Chapter 20 Flashcards
What is the difference between geochronological and a chronostratigraphic unit?
Time = geochron
Space = Chronostrat
Main geochronological units from largest to smallest
Eons, Eras, Periods, Epochs, Ages
Main chronostratigraphic units from largest to smallest
Systems, Series, Stages
Why do some geologists not want to distiguish between geochron and chronostrat?
Now that we have better methods of dating the rocks, it seems redundant to distiguish the two
What is the purpose of the Global Standard Section and Point (Golden spike)?
Internationally agreed upon standard for geochronological boundaries to be used as a reference.
What criteria are used to establish a golden spike?
Accessible
Usually fossil based
Adequate thickness
Not effected by tectonics
Continuous sedimentation
What are the major rules for defining relative stratigraphic postion? What is up?
a) Superposition
b) Unconformity: All rocks under the unconformity must be older than those above it
c) Cross-cutting relationship
d) Inclusions and fragments
e) way up indicators
4 ways to determine “up”
Mudcracks
Sharp crests
asymptotic cross-bedding
Fossils (tree trunks, worm holes)
how is the top unit of the rock defined when it is gradational?
It is arbitrary, but when you have about a 50/50 split, that is the transition line
What is the purpose of a type section
To have a standard to reference that has all the notable features.
What are the rules for naming lithography?
Has to be geography based and with a lithologic term (Jacobsville Sandstone)
