Magnetic and Geochemical Characterization of In Situ Obsidian, New Mexico

What: Magnetic and chemical characterization of obsidian samples, New Mexico

When: June 12 – July 10, 2013

Where: New Mexico. After some initial time in Albuquerque, we plan to visit three field sites (Fig. 1): Mule Creek, Mt. Taylor (e.g., Grants Ridge, Fig. 1; also Fig. 2), and Valles Caldera (e.g., Obsidian Ridge, Fig. 1; Fig. 3).

Who: Participating faulty are Rob Sternberg, Department of Earth and Environment, Franklin & Marshall College (director); Joshua Feinberg, Dept. of Geology and Geophysics, and Institute for Rock Magnetism, University of Minnesota; Steven Shackley, Department of Anthropology, University of California, Berkeley, and University of New Mexico; and Ellery Frahm, Marie Curie Experienced Research Fellow, Dept. of Archaeology, The University of Sheffield.

Project Overview and Goals

Much work has gone into the sourcing of archaeological obsidian artifacts by matching their geochemical “fingerprints” to those of geologic source areas (Hughes and Smith, 1993; Tykot, 1997; Glascock et al., 1998; Shackley, 2005; IAOS, 2011). A number of investigators have explored the use of magnetic properties (not paleomagnetic directions) for provenancing of obsidians in the western Mediterranean (McDougall et al., 1983; Weaver et al., 2005; Weaver et al., 2009), the American Southwest (Church and Caraveo, 1996; Urrutia-Fucugauchi, 1999; Sternberg et al., 2010; Sternberg and Jackson, 2011, Fig. 4), and other regions (Vasquez et al., 2001; Johnson et al., 2009; Hillis et al., 2010). This has mostly been done on specimens in existing collections. In this project, we will collect specimens so that field relations can be considered as part of the magnetic/geochemical provenance problem. There is also a more general archaeological/anthropological perspective involving sourcing theory, technological choices, and economic models for the students to balance the strictly geological aspects of this project.

Mt. Taylor

Our goals are:

  1. to look at intra-site variability of magnetic properties within two or three specific geologic source areas, as controlled by a mapping of sample locations;
  2. to look at the between-site variability of nearby geologic source areas of obsidians;
  3. to add data to a growing database of rock magnetic properties of obsidians (Feinberg and Johnson, 2009);
  4. to compare bivariate vs. multivariate approaches to distinguishing obsidians according to a number of magnetic properties; and
  5. to compare portable x-ray fluorescence measurements of obsidians in the field with bench-top measurements made back in the laboratory.

Potential Student Projects

We hope to use a portable XRF unit as part of the field component of our project. This instrument will allow our students to collect measurements of an obsidian sample’s major and trace composition. Both Frahm and Shackley have experience operating and calibrating these instruments and we plan to either rent one or borrow one from one of the Keck Schools. Basic paleomagnetism can be done in Sternberg’s lab, and in labs at or nearby several of the Keck schools. More sophisticated magnetic analyses and electron microprobe analyses can be done at the University of Minnesota.

  • Portable X-ray flourescence (XRF) and/or petrography, one project per site
  • Lab XRF and/or petrography, one project per site
  • Petrography and/or electron microprobe analysis on inclusions
  • Magnetics, NRM (natural remanent magnetization) and susceptibility, one project per site
  • Magnetics, IRM (isothermal remanent magnetization) and more sophisticated rock magnetism, one project per site
  • Field mapping, and a GIS (geographic information system) database of all results
  • Multivariate statistical analysis of the magnetic results

Logistics/Field Conditions

Valles calderWhile in Albuquerque we will stay in residential facilities at the University of New Mexico. Lab work and lectures will partly follow the model of Shackley’s field school for Field Practice in Archaeological Petrology. For the field work at Mule Creek, we will camp near the site. At Mount Taylor, we will camp in the Cibola National Forest and use Grants, NM, as a resource base. We will stay in one of the research stations at the Valles Caldera National Preserve. We plan to work in the field or lab six days a week, with one day off.

  • All field sites are somewhat remote from populated areas.
  • Students will be responsible for their own camping gear.
  • We can arrange for sharing of tent space.
  • The weather will be hot and dry.
  • There will be hiking in these sometimes challenging conditions.
  • Electricity may not be availability when camping.

Recommended Courses/Prerequisites

Mineralogy and Petrology, or Geophysics, are required. Anthropology or Archaeology would he helpful.