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

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. Modern Stratigraphy Still focuses on synthesis
Has evolved to include many new techniques + deep marine realm
many of the advances are driven by need to have very precise age control
Can resolve:
events in some section to the order of < 20 ky
patterns of events within a basin (regional)
patterns by correlating between basins (need more than 1 data point) (global)

4. Stratigraphy Initially used informally Now, governed by
North American Stratigraphic Code
International Stratrigraphic Code

5. History of Stratigraphy
Based on idea that strata (layers of sediment) are deposited one on top of another
oldest at bottom and youngest at top, over long period of time (ky - my) (1000s to 1,000,000s of years)
Relatively recent concept

6. History of Stratigraphy
Greeks and Romans
Recognized world was ever changing and thought of it as eternal
Fall of Rome and Rise of Church
Developed idea of world based on literal interpretation of bible
Attributed variations to Noah’s flood
e.g., seashells high in Italian Appenines (near Florence)
Either Noah’s flood brought them or God’s mystery

7. History of Stratigraphy
Renaissance and age of Reason
Began to move away from extreme views and began to develop scientific principles
Da Vinci ( )
Suggested rivers had carried the shells down from the Alps
Mix of mud and fossils turned to stone, uplifted
wrong, but significant in that it showed beginning of change in thought

8. Da Vinci’s Insight
In 1500 C.E. Leonardo Da Vinci recognized that fossil shells in the layered rocks represented ancient marine life
Observed that many fossil rich layers were separated by unfossiliferous layers thereby repudiating the concept of one flood
Had the idea that seasonal events responsible

10. History of Stratigraphy
Nicolaus Steno
Niels Stensen ( )
famous for Stenos’ laws
Worked near Tuscany
First to suggest IN PRINT that rocks enclosing fossils had at one time been soft
Sharks’ teeth convinced him
Noticed living sharks had teeth identical to ‘tonguestones’
Petrified tongues of dragons and snakes
Realized shark’s teeth were deposited in mud, which encased the teeth and then hardened

11. History of Stratigraphy
Steno’s Laws
Original horizontality
Original continuity
Superposition
Provides set of rules for organizing or ordering strata into relative ages
Idea caught on but was derailed by the Neptunians

12. History of Stratigraphy
Neptunians
Arduino
Ordered same Tuscan rocks as Steno into 4 groups
Primitive (Schists, basalts, granite cores of mountains)
Secondary (ls, shale; fossiliferous sedimentary rocks)
Tertiary fossiliferous sedimentary rocks found in hills
Not universally applicable!

13. History of Stratigraphy
Werner
Rocks form from flood and then precipitated in flood
(goofy, but not that unreasonable!)
Primitive
Transition
Stratified
Alluvial

14. History of Stratigraphy
Plutonists
Fought for fiery, volcanic rock
Hutton
Father of Geology!
Uniformitarianism
No begninning and no end
Saw Earth as an engine
1795- published the Theory of the Earth
“anti- church”; not easy to read
Lyell
Took extreme view to defend plutonisms against neptunists
Actualism (uniform natural laws and processes)
Gradualism (uniform RATES of change)

15. History of Stratigraphy
William Smith
Engineer; surveyor (late 1700’s)
Analyzed rocks exposed in mines, canals of England
Realized rock units had distinct fossils and could use them to recognize rock units, and named them
Law (Principle of ) Faunal Succession
Can divide rock record based on fossils
Cuvier
1769 – 1832
Also recognized faunal succession but didn’t use it like Smith for correlation
(Focused on Paris Basin)

16. William Smith, Father of Stratigraphy
The Map that Changed the World, Simon Winchester
1796 wrote “wonderful order and regularity with which nature has disposed of these singular productions [fossils] and assigned to each its class and peculiar stratum”
1815 Publication of the 1st geologic map of England intended for the development of canals, quarries and mines as well as natural resources

19. William Smith’s "Strata Identified by Organized Fossils"
Soon after the first issue of his great geological map of England in 1815, William Smith published the Strata Identified by Organized Fossils.
It was intended as a kind of geological users manual with illustrations to identify fossils.
But Smith’s work went beyond the mere illustration of fossils. Smith had deciphered the hieroglyphics of nature-the distinctive inscriptions borne by the different strata. With the Strata Identified and its colored plates in hand, anyone would be able to compare the plates with fossils collected in the field and immediately identify the strata from which they came.
The strata once identified, their place in the orderly succession of the strata-which lay above and which lay below, as Smith had determined it - was then known. All this, Smith wrote, "without the necessity of deep reading, or the previous acquirement of difficult arts."

21. Georges Cuvier and Alexandre Brongniart- Paris Basin
Development of geologic map of Paris Basin
The strata of the Paris Basin were close to horizontal.
As of 1811, Cuvier and Brongniart employed fossils but only in the few instances where more obvious evidences of sequence were absent.
The title of their work was Géographie Minéralogique by which they meant the distribution of what Werner had called the "external" characteristics of the mineral and fossil contents, shapes, colors, and textures of the strata within the Paris basin.
Today call this lithology. They determined the order of the strata from their superposition, their lithology and by tracing them across the basin
Cuvier firmly established the fact of the extinction of past lifeforms

23. History of Stratigraphy
Time Scale
A way of formally organizing rocks and time
Artificial division of time
Evolved as workers began to apply scientific principles to the study of rocks
Smith, Cuvier, others
Named rocks
Rock names became basis for time scale

24. GEOLOGIC TIME SCALE

25. Subdivision of the Rock Record
Lithostratigraphy –
Study of the physical relationship among rock units;
No time connotation other than superposition
Physical properties and stratigraphic position relative to other lithostratigraphic units
Chronostratigraphy –
Integrated approach to establishing the time relationships among geologic units

26. 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 using 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

28. Stratigraphic Correlation

29. Types of Stratigraphy Each has separate role
Ultimate goal is integration and better interpretation (more refined)
Additional divisions of stratigraphy
Stratigraphic Code
Divided into sub-disciplines based on physical limits or geologic age

30. Lithostratigraphy Definition
Study of the sequence and interpretation of layered rock sequences, based on PHYSICAL CHARACTERISTICS (lithology) of the rocks
Essentially, study of TIME
Allows us to ORDER events!

31. Lithostratigraphy 2 uses of term lithology
Study and description of physical characteristics of rocks
Especially hand specimen and outcrop
e.g., investigate the lithology
Term that refers to these physical characteristics
e.g., lithology of a stratigraphy unit- such as sandstone

32. Lithostratigraphy Divide rocks on basis of lithology Stratotype
Designated type unit of readily accessible rocks in natural outcrops, mines or bore holes.
Type section
Formal designation
Lithosome
Masses of rock with uniform character
Dissolve away all other rock Sloss (1963)
Informal designation

33. Lithostratigraphy Some generalizations about lithostratigraphic units
Sedimentary, extrusive igneous, meta-sedimentary, meta-volcanic
Generally conforms to law of superposition
Commonly stratified (layered) and tabular in form
Identification is based on observable rock characteristics
Boundaries can be either sharp and clear, or gradational

34. Uses of Lithostratigraphy
What lithostratigraphy can do for you
Place unit in geologic framework
Establish stratigraphic relationship with units above and below
Aid in correlation between other LITHOLOGIC units
What it CAN’T do for you
Denote time

35. Units of Lithostratigraphy
Lithostratigraphic classification and nomenclature
System for standardization
Fundamental unit
Formation
Lithologically distinctive stratigraphic unit that is large enough in scale to be mappable at the surface or traceable in the subsurface.
May be just 1 lithosome or multiple
Subdivision of formation

36. Lithostratigraphy Other formal lithostratigraphic units
Smaller than a formation
Member
Subdivision of a formation
Bed
Smallest formal lithostratigraphic unit
Collections of formations
Group
2 or more adjacent formations that have some unifying lithological and/ or genetic features
Supergroup
Groups of groups
e.g., Newark Supergroup

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

38. Types of Contacts Conformable boundaries Abrupt or gradational
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

39. Types of Contacts Intercalated contact Laterally adjacent contacts
Increasing number of interbeds of another lithology
Laterally adjacent contacts
Pinch-outs
Inter-tonguing
Progressive lateral gradation

40. Geometry of Facies/Lithostratigraphic Relationships

41. Unconformable Break in deposition Unconformity: Diastem Interpretation
Strata do not succeed 1 another as a continuous whole
Separated by an unconformity
Lack of continuity in deposition
Unconformity:
Surface of erosion or non- deposition separating younger strata from older rocks
Represents a significant hiatus
Diastem
Minor interruption in depositional conditions
Interpretation
Period of non-deposition, weathering or erosion
Such processes may occur sub-aerially (exposed to air) or sub-aqueously (under water)

42. Unconformities Types of unconformities Angular unconformity
Nonconformity
Disconformity
Erosional surface between // units
Paraconformity (obscure)-
// units with no obvious erosional surface b/n the units
use obscure traits to identify it

43. Unconformity

44. Following Stratigraphic Code

45. Unconformities Hiatus
Total interval of geologic time represented by missing strata
At a specific position along a stratigraphic sequence
Don’t confuse syndepositional variations with post-depositional alteration of beds
Groundwater changes color (Fe) or resistance (cementation)

46. Vertical/lateral variations in rock
Recognition of lateral variation
Because rocks are not constant through space, you get a variation in lithology within one unit.
Initially people didn’t recognize this-
Thought Noah’s flood left layer cake layers of strata that extended to ends of Earth without change in lithology or thickness
Began to trace beds
walked them
looked at how the rocks between the boundaries changed
realized fallacy of idea
We retain layer cake to describe stacking pattern; not infinite nature

47. 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

48. 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.”

49. 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

50. 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

51. 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

52. 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

53. 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!

54. Causes of Sea Level Change
Relative
Change
Eustatic
Change

55. 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

56. Transgression and Regression/ Relative Sea Level

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

58. base level of aggradation
Base level of erosion
level below which erosion cannot occur ( = sea level)
not strictly true!
you do get erosion below sl.
storms = erosion on shelf
downcurtting = canyons on slopes
deep sea currents = erosion of sea floor
base level of aggradation
level above which sediments cannot accumulate permanently
most marine sediments dominate record
rise in sea level tends to result in increased preservation of seds
high rate of erosion explains why there are “more gaps than record” in geol. record.

59. Correlation Lithostratigraphic Correlation PROCEDURE Match Correlate
match lithologies
Correlate
link units of similar lithology and stratigraphic position
PROCEDURE
identify environments of deposition
(use simple depositional model)
draw lines of correlation between adjacent facies
make interpretation- trans/ regression/ no change

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

61. 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)

62. Diachronous Stratigraphic Units

63. Diachronous Stratigraphic Units
Basement