Geologic Time Scale
• Our calendar of Earth History - Geologic Time Scale
• Constructed using relative concepts - calibrated numerically
• Units of time
• Eon, Era, Period
Rocks versus Time
• With the person next to you discuss the following
• Why do geologists treat time and rocks as separate entities…even
going so far as having different divisions or units when dealing with rock versus
time?
Rocks versus Time
• Time divisions
– Eon, Era, Period, Epoch, Age
• Rock Divisions
– Eonothem, Erathem, System, Series, Stage
The Formation
• The study of sedimentary rocks in time and space
– stratigraphy
• Formation - similar origins
• Groups, members, and beds
Lateral Variation of Formations
• Lateral extent limited - size and shape of basin
• Changes in thickness and rock type
• intertonguing
DEPOSITIONAL ENVIRONMENTS AND SEDIMENTARY FACIES
• What is a formation and why does it change laterally?
• Sedimentary Facies
– Total aspect of the rock
• Depositional Environments
– Have limited lateral extent and grade into one another
T & R and Facies Patterns
• Why are sedimentary rocks/strata layered?
• Facies shift positions through time
• Transgression - landward shift
• Regression - seaward shift
Walther’s Law
• Vertically stacked facies were once adjacent environments
• Only applies within conformable intervals of rock
• Does this interval represent a transgression or regression?
Local vs. Worldwide T&R’s
• Global Changes in Sea Level = Eustatic Changes
• Mechanisms
– Plate tectonics
– Changes in Global Ice Volume
Local vs. Worldwide T&R’s
• Local Changes in Sea Level = Relative Change
• Change along any coastline function of
– Eustacy
– Sediment supply
– Tectonics - subsidence and uplift
– Coastal configuration
Biostratigraphy
• Since formations and facies change laterally - how do we keep track
of time?
• Biostratigraphy
• Biozones (index fossils)
– Range of occurrence
– FAD’s and LADS
– Concurrent range zones
Biostratigraphy
• What are the requirements of a good index fossil
– Common
– Widespread
– Distribution not determined by environment - facies fossils
– Short lived (as a species)
Biostratigraphy
• Common Groups
– Ammonites
– Conodonts
– Foraminifera