GEOL 3000GEOL 3000Geologic MapsGeologic Maps

Determining the Relative and Determining the Relative and Absolute Age of Map UnitsAbsolute Age of Map Units

Relative Age Dating - SuperpositionRelative Age Dating - Superposition

Up isn’t always Up isn’t always YoungingYounging

Up IndicatorsUp Indicators

Cross-bedding

Ripple Marks

Graded Bedding

Amygdaloidal Zones in Lavas

Pillowed Lavas

Sedimentary Facies – Time Trangressive UnitsSedimentary Facies – Time Trangressive Units

Paleogeography of Middle Laurentia in the PaleozoicPaleogeography of Middle Laurentia in the Paleozoic

Advanced TransgressionAdvanced Transgression RegressionRegression

Paleozoic Formations of the Upper MidwestPaleozoic Formations of the Upper Midwest

Principles of Principles of Faunal SuccessionFaunal Succession

and Faunal Assemblageand Faunal Assemblage

Index Fossils - Widespread distribution- Restricted, known time of existence- Common to many environments

The Jordan SandstoneThe Jordan SandstoneUnconformityUnconformity

Missing FossilsMissing Fossils

Gaps in the Geological RecordGaps in the Geological RecordUnconformitiesUnconformities

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 Creating UnconformitiesUnconformities

Angular Unconformity

Disconformity

Nonconformity

Grand Canyon Stratigraphy

Unconformities Unconformities or or

Pinch-outs?Pinch-outs?

Gaps in the Minnesota TimescaleGaps in the Minnesota Timescale

Regional Correlation of UnitsRegional Correlation of UnitsPiecing the Rock Record TogetherPiecing the Rock Record Together

Relative Time Relative Time for Intrusive for Intrusive

Igneous Igneous RocksRocks

Principle of Cross-cutting Relationships

Global Time MarkersGlobal Time MarkersVolcanic Ash EruptionsVolcanic Ash Eruptions

Global Time MarkersGlobal Time MarkersMeteor ImpactsMeteor Impacts

K-T impact site

K-T Boundary

coal

mudstone-impact layer

The 1.875 Ga Sudbury ImpactThe 1.875 Ga Sudbury ImpactThe First Major Extinction Event ??The First Major Extinction Event ??

Global Time MarkersGlobal Time MarkersMagnetic ReversalsMagnetic Reversals

Global Time Global Time MarkersMarkers

Climate ChangeClimate Change

Absolute Age DeterminationsAbsolute Age DeterminationsRadiometric DatingRadiometric Dating

Radioactive IsotopesRadioactive Isotopes

Radioactive DecayRadioactive Decay

Radioactive Radioactive Decay Half-Decay Half-

lifelife

ZirconZrSiO4

U substitutes for Zr, but Pb does not.

87Rb 87Sr; 86Sr is stableRb – chemically substitutes for KSr – chemically substitutes for Ca

87Rb/86Sr

87Sr/86Sr

Ca-plagioclaseGranite whole rockK-feldsparBiotite (K-rich)

t=087Sr/86Sr°

t=1

Metamorphismat t=1

t=2Isochron

87Sr/86Sr°(m)

Rb-Sr Dating of a Rb-Sr Dating of a GraniteGranite