1. Stratigraphy
The study of strata (layers) of rocks with an eye toward interpreting the geologic history of the region
Closely tied to dating methods
Uses a variety of methods - fossils, stable isotopes, paleomagnetics, sedimentary cycles - to correlate and distinguish layers
Very important for oil exploration and mining

2. Basin Analysis
Use stratigraphic methods to work out sequence and timing of deposition of rocks
usually sedimentary
Synthesis of data from multiple disciplines
sedimentology to determine environment of deposition
paleontology to get time
Used to be main objective
Petroleum industry

3. Correlation
Correlation is determining that rocks are the same formation (may mean rocks are the same age) A B C B C A

4. Geochronological units
CHRONOSTRATIGRAPHY
Geochronological units

6. LITHOFACIES

7. Stratigraphic Contacts
Plane or irregular surfaces between different types of rocks
Separate units
Conformable
Unconformable

8. Types of Contacts Conformable boundaries
Conformable strata form unbroken depositional sequences
Layers are deposited by ~ uninterrupted deposition
Abrupt or gradational
Abrupt
Sudden distinctive changes in lithology
Often, local change
Gradational
Gradual change in depositional conditions with time progressive gradual contact
One lithology grades into another
e.g., ss becomes finer upsection until it becomes a siltstone

9. Lithostratigraphic units
Supergroup
Group
Formation – a mapable unit with distinctive lithic characteristics
Member
Bed

10. Facies “aspect” or “appearance”
Can be genetic (fluvial facies) or descriptive (sandstone facies)
Lithofacies – a constant lithological character within a formation E.G an evaporite
Walther Law (1894)- facies that occur in conformable vertical succession also occur in laterally adjacent environments

11. Preservation potential of rocks that are deposited
Majority of sediments in fossil record
Marine
Most sub-aerial environments
Erosional
WHY?
Accommodation space!
Space available controls accumulation
no place to put it, then no deposition
base level
balance between erosion and deposition

12. Walther’s Law of Correlation of Facies
Relationship between vertical and lateral variations
The fact that there is lateral variation in facies leads to vertical variation in facies
Walther’s Law of Correlation of Facies
Lateral variations are expressed in the vertical due to the succession of facies

13. Walther's Law of Correlation of Facies
“Only those lithofacies which are a product of sedimentary environments found adjacent to one another in the modern can be occur superimposed in continuous, uninterrupted stratigraphic succession.”

14. Walther’s Law: Transgression-Regression
Landward movement of shoreline (progessive deepening)
Stand on beach
Over time, you would be under water as shoreline moved landward
Regression
Seaward movement of shoreline
(progessive shallowing)
Results in lateral and vertical changes

15. Transgression
Geometric relationship of "graded, shore parallel facies belts“
Fining Upwards Sequence: FUS
More basin-ward facies overlie more landward facies
Compared to depositional systems models

16. Transgression and Regression
Shallowing upwards, shoreline moves basinward through time--> Regression
Sea level drop +/- uplift +/- sediment supply
Progradation
excess sediment supply relative to accommodation space
Forced Regression
Relative sea level drop and formation of erosion surfaces: Unconformity (surface of subaerial exposure)
Soils; kaolinitized, clay-rich layers
Angular discordance with underlying units (disconformity)
Plant remains, rooted zones
Non-genetic stratal relationships: basinward shift in sedimentary facies
Strata across lithologic boundaries NOT in accordance with Walther’s law

17. Regression
Geometric relationship of "graded, shore parallel facies belts“
Coarsening Upwards Sequence: CUS
More landward facies overlie more basin-ward facies
Compared to depositional systems models

18. Transgression - Regression
What drives transgression/ regression?
can’t tell from this information!
sea level change has so many components
relative = local
eustatic = global
sediment supply
can drive a regression/ transgression
ONLY KNOW that shoreline has shifted position
multiple factors responsible for sea- level change
Say sea level rise or fall and you are WRONG!
Say transgression or regression!

19. Causes of Sea Level Change
Relative
Change
Causes of Sea Level Change
Eustatic
Change

20. Sea Level Cycles 1st Order Cycles 2nd Order Cycles 3rd Order Cycles
100’s my
100’s of meters
2nd Order Cycles
10’s my
3rd Order Cycles
1-10 my
10’s of meters
Falling
Rising

21. Biostratigraphy
If two rocks contain the same fossils they must be the same age

22. Evolution Variations exist within a population
Result from mutations and other genetic accidents
Some variations are advantageous but others are not
Some are neutral
Natural Selection works on these variations
Characteristics of population shift through time = evolution

23. Bio-Events First appearances of new species
First appearances of new higher taxa
Extinctions of species
Mass extinctions of multiple taxa
Bio-events are unique points in geologic time

24. Index Fossils
Some fossils are more useful than others for relative age determinations
Fossils that are most useful are called INDEX FOSSILS
What factors would maximize a fossil’s usefulness? (i.e., What makes a good index fossil?)

25. Illustration of Principle of Faunal Succession

26. What makes a good index fossil?
Distinctive appearance/easy to recognize
Short duration between first appearance and extinction (a.k.a. RANGE)
Widespread geographic distribution (makes correlation possible across a wide area/multiple continents)

27. Characteristics of Index Fossils
Limited Stratigraphic Range
Widespread Geographic Distribution
Commonly Pelagic
Or tolerant of a wide variety of environments (found in many facies)

30. Unconformities
Unconformities are surfaces in rock that represent periods of erosion or non-deposition. In other words, time has been left out of the physical geologic rock record.
There are three (3) principal types of unconformities:
Angular Unconformity
Rocks above and below unconformity have different orientations. Shows that there was a period of deformation, followed by erosion, and then renewed deposition. Easiest of the three types to recognize because the units are at an angle truncated with the units above them.

31. Nonconformity
Rocks in a horizontal fashion were eroded down to igneous bedrock material at which time subsequent deposition of sedimentary layers commenced. Shows that there was a period of deformation, followed by erosion, and then renewed deposition. Represents the greatest amount of time left out of the geologic rock record.
Disconformity
Rocks in a nearly horizontal fashion were eroded and an erosional profile remains covered by subsequent sedimentary deposition. Shows that there was a period of erosion and then renewed deposition in nearly horizontal layers. Most difficult to recognize because the units are nearly horizontal and only a small discontinuous layer can be observed (rubble zone or soil profile).

32. Angular
Unconformity

33. Disconformity

34. Nonconformity

35. Unconformity Types Using Grand Canyon as Example

36. Stratigraphic Thinking
From D. McConnell, Geologic Time,

37. One possible interpretation...

39. Look Bob – a shooting star! Lets make a wish….

41. Were The Dinosaurs Failures?
Dinosaurs: 150,000,000 years
Recorded History: 5000 years
For every year of recorded history, the dinosaurs had 30,000 years
For every day of recorded history, the dinosaurs had 82 years
For every minute of recorded history, the dinosaurs had three weeks