The document discusses facies and stratigraphy, detailing properties of rock bodies that distinguish them from adjacent units, including lithology, composition, and sedimentary structures. It explains the significance of facies in relation to depositional environments, migration due to environmental factors, and their arrangement in vertical sequences following Walther's law. Additionally, it covers concepts of stratigraphy, including lithostratigraphy, biostratigraphy, and unconformities, emphasizing their roles in interpreting geological history.

1. Facies and
Stratigraphy

2.  Facies
 All the properties of a body of rock that allow us to differentiate
it from those above, below or laterally adjacent to it
 Properties include
 Lithology – rock type, including color, etc.
 Composition – mineral content
 Texture – grain size, sorting, roundness
 Sedimentary structures
 Fossils
 Facies means aspect – same Latin root as “face”
 Overall appearance of a rock body
 Facies are the products of depositional environments
 Examples:
 Planar laminated fine quartz arenite facies
 Bioturbated, poorly sorted muddy skeletal limestone facies
 Cross-stratified arkosic conglomerate facies
 Stromatoporoid-tabulate coral reef facies

3. • Facies:
• Can be genetic (fluvial facies) or descriptive
(sandstone facies)
• Lithofacies – a constant lithological character
within a formation E.G an evaporate

4.  An idealized description of a facies
 Constructed from modern environments and
ancient rocks
 Serves as a
 Norm for comparison
 Framework for observation
 Predictor of patterns

5.  Groups of facies commonly show patterns
 Proximal Facies (near the source) tend to be
coarse grained
 Distal Facies (far from source) tend to be
finer grained
 This pattern is displayed upstream and down
in rivers and onshore to offshore in coastal
areas
 Facies are arranged according to distribution
of depositional environments

6.  Facies migrate through space and time
 Migration is in response to environmental
factors
 Sediment supply
 Sea level change
 Subsidence
 Facies become stacked during migration
 A single facies is likely to be different ages in
different locations

7. Named after Johannes Walther (1860-1937), a German
geologist, who in 1894, noted a fundamental relationship
between the vertical and lateral distribution of facies.

8.  Sedimentary environments that started out
side-by-side will end up overlapping one
another over time due to transgressions and
regressions. The result is a vertical sequence
of beds. The vertical sequence of facies
mirrors the original lateral distribution of
sedimentary environments.

11.  But…
Walther's Law can only apply to sections
without unconformities.

12.  Only works where there are no unconformities
 Only facies that were laterally adjacent during
deposition (result of laterally adjacent environments)
can be stacked vertically
 Vertical arrangement of facies gives us information on
 Distribution of environments
 How environments migrated through space and time
 Used as a basis to build facies maps or
paleogeographic maps
 Accurate time correlation of facies is essential
 Time lines provide framework for correlation
 Bio-events
 Volcanic ashes
 Other thin, unique lithologies or marker beds

13.  Only those lithofacies which are a product of
sedimentary environments found adjacent to
one another in the modern can occur
superimposed in continuous, uninterrupted
stratigraphic succession.”

15. • Transgression
 Landward movement of shoreline (progressive
deepening)
 Stand on beach
 Over time, you would be under water as shoreline moved
landward
• Regression
 Seaward movement of shoreline
 (progressive shallowing)
• Results in lateral and vertical changes

16.  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

17.  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. • Shallowing upwards, shoreline moves basin ward 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

19. Relative
Change
Eustatic
Change

20.  The study of strata (layers) of rocks with an eye
toward interpreting the geologic history of the
region
 Types of stratigraphy
 Lithostratigraphy
 Biostratigraphy
 CHRONOSTRATIGRAPHY


21.  Supergroup
 Group
 Formation – a mappable unit with distinctive
lithic characteristics
 Member
 Bed

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.  Characteristics of a good index fossil:
 Distinctive appearance/easy to recognize
 Short duration between first appearance and
extinction.
 Widespread geographic distribution (makes
correlation possible across a wide
area/multiple continents

26.  Limited Stratigraphic Range
 Commonly Pelagic
 Or tolerant of a wide variety of environments
(found in many facies)

27. CHRONOSTRATIGRAPHY
Geochronological units
27

28. 28

29.  Contacts
• Plane or irregular surfaces between different types
of rocks
• Separate units

30.  Conformable
 Unconformable

31. • 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

32. 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.

33.  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).

34. Angular
Unconformity

35.  Disconformity

36.  Nonconformity

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