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Stratigraphy Understanding site deposits. Reading the Layers
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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?
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What it reveals… Site history Environmental changes Human behaviors Culturally sterile: without evidence of human activity
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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.
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Basic shovel test
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Dry screening.
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1x2 test unit.
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Unit sidewall (west)
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Isometric view (adjacent sides shown)
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Ceramic pot in situ
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Artifacts left in position for photography.
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Rocker screen.
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Elements to note Soil composition Soil colors Strata boundaries Moisture Strata lenses Artifact content Compaction Boundary zones
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Multiple strata revealed in cave site.
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Back hoe trench.
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Most excavation is conducted by arbitrary levels of 10 or 20 cm.
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Illustrating stratigraphy
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Tags indicate both arbitrary 10 cm levels and natural stratigraphy.
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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.
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With grid sheets
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Completed complex site profile.
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Field notes The side walls provide the data. Take note of characteristics. Use a Munsell soil color guide.
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Composition terms Granular Organic Clay-like Sandy Dry/wet Acidic/basic
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Boundaries
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Results from skim shoveling by natural levels.
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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
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Road cut inadvertently exposes ancient settlement evidence.
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Artificial mound
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Special cases Shipwreck The wrecking episode will dramatically affect site formation. Slow deterioration or rapid destruction? Environmental conditions will impact deposition and site preservation
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The “classic” Disney concept of shipwrecks. Shipwrecks and underwater archeology will be discussed later in the term.
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Roman shipwreck shown after complete clearing.
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Intro to Sampling methods (each has statistical merits and drawbacks) Random Systematic Stratified Combined (ex: stratified random)
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Systematic Along a grid at specified intervals
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Random Using a grid but at non-systematic intervals.
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Stratified Systematic or random but the sample is weighted to provide coverage in particular zones.
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Exercise Part 1 Simulated stratigraphic analysis Partners for analysis. Determining order of layers. Asking critical questions about variations. Interpreting deposits sequentially.
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Part II Hypotheses formation concerning site history. Developing supporting arguments for conclusions.
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Part III Illustrating a stratigraphic profile. Using mock profile Using Munsell color guide
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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.
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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.
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