Excavation Techniques and Analysis


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Covers the basics of archaeological techniques and Analysis

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Excavation Techniques and Analysis

  1. 1. Excavation Techniques and Analysis Recovering Fossil Forms
  2. 2. Fundamentals of Archaeology <ul><li>Site discovery and selection </li></ul><ul><li>Excavation of artifacts, ecofacts, and features </li></ul><ul><li>Analysis for dates, attributes, and environment </li></ul>
  3. 3. How are Sites Formed? <ul><li>Taphonomy: Study of how lifeforms or artifacts wound up at a particular location </li></ul><ul><li>Fossils: </li></ul><ul><ul><li>Remains of life form from the past </li></ul></ul><ul><ul><li>Petrification: replacement of bone with mineral or stone </li></ul></ul>
  4. 4. How are Items Preserved? <ul><li>Some materials resist deterioration: </li></ul><ul><ul><li>Bone: Skulls and teeth </li></ul></ul><ul><ul><li>Stone or Metal (tools, ornaments) </li></ul></ul><ul><ul><li>Seeds, with protective covers </li></ul></ul><ul><li>Others may be preserved by </li></ul><ul><ul><li>Arid climates (Peruvian coast) </li></ul></ul><ul><ul><li>Water: Planks in Lakes in France </li></ul></ul><ul><ul><li>Peat moss: the “Bog People” </li></ul></ul>
  5. 5. More Examples of Preservation <ul><li>Waterlogged Sites: Bog People, Denmark </li></ul><ul><li>Arid Sites: Puruchucho-Huaqerones Mummies, Peru </li></ul><ul><li>Cold Sites: The Iceman, Italian Alps </li></ul><ul><li>Volcanic Ash, Cerén, El Salvador </li></ul>
  6. 6. Site Discovery <ul><li>Lucky finds </li></ul><ul><li>Consulting available sources: studies, records, even older informants </li></ul><ul><li>Maps and aerial photographs </li></ul><ul><li>Geographical Information Systems/Remote Sensing </li></ul>
  7. 7. Site Selection <ul><li>Learning everything possible about each site </li></ul><ul><li>Selecting as large and representative a site as possible </li></ul><ul><li>Preliminary work: surface finds, features, perhaps test pits or trenches </li></ul><ul><li>Problem-Oriented Research and Deliberate Surveys: Hadar, Ethiopia </li></ul>
  8. 8. Survey: Mapping, Part 1: General <ul><li>First principle: Digging is destructive--record everything! </li></ul><ul><li>Mapping </li></ul><ul><ul><li>Latitude, longitude, and elevation </li></ul></ul><ul><ul><li>Benchmarks or features </li></ul></ul><ul><li>Measurements </li></ul><ul><ul><li>Horizontal </li></ul></ul><ul><ul><li>Vertical </li></ul></ul>
  9. 9. Survey: Mapping Part 2: Horizontal Measurement <ul><li>Select and draw west-east (X-axis) and north-south (Y-axis) baselines from primary site datum </li></ul><ul><li>Mark off intervals at meters and centimeters from baselines </li></ul><ul><li>Label the intervals along axes of the grid by letters, numbers, or both </li></ul><ul><li>Adapt procedure according to topographical or archaeological features </li></ul>
  10. 10. Survey: Mapping Part 3: Vertical Measurements <ul><li>Surveying using transit or alidade and measuring rod </li></ul><ul><li>Vertical base: benchmark or permanent feature of known elevation </li></ul><ul><li>Convert measures to meters above sea level. </li></ul>
  11. 11. Survey: Test pits and trenches <ul><li>Test pits provide sample of site stratigraphy </li></ul><ul><li>Stratigraphy: profile of two or more layers of </li></ul><ul><ul><li>Natural sediment </li></ul></ul><ul><ul><li>Human remains and artifacts </li></ul></ul><ul><li>Test pits provide sample of overall site </li></ul><ul><li>Test Trenches reveal stratigraphy </li></ul>
  12. 12. Tools for Excavation <ul><li>Dental picks or paint brushes </li></ul><ul><li>Ice picks </li></ul><ul><li>Tweezers (fragile objects) </li></ul><ul><li>Trowels (pointed and square) </li></ul><ul><li>Shovels (pointed and square-nosed) </li></ul><ul><li>Heavy equipment (backhoes) </li></ul><ul><li>Buckets and Screens </li></ul>
  13. 13. Vertical Excavation: Some “Laws” <ul><li>Law of Association: </li></ul><ul><ul><ul><li>Artifacts found at the same stratum (layer) are in association with one another </li></ul></ul></ul><ul><ul><ul><li>Artifacts found at different strata are not in association with one another </li></ul></ul></ul><ul><li>Law of Superposition: Geological layers are stratified one upon another </li></ul><ul><ul><ul><li>Lower strata are older than higher ones </li></ul></ul></ul><ul><li>Uniformitarianism: Geological processes similar throughout time </li></ul>
  14. 14. Vertical Excavation: Stratigraphy <ul><li>Layer deposited in chronological order: lowest layer is oldest and so on. </li></ul><ul><li>Disturbances can change stratigraphy </li></ul><ul><ul><li>Erosion from hillside: oldest is top layer </li></ul></ul><ul><ul><li>Structure foundation disturbs layers </li></ul></ul><ul><ul><li>Burrowing animals may move objects </li></ul></ul><ul><ul><li>Then there are golddiggers and pothunters </li></ul></ul>
  15. 15. Vertical Excavation: Procedure: <ul><li>Each artifact is recorded and removed </li></ul><ul><ul><li>Photographed, sketched, or described </li></ul></ul><ul><ul><li>Vertical and horizontal position </li></ul></ul><ul><li>Soils analyzed for chemistry, pollen, etc </li></ul><ul><li>Associations between artifacts are recorded </li></ul><ul><ul><li>Assumption: artifacts found at same layer occurred at same time period </li></ul></ul>
  16. 16. Vertical Excavation: Proveniencing <ul><li>Definition: recording artifacts in three-dimensional space </li></ul><ul><li>Transit and stadia rod: record is set from a secondary datum point </li></ul><ul><li>Theodolite: records the position of an artifact using a laser bouncing off a prism of known height </li></ul>
  17. 17. Horizontal Excavation: Procedure <ul><li>As each layer or stratum is excavated, it is removed </li></ul><ul><li>Same procedure of excavation is repeated for next layer </li></ul><ul><li>One or two layers: prefer horizontal excavation to get lay of the site </li></ul><ul><li>Different samples are taken for different layers: soil, pollen, charcoal, bone </li></ul><ul><li>Some layers may be left for control </li></ul>
  18. 18. Analysis: Aims and Objectives <ul><li>Dating </li></ul><ul><li>Artifact: classification </li></ul><ul><li>Bone analysis </li></ul><ul><li>Paleobotany </li></ul><ul><li>Palynology (pollen analysis) </li></ul><ul><li>Paleozoology </li></ul><ul><li>Structures </li></ul><ul><li>Other features </li></ul>
  19. 19. Overview of Dating <ul><li>Unifomitarianism </li></ul><ul><li>Relative Dating </li></ul><ul><ul><li>Stratigraphy </li></ul></ul><ul><ul><li>Association </li></ul></ul><ul><li>Absolute Dating </li></ul><ul><ul><li>Calendrical </li></ul></ul><ul><ul><li>Natural Features </li></ul></ul><ul><ul><li>Isotopic </li></ul></ul>
  20. 20. Dating: Uniformitarianism <ul><li>Uniformitarianism vs. Catastrophism </li></ul><ul><li>Uniformitarianism: All geological processes--erosion, weathering--observable today have always been present and at the same rate </li></ul><ul><li>Uniformitarianism is the basis of dating. </li></ul><ul><li>Catastrophism: Changes have been sudden and have occurred at different rates in the past from those of the present. </li></ul>
  21. 21. Relative Dating <ul><li>Stratigraphy: Establishment of sequences by soil strata </li></ul><ul><ul><li>Exceptions: soil disturbance, erosion. </li></ul></ul><ul><li>Law of Association: Dating of finds within a stratum </li></ul>
  22. 22. Chronometric Associations: Relative and Absolute Dating Combined? <ul><li>Basic principle: Materials associated with other materials of known age are the same age range </li></ul><ul><ul><li>Bottle styles and clay pipes . </li></ul></ul><ul><ul><li>Gravestones in Stoneham, MA (Deetz) </li></ul></ul>
  23. 23. Absolute Dating: Calendrical <ul><li>Entails use of traditional calendars </li></ul><ul><ul><li>Mayan </li></ul></ul><ul><ul><ul><li>Long Count: Beginning date fixed at 3113 BC </li></ul></ul></ul><ul><ul><ul><li>Calendar Rounds: 260- and 365-day calendars </li></ul></ul></ul><ul><ul><li>Egyptians: </li></ul></ul><ul><ul><ul><li>332 BC Conquest by Alexander the Great </li></ul></ul></ul><ul><ul><ul><li>Traced back through recorded dynasties </li></ul></ul></ul><ul><ul><ul><li>Astronomical events checked by present data </li></ul></ul></ul><ul><ul><li>Others: Chinese, Romans, Greeks </li></ul></ul>
  24. 24. Absolute Dating: Natural Features <ul><li>Dendrochronology: Tree ring dating </li></ul><ul><ul><li>Tree rings vary from year to year </li></ul></ul><ul><ul><li>Local stumps or timber compared with master sequence (e.g., Univ. of Arizona) </li></ul></ul><ul><li>Varve analysis: Clay deposits in lakes from melting ice. </li></ul><ul><ul><li>Patterns also differ yearly </li></ul></ul><ul><ul><li>Likewise compared with master chart. </li></ul></ul>
  25. 25. Absolute Dating: Isotopic Techniques <ul><li>Common Principles </li></ul><ul><ul><li>Isotopes: Radioactive variants of elements (e.g. carbon, potassium) </li></ul></ul><ul><ul><li>Isotopes decay from radioactive to nonradioactive element </li></ul></ul><ul><ul><li>They do so at a constant rate </li></ul></ul><ul><li>Half Life: The period in which radioactivity rate reaches half the original rate. </li></ul>
  26. 26. Isotopic Techniques: Radiocarbon Dating <ul><li>Carbon is found in all lifeforms </li></ul><ul><li>Carbon 12 is the stable element </li></ul><ul><li>All living things accumulate Carbon 14 </li></ul><ul><li>At death, carbon 14 decays at a constant rate to Carbon 12 </li></ul><ul><li>It reaches half the rate of original radioactivity in 5730 years </li></ul><ul><li>At 11460 years, radioactivity is half the second rate--and so on </li></ul>
  27. 27. Isotopic Techniques: Accelerator Mass Spectrometry <ul><li>In dating, a sample is cleaned then burned to produce gas </li></ul><ul><li>Proportion of C14 to C12 is then counted using Geiger counter </li></ul><ul><li>Several grams are required for the count </li></ul><ul><li>Accelerated Mass Spectrometer: counts individual molecules </li></ul><ul><li>Advantage: High accuracy, less material </li></ul>
  28. 28. Isotopic Techniques: Radiopotassium Dating <ul><li>Half life: 1.3 billion years </li></ul><ul><li>Potassium is found in granite, basalt, clay </li></ul><ul><li>Potassium 40 decays to a gas, Argon 40 </li></ul><ul><li>Argon 40 accumulate when a rock is formed </li></ul><ul><li>Disadvantage: materials less than 500,000 years old cannot be dated </li></ul>
  29. 29. Other Absolute Dating Techniques <ul><li>Electronic Spin Resonance: </li></ul><ul><ul><li>Accumulation of unpaired electrons in crystals in tooth enamel and other items with calcium (inaccurate in bone) </li></ul></ul><ul><li>Geomagnetism: </li></ul><ul><ul><li>Alignment of particles on magnetic rock; this is approximate and there are few labs </li></ul></ul><ul><li>Obsidian Hydration: </li></ul><ul><ul><li>Reaction with water; measured by thickness of accretion. </li></ul></ul>
  30. 30. Conclusion: Dating <ul><li>All techniques are problematic </li></ul><ul><ul><li>Appropriate labs may be rare </li></ul></ul><ul><ul><li>Analyzable material must be present: no volcanic rock, no radiopotassium dates </li></ul></ul><ul><ul><li>Inherent problems: radiocarbon dating may be off by centuries </li></ul></ul><ul><li>Best strategy: use several techniques </li></ul><ul><ul><li>e.g. dendrochronology with radiocarbon. </li></ul></ul>