fossil succession

The definite and determinable order in which fossil organisms occur. Fossil succession enables us to identify many time periods by their fossil content.

Hadean

The earliest time interval (eon) of earth history. The time before the planets first rocks.

Proterozoic eon

The eon following the Archean and preceding the Phanerozoic. It extends between 2500 and 542 millions years ago

Archean Eon

The first eon of Precambrian time.the eon preceding the Proterozoic. It extends between 4.5 and 2.5 billions years ago

Eon

The largest time unit on the geological time scale

What is a formation? What are the different ways (criteria) by which rocks can be grouped into formations?

The most basic local unit of stratigraphy is the formation • A particular rock unit is grouped into a formation based on a distinctive appearance and/or other characteristics: - Lithology (rock type) - Color - Sedimentary structures - Certain depositional patterns

Numerical dating

The numbers of years that have passed since an event occurred

Phanerozoic eon

The part of geological time that is represented by rocks containing abundant fossil evidence. The eon extending from the end of the Proterozoic eon (540 Millions years ago) to The present

Radio metric dating

The procedure of calculating the absolute ages of rocks and minerals that contain certain radioactive isotopes

Correlation

The process of establishing the equivalence of rocks of similar age in different areas

Fossil

The remains or traces of organisms pre reserved from the geologic past

Paleontology

The systematic study of fossils and the history of life on earth

Half life

The time required for one-half of the atoms of a radioactive substance to decay

Define an unconformity? What do unconformities represent in terms of rock units and geologic time? How do unconformities form? Be able to sketch and describe the following: Angular unconformity, disconformity and nonconformity.

erosional surfaces or intervals of missing strata within a rock sequence. Types of Unconformities • Angular unconformity • Nonconformity • Disconformity

What is the Principle of Fossil Succession? How is this principle useful for correlating rocks from one exposure to another? What are the criteria for a good index fossil?

fossil organisms succeed one another in a definite and determinable order Geographically widespread fossil that is limited to a short span of geologic time.

What is meant by the correlation of rock units? Identify different criteria (e.g. lithology, sedimentary structures, color, fossils, etc.) that can be used to correlate rocks from one exposure to another.

matching a particular rock layer (formation) in one exposure with its counterpart at a different locality

What are fossils? Describe at least five different types of fossils.

traces or remains of prehistoric life now preserved in rock The remains of relatively recent organisms - teeth, bones, etc. - Entire animals, flesh included - Given enough time, remains may be petrified (literally "turned into stone") - Molds and casts - Carbonization