Biostratigraphy

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Biostratigraphy

• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy

Text Manual, p. 31 Boggs, Ch. 17
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Biostratigraphy
Biostratigraphy divide and correlate rock
packages using fossils.
Boundaries may or may not correspond to
lithostratigraphic boundaries.
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Basis of Biostratigraphy
Faunal Succession
Systematic progression of fossils with time.
Extinct fossils do not reappear in younger rocks.
http//www.geo.utexas.edu/courses/401/
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Basis of Biostratigraphy
Evolution all living things share a common
history

• Genetic Variation and Inheritance
• Changing Environmental Conditions
• Natural Selection

(Stanley, 1993)
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Basis of Biostratigraphy

• rapid burst
• small populations
• geographic isolation

(after Gould, 1989)
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Basis of Biostratigraphy
http//evolution.berkeley.edu/
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Basis of Biostratigraphy
Extinctions
Ordovician Devonian Permian Triassic Cretaceous
http//evolution.berkeley.edu/

• catastrophic events
• local environmental change

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Biostratigraphy
Methods

• Determine ranges of fossils in section
• Divide into Biozones

Range First to last occurrence of a taxon
Biozone basic unit of biostratigraphy
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Basis of Biostratigraphy
index fossil a fossil that is useful to
determine biozones
Characteristics of Good Index Fossils

• abundant fossils
• widespread distribution
• lived for short period of time
• readily preserved
• clear identifcation

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Basis of Biostratigraphy
Index Fossils
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Basis of Biostratigraphy
Index Fossils
http//www.ucl.ac.uk/GeolSci/micropal/
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Biostratigraphy

• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy

Text Manual, p. 31 Boggs, Ch. 17
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Biozones
Types of Biozones
1. Interval Zones 2. Assemblage Zones 3.
Abundance Zones
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Biozones
Types of Biozones
1. Interval Zones based on occurrences of 1 or
2 taxa.

• 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

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Biozones
Types of Interval Zones
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Biozones
Types of Biozones

1. Interval Zones based on occurrences of 1 or 2
   taxa.
2. Assemblage Zones based on association of 3 or
   more taxa.

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Biozones
Assemblage Zones
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Biozones
Types of Biozones

• Interval Zones based on occurrences of 1 or 2
  taxa.
• Assemblage Zones based on association of 3 or
  more taxa.
• Abundance Zones based on peak abundance of
• one or more taxa.

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Biozones
Abundance Zones
Not Necessarily Time Equivalent!
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Biozones

• Taxon Range Zone?
• Concurrent Range Zone?
• Assemblage Zone?

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Biozones

• Partial Range Zone?
• Abundance Zone?
• Lineage Zone?

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Biostratigraphy

• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy

Text Manual, p. 31 Boggs, Ch. 17
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Examples
Correlation

• index fossils
• principles of stratigraphy
• marker horizons
• geophysical properties
• geochemical properties

http//www.uwsp.edu/geo/faculty/ozsvath/images/str
atigraphy.jpg
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Examples
Multiple Zones
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Examples
Sedimentation Rates
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Biostratigraphy

• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy

Text Manual, p. 31 Boggs, Ch. 17
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Problems

• Facies Control on Distribution
• Taphonomy
• Collection and Identification Bias

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Problems
Environmentally Restricted Distribution of Species
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Biostratigraphy

• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy

Text Manual, p. 31 Boggs, Ch. 17
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Magnetostratigraphy
Magnetostratigraphy divide and correlate rock
packages using magnetic properties of the rock.
(Stanley, 1989)

• normal magnetic field polarity like today
• reversed magnetic field polarity opposite of
  today

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Magnetostratigraphy

• decrease in magnetic field strength
• reversal
• increase in magnetic field strength

Remnant Magnetism
(Long, 2005)
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Magnetostratigraphy
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Magnetostratigraphy
Polarity Zone
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Magnetostratigraphy
Correlation
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Biostratigraphy

• Basis of Biostratigraphy
• Biozones
• Examples
• Problems
• Magnetostratigraphy
• Chemostratigraphy

Text Manual, p. 31 Boggs, Ch. 17
37
Chemostratigraphy
Chemostratigraphy divide and correlate rock
packages using chemical properties of the rock.
Isotope
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Chemostratigraphy
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Chemostratigraphy
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Chemostratigraphy

• Strontium Isotopes
• 87Rb ? 87Sr
• Old Crust High 87Sr/86Sr
• Sr sources vary