Stratigraphy - study of stratal relationships in time and space.
 
 
 

 2.  Sediments Change Laterally:
Facies - body of rock with characteristics that identify it as different from other bodies of rock.
 
 
 
 

Usually named for the defining characteristics:
- Cross-Bedded Facies

- Trilobite Facies

- Garnet Facies
 

Depositional facies: facies that suggest definite depositional environments.
 
 
 
 
 
 
 
 

- Nearshore Facies  (sandstone)
 
 

- Offshore Facies   (shale)
 
 

- Shelf Facies    (limestone).
 
 

Subsidence - sinking of earth's surface.  Opposite of uplift.
 

Sea level - rise makes room for more sediment.  And erodes shorelines.
 
 

4.  Stack 'em up:

Walther's Law of the Correlation of Facies - in a conformable stratigraphic succession, only those facies can be superposed that occur beside each other at the time of deposition.
(stacked facies originated beside each other)
 
 
 
 
 
 
 

 5.  Interpreting Stratigraphy: (draw the T/R cycle)
 
 
 
 
 
 
 
 
 
 

Regression (of the sea) - the movement of a shoreline in a seaward direction

-

-

Transgression (of the sea)- the movement of a shoreline in a landward direction

-

-
 

Similar Terms: Progradation ( = regression) & Retrogradation ( = transgression)
- these refer to the shoreline instead of to the sea.
 

 Transgressions and Regressions

- record a relative change in sea level.
 
 
 
 
 

Relative Sea Level - rise or fall of sea level relative to one point in the stratigraphic record.

-

-
 

Eustatic Sea Level - a synchronous change in worldwide sea level.

- Evidence?
 
 
 

- For example:  Mid-Cretaceous sea level.
 
 
 

 Causes of Eustasy - Change water or the tub!

- Change in ocean water volume:
 
 
 
 
 

- Change in ocean basin volume:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

  : Note that the figure in the book (Fig 4.15, page 84) is not quite correct.
 
 

- Lithologic Correlation - correlating rocks - easy(?)
 
 
 
 
 
 
 
 
 
 
 

- Age Correlation - are rocks the same age? - tough.
 
 
 
 
 
 
 
 

Compare lithologic correlations vs time correlations.
 
 
 
 
 

These Lithologic units (shale, sand, cgl) are called Time Transgressive units -- each unit cuts across time lines; is a different age at different places (the unit "transgresses" geologic time boundaries).  Note that the conglomerate is younger than the shale straight below it, but older than the shale in some areas (follow the time lines).  Don't confuse "Time Transgressive" units with Transgressions and Regressions (two very different terms).
 
 

- code devised to straighten out stratigraphy ("Triumph of Terminology over Common Sense")
 
 

1.  Geologic Time - absolute time as related to geological events

- Period - fundamental unit of geologic time

- Epoch - subdivision of Period

- Era - group of related Periods
 

2.  Lithostratigraphy - defined by lithologies

- Formation - fundamental unit of lithostratigraphy

 - DEF: mappable, lithologically distinct body of rock having recognizable boundaries

- Member - local unit within a formation

- Group - set of formations grouped together
 

3.  Biostratigraphy - defined by fossils in the rocks

- Biozone - body of rock whose boundaries are defined by fossil content.
 
 
 

Geologic Time	Lithostratigraphy	Biostratigraphy
Eon	(Supergroup)
Era	Group
Period	Formation	Biozone
Epoch	Member	(Subbiozone)
(Age)	(Bed)

 

4.  *Key Question*  We can date volcanic rocks using radiometric methods, but we want to know the age of the fossiliferous limestones we love so much.  How do we find find their age?
 

Question:  Explain how a lithostratigraphic Formation can belong to one Period in one area, and to a different Period in another area.  Draw a picture.
 
 
 

- many fossils are unaltered remains, such as pollen and spore grains.
 

Preservation of Body Fossils:
Petrifaction (or fossilization): general term for fossils turning into stone.
 

Permineralization - pore-filling of original material by minerals (dinosaur bones).
 

Replacement - one mineral taking the place of original skeletal material (petrified wood).
 

Carbonization preserves the non-volatile fraction of the original fossil's carbon content (leaves).
 

Molds and casts preserve fossil's shape only.
 

Amber - Sap from trees may cover insects and fossil pollen or spores and preserve it very well.
 

Trace Fossils and Bioturbation (disruption of strata by burrowing activity):
- Indicators of: (1) behavior, (2) behavior related to environment of deposition.
 
 
 
 
 
 
 
 

William Smith (~1800) - groups of fossils occur in the geologic record in a distinct and recognizable order.
 
 

- Principle of Fossil Succession - first usable method of Correlating reliably.
 
 
 
 
 
 
 
 
 
 
 

Composition of Detrital Sandstones - reflects provenance.
 - Quartz sandstone
 

 - Arkose
 

 - Lithic sandstone
 

Maturity - descriptive indicator of the distance of transport of the sand grains.
 
 
 

 - Weathering of rocks.  Silicate minerals weather to form Clays + Ions in Solution.

 - The more abundant quartz is, the more mature the sandstone is thought to be.
 

Sedimentary structures - desiccation cracks, cross-bedding, graded bedding, ripple marks, sole marks
 
 
 

Biogenic sedimentary structures - trace fossils.  Behavior <=> Energy level of environment.
 Grain Size  - Provenance, Energy (Low or High)
 
 

 :Energy of Environment <=> Velocity of Currents
 

- High energy versus Low energy conditions - amount of current activity in the environment.
 
 

- High Energy - currents can transport sand grains most of the time.
 -
 

- Low energy - rarely currents strong enough to transport sand.
 -

 
-  Hjulstrom's diagram: relates current velocity and grain size
 
 
 
 
 
 
 
 
 
 
 

 Sorting - uniformity of grain size

 - (well-sorted to poorly sorted)

 - Source, Energy, Processes.

Example: rock with fine-grained matrix, lithic fragments, very poorly sorted
 

Roundness - whether grains are smooth or angular
 

 - related to source, environment
 
 

Example: TURBIDITES - produce "Bouma" sequence:
E) bioturbated mud
D) laminated mud
C) ripple cross-bedded sand
B) laminated sand
A) graded sand&gravel
 
 
 
 
 
 

 Carbonates: Limestones and Dolostones.

- Calcite: CaCO3  and Dolomite: (CaMg)CO3

-   >90% are from biogenic sources.

- Bioclasts - broken shells of organisms with hard parts.
 

Factors favoring Limestone Deposition = Factors favoring chemical precipitation of calcite.

- Limestones are found mostly where Calcite is supersaturated in the water.
 
 

Solubility: a tendency to be dissolved.  High solubility or highly soluble means it dissolves easily.

Carbonic Acid: (from CO2 in air)
 CO2 + H2O <=> H+ + HCO3- <=> 2H+ + CO3--
 
 

Carbonic acid serves to dissolve calcite.
 Ca++ + CO3--  <=>  CaCO3

 Chemical Factors Controlling Worldwide Carbonate Distribution:
1. Temperature - High temperature causes Calcite to be less soluble. (Opposite of expected). Hot!
 
 
 

2. Pressure - High pressure causes Calcite to be more soluble.  Shallow!
 
 
 

3. Dissolved CO2 - causes Calcite to be more soluble. (cold water holds more CO2).  Turbulence!
 
 

Translates into Warm, Shallow, Turbulent waters.  Like Coral Reefs!
 
 
 
 

Most carbonate sediment produced in the world comes from plants:  Calcareous Algae and Phytoplankton.  Why Plants?  What do plants do that animals don't?
 
 

CO2 (gas) + H2O  =>  CH2O(sugar) + O2  (gas)
 
 
 

 Non-chemical Factors Controlling Carbonate Distribution:

1. Water clarity: clear water = light for marine algae.  Muddy water is Bad.
 
 
 

2. Water depth: controls light, temperature, pressure.
 
 
 

3. Nutrient-richness of water: need just a little
- stimulates calcareous algae growth
 
 

- too much: plankton clouds water (less light).
 
 
 
 

Environment of Deposition (EOD):
 :: geographic conditions where deposition occurs.
- Includes chemical, physical, biological, geological components of the environment.
 

1. Calcilutites - mud-sized - low energy
- Sources:  plankton (forams & nannos)

   algae (Penicillus)

   inorganic precipitation (whitings).

- EOD: deep sea & tidal flats
 
 
 
 

2. Calcisiltites - silt-sized - low energy
- Sources: small bioclasts.

- EOD: continental shelves
 
 
 
 
 

3. Calcarenites - sand-sized - high energy
- Sources: Bioclasts & Ooids.
 

- EOD: beaches, nearshore, sand bars
 
 
 
 

 4. Calcrudites - gravel-sized or larger
 either: - high energy
 or   - big carbonate producers
- Sources: Bioclasts -

Coquina -

Intraclasts -
 

- EOD:  reefs

channels

tidal flats (thin layers)

Environment of Deposition (EOD):
 :: geographic conditions where deposition occurs.
- Includes chemical, physical, biological, geological components of the environment.

Three Categories of EOD.
1. Terrestrial - on land

2. Transitional - shoreline region

3. Marine - wholly underwater
 

 - Common Marine Carbonate Environments:
(Draw a Profile of Carbonate EOD)
 
 
 
 
 
 
 
 
 
 

- Tidal Flat
:: broad, flat region between high, low tide level

- Carbonate Bank
:: broad, shallow regions of carbonate deposition.

- Reef
:: Biologically created, rigid wave-resistant structure.

- Continental Slope
:: Gentle slope connecting Bank&Reef with DeepSea.

- Deep Sea
:: deep ocean, dark, cold, quiet
 

 1. Tidal Flat : calcilutite, intraclasts
- Low energy environment (rarely high)
- High salinity, some evaporites
- Low organism abundance and diversity.

2. Carbonate Bank : calcilutite to calcirudite
- Shallow marine, continental shelf
- Low to High energy conditions.
- Ooids common.

3. Reef - calcirudite mostly
- Today formed by corals
- In the Past by clams, worms, sponges, others.
- Typically High energy, calcirudite producers.

4. Continental Slope - calcilutite, some calcirudite
- excess fine carbonate from banks (calcilutite)
- slumping from reefs (calcirudite)

5.  Deep Sea - calcilutite (chalk), chert, others rare.
a) planktonic ooze: from floating algae and amoebas.
 - carbonate: nannos and forams
 - silica: diatoms and radiolarians
b) turbidites - generated from slumping on Slope.
- deep ocean (>4km) dissolves Carbonates (=>chert).
 
 

 Walther's Law of the Correlation of Facies - in a conformable stratigraphic succession, only those facies can be superposed that occur beside each other at the time of deposition.
(stacked facies originated beside each other)

Example #1.  Carbonate Reef System (draw).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

- Reef Front Facies - talus slopes, steeply dipping away from the reef, composed of reef debris.
- Reef Facies - positive structural feature, wave resistant, built by any framework building organism.
- Back Reef Facies - quieter water, lagoonal, patch reefs common, calcareous algae & fecal pellets common.
- Tidal Flat Facies - micrites with bird's eye structures, desiccation cracks, flat-pebble conglomerates (intraclasts), stromatolites.
- Vertical succession: (from base) Reef-front, Reef, Back-reef, Tidal flat carbonates.
- Note: progradation of reef produces time lines that cross lithofacies boundaries. (time-transgressive)
- Note: vertical succession of facies reflects the lateral association of facies.
 
 

 Example #2.  Facies of a Meandering River System.
Lateral migration of a Point Bar across a Channel (draw).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

- Channel Facies - conglomeratic, wood fragments, shale rip-up clasts.
- Lower Point Bar Facies - large-scale, trough cross-bedded sandstone, well-sorted, medium grained.
- Upper Point Bar Facies - ripple-cross-bedded sandstone, well-sorted, fine-grained.
- Levee and Floodplain Facies - mudstones with root marks and desiccation cracks. Few thin ss.
- Peat Swamp Facies - coal develops from stagnant swamps or lakes with little clastic input.
 

- Vertical succession: Fining-upward sequence.
- Time lines don't follow lithostratigraphy.
- Meandering of a sinuous river channel creates a laterally continuous sandstone layer.
- Vertical facies reflects lateral association of facies.
 
 
 

 Example #3.  Facies of a Delta System (draw).
 - River delta progrades into lake or ocean.
 
 
 
 
 
 
 
 
 
 

- Prodelta Facies - laminated muds from floods, terrestrial organic debris, widespread distribution.
- Delta Front Facies - fine sands and silts with laminated muds, ripple cross-beds, organic debris, laterally restricted to one distributary.
- Distributary Channel Facies - sandy to conglomeratic, cross-bedded, well sorted, downcutting into delta front sands, narrow elongate distribution.
- Delta Plain Facies - mudstones and thin siltstones in floodplain deposits, root casts.  Some coals.

- Vertical succession: Coarsening-upward sequence.
- Time lines don't follow lithostratigraphy.
- This is typical River-dominated environment.  May be tide- or wave-dominated.  What differences might this cause???
- Vertical facies reflects lateral association of facies.