biostratigraphy the art and science of telling time from rocks. traditional core of paleontology,...
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Biostratigraphy
The art and science of telling time from rocks.
Traditional core of paleontology, and of geology.
The geologic time scale is all based on fossils, relative time scale.
Most paleontologists working in industrydo biostratigraphy.
GG 309Craig GlennSpring 2012
Biostratigraphy:• Characterization and correlation of rock units
based on fossil content• Based on the recognition that organisms have evolved• Closely linked to paleontology
FossilsIndex Fossils and Fossil Assemblages Good for 3 Things:
• Understanding Evolution• Biostratigraphy (Stratigraphic Correlation)• Environmental Interpretation
UNDERSTANDING THE ENVIROMENTAL CONTROLS IS CRITICAL TO:
• SUCCESSFUL BIOSTRATIGRAPHIC ANALYSIS • SUCCESSFUL INTERPRETATION OF DEPOSTIONAL SYSTEMS
THE MOST CRITICAL FACTORS AFFECTINGCHRONOSTRATIGRAPHIC SIGNIFICANCE
IN BIOSTRATIGRAPHY ARE:
1. EVOLUTION
2. MIGRATION
3. EXTINCTION
4. ENVIRONMENT
5. PRESERVATION
EVOLUTION
Ch
arl
es
Darw
in
A. Phyletic gradualism
B. Punctuated equilibrium
Schematic ‘family tree’
Schematic ‘family tree’Morphology(body characteristics)
Morphology
(body characteristics)
RATES?
Gradual
Rapid
In punctuated model, speciation occurs only1000s (100s?) yrs, after population becomes reproductively isolated from the parent population.
THE TAXONOMIC CLASSIFICATION OF LIFE
- based on # shared characteristics (or differences) -
Carolus Linnaeus
Cover of Linnaeus’ 10th edition of
Systema Naturae (1758)
Animal, Plant, Fungi, Protist, Archaebacteria
single-celled animal-likeProtozoa:Forams & Radiolaria
single-celled plant-likeProtophyta algae:Coccoliths & Diatoms
Tertiary Sediments of the Gulf Plain
Biostratigraphic Units are Not Lithostratigraphic Units - Not the Same Thing
The Biostratigraphic Unit will correspond to the Lithostratigraphic unit if the fossils are FACIES CONTROLLED.
INDEXFOSSILS:
ImportantMarineFormsof the Phanerozoic
Methodology
INDEXFOSSILS ARE:
• independentof environment
• short range
• widespread
white bars show total range; black bars show times when imp. Index fossil.
The Finer Points of Stratigraphy
Index Fossils:Which One’s Better?
This Classic
The Classic Utilitarian Volkswagen Beetle?(the “people’s car”)
1958 Edsel Beauty?
OR
You decide…
INDEXFOSSILS:
• independentof environment
• short range
• widespread
Volkswagen Beetle“Type 1”
Protype 1937
“Lookie there, itsgots its darn engine in the back!”
Index Fossil?
Deliberately designed to be as simple as possible mechanically, there was simply less that could go wrong; the air-cooled 985 cm³ 25 hp (19 kW) motors proved especially effective in action in North Africa's desert heat.
A handful of civilian-specific Beetles were produced, primarily for the Nazi elite, in the years 1940–1945, but production figures were small.
1950 VW Convertible
Pseudo-Extinction Species (read Boggs, p. 488). Still, this beetle’s lineage lives on.
1935 KdF-Wagen sp. (Porsche)
The Beetle evolvesBy 1938, the "Beetle" shape had fully evolved. A rigorous testing programme was launched, with men of the feared SS driving a batch of the cars for many thousands of miles through the worst winter weather.
Herbie goes abroad
By 1951, the car was available in 29 countries.
By 1972, 15,007,034 Produced
The Neputinist approach of Werner
Abraham Werner (1749-1817) Did not agreed with the theory of the catastrophes of the Cuvier. For him, allthe rocks (including the igneous) would have precipitated in a huge global ocean ("neptunisme").
In furthering Hutton’s magic formula "the present is the key to the past,” Lyell’s book "Principles of Geology" (1830) was a big success.
Charles Lyell (England; 1797-1875)
According to him, the geological processes such as the uplift and erosion operated at a slow and uniform speed. Further, every geological period lasted a long time (eventually hundreds of million years) and the age of the Earth must correspond to a multiple of these long lengths.
See next slide
Unlike Will Smith, who used fossils as an aid to identify strata, Lyell (and others at the time) recognized the utility of subdividing the Tertiary on the basis of its fossil content alone.
Lyell’s approach was to use the proportions of living and extinct species in the rocks. It is here that fossils became the essential part of subdividing Geologic Time.
(183
3)
Working in the Jurassic of Europe, Albert Oppel invented the concept of overlapping (aka concurrent) « zones » of fossils and thereby altered for all time the practice of biostratigraphy.
No one since Oppel’s time has been able to devise a more precise and reliable kind of time-stratigraphic fossil zone.
(18
56
)CONCEPT OF THE BIOZONE
Carl Albert Oppel (1831–1865), Germany paleontologist
Boggs,14.2
An Oppel Zone:Overlapping ranges of two or more taxa
Oppel Named his Zones after a particularly distinctive fossil, which he called the Zone’s “Index Fossil.”
PRINCIPALTYPES OF BIOZONES
Gap Biozone
Biozonesmay begrouped orsubdivided
Named forone or moredistinctivetaxa in it
- An Assemblage Zone is Different - It’s usually a biogeographic group of three or more taxa
- Range of One -An Overlap of Ranges
-Lowest occurrrences(LADs)
Highestoccurrrences(FADs)
GAPZONE
?
Examples of Correlations based on “Taxon-Range Zones” and “Interval Zones”
LAD A
A/B Gap Zone
FAD B
FAD C
FAD E
LAD D
C/D Gap Zone LAD C
LAD B
LAD A
FAD C
LAD B
Zone 8 AnotherConcurrent RangeZone
Concurrent RangeZone
AbundanceBiozones
AKA:Acme Zones
Time Transgressive Abundance Zones
Local vs.Total (Global) Range
?
Species F is different ages
in different places?
Biogeographic Dispersal and Stratigraphic Range
Ocean A Ocean B
TimeinA
Time in B
TOTAL Time in A and B
Barrier
If Total Time is Global, becomes aBIOCHRONOZONE
REMEMBER:• Evolution• Migration• Extinction• Environment• Preservation
Correlation by Assemblages
Assemblage Zone = Characteristic group of 3 or More Taxa.Commonly, these are environmentally restricted by facies
Boggs, 14.8
Shaw’s Graphic Correlation Method
What can we do here?
Shaw’s Method is to plot the heights of the fossil datums in each section
versus each other.
• Here, the correlation line is straight, meaning there was a constant offset in sediment accumulation rates between the sites
• Using the fossil datum correlation line, any part of Section A can be correlated to an equivalent part of Section B.
Shaw’s Method is to plot the heights of the fossil datums in each section
versus each other.
• The point at 50 m in A corresponds in time to the point at 25 m in B.
• The point at 50 m in B corresponds to 100 m in A!
Shaw’s Method is to plot the heights of the fossil datums in each section
versus each other.
• The point at 50 m in A corresponds in time to the point at 25 m in B.
• The point at 50 m in B corresponds to 100 m in A!
So, what exactly is the relative rate of sedimentation between these two sections?
Answer: y = mx +b or, rate in A = 2 times rate in B
But, what is there if the sedimentation rate changes in one section relative to the other section?
What if there are unconformities?
Or….
See Nichols, Fig. 20.5
Deposition stops in “A” while continuing in “B”
“A” speeds up OR “B” slows down
Shaw
Dia
gra
ms
to t
he R
esc
ue!
Globorotalia truncatulinoides
WarmCold
1.5
Ma
A prelude to Oxygen Isotope Stratigraphy: Planktonic Foraminiferal Coiling Ratios
TEMPORAL RESOLUTION ISSUES
Go Steve Go!
RELATIVE STRATIGRAPHIC RESOLUTIONBIOCHRONOLOGIC VS RADIOMETRIC DATING
Average biochronologic resolution: 1 Ma Typical uncertainty range of radiometric dating: 1% - 10%
Biochronological precision exceeds isotopic dating methods for most of Phanerozoic. Isotopic dating, however, is used to calibrate ages of biostratigraphic zones and convert zonal schemes to an equal-interval time scale, an objective that can not be achieved by fossils alone.
Mioc
ene
Cretaceous
1 Ma
Precambrian
(From Taylor, A. , 1987, Stratigraphic Resolution)