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Biostratigraphy
• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy
Text: Manual, p. 31; Boggs, Ch. 17
Biostratigraphy
Biostratigraphy: divide and correlate rock packages using fossils.
* Boundaries may or may not correspond to lithostratigraphic boundaries.
Basis of Biostratigraphy
http://www.geo.utexas.edu/courses/401/
Faunal Succession
Systematic progression of fossils with time. Extinct fossils do not reappear in younger rocks.
Basis of Biostratigraphy
• Genetic Variation and Inheritance
• Changing Environmental Conditions
• Natural Selection
Evolution: all living things share a common history
(Stanley, 1993)
punctuated evolution
gradual evolution
(after Gould, 1989)
Basis of Biostratigraphy
• rapid burst
• small populations
• geographic isolation
http://evolution.berkeley.edu/
Basis of Biostratigraphy
Basis of Biostratigraphy
• catastrophic events
• local environmental change*
http://evolution.berkeley.edu/
Extinctions
OrdovicianDevonianPermianTriassic Cretaceous
Biostratigraphy
• Determine ranges of fossils in section
• Divide into Biozones
Methods
Range: First to last occurrence of a taxon
Biozone: basic unit of biostratigraphy
index fossil: a fossil that is useful to determine biozones
• abundant fossils
• widespread distribution
• lived for short period of time
• readily preserved
• clear identifcation
Basis of Biostratigraphy
Characteristics of Good Index Fossils
Basis of Biostratigraphy
Index Fossils
http://www.ucl.ac.uk/GeolSci/micropal/
conodonts
diatoms
foraminifera radiolaria
pollen
Basis of Biostratigraphy
Index Fossils
Biostratigraphy
• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy
Text: Manual, p. 31; Boggs, Ch. 17
Biozones
1. Interval Zones
2. Assemblage Zones
3. Abundance Zones
Types of Biozones
Biozones
1. Interval Zones – based on occurrences of 1 or 2 taxa.
Types of Biozones
• Taxon Range Zone – FAD and LAD of one taxon
• Concurrent Range Zone – overlap between: FAD Taxon 1 and LAD Taxon 2
• Partial Range Zone – gap between: LAD Taxon 1 and FAD Taxon 2
• Lineage Zone – FAD of Taxon 1 and FAD of Taxon 2 (a descendent)
• Interzones – interval with no fossils
Types of Interval Zones
Biozones
Biozones
1. Interval Zones – based on occurrences of 1 or 2 taxa.
2. Assemblage Zones – based on association of 3 or more taxa.
Types of Biozones
Biozones
Assemblage Zones
Biozones
1. Interval Zones – based on occurrences of 1 or 2 taxa.
2. Assemblage Zones – based on association of 3 or more taxa.
3. Abundance Zones – based on peak abundance of one or more taxa.
Types of Biozones
Biozones
Abundance Zones
Not Necessarily Time Equivalent!
• Taxon Range Zone?
• Concurrent Range Zone?
• Assemblage Zone?
Biozones
• Partial Range Zone?
• Abundance Zone?
• Lineage Zone?
Biozones
Biostratigraphy
• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy
Text: Manual, p. 31; Boggs, Ch. 17
Examples
• index fossils• principles of stratigraphy• marker horizons• geophysical properties• geochemical properties
http://www.uwsp.edu/geo/faculty/ozsvath/images/stratigraphy.jpg
Correlation
Examples
Multiple Zones
Examples
Sedimentation Rates
Biostratigraphy
• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy
Text: Manual, p. 31; Boggs, Ch. 17
Problems
• Facies Control on Distribution
• Taphonomy
• Collection and Identification Bias
Problems
Environmentally Restricted Distribution of Species
Biostratigraphy
• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy
Text: Manual, p. 31; Boggs, Ch. 17
Magnetostratigraphy
• normal magnetic field – polarity like today
• reversed magnetic field – polarity opposite of today
(Stanley, 1989)
Magnetostratigraphy: divide and correlate rock packages using magnetic properties of the rock.
Magnetostratigraphy
• decrease in magnetic field strength
• reversal
• increase in magnetic field strength
(Long, 2005)
Remnant Magnetism
Magnetostratigraphy
Magnetostratigraphy
Polarity Zone
Magnetostratigraphy
Correlation
Biostratigraphy
• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy
Text: Manual, p. 31; Boggs, Ch. 17
Chemostratigraphy: divide and correlate rock packages using chemical properties of the rock.
Chemostratigraphy
Isotope
Chemostratigraphy
Chemostratigraphy
Chemostratigraphy
Strontium Isotopes
• 87Rb 87Sr
• Old Crust – High 87Sr/86Sr
• Sr sources vary