UNIVERSITY OF SOUTH ALABAMA
GY 112L: Earth History
Lab Lecture 2:
Sequence of Events, Unconformities,
Transgressions/Regressions
Today’s Agenda
1. Geological Time
2. Unconformities
3. Sequences of events
4. Transgressions and Regressions
Geological Time
Time
Eon
0 MA (today)
Phanerozoic
Proterozoic
Era
Time
Cenozoic
65 MA to 0 MA
Mesozoic
245 MA to 65 MA
Paleozoic
550 MA to 245 MA
Neoproterozoic
900 MA to 550 Ma
Mesoproterozoic
1.6 GA to 900 MA
Paleoproterozoic
2.5 GA to 1.6 GA
Archean
4.1 Ga to 2.5 Ga
Hadean
4.6 Ga to 4.1 Ga
4.6 GA
Geological Time
Time
Eon
0 MA (today)
Phanerozoic
Proterozoic
Era
Time
Cenozoic
65 MA to 0 MA
Mesozoic
245 MA to 65 MA
Paleozoic
550 MA to 245 MA
Neoproterozoic
900 MA to 550 Ma
Mesoproterozoic
1.6 GA to 900 MA
Paleoproterozoic
2.5 GA to 1.6 GA
Archean
4.1 Ga to 2.5 Ga
Hadean
4.6 Ga to 4.1 Ga
4.6 GA
Geological Time
Periods: the most
useful subdivisions of
(mostly) the
Phanerozoic eon
65 MA
245 MA
550 MA
Unconformities
1) Angular Unconformity
2) Disconformity (sedimentary rock on top of sedimentary rock)
3) Non-conformity (sedimentary rocks on top of “basement”)
Sequences of Events
Geologist can time events by
putting them in order of
occurrence.
But, this does not allow you to
actually date when those events
actually occurred.
Source: http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/history1e.gif
Relative Dating Principles
1) The principle of superposition that states in any sedimentary succession that
has not been overturned, the oldest strata occur on the bottom.
2) The principle of original horizontality that states sedimentary layers are
originally deposited as horizontal sheets
3) The principle of original lateral continuity that states that sedimentary
layers are originally deposited as laterally continuous sheets that naturally
terminate against basin margins or barriers or which grade into other
sedimentary layers.
Relative Dating Principles
Principle of cross-cutting relationships in a succession
penetrated by other rock units (e.g., an igneous dike cutting
across sedimentary strata) the cross-cutting body is younger
than the stuff it is cutting.
Relative Dating Principles
Principle of Inclusions: A rock containing fragments of
“country rock” (e.g. a pluton might rip off some of the
surrounding rock that it is pushing through and incorporate it
into the magma before cooling), must be younger than the
country rock it contains.
Sea level change vs tides
250,000 miles
The Earth Moon System Today
Sea level change vs tides
250,000 miles
Gravitational Attraction = tides
http://library.thinkquest.org/C003124/images/tides.jpg
Sea level change vs tides
This is not sea
level change.
By the way…
Sea level change vs tides
250,000 miles
The Earth Moon System Today
Sea level change vs tides
The Earth Moon System 400 million years ago
Sea level change
The position of sea level is not
fixed. It has varied considerably
(+/- 100-300m) over time. The
world wide change is sea level is
called Eustasy.
Sea level change
•Transgression: rise in sea level
•Regression: fall in sea level
Today’s Lab Overview
Lab 2: Vertical Successions and Sequences of Events