2. Concepts Related to Subdivision of the Rock Record
Stratigraphy
Concepts Related to Subdivision of the Rock Record

3. Inextricably Related Issues in Geology (that must be distinguished!)
Material Units: The Rock Record
Have physical extent and consist of tangible material
The material record of events that have occurred during the passage of geological time
Geological Time: The Abstraction of Time Since the Advent of the Earth
Measured in years before present
Divided into discrete intervals
Ma; millions of years before present
Ga; billions of years before present

4. Subdivision of the Rock Record
Lithostratigraphy –
study of the physical relationship among rock units;
no time connotation other than superposition
Otbo physical properties and stratigraphic position relative to other lithostrat units
Chronostratigraphy –
integrated approach to establishing the time relationships among geologic units

5. Chronostratigraphy: Integrated Approach to Establishing the Time Relationships Among Geologic Units
Biostratigraphy
Study of the fossil record with emphasis on faunal succession to establish relative time relationships
The correlation web
Magnetostratigraphy
Study of the magnetic properties of rock units for the purpose of correlation otbo magnetic polarity reversals
Allostratigraphy
Study of rock units defined by unconformities and other features generated by base level change
Geochronology
various techniques, especially isotope geochemistry, to establish the absolute age of rock units

6. M o r e L a t e r

7. Stratigraphic Correlation

8. Lithostratigraphy Formations, Members, Groups, etc.
Material Units and "Classical Layer Cake Stratigraphy“
catastrophism: continuous layering = time equivalence
NO!
Further organization and subdivision of the rock record otbo
Relative age
Superposition, unconformities, cross cutting relationships, included fragments
Original Horizontality
Lateral Continuity

9. Objective Subdivision of the Stratigraphic Record Into Distinct Lithostratigraphic Units
Formations
with a type section, geographic or lithologic name, and definition based on
limited and distinctive lithologic variability
consistent stratigraphic context
“extensive” map distribution in the surface or subsurface
Groups and Supergroups
Are formations lumped otbo stratigraphic association
Members and beds
Subdivisions of Formations
lithostrat units with less areal extent defined as it is useful

10. Actualism and "Genetic Stratigraphy"
Recognition of Uniformitarianism
the relationship between modern processes of sedimentation and the rock record

11. Actualism and "Genetic Stratigraphy"
Sediments with distinct lithologic aspect are deposited in only limited areas in a given time period.
This results from the limited lateral extent of contiguous depositional environments.
Distinct depositional environments migrate in space, through time so that lithofacies units are inherently diachronous (variable in age throughout)

12. Diachronous Stratigraphic Units

13. Diachronous Stratigraphic Units
Basement

14. Actualism and "Genetic Stratigraphy"
Sedimentary (litho)Facies:
lithologic aspect; a result of depositional process not age.
Lithologically distinct sediment bodies deposited synchronously in adjacent sites (distinct lithofacies) must be separated across some kind of boundary.
Such contemporaneous and physically associated strata are said to be in Facies Relationship.
Lithologic aspect in space is not directly equitable to time but rather depositional process at that place at some time.

15. Geometry of Facies/Lithostratigraphic Relationships

16. Actualism and "Genetic Stratigraphy"
Depositional Processes -----> Geological Product
Sedimentary Depositional Environments Sedimentary Lithofacies
Defined by
Lithology
Sedimentary structures (physical, chemical, deformational, etc)
Geometry: bedding scale and outcrop scale, vertical trends
Paleocurrent indicators
Fossils

17. 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.”
Also, lith units in conformable vertical relationship were in lateral relationship during deposition

18. Autostratigraphic Variation Autocyclicity
Lithologic variability, within distinct geomorphic settings, in space and time may be the result of variations in depositional conditions inherent to that depositional environment----->

19. External Controls on Stratigraphic Architecture: Allocyclicity
Variation in lithologic character due to regional scale variations in Base Level
level at the earth's surface above which permanent sediment accumulation does not occur
Closely related to local sea level
Basin Subsidence (tectonic)
Eustacy (global sea level)
Sediment input (climate and topography/tectonics)

20. Unconformity

21. Transgression and Regression Geometric relationship of idealized "graded, shore parallel facies belts“
deepening upwards, shoreline moves landward through time:
Transgression
Basin Subsidence, +/- Sea Level Rise, +/- Sediment Starvation (With Subsidence)
May (rarely) leave a distinct material record--->
Marine flooding surfaces
Ravinement surfaces
Landward shift in sedimentary facies up section

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

23. Transgression and Regression
Shallowing upwards, shoreline moves basinward through time
Regression
sea level drop, +/- uplift, +/- sediment supply
Progradation; Normal Regression
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:
Abrupt Basinward Shift In Sedimentary Facies Upsection
Strata across lithologic boundaries NOT in accordance with Walther’s law

24. 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

25. Causes of Base Level Change
Relative
Change
Eustatic
Change

26. 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

27. Transgression/Regression vs. Relative Sea Level
Relative Sea Level Curves

28. Transgression/Regression and Relative Sea Level