Lab13_Paleogeography
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Dec 6, 2023
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GEOL 4200: Sedimentology and Stratigraphy
Lab 13: An Introduction to Biostratigraphy and the Paleobiology Database
Due 11/21
Revised from
“Life Through Time: Investigating Biostratigraphy with the PBDB by
Christian George,
High Point University
Open the PBDB Navigator and spend some time getting comfortable with how it works:
https://paleobiodb.org/navigator/
This web app allows you to browse the contents of the Paleobiology Database. The map
shows the localities of fossils that are entered into the database color
-
coded by age; the
size of the dot corresponds to the number of collections (Figure 1).
Figure 1
The Navigator consists of three parts:
1.
Map (
CENTER
) showing continents with dots representing fossil occurrences. The
color of these dots represents their geologic age. If you click on the dots, you can see
all of the information on eachsite and the fossil species that occur there.
If you click on the map it will zoom into that location. You can also use the plus or minus
buttons in the toolbar (left side of screen), or the scroll wheel on your mouse to zoom
in and out. Once you zoom in you can use the mouse to click and drag the map around.
2.
Geologic time scale (
BOTTOM
) showing the major eras, periods, and stages. Selecting
any of thetime units on time scale will restrict the data that is displayed to that time
interval.
3.
Tool bar (
LEFT
) showing the tools you can use to explore the database. These include:
zoom in/out on the map
reconstruct plate tectonic configurations for time interval (era or smaller) you are
exploring
narrow down which taxonomic group is plotted on map
create a diversity curve for the occurrences currently plotted on map
download the data (lat/long, geologic age, etc.) for the occurrences plotted on map
If you click on any time units in the geologic time scale, the occurrences displayed on the
map will be restricted to those time intervals; if you click on a taxon on the right side,
only the localities where that taxon is found will be shown. As you click on things (e.g.
Paleozoic), they are added as search terms. The search terms are listed in the lower
left corner of the map. You can clear them by clicking the X next to each one.
Biostratigraphy
–
Investigating Life through Time
As you may know, the geologic time scale was assembled over many years by correlating
rock units based on fossils (among other things). Using the Principle of Faunal
Succession, geologists organized rock units into groups of similar ages.
Click on different time units on the geologic time scale. Note that the taxa may
change in the taxon list. Write down three Time Intervals and the three most
Abundant Taxa for each:
Time 1:
Time 2:
Time 3:
1
st
Taxon
2
nd
Taxon
3
rd
Taxon
This is a rough approximation of the different kinds of life that geologists used to recognize
stratigraphic units of distinct ages, you should be able to note differences in the
faunas between time intervals.
Which two of the time units you selected were most distinct from one another?
How many years passed between these two units of time? Explain why this makes
sense based on your answer above.
How does this relate to role that evolution has played in history or life?
The Phanerozoic Eon contains three eras. What are they?
Those eras were recognized early on by geologists because they have quite distinctive
faunas. Each era after the Paleozoic was preceded by a mass extinction.
Mass
extinctions cause large
-
scale turnover in fossils that are preserved in the rock record.
Describe the Principle of Faunal Succession in your own words:
The first mass extinction we will examine is the end
-
Cretaceous mass extinction. This
separates the Mesozoic from the Cenozoic. The end of the Cretaceous Period and the
start of the Paleogene were recognized in part because of the extinction of the non
-
avian dinosaurs.
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First, clear any previous search terms by clicking on the
“
x
”
next to the name in the
Filters box (lower left of the map window). Then search for Ornithischia in
Navigator.
Ornithischia were the group of dinosaurs that includes many well
-
known
dinosaurs such as Triceratops and Stegosaurus.
We can now see the complete distribution of ornithischian fossils across the world.
Click
on Cretaceous in the timeline at the bottom of the window
. This restricts the
fossils to just those found in Cretaceous rocks.
Next click on the Paleogene in the
timeline
.
What is the difference between the distribution of Ornithischia in the Cretaceous and
the Paleogene?
Another important taxon for determining the age of
rocks are the trilobites. Trilobites are extinct
arthropods, so they are distantly related to
insects and crustaceans. They were most
common during the Cambrian Period, but their
abundance decreased through time until they
finally went extinct.
Determine which geologic period had the last
appearance of trilobites (Search for
Trilobita)
Biostratigraphic units (biozones) are bodies of strata that are defined or characterized on
the basis of their contained fossils. A biostratigraphic unit may be based on a single
taxon, on combinations of taxa, on relative abundances, on specified morphological
features, or on variations in any of the many other features related to the content and
distribution of fossils in strata.
One type of biostratigraphic unit can be defined on when a taxon disappears from the rock
record, like the extinction of the ornithischian dinosaurs or the trilobites. This type of
unit is called a Last Appearance Datum. The last appearance of a taxon sets a limit on
the youngest age of rocks that the fossil can be found within, and the First Appearance
Datum sets a limit on the oldest rocks.
Using first and last appearance, what is the age range of trilobites and the age range
of ornithischian dinosaurs?
The difference can be attributed to the mass extinction that occurred at the end of the
Cretaceous. The end Permian mass extinction that separates the Paleozoic from the
Mesozoic was even greater, with as many as 90% of the living genera going extinct at
that time.
Clear the search terms and just select the Permian. You can click on any of the
localities and look for fossils. See if those species survive the extinction by then
switching the time to the Triassic and search for the fossils. Find an example of
at least one that did and one that did not make it through, and discuss why one
might have survived while another did not:
Figure 2: https://pixabay.com/en/arctinurus-
boltoni-
trilobite
-
fossil
-
883871/
Index Fossils
–
Time from Life
Fossils were once living organisms and as such are sensitive indicators of past
environments, sedimentation patterns, and the organism’s distributions. In addition,
because of the irreversibility of evolution, fossils are particularly useful in working
out the relative times of the origin of sedimentary strata.
An index fossil is a fossil that can be used to determine the age of the sediments in which it
is found.
Good index fossils are wide ranging, can be found in a variety of habitats, have
short geologic ranges, and are easily identifiable.
Search
Navigator
for
Pecten
.
That is the genus of many species of scallops
1.
Do scallops make for good index fossils? Why or why not?
2.
What is the time range for scallops?
Compare
Pecten
to
Mariella
, a Cretaceous ammonite.
3.
What is the range of
Mariella
? Which would make a better index fossil, and why?
4.
If you found a
Mariella
fossil, about how old would its host rocks be in millions of
years?
How confident are you in that age range?
Figure 3: https://pixabay.com/en/seashell-
scallop
-
nature-
molluscum
-
1063437/
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