Stratigraphy

Understanding site deposits.Reading the Layers

Layer upon layer…

Stratigraphy represents the depositional history of a site.

Key ideas: Site depth

When do cultural deposits begin or stop as we dig down?

Site integrity Has the site been disturbed and by what?

What it reveals…

Site history Environmental changes Human behaviors

Culturally sterile: without evidence of human activity

Concept review

Principle of superposition Age of each layer/order of each layer

Principle of association Artifacts and strata deposited

together Provenience and context

Where on the site a feature is located or from where an artifact came.

Basic shovel test

Dry screening.

1x2 test unit.

Unit sidewall (west)

Isometric view (adjacent sides shown)

Ceramic pot in situ

Artifacts left in position for photography.

Rocker screen.

Elements to note Soil composition Soil colors Strata boundaries Moisture Strata lenses

Artifact content Compaction Boundary zones

Multiple strata revealed in cave site.

Back hoe trench.

Most excavation is conducted by arbitrary levels of 10 or 20 cm.

Illustrating stratigraphy

Tags indicate both arbitrary 10 cm levels and natural stratigraphy.

Strive for clarity and simplicity in graphic representation. It is not necessary or desirable to illustrate every pebble, rock, or root.

Usually best to include a key rather than jumble the drawing with superimposed text.

With grid sheets

Completed complex site profile.

Field notes

The side walls provide the data. Take note of characteristics. Use a Munsell soil color guide.

Composition terms

Granular Organic Clay-like Sandy Dry/wet Acidic/basic

Boundaries

Results from skim shoveling by natural levels.

Confusion Site formation processes =

taphonomy Human disturbances:

Quarry/mining, storage pits, borrow pits, purposeful restructuring

Bioturbation Worms, crabs, gophers, tree roots,

Environmental flooding, land subsidence, etc

Road cut inadvertently exposes ancient settlement evidence.

Artificial mound

Special cases

Shipwreck The wrecking episode will

dramatically affect site formation. Slow deterioration or rapid destruction?

Environmental conditions will impact deposition and site preservation

The “classic” Disney concept of shipwrecks.

Shipwrecks and underwater archeology will be discussed later in the term.

Roman shipwreck shown after complete clearing.

Intro to Sampling methods(each has statistical merits and drawbacks)

Random Systematic Stratified Combined (ex: stratified random)

Systematic

Along a grid at specified intervals

Random

Using a grid but at non-systematic intervals.

Stratified

Systematic or random but the sample is weighted to provide coverage in particular zones.

Exercise Part 1

Simulated stratigraphic analysis Partners for analysis. Determining order of layers. Asking critical questions about

variations. Interpreting deposits sequentially.

Part II

Hypotheses formation concerning site history.

Developing supporting arguments for conclusions.

Part III

Illustrating a stratigraphic profile. Using mock profile Using Munsell color guide

Remember

Layers should be described from the bottom up (oldest to newest).

Both human and natural activity at a site should be described whenever possible.

Final products for grading

Written site description and analysis; making a case for your interpretation and generating at least one testable hypotheses.

Stratigraphy model illustration using appropriate scale.