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Class Notes: Geoarchaeology

Sunday: September 25, 2011

Week 3: Archaeological Stratigraphy


Stratigraphy refers to the layers of deposition of sediments and soils (which are not the same thing!). All else being equal, there are five geological principals that apply to archaeological strata:

  • Superposition: The oldest layer will be the deepest layer.
  • Original Horizontality: Due to gravity, deposits are layered horizontally.
  • Lateral Continuity: Strata will continue until the materials run out or reach the edge of the depositional basin.
  • Cross-cutting Relations: In order for a deposit to be cut through by another, it must have existed first.
  • Included Fragments: The stuff the deposit is made of is older than the deposit itself (similar to cross-cutting relations).
There are also a few different approaches to defining stratigraphic layers:
  • Lithostratigraphy: Layers are defined by their visible physical properties (color and texture, for instance).
  • Pedostratigraphy: Layers are defined through the soil horizons that separate them (remember, soils are not sediments).
  • Biostratigraphy: Layers are defined by the flora/faunal fossils found in them (changing of shell types, seed types, etc.).
  • Chronostratigraphy: Layers are defined through datable objects found in them.

Depending on the research question, an archaeologist may use any one of these approaches to sort what artifacts are found.

We had a Stratigraphy & Correlations lab to understand how Shovel Test Probes can provide an idea of what the strata look like. We also had to determine, using the geological principals, how the strata became the way they were.


 Microstratigraphy is a technique geoarchaeologists use to determine site use (is this feature a hearth or where the ash was dumped?), and uses over time (was the hearth used consistently for a long period or was the place chosen over and over again through time?). They take a thin section of soil and can identify different stages of weathering, which means different surfaces over time, through a microscope. To understand this further, we read chapter two and discussed three articles (see the Library for bibliographic information):

  • Microfacies Analysis Assisting Archaeological Stratigraphy
  • Discontinuity in the Stratigraphic Record: Snapshots from Franchthi Cave
  • Chronology and Stratigraphy at Dust Cave, Alabama


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