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 Faunal Succession Systematic progression of fossils with time. Extinct fossils do not reappear in younger rocks. The fifth tool that will help us determine the age relationships of rock layers in the Grand Canyon is a tool called Faunal Succession. This principle recognizes that organisms evolve through time, When, a species goes extinct, it will never reappear again in younger rocks. You can see on the chart above that there are established ranges in time during which different organisms like dinosaurs and humans have lived. The important thing here is that there are predictable sequences of fossils that we will see as we look at a progression of older to younger rocks. The patterns reproduce themselves in many places throughout the globe and are very useful to determining when a rock formed relative to other rocks. http://www.geo.utexas.edu/courses/401/

Basis of Biostratigraphy Evolution: all living things share a common history Genetic Variation and Inheritance Changing Environmental Conditions Natural Selection The fifth tool that will help us determine the age relationships of rock layers in the Grand Canyon is a tool called Faunal Succession. This principle recognizes that organisms evolve through time, When, a species goes extinct, it will never reappear again in younger rocks. You can see on the chart above that there are established ranges in time during which different organisms like dinosaurs and humans have lived. The important thing here is that there are predictable sequences of fossils that we will see as we look at a progression of older to younger rocks. The patterns reproduce themselves in many places throughout the globe and are very useful to determining when a rock formed relative to other rocks. (Stanley, 1993)

Basis of Biostratigraphy punctuated evolution gradual evolution rapid burst small populations geographic isolation (after Gould, 1989)

Basis of Biostratigraphy http://evolution.berkeley.edu/

Basis of Biostratigraphy Extinctions Ordovician Devonian Permian Triassic Cretaceous http://evolution.berkeley.edu/ catastrophic events local environmental change*

Biostratigraphy Methods Determine ranges of fossils in section Divide into Biozones Range: First to last occurrence of a taxon Biozone: basic unit of biostratigraphy

index fossil: a fossil that is useful to determine biozones 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

Basis of Biostratigraphy Index Fossils

Basis of Biostratigraphy conodonts pollen diatoms foraminifera radiolaria In the Grand Canyon, some of the best indicators of relative ages in the rocks are the fossils that we can’t even see. Microscopic fossils like the single-celled group of foraminifera are extremely valuable in assigning ages to many of the rock layers of the Grand Canyon. As are the microscopic fossils called conodonts which are found widespread in rocks that formed in marine environments. Because they are so widespread, and composed of the mineral apatite, they are believed to be the teeth of sea creatures that swam around the oceans losing quite a few teeth, Conodonts and foraminfera and other plankton like radiolarians and even tiny grains of fossil pollen are widespread in rocks around the world and show a pattern of species evolution through time and are extremely valuable in determining relative ages of rocks in the Grand Canyon and around the world. Index Fossils http://www.ucl.ac.uk/GeolSci/micropal/

Biostratigraphy Basis of Biostratigraphy Biozones Examples Problems Magnetostratigraphy Chemostratigraphy Text: Manual, p. 31; Boggs, Ch. 17

Biozones Types of Biozones 1. Interval Zones 2. Assemblage Zones 3. Abundance Zones

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

Biozones Types of Interval Zones

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

Biozones Assemblage Zones

In this example, you see that in a sequence of rocks, you might find an assemblage of different fossils, some with shorter and some with longer periods of time in which they lived. So we can you the presence of not just one, but a combination of different fossils to constrain the time period in which that rock layer formed.

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.

Biozones Abundance Zones Not Necessarily Time Equivalent!

Biozones Taxon Range Zone? Concurrent Range Zone? Assemblage Zone?

Biozones Partial Range Zone? Abundance Zone? Lineage Zone?

Biostratigraphy Basis of Biostratigraphy Biozones Examples Problems Magnetostratigraphy Chemostratigraphy Text: Manual, p. 31; Boggs, Ch. 17

principles of stratigraphy marker horizons geophysical properties Examples Correlation index fossils principles of stratigraphy marker horizons geophysical properties geochemical properties http://www.uwsp.edu/geo/faculty/ozsvath/images/stratigraphy.jpg

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 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

Magnetostratigraphy decrease in magnetic field strength reversal increase in magnetic field strength Remnant Magnetism (Long, 2005)

Magnetostratigraphy

Magnetostratigraphy Polarity Zone

Magnetostratigraphy Correlation

Biostratigraphy Basis of Biostratigraphy Biozones Examples Problems Magnetostratigraphy Chemostratigraphy Text: Manual, p. 31; Boggs, Ch. 17

Chemostratigraphy Chemostratigraphy: divide and correlate rock packages using chemical properties of the rock. Isotope

Chemostratigraphy

Chemostratigraphy

Chemostratigraphy Strontium Isotopes 87Rb  87Sr Old Crust – High 87Sr/86Sr Sr sources vary