E. F. McBride
Geo. 420K
Spring, 2000

• Lithostratigraphy - Lithostratigraphic unit
   [Group, Formation, Member]
  • Lithodemic unit (intrusives, etc.)
• Pedostratigraphy - Pedostratigraphic unit
• Biostratigraphy - Zones
• Chronostratigraphy - Chronostratigraphic units
  [Period, Epoch, Age]
• Geochronostratigraphy — Geochronostratigraphic unit 
  [System, Series, Stage]
• Magnetostratigraphy - Reversals, chrons
• Chemostratigraphy - Isotope zones
• Sequence Stratigraphy - Allostratigraphic units
  [Unconformity-bounded units]

II. IMPORTANT SURFACES & TIME IMPLICATIONS

1) FAULTS, FRACTURES

2) UNCONFORMITIES = Buried erosion surfaces

• Physical erosion
• Biological erosion
• Chemical erosion

Hiatus = amount of time record missing

Diastem = small amount of rock missing

Paraconformity " " " "

Non-conformity: sedimentary rocks on top of igneous or metamorphics

Disconformity: sediments conformable with sediments

Angular unconformity: angular discordance

Problem: how much time is represented by each bedding plane?

FACIES Definitions:

4) A body of rock distinguished on the basis of its fossil content: Ophiomorpha facies, Exogyra texana facies.

• PROCEDURE: plot range of every fossil in a local section; decide on practical biozone boundaries.
• RANGE: [first to last occurrence]: vertical distribution of a taxa through time as indicated by its distribution in rocks of known age.
  • BIOZONES: various classes of zones.
    • Range zone: all strata that contain a local species
    • Teilzone: observed local range of given fossil
  • OPERATIONAL BIOZONES:
    • Interval: based on 2 taxa
    • Assemblage: based on 3 or more taxa
    • Abundance (peak or acme): relative abundance of certain taxa
• FAD = first appearance datum
• LAD = last appearance datum
• LOD = last occurrence datum

Transgression

Regression

Aggradation

Progradation

Isochronous

Diachronous

Hierarchy of rock units (lithostratigraphic units): supergroup, group, formation, member, tongue, lentil, bed

Heirarchy of time units (geochronometric units): era, period, series, stage

Heirarchy of time-rock units (chronostratigraphic units) : erathem, system, epoch, age

Allostratigraphic units

Sequence

Biozone

Formation

Lithostratigraphy

Biostratigraphy

Chronostratigraphy

Magnetostratigraphy

Chemostratigraphy

Sequence Stratigraphy

Chron

Polarity chron

FAD

LAD (LOD)

Law of Original Horizontality

Law of Lateral Continuity

Law of Law of Stratigraphic Succession (Superposition)

Law of Faunal Succession

McBride's Law

Wheeler diagram

Unconformity: diastem: disconformity: non-conformity; angular unconformity

Hiatus

Allocyclic

Autocyclic

Milankovitch cycles

1st, 2nd, 3rd, 4th order cycles

On lap; Off lap; Down lap; Top lap

Erosional truncation

Radiometric age

a, Ka, Ma, Ga (time before present)

y, Ky, My, By (time span)

STRATIGRAPHY = concerned with the 3-dimensional relations of rocks and their ages.  It is the basis of reconstructing geologic history.

• Lithic Units (Lithostratigraphy)

  Group

Formation: mappable rock unit, definable boundaries

Member

Lentil, tongue

• Time Units (Chronostratigraphy)

  Era

Period

Epoch

• Time-Rock Units (Geochronostratigraphy)

Erathem

System

Series

Stratigraphic Sequence = body of rock bounded by unconformities and their correlative conformities.

Law of Superposition: oldest rocks at the base, youngest at the top.

Law of Faunal Succession: fossils of different types occur in rocks of different ages and in a logical progression; once a fossil disappears it does not recur at a younger level.

Correlation = determining that rocks at geographically distant places are either the same rock body or the same age.

Wheeler Diagram = diagram showing the lateral geographic distribution of rocks on the abscissa (a axis) and time on the ordinate.

Geologic Time Scale = Age of the Earth subdivided into named and dated intervals.

efmcbride@mail.utexas.edu
Geological Sciences
U. Texas at Austin