I. Stratigraphic Principles, Concepts and Definitions

A. Stratigraphy- Descriptive science of strata. Deals with the:

• 1. arrangement,
• 2. form,
• 3. distribution,
• 4. chronologic succession,
• 5. classification, and
• 6. relationship of rock strata

B. Stratigraphy involves:

• 1. origin,
• 2. composition
• 3. environment,
• 4. age,
• 5. history,
• 6. relationship to organic evolution,
• 7. and other features of rock strata (igneous, metamorphic, and sedimentary).

C. Definitions

• 1. stratum-"a layer (a generally tabular body) of rock characterized by certain unifying characters, properties or attributes, distinguishing it from adjacent layers."
• 2. zone-minor stratigraphic interval in any category of stratigraphic classification. e.g. lithozones, biozones, chronozones, mineral zones, etc.
• 3. interval- a body of strata between two stratigraphic markers
• 4. horizon-an infinitely thin surface (or, in practice, a very thin bed) indicative of a certain position in a stratigraphic sequence.
• 5. correlation- The process of showing correspondence in character and stratigraphic position.
• 6. geochronology-science of dating and determining the time-sequence of events in the history of Earth.

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D. Catagories of Stratigraphic classification

• 1. Lithostratigraphic Units- "a body of rock strata which is unified by consisting of a certain lithologic type, or combination of lithologic types, or by possessing other impressive and unifying lithologic features."
a. Group- two or more Formations

b. Formation- the fundamental unit of lithostratigraphy.

• distinctive appearance
• type locality - well exposed section
• characteristics:
1. composition of mineral grains
2. color lithology
3. texture lithos = rock
4. thickness and geometry of stratification
5. character of organic remains
6. outcrop character
c. Member- a named or unnamed lithologic entity within a Formation. Formations need not be divided in members. Members may extend from one formation to another.

d. Bed- a named or unnamed distinctive individual layer
e.g. Baker Coal Bed

• 2. Biostratigraphic Units- A body of rock or strata which is unified by its fossil content or paleontologic character and thus differentiated from adjacent strata. Quotations from An International Guide to Stratigraphic Classification, Terminilogy, and Usage. 1972. International subcommission on Stratigraphic Classification, Report No. 7 (Read Section on Biostratigraphic Units, marked by post-it note).
a. Assemblage zone - "A body of rock or strata whose content of fossils, or fossils of a certain kind, taken in its entirety, constitutes a natural assemblage or association which distinguishes it in biostratigraphic character from adjacent strata."
e.g. Eponides-Planorbulinella Assemblage-zone

b. Taxon-range-zone - A body of rock or strata "representing the total range of occurrence (horizontal and vertical) of specimens of the taxon (species, genus, family)."
e.g. Dictyoha aculeata Range-Zone

c. Concurrent-range-zone - A body of rock or strata "defined by those parts of the ranges of two or more selected taxons which are concurrent or coincident." Also known as an overlap or range overlap zone.
e.g. Globigerina selli - Pseudohastigerina barbadoensis Concurrent-range-Zone

d. Lineage-zone - A body of rock or strata "containing specimens of a bioseries representing the evolutionary or developmental line of trend of a taxon or biologic group, any segment of such, defined above and below by features of the line or trend."
e.g. Globorotalia fohsi Lineage-zone
e.g. G. peripheroacuta/ G. praefohsi Lineage-segment-zone

e. Acme-zone - A body of rock or strata "representing the acme or maximum development of some taxon but not its total range."
e.g. Rocella gelida Acme-zone

f. Interval-zone- A body of rock or strata " between two distinctive biohorizons but does not itself represent any distinctive range or even any particularly distinctive biostratigraphic assemblage."
e.g. Exus albus (last) to Exus magnus (last) Interval-zone.

g. Barren interzone- A body of rock or strata " lacking in fossils between adjacent biozones may be referred to as barren interzones and referred to informally by reference to adjacent zones."
e.g. Exus parvus to Exus magnus barren interzone

h. Barren intrazone- A barren interval within biozones
e.g. the barren intrazone within the Exus albus Assemblage-zone.

3-4. Chronostratigraphic and Geochronstratigraphic Units- The purpose of such a classification is "to organize systematically the Earth's sequence of rock strata into named units (chronostratigraphic units), corresponding to intervals of geologic time (geochronologic units), so that these may facilitate time-correlation and age-determination of strata and serve as a reference system for recording events of geologic history." For each chronostratigraphic unit-term (rock strata) there is a corresponding geochronologic unit-term (interval of geologic time).

e.g. All rocks of the Devonian System are buried by surficial rocks in the State of Florida.

e.g. During the Cretaceous Period, dinosaurs ruled the vertebrate world.

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E. OTHER IMPORTANT PRINCIPLES

1. PRINCIPLE OF ORIGINAL HORIZONTALITY: particles which settle in water under the influence of gravity settle as horizontal or nearly horizontal layers

2. PRINCIPLE OF SUPERPOSITION: in any undisturbed succession of strata, oldest strata at bottom with successively younger ones above

3. PRINCIPLE OF CROSS-CUTTING RELATIONSHIPS: disturbed rocks or strata are older than those rocks which disturb them

4. PRINCIPLE OF ORIGINAL LATERAL CONTINUITY: strata extend in all directions until they thin against edges of basins they accumulate in

5. PRINCIPLE OF FOSSIL SUCCESSION: in a succession of strata fossil species succeed one another in a definite and recognizable order

6. PRINCIPLE OF FOSSIL ASSEMBLAGES: like assemblages of fossils are of similar age

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F. LATERAL CHANGES IN UNITS: SEDIMENTARY FACIES

• Facies means - total aspect of strata
• a 3-dimensional body of sediment characterized by some properties which grade into anther adjacent facies (e.g. sand and mud facies)

TRANSGRESSIVE

• shrinkage of land
• erosional unconformity/base
• landward facies shift
• fine upward

• expansion of land
• erosional unconformity/top
• seaward facies shift
• coarser upward

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G. UNCONFORMITIES

• 1. Angular
• 2. Disconformity
• 3. Nonconformity