Transcript PwrPt

GEOL 3000
Geologic Maps
Determining the Relative and
Absolute Age of Map Units
Relative Age Dating - Superposition
Up isn’t always
Younging
Up Indicators
Graded Bedding
Pillowed Lavas
Amygdaloidal Zones in Lavas
Cross-bedding
Ripple Marks
Sedimentary Facies – Time Trangressive Units
Paleogeography of Middle Laurentia in the Paleozoic
Advanced Transgression
Regression
Paleozoic Formations of the Upper Midwest
Principles of
Faunal Succession
and Faunal Assemblage
Index Fossils
- Widespread distribution
- Restricted, known time of existence
- Common to many environments
The Jordan Sandstone
Unconformity
Missing Fossils
Gaps in the Geological Record
Unconformities
Siccar Point, Scotland
“The mind seemed to grow giddy
looking so far into the abyss of
time”
John Playfair – Illustrations of
Huttonian Theory (1809)
Creating
Unconformities
Angular Unconformity
Nonconformity
Grand Canyon
Stratigraphy
Unconformities
or
Pinch-outs?
Gaps in the Minnesota Timescale
Regional Correlation of Units
Piecing the Rock Record Together
Relative Time
for Intrusive
Igneous
Rocks
Principle of
Cross-cutting
Relationships
Global Time Markers
Volcanic Ash Eruptions
Global Time Markers
Meteor Impacts
K-T Boundary
mudstone-impact layer
coal
K-T impact site
The 1.875 Ga Sudbury Impact
The First Major Extinction Event ??
Global Time Markers
Magnetic Reversals
Global Time
Markers
Climate Change
Absolute Age Determinations
Radiometric Dating
Radioactive Isotopes
Radioactive Decay
Radioactive
Decay Half-life
Zircon
ZrSiO4
U substitutes
for Zr, but Pb
does not.
Rb-Sr Dating of a Granite
 87Sr; 86Sr is stable
Rb – chemically substitutes for K
Sr – chemically substitutes for Ca
87Rb
Isochron
t=2
t=1
87Sr/86Sr
Metamorphism
at t=1
87Sr/86Sr°(m)
t=0
87Sr/86Sr°
87Rb/86Sr
Ca-plagioclase
Granite whole rock
K-feldspar
Biotite (K-rich)