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