SAGE 2004 Archaeological Magnetics Survey

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SAGE 2004 Archaeological Magnetics Survey
San Marcos Pueblo, New Mexico J. Mark
Hale University of Utah
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San Marcos Pueblo, NM
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Outline

• Introduction to Magnetics
• Archaeological Contributions
• Instrumentation
• Software and Data Analysis
• Archaeological implications of the magnetic data
  at San Marcos Pueblo
• Conclusions
• Caveats and Improvements

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Possible Sources of Remnant Magnetism

• TRM Thermo-Remnant Magnetism, Curie point
  volcanic rocks and archaeological hearths.
• DRM Depositional Remnant Magnetism, sedimentary
  rocks and sedimentary cores.

Dipole Profile is Dependent on the Orientation of
the Body
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G-858 Magnetometer

• Operating Principle Self-oscillating split-beam
  Cesium Vapor with automatic hemisphere
  switching.
• Heading Error 1 nT
• Sensor Height 0.5 m

Data Analysis Software
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Pros and Cons of Magnetic Data for Archaeological
Use
Benefits - Magnetics can cover a wide area in a
short amount of time. Reduction of survey
area. - Easily obtained approximate depths.
Detriments - Approximate depths carry large
discrepencies and are subjective in nature. -
Anomaly type remains a mystery until
excavation
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Mission Complex Magnetic Anomalies
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Mission Site Anomaly Profiles
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Mission Site Anomaly Depths(Acquired using
maximum slope approximation)
Maximum slope approximation
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Mission Complex1st Horizontal Derivative(as an
estimate of depth)
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Midden 2 Magnetic Anomalies
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Volkswagen Anomaly

• Strong dipole signature
• Dipole low trends towards magnetic north
• Reasonable depth estimate 1.5 m
• Great profile!

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Midden 2 Site Anomaly Profiles
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Midden 2 Site Anomaly Depths
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Conclusions

• The San Marcos Pueblo has several magnetic
  anomalies with reasonable depths.
• The Galisteo fins contribute to the DRM of the
  site.
• The Mission site still has unearthed anomalies at
  reasonable depths
• The Volkswagen anomaly is the strongest in the
  Midden 2 site.

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Caveats and Improvements
Caveats

• Depth estimates are just estimates
• Anomalies are highly ambiguous
• There is no such thing as untainted data

Improvements for Further Research

• Plotting magnetometer data using real GPS data
• Use forward modeling to determine size and shape
  of magnetic body
• More time to conduct a proper evaluation
• More computer power!