Textbook Notes (380,786)
CA (168,213)
UTSC (19,296)
EESA06H3 (240)
Nick Eyles (207)
Chapter 19

Chapter 19

6 Pages
125 Views

Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

This preview shows pages 1-2. Sign up to view the full 6 pages of the document.
Chapter 19: Time and Geology
Determining age relationships between geographically widely separated rock units is necessary for
understanding the geologic history of a region, continent, or whole Earth
What is Uniformitarianism?
In 18th century, James Hutton, father of modern geology
oRealized that geologic features could be explained through present-day processes
oMountains are not permanent, but have been carved into present shapes and will be worn down
by slow agents of erosion now working on them
oGreat thicknesses of sedimentary rock are products of sediment removed from land and deposited
as mud and sand in seas
o1788- “we find no sign of a beginning-no prospect for an end”
Charles Lyell- Huttons concept that geologic processes operating at present are the same processes that
operated in the past as the principle of uniformitarianism
oThe present is the key to the past
Suggests that changes take place at uniform rate, but sudden, violent events also influence Earths history
oSome countries used actualism instead
Dating based on radioactivity allows us to determine a rocks numerical age (absolute age)- age given in
years or some unit of time
Geologists more concern with relative time, the sequence in which events took place
Relative Time
Geology of Grand Canyon can be analyzed in four parts:
oHorizontal layers of rock
oInclined layers
oRock underlying the inclined layers (plutonic and metamorphic rock)
oCanyon itself, carved into these rocks
Principles Used to Determine Relative Age
Contacts are particularly useful for deciphering the geologic history of an area
oContacts: the surfaces separating two different rock types or rocks of different ages)
Formations: bodies of rock of considerable thickness with recognizable characteristics that make each
distinguishable from adjacent rock units
Stratigraphy: uses interrelationships between layered rock/sediment to interpret history of area or region
oUses four principles to determine the geologic history of locality or region:
Original horizontality: States that beds of sediment deposited in water formed as
horizontal or nearly horizontal layers
Superposition: within a sequence of undisturbed sedimentary or volcanic rocks the payers
get younger going from bottom to top
Lateral continuity: an original sedimentary layer extends laterally until it tapers or thins at
its edges
Cross-cutting relationships: a disrupted pattern is older than the cause of disruption
Contacts representing buried erosion surfaces such as these are called unconformities
Inclusion: fragments included in a host rock are older than the host rock
Pages 513 to 516 for examples
Unconformities
www.notesolution.com
A surface or contact that represents a gap in the geologic record, with the rock unit immediately above
the contact being considerably younger than the rock beneath
Most unconformities are buried erosion surfaces
Classified into three types:
oDsiconformities
oAngular unconformities
oNonconformities
Disconformities
Contact representing missing rock strata separates beds that are parallel to one another
Probably what happened is that older rocks were eroded away parallel to the bedding plane; renewed
deposition later buried the erosion surface
Often appears to be just another sedimentary contact (or bedding plane) in a sequence of sedimentary
rock, disconformity is hardest type to detect
Angular Unconformities
Contact in which younger strata overlie an erosion surface on tilted or folded layered rock
Implies following sequence of events, from oldest to youngest:
oDeposition and lithification of sedimentary rock
oUplift accompanied by folding or tilting of the layers
oErosion
oRenewed deposition on top of erosion surface
Nonconformities
Contact in which an erosion surface on plutonic or metamorphic rock has been covered by younger
sedimentary or volcanic rock
Generally indicates deep or long continued erosion before subsequent burial, because metamorphic or
plutonic rocks form at considerable depths in Earths crust
How can rock unites be traced from one area to another?
Correlation usually means determining time equivalency of rock unites
Rock units may be correlated within a region, a continent and even between continents
Physical Continuity
Being able to trace physically the course of a rock unit- is one way to correlated rocks between two
different places
Grand Canyon is ideal location for correlating rock units by physical continuity, but not possible to
follow rock unit from Grand Canyon into another region because it is not continuously exposed
Similarity of Rock Types
Under some circumstances, correlation between two regions can be made by assuming that similar rock
types in two regions formed at same time
This method must be used with extreme caution, especially if rocks being correlated are common ones
Correlation by similarity of rock types is more reliable if a very unusual sequence of rocks is involved
In some regions, a key bed, a very distinctive layer, can be used to correlated rocks over great distances
oExample, layer of volcanic ash produced from a very large eruption and distributed over a
significant portion of a continent
Correlation by Fossils
www.notesolution.com

Loved by over 2.2 million students

Over 90% improved by at least one letter grade.

Leah — University of Toronto

OneClass has been such a huge help in my studies at UofT especially since I am a transfer student. OneClass is the study buddy I never had before and definitely gives me the extra push to get from a B to an A!

Leah — University of Toronto
Saarim — University of Michigan

Balancing social life With academics can be difficult, that is why I'm so glad that OneClass is out there where I can find the top notes for all of my classes. Now I can be the all-star student I want to be.

Saarim — University of Michigan
Jenna — University of Wisconsin

As a college student living on a college budget, I love how easy it is to earn gift cards just by submitting my notes.

Jenna — University of Wisconsin
Anne — University of California

OneClass has allowed me to catch up with my most difficult course! #lifesaver

Anne — University of California
Description
Chapter 19: Time and Geology Determining age relationships between geographically widely separated rock units is necessary for understanding the geologic history of a region, continent, or whole Earth What is Uniformitarianism? In 18 century, James Hutton, father of modern geology o Realized that geologic features could be explained through present-day processes o Mountains are not permanent, but have been carved into present shapes and will be worn down by slow agents of erosion now working on them o Great thicknesses of sedimentary rock are products of sediment removed from land and deposited as mud and sand in seas o 1788- we find no sign of a beginning-no prospect for an end Charles Lyell- Huttons concept that geologic processes operating at present are the same processes that operated in the past as the principle of uniformitarianism o The present is the key to the past Suggests that changes take place at uniform rate, but sudden, violent events also influence Earths history o Some countries used actualism instead Dating based on radioactivity allows us to determine a rocks numerical age (absolute age)- age given in years or some unit of time Geologists more concern with relative time, the sequence in which events took place Relative Time Geology of Grand Canyon can be analyzed in four parts: o Horizontal layers of rock o Inclined layers o Rock underlying the inclined layers (plutonic and metamorphic rock) o Canyon itself, carved into these rocks Principles Used to Determine Relative Age Contacts are particularly useful for deciphering the geologic history of an area o Contacts: the surfaces separating two different rock types or rocks of different ages) Formations: bodies of rock of considerable thickness with recognizable characteristics that make each distinguishable from adjacent rock units Stratigraphy: uses interrelationships between layered rocksediment to interpret history of area or region o Uses four principles to determine the geologic history of locality or region: Original horizontality: States that beds of sediment deposited in water formed as horizontal or nearly horizontal layers Superposition: within a sequence of undisturbed sedimentary or volcanic rocks the payers get younger going from bottom to top Lateral continuity: an original sedimentary layer extends laterally until it tapers or thins at its edges Cross-cutting relationships: a disrupted pattern is older than the cause of disruption Contacts representing buried erosion surfaces such as these are called unconformities Inclusion: fragments included in a host rock are older than the host rock Pages 513 to 516 for examples Unconformities www.notesolution.com
More Less
Unlock Document


Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


OR

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit