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Stratigraphy

Stratigraphy is the study of spatial and temporalrelationships between sediments and soils(Waters 1992).

Soils are the weathering profiles developed by the in - p lace physical and chemical alteration of preexis t ing sed iments (Waters 1992).

A soil is the result of the complex interaction of avariety of physical, chemical, and biological processesacting on rock o r sed im ent over t im e (Holliday ).

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Stratigraphy

Stratigraphy comes from two root words: Latinstratum and the Greek word graphia. Broadlydefined stratigraphy is the descriptive scienceof strata.

Stratum is singular while Strata are plural

Stratum - is a layer characterized by certainunifying characteristics, properties or attributesthat distinguish if from adjacent layers.

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StratigraphyStratigraphic objectives at archaeological sites include thefollowing from Waters (1992:)1) to subdivide and group sediments and soils into

meaningful packages and to record the nature of thecontacts between strata

2) to order the stratigraphic units in their relative temporalsequence

3) to determine the absolute age of the stratigraphic unitsalong with amount of time represented by accumulation,stability or erosion

4) to correlate stratigraphic units with regional stratigraphy

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Stratigraphy

The concept of geological stratigraphy was introduced byan engineer and surveyor in England in the late 1700s andearly 1800s, named William (Strata) Smith

Archaeological stratigraphy on the other hand may havebeen first practiced by an American (again not anarchaeologist) in 1784. Thomas Jefferson usedstratigraphy to answer questions about the origin of the

barrows or burial mounds in Virginia.

Sir Mortimer Wheeler labeled Jeffersons work the firstscientific excavation in the history of archaeology.

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Stratigraphy

Nicholaus Steno (Danish) in the mid-1600s recognizedthat rocks were once soft sediments.

Laws of Sedimentary Stratigraphy (Stenos Laws)

Three important Laws:Law of SuperpositionLaw of HorizontalityLaw of Original Continuity

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Stenos LawsThe law of superposition : This law states that the oldest

rock layer is the layer on the bottom and the youngest layer is the layer on top . Unless rocks have beenoverturned by extreme mountain building, the layers arein the same order that they formed.

Oldest

Youngest

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Stenos LawsSteno's second law is the Law of Original Horizontality , whichstates that sediments are deposited in flat, horizontal layers .We can recognize this easily if we consider a sedimentaryenvironment such as the sea floor or the bottom of a lake. Anystorm or flood bringing sediment to these environments willdeposit it in a flat layer on the bottom because of thesedimentary particles settling under the influence of gravity. Asa result, a flat, horizontal layer of sediment will be deposited.

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Stenos Laws

Law of Original Continuity - sedimentary layers normally formcontinuous sheets that covered the entire earth or werebounded by solid substances. Discontinuous layers that aresimilar on either side of a valley must have been separated byerosion from their original continuous state.

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StratigraphyDigging Practices Darkmold Site

Strata (Plural of Stratum)

The major natural (geologic) or/cultural units notlocated within a feature or structure

LevelsArbitrary units of thickness such as 5cm, 10cm,or 20cm

LayersCultural fill within structures or features

With Slope

Mirroring the present or original ground surface

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Excavation in arbitrary levels

10cm levels

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Excavation in arbitrary levels

10 cm levels

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Excavation in arbitrary levels

Archaic

Basketmaker III

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Excavation in arbitrary levels

Basketmaker III

Archaic

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Excavation in arbitrary Levels

Stratum K

Level 1

Level 2

Level 3, Stratum 1

Level

Level 5

Level 6Level 1, Stratum 3

Level 2, Stratum 3

Level 4

Level 3

L Level 6

S t r a t u m

1

S t r a t u m

2

S t r a t u m

3

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Excavation in Strata and in Levels

Stratum K

Level 1

Level 2

Level 3, Stratum 1

Level

Level 2, Stratum 2

Level 1, Stratum 3

Level 2, Stratum 3

Level 3, Stratum 2

Level 3

L Level 1, Stratum 3

Level 2, Stratum 3

Level 4

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Excavation with the ground surface

Stratum KLevel 3, Stratum 1

Level

Level 1, Stratum 3

Level 2, Stratum 3

LStratum 3

Stratum 2

Stratum 1