Thanks for asking!
Yes, angular unconformities and nonconformities -as a general rule-
imply a greater break in geologic time than disconformities. The
lengths of the individual processes required for each type of
unconformity to take place are indicators of relative intervals.
When layers of rock formed without interruption, they're called
conformable. However, no place has a complete set of conformable
strata. A hiatus, or unconformity, represents a period when
deposition ceased and erosion removed previously formed rocks before
deposition resumed.
Angular unconformities
An angular unconformity consists of tilted or folded sedimentary rocks
that are overlain by younger, more horizontal, strata. An angular
unconformity indicates a long period of rock deformation and erosion.
Disconformity
A disconformity is a minor irregular surface separating parallel
strata on opposite sides of the surface. A disconformity indicates a
history of uplifting above the sea level, undergoing erosion, and
lowering below the sea level again, often considered only a pause in
the geologic process.
Nonconformity
A nonconformity is a break surface that developed when igneous or
metamorphic rocks were exposed to erosion, and younger sedimentary
rocks were subsequently deposited above the erosion surface. The
intrusion, uplift, erosion, subsidence and deposition indicate fairly
long periods of geologic time.
Of course there are exceptions, the same geologic event can cause all
three types of unconformities over distance. See the illustration at:
Geologic Time - Basic Geology, Stephen A. Nelson
http://earthsci.org/teacher/basicgeol/geotim/geotim.html#Variation of
unconformities
Further Study:
**********************************************************************
Geologic Structure, A Primer (.PDF format, requires Acrobat Reader)
Charles Merguerian, Hofstra University
http://www.people.hofstra.edu/faculty/Charles_Merguerian/Geology%2019/19%20Primer.pdf
Geology/Geophysics 101
University of Hawaii
http://www.hcc.hawaii.edu/hcconline/gg101/program9%20EarthStructures/program9.html
Geologic Time (HTML cache of PowerPoint version)
http://216.239.53.104/search?q=cache:Ohy2UHN-g9gC:www.geo.utep.edu/pub/hurtado/1301/lectures/week1/3/ppt/Lecture03_02_Intro3.ppt
Google Search Terms:
disconformity nonconformity "angular unconformity" "geologic time"
classification unconformities geology
geochronology relationship nonconformities
I hope this information meets your requirements. Should you have any
questions about the material or links provided, please, feel free to
ask.
--larre |
