Excavation Techniques

Excavation Techniques and Analysis Applications to Paleoanthropology

About Excavation and Analysis
Authors’ definition:
Study of past cultures analyzing material remains of human behavior
Study entails
Time: Date of the site and its contents
Space: Location of the site and its contents
Material remains: siting, retrieval, analysis

Fundamentals of Excavation and Analysis
Site discovery and selection
Excavation of artifacts, ecofacts, and features
Analysis for dates, attributes, and environment

An Example: Flow Chart for Combe Capelle (A Neanderthal Site)
Research Design
Discovery
Preparation
Data Collection (The Dig)
Analysis
Interpretation/Synthesis

Some Definitions
Ecofacts: remains of plants, animals, sediments, or other materials not modified by human activity
Features: immovable structures, pits, posts, burial sites
Artifacts: all portable objects altered by human activity
Sites: Landscape where human activity took place, as indicated by the above

How are Sites Formed?
Taphonomy: Study of how lifeforms or artifacts wound up at a particular location
Primary refuse: items left at site of use
Secondary refuse: Items moved elsewhere

How are Items Preserved? Material
Some materials resist deterioration:
Bone: Skulls and teeth
Stone or Metal (tools, ornaments)
Seeds, with protective covers

How Are Objects Preserved? Environment
Arid climates (Peruvian coast)
Water: Planks at Ozette, WA or France
Peat moss: the “Bog People” in Scandinavia
Ice: Ötzi the “Iceman” in Austrian/Italian Alps
Volcanic Ash, Cerén, El Salvador

Site Discovery
Lucky finds
Consulting available sources: studies, records, even older informants
Maps and aerial photographs
Geographical Information Systems/Remote Sensing

Site Selection
Learning everything possible about each site
Selecting as large and representative a site as possible
Preliminary work: surface finds, features, perhaps test pits or trenches
Problem-Oriented Research and Deliberate Surveys

Survey: Mapping, Part 1: General
First principle: Digging is destructive--record everything!
Mapping
Latitude, longitude, and elevation
Benchmarks or features
Measurements
Horizontal
Vertical

Surveying: Mapping Part 2: Horizontal Measurement
Select and draw west-east (X-axis) and north-south (Y-axis) baselines from primary site datum
Mark off intervals at meters and centimeters from baselines
Label the intervals along axes of the grid by letters, numbers, or both
Adapt procedure according to topographical or archaeological features

Laying Out an Alternative Grid

Survey: Mapping Part 3: Vertical Measurements
Surveying using transit or alidade and measuring rod
Vertical base: benchmark or permanent feature of known elevation
Convert measures to meters above sea level.

Example: Work In Progress

Virtual Dig: Mapping in Combe-Capelle
Retraced excavation by Henri-Marc Ami
Excavated sample squares of the site
Squares distinguished by
Letter (X axis)
Numbers (Y axis)
Vertical measurements by 4 strata.

Survey: Test pits and trenches
Test pits provide sample of site stratigraphy
Stratigraphy: profile of two or more layers of
Natural sediment
Human deposits
Test pits provide sample of overall site
Several pits suggest which part should be excavated most extensively

Survey: Test Pits
Advantages: Provide preliminary information on site
Disadvantages
Need more pits to round out information
May not yield full stratigraphy

Survey: Trenches
Uses
Provide full stratigraphy
Provide sample of artifacts to establish chronology
Locate features
Find site boundaries
Types
Slit trenches
Step trenches
Backhoe trenches
Wall trenches

Survey: Trenches—Advantages and Drawbacks
Advantages:
Good samples of artifacts
Find buried features
Good time depth
Drawbacks
Destructive, especially with backhoe
Can destroy potential activity areas before knowing what’s there
Danger of collapse

Deciding Where to Excavate
Sampling depends on research questions
Judgmental Sampling: based on prior knowledge of site; used at Combe-Capelle
Probabilistic Sampling
Random sampling
Stratified sampling: based on prior knowledge
Known trash deposits or architectural features
Ensure everything significant is included

Tools for Excavation
Dental picks or paint brushes
Ice picks
Tweezers (fragile objects)
Trowels (pointed and square)
Shovels (pointed and square-nosed)
Heavy equipment (backhoes)
Buckets and Screens

Tools Used for Rough Excavation
Shovel, Round Nose Club Hammer
Pick Chisel, Flat
Pry Bar Scraper, Long Handle
Sledge Hammer

Tools Used for Fine Excavation
Top row: plastic paint trowel, rubber air puffer, large brushes, small brush, wooden/plastic sculpting tools/small paint trowel), plastic spoon Bottom row: note pad, folding ruler (in cm.), Marshalltown trowel (45-5), 8"mill bastard file, plastic spoon, plastic trowel, tape measure (3-4 m. is sufficient)

Vertical Excavation: Some “Laws”
Law of Association:
Artifacts found at the same stratum (layer) are in association with one another
Artifacts found at different strata are not in association with one another
Law of Superposition: Geological layers are stratified one upon another
Lower strata are older than higher ones
Uniformitarianism: Geological processes similar throughout time

The “Laws” Illustrated
a) Law of Association: Skeleton, dagger, and burial pit are at the same level
b) Law of Superposition: pot is at the higher stratum and
stone axe is at the lower stratum

Vertical Excavation: Stratigraphy
Layer deposited in chronological order: lowest layer is oldest and so on.
Disturbances can change stratigraphy
Erosion from hillside: oldest is top layer
Structure foundation disturbs layers
Burrowing animals may move objects
Then there are golddiggers and pothunters

Vertical Excavation: Procedure:
Each artifact is recorded and removed
Photographed, sketched, or described
Vertical and horizontal position
Soils analyzed for chemistry, pollen, etc
Associations between artifacts are recorded
Assumption: artifacts found at same layer occurred at same time period

Vertical Excavation: Proveniencing
Definition: recording artifacts in three-dimensional space
Transit and stadia rod: record is set from a secondary datum point
Theolodite: Records the position of a artifact
Using both vertical and horizontal coordinates

What is a Theolodite?
Left: Front View Right: Back View
Front Lens Viewing Lens and Focus
Gun Sights Adjustment knobs (v and h)

Laser Theolodite
Adds an electronic distance meter (EDM)
And a laser device to the theolodite
It records the position of an artifact
Using a laser bouncing off a prism of known height
Results can be written down or linked to a portable computer
Printer can produce tags that are detached
And put with the artifact to be photographed before removal

Horizontal Excavation: Procedure
As each layer or stratum is excavated, it is removed
Same procedure of excavation is repeated for next layer
One or two layers: prefer horizontal excavation to get lay of the site
Different samples are taken for different layers: soil, pollen, charcoal, bone
Some layers may be left for control

Overview of Dating
Unifomitarianism
Relative Dating
Stratigraphy
Association
Absolute Dating
Calendrical
Natural Features
Isotopic

Dating: Uniformitarianism
Uniformitarianism vs. Catastrophism
Uniformitarianism: All geological processes--erosion, weathering--observable today have always been present and at the same rate
Uniformitarianism is the basis of dating.
Catastrophism: Changes have been sudden and have occurred at different rates in the past from those of the present.

Relative Dating
Stratigraphy: Establishment of sequences by soil strata
Exceptions: soil disturbance, erosion.
Law of Association: Dating of finds within a stratum

Chronometric Associations
Basic principle: Materials associated with other materials of known age are the same age range
Bottle styles and clay pipes .
Gravestones in Stoneham, MA (Deetz)

Absolute Dating: Calendrical
Entails use of traditional calendars
Mayan
Long Count: Beginning date fixed at 3113 BC
Calendar Rounds: 260- and 365-day calendars
Egyptians:
332 BC Conquest by Alexander the Great
Traced back through recorded dynasties
Astronomical events checked by present data
Others: Chinese, Romans, Greeks

Absolute Dating: Natural Features
Dendrochronology: Tree ring dating
Tree rings vary from year to year
Local stumps or timber compared with master sequence (e.g., Univ. of Arizona)
Varve analysis: Clay deposits in lakes from melting ice.
Patterns also differ yearly
Likewise compared with master chart.

Absolute Dating: Isotopic or Radiometric Techniques
Common Principles
Isotopes: Radioactive variants of elements (e.g. carbon, potassium)
Isotopes decay from radioactive to nonradioactive element
They do so at a constant rate
Half Life: The period in which radioactivity rate reaches half the original rate.

Isotopic Techniques: Radiocarbon Dating
Carbon is found in all lifeforms
Carbon 12 is the stable element
All living things accumulate Carbon 14
At death, carbon 14 decays at a constant rate to Carbon 12
It reaches half the rate of original radioactivity in 5730 years
At 11460 years, radioactivity is half the second rate--and so on

Isotopic Techniques: Accelerator Mass Spectrometry
In dating, a sample is cleaned then burned to produce gas
Proportion of C14 to C12 is then counted using Geiger counter
Several grams are required for the count
Accelerated Mass Spectrometer: counts individual molecules
Advantage: High accuracy, less material

Isotopic Techniques: Radiopotassium Dating
Half life: 1.3 billion years
Potassium is found in granite, basalt, clay
Potassium 40 decays to a gas, Argon 40
Argon 40 accumulate when a rock is formed
Disadvantage: materials less than 500,000 years old cannot be dated

Other Absolute Dating Techniques
Electronic Spin Resonance:
Accumulation of unpaired electrons in crystals in tooth enamel and other items with calcium (inaccurate in bone)
Geomagnetism:
Alignment of particles on magnetic rock; this is approximate and there are few labs
Obsidian Hydration:
Reaction with water; measured by thickness of accretion.

Conclusion: Dating
All techniques are problematic
Appropriate labs may be rare
Analyzable material must be present: no volcanic rock, no radiopotassium dates
Inherent problems: radiocarbon dating may be off by centuries
Best strategy: use several techniques
e.g. dendrochronology with radiocarbon.

Conclusion
All excavation involves destruction
Therefore, sites have to be
Excavated carefully, often with trowels
Recorded for location and elevation
Artifacts catalogued before removal
Features have to be mapped
Ideal: Sites could be reconstructed
Based on recording of data

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Excavation Techniques

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