Determining the Relative and Absolute Age of Map Units 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 Nonconformity Angular Unconformity Grand Canyon Stratigraphy Disconformity

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 First Major Extinction Event ?? 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 87Rb  87Sr; 86Sr is stable Rb – chemically substitutes for K Sr – chemically substitutes for Ca 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)