Geological applications of fossils

Geological Applications of Fossils
Sue Rigby

1. An introduction to palaeontological
data
2. Biostratigraphy
3. Palaeobiogeography
4. Palaeoenvironments
5. Taphonomy
+ practicals and computer assignments
Assessment by practical folder and exam


1. An introduction to
palaeontological data
a. Types of fossil
b. The potential of the fossil record
c. How good is the fossil record?
d. Taxonomy and phylogeny
e Data from a single fossil
f. Data from a set of fossils
Practical:
A crash course in fossil identification
Computer assignment:
Manipulating data from fossils


a. Types of fossil
Body fossils
Trace fossils
Biomarkers, eg dinosterane

Isotopic signatures eg light C isotopes
Rocks - reefs, coal, oil, black shale etc.
Temporal information in DNA/RNA


b. The potential of the fossil record.
Secular changes in organisms
Secular changes in Earth system
Local changes in environment
Local changes in palaeogeography
Short term records of events - ontogeny,
population dynamics
Relative timescales
Post-mortem events


c. Is the fossil record good enough?
For some things but not for others.
Fossil record is of about 250 000 species
About 2 million species known today.
Probably less than half the total number
(But most of these are insects and their
fossil record is terrible)
Fossil record lasts 3.5 billion years
Hence a small sample.
In addition it is a biased sample


Bias in the fossil record
1. To skeletonised organisms, and

within this group to organisms with
robust skeletons.
2. To common organisms - this carries
ecological implications.
3. To organisms living in environments
of net deposition, or at times of the year
when deposition occurs. And in areas of
rapid deposition.
4. To more recent fossils.
5. Towards higher taxonomic groups
6. To particular sea level stands/
systems tracts.





d. Taxonomy and phylogeny
Organisms have a name and are assigned a
place in a hierarchy - eg
Phylum Vertebrata
Order Primates
Genus Homo
Species sapiens
This may also reflect an evolutionary
succession, but it may not. Eg
Climacograptus
Phylogeny is the study of evolutionary
relationships, usually undertaken with
cladistic methods.

Naming a fossil gives it utility and implies
the possibility of deducing its family tree.


e. Data from a single fossil
Complete/ damaged
Ontogeny?
Phylogeny
Characteristics relative to its group - big,
small, odd?
Unique indicator of conditions?
Eg Kodonophyllum from Torquay
Limestone.

f. Data from a set of fossils
Variations within and between sets of
fossils
Univariate
Bivariate
Multivariate measures of form data
Explored in computer assignment.




2. Biostratigraphy
a. Stratigraphic procedure
b. Correlating with fossils evolution vs ecology
c. Calibration of the fossil record
d. Confidence limits on

stratigraphy
e. Sequence stratigraphy and fossils
Practical:
A crash course in microfossil
identification
Computer assignment:
Producing a functional biostratigraphic
solution from outcrop data.


a. Stratigraphic procedure
‘Stratigraphy is the study of the
geometry, composition and time relations
of stratified rocks.’
Biostratigraphy addresses these questions
via fossil data.
Three aims:
1. Lithostratigraphy - define and
describe individual rock units in the area
of study.
2. Correlation - correlate these units with
units elsewhere and with standardised
time scales.
3. Chronostratigraphy - to define and
refine a standard global timescale.


Elements of Stratigraphy

Lithostratigraphy
Hierarchy:
Supergroup
Group
Formation
Member
Bed
Formation is the basic mappable unit.
Usually named after a locality and a
rock type, eg. Speaton Clay Formation.
Formation boundaries need not by
isochronous.
Definition of formations is the choice of
the individual mapper.


Correlation
Primary unit: Biozone (or zone)
This is visualised as a bed or set of beds
characterized by a particular fossil, not
a time period.
Different types of zone include:
Total range zone
Partial range (Overlap) zone
Assemblage zone
Acme zone
Should always define which is being
used, as each had advantages and
disadvantages.
Most people don’t do this.

Zone fossil

Younger

Lower
Ordovici
an

Isograptus
Didymograpt
us
Tetragraptus
Clonograptus

Older


Chronostratigraphy
Establishes age relationships based on
rock sequences to build up a globally
applicable timescale.
Divides time equivalent rock packages
into:
System, series and stage.
Time equivalents are
Period, epoch and age.

Absolute age tie-points for Lower Palaeozoic


b. Correlating with fossils - evolution
vs ecology
Why it works:
Evolution changes morphology
Species disperse
Why it doesn’t work
Morphology may not reflect phylogeny
Local variation may not be an evolutionary
signal
Species don’t completely disperse
Bioturbation
Good zone fossils
Evolve rapidly
Have a wide geographic range
Are common


c. Calibration of the fossil record
By isotopic dating, usually U-Pb for best
accuracy.
About 32 dates for the period 580-380 Ma.
Correlation is often imprecise because
sections with appropriate lavas may lack
good zone fossils. The
Precambrian/Cambrian boundary is a
good example of this.
By contrast there are around 50 graptolite

biozones for the Silurian (443-417 Ma), so
many of these, and their relative lengths
remain unconstrained.



d. Confidence limits on
stratigraphy
Fossils disappear in most places before
they really went extinct.
If fossiliferous horizons are randomly
distributed then Rc=αr
where Rc is the confidence interval for the
true end-point of a range and α is given
by
α = [(1-C)-1/(H-1) -1]
where H is the number of fossiliferous
horizons that contain the fossil and C is
the desired confidence level (say 95%).
In other words, real extinction is more likely to be close
to the last occurrence in fossiliferous sections (not rocket
science but useful)