Quiz Four (9:30-9:35 AM)
UNIVERSITY OF SOUTH ALABAMA
GY 112: Earth History
Fossils Part:
Telling Time
Predicting Paleoenvironments
Instructor: Dr. Douglas W. Haywick
Last Time
A) Stable isotopes of use to geology (fractionation)
B) Delta values and isotopic standards
C) Delta Oxygen applications (sea level change)
Web notes: 8a
Isotopes
Elements with the same number
of protons, but different numbers
of neutrons
12
C
13
C
14
C
http://sawardo.blogspot.com/
Stable Isotope Geochemistry
Fractionation: The ratio of stable isotopes in a substance before
and after the process.
The amount of fractionation nation is expressed via the
fractionation factor (α):
α=
H2/H1 (cloud)
H2/H1 (water)
Stable Isotope Geochemistry
There is a minor problem with this type of analysis. The
abundance of 18O to 16O is very low, and the amount of
fractionation is minute (but still measureable).....
http://www.sahra.arizona.edu/programs/isotopes/images/oxygen.gif
... but the resulting data are really, really, really small
numbers (and this is annoying!)
Stable Isotope Geochemistry
Isotopic data are usually presented using the delta value (δ)
δ18O =
O18/O16 (sample) - O18/O16 (standard)
O18/O16 (standard)
x 1000
and are reported in parts per thousand (ppt or ‰)
Stable Isotope Geochemistry
Isotopic fraction of oxygen in the hydrologic cycle
http://serc.carleton.edu/images/microbelife/research_methods/environ_sampling/isotope_fractionation.jpg
Eustatic Sea level Rise
Stable isotopes provide information about world wide (eustatic)
sea level change
sea level
↑rise
↓fall
http://portale.ingv.it/research-areas/climate-oceans-environments/reconstruction-of-paleoclimatic-variations
Today’s Agenda
1. Chronostratigraphy versus biostratigraphy
2. Paleontological correlations
3. Index fossils
4. Fossils and the Environment
Web notes: 9/10
Fossils & Time
Types of Stratigraphy
Fossils & Time
Types of Stratigraphy
Lithostratigraphy: using rocks to correlate
Fossils & Time
Types of Stratigraphy
Lithostratigraphy: using rocks to correlate
Chronostratigraphy: actual dates to correlate
(absolute dating)
Fossils & Time
Types of Stratigraphy
Lithostratigraphy: using rocks to correlate
Chronostratigraphy: actual dates to correlate
(absolute dating)
Biostratigraphy: using fossils to establish dates and
correlate (relative dating)
Lithostratigraphy
Lithostratigraphy
Lithostratigraphy
Lithostratigraphy
Lithostratigraphy only works if you have sufficiently
different rock types or distinctive fossil content
Cambrian
Ordovician
Silurian
Biostratigraphy
Mid-Miocene
5 million years
7.5 MA
10 MA
Lower Pliocene
5 MA
Upper Miocene
Biostratigraphy
Biostratigraphy
Biostratigraphy
Note pinch outs and facies changes
Biostratigraphy
There are a lot of fossils in the rock record, but not all are useful for
biostratigraphy.
Biostratigraphy
There are a lot of fossils in the rock record, but not all are useful for
biostratigraphy.
Some are too restricted (they only occur in one particular place or
environment (Endemic Species).
Biostratigraphy
There are a lot of fossils in the rock record, but not all are useful for
biostratigraphy.
Some are too restricted (they only occur in one particular place or
environment (Endemic Species).
The best fossils for biostratigraphy are Cosmopolitan species (wide
ranging)
Biostratigraphy
Cosmopolitan species that occur over a very narrow time range (e.g.,
less than 1 million years) can be used to tell time.
They are called Index Fossils
Biostratigraphy
Examples of Index
Fossils from the
USGS website
How to use fossils to tell time
Consider trilobites, which lived during the Paleozoic era
Late
Silurian
Middle
Silurian
Early
Silurian
Late
Ordovician
Source: http://www.ideofact.com/archives/trilobite.jpg
How to use fossils to tell time
Species A (Late Ordovician to Earliest Silurian)
Late
Silurian
Middle
Silurian
Early
Silurian
Late
Ordovician
Species A
Source: http://www.ideofact.com/archives/trilobite.jpg
How to use fossils to tell time
Species B (Early Silurian to Middle Silurian)
Late
Silurian
Middle
Silurian
Species B
Early
Silurian
Late
Ordovician
Species A
Source: http://www.ideofact.com/archives/trilobite.jpg
How to use fossils to tell time
Species B (Early Silurian to Middle Silurian; a good index
fossil if it’s cosmopolitan)
Late
Silurian
Middle
Silurian
Species B LAD
Species B
Early
Silurian
Species B
Biozone
Species B FAD
Late
Ordovician
Species A
Source: http://www.ideofact.com/archives/trilobite.jpg
How to use fossils to tell time
Species C (Early Silurian to Late Silurian)
Late
Silurian
Species C
Middle
Silurian
Species B
Early
Silurian
Late
Ordovician
Species A
Source: http://www.ideofact.com/archives/trilobite.jpg
How to use fossils to tell time
The age of the interval shown in blue can be relatively well
constrained. It is the only time all 3 beasties were alive at
the same time – sometime during the Early Silurian
Late
Silurian
Species C
Middle
Silurian
Species B
Early
Silurian
Late
Ordovician
Species A
Source: http://www.ideofact.com/archives/trilobite.jpg
How to use fossils to tell time
The age of the interval shown in yellow can be relatively
well constrained. It is the only time all 3 beasties were
alive at the same time – sometime during the Early Silurian
Late
Silurian
Species C
Middle
Silurian
Species B
This is called an assemblage zone and
it is how most biostratigraphy is done
Early
Silurian
Late
Ordovician
Species A
Fossils & Environment
The Oceans today
Morphological (Bathymetrical) Zonation
Fossils & Environment
The Oceans today
Trophic (Beastie Habitat) Zonation
Fossils & Environment
Interpreting paleowater depth
On the shelf
On the slope
Fossils & Environment
Interpreting paleowater depth
On the shelf
On the slope
Fossils & Environment
Interpreting paleowater depth
Sediment samples would
only contain epipelagic
and sublittoral beasties
Sediment samples would
contain epipelagic,
mesopelagic and bathyal
benthic beasties
Fossils & Environment
But what about a finer estimate of paleowater
depth? How good can you get?
Fossils & Environment
Introducing… the foraminifera
0.25 mm
Pelagic
Benthic
Fossils &
Environment
One group of foraminifera
from one small interval of
the Tertiary Period
Fossils & Environment
Consider 10 different species of forams and their
paleowater depth ranges
Species
Depth
A
25 to 75 m
B
25 to 75 m
C
50 to 100 m
D
50 to 250 m
E
0 to 100 m
F
25 to 250 m
G
150 to 250 m
H
0 to 50 m
I
10 to 1000 m
J
0 to 500 m
Chalk board
Fossils & Environment
Consider 10 different species of forams and their
paleowater depth ranges
Fossils Adaptations to Environment
Sand dollar
Sea urchin
Fossils Adaptations to Environment
Sand dollar
Sea urchin
Question: Which beasties is best suited for living on a beach?
Which one is best suited for living on a reef?
Why?
Today’s Homework
1) Study! Lecture test is coming up!
Next Time
Tuesday: Nothing! Mardi Gras holiday
Thursday: Quiz: fill in the blanks cartoon from today’s
lecture; More fossils (Paleogeography and
taxonomy) Lectures 11 and 12
GY 112: Earth History
Lectures 9 & 10: Fossils: Time &
Environment
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.