«By Celeste Nicole Henrickson A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in ...»
Shane Macfarlan is a PhD student at Washington State University and has an archaeology specialty in Museum Science and curation. Mr. Macfarlan is a volunteer and will help with excavation and curation of artifacts. Samuel Willis es estudiante de la Maestría en Antropología en la Universidad Estatal de Oregon, especializando en el estudio de la tecnología de lítica en prehistoria. Sr. Willis tiene experiencia en el análisis e interpretación de la tecnología en el único sitio costero del periodo Pleistocene tardío en Oregon bajo la dirección del Dr. Loren Davis. Sr. Willis es voluntario y ayudará en las excavaciones y análisis de artefactos. REPORTING OF RESULTS The principal investigator is to provide the INAH with a full technical report that provides detailed discussion and summaries of the following aspects of the project: overall approach, detailed description of methods, results, and interpretation. Artifacts will be placed in an INAH approved repository. Additional papers in professional journals and presentations at academic meetings are expected to follow the report. Depending on the archaeological context and preservation of artifacts at Cueva Santa Rita, the results of these investigations will generate great interest in the scientific community. Credit will be given to INAH and the archaeologists of southern and central Baja California Sur. WORK SCHEDULE Julio 2008: Arrive in La Paz and begin landscape survey Agosto Septiembre 2008: Conduct archaeological test excavations. Give all artifacts to INAH before leaving Baja California Sur, Mexico. Octubre Noviembre 2008: Análisis de material en el laboratorio en La Paz. Elaborar catalogo de artefactos y entrega de material a la oficina de Centro INAH B.C.S. Septiembre 2009: Submit final report of findings
The analysis here of source standard obsidian from two localities in southern Baja California indicates a high silica rhyolite glass, likely from a single magma source. The signature may be similar to an unlocated source present in small proportions in archaeological assemblages in central and southern Baja California (Shackley and Henrickson 2009).
ANALYSIS AND INSTRUMENTATIONAll rock samples are analyzed whole. The trace element results presented here are quantitative in that they are derived from "filtered" intensity values ratioed to the appropriate x-ray continuum regions through a least squares fitting formula rather than plotting the proportions of the net intensities in a ternary system (McCarthy and Schamber 1981; Schamber 1977). Or more essentially, these data through the analysis of international rock standards, allow for inter-instrument comparison with a predictable degree of certainty (Hampel 1984).
The analyses were performed in the Archeological XRF Laboratory, El Cerrito, California, using a Thermo Scientific Quant’X energy dispersive x-ray fluorescence spectrometer. The spectrometer is equipped with a ultrahigh flux peltier air cooled Rh x-ray target with a 125 micron beryllium (Be) window, an x-ray generator that operates from 4-50 kV/0.02-1.0 mA at 0.02 increments, using an IBM PC based microprocessor and WinTraceTM
4.1 reduction software. The spectrometer is equipped with a 2001 min-1 Edwards vacuum pump for the analysis of elements below titanium (Ti). Data is acquired through a pulse processor and analog to digital converter. For samples over 10 mm in minimum diameter, a 8.8 mm tube collimator is fitted. For samples under 10 mm in
minimum diameter or extreme angular character (Toris samples 7, 9-13, 18) a 3.5 mm tube collimator is used to concentrate energy in a smaller diameter.
For Ti-Nb, Pb, Th elements the mid-Zb condition is used operating the x-ray tube at 30 kV, using a 0.05 mm (medium) Pd primary beam filter in an air path at 200 seconds livetime to generate x-ray intensity Kα1-line data for elements titanium (Ti), manganese (Mn), iron (as FeT), cobalt (Co), nickel (Ni), copper, (Cu), zinc, (Zn), gallium (Ga), rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), lead (Pb), and thorium (Th). Not all these elements are reported since their values in many volcanic rocks is very low. Trace element intensities were converted to concentration estimates by employing a least-squares calibration line ratioed to the Compton scatter established for each element from the analysis of international rock standards certified by the National Institute of Standards and Technology (NIST), the US. Geological Survey (USGS), Canadian Centre for Mineral and Energy Technology, and the Centre de Recherches Pétrographiques et Géochimiques in France (Govindaraju 1994). Line fitting is linear (XML) for all elements but Fe where a derivative fitting is used to improve the fit for iron and thus for all the other elements. When barium (Ba) is acquired, the Rh tube is operated at 50 kV and 0.5 mA in an air path at 200 seconds livetime to generate x-ray intensity Kα1-line data, through a 0.630 mm Cu (thick) filter ratioed to the bremsstrahlung region (see Davis et al. 2011). Further details concerning the petrological choice of these elements in North American obsidians is available in Shackley (1988, 1990, 1995, 2005; also Mahood and Stimac 1991; and Hughes and Smith 1993). A suite of 17 specific standards used for the best fit regression calibration for elements TiNb, Pb, and Th, include G-2 (basalt), AGV-2 (andesite), GSP-2 (granodiorite), SY-2 (syenite), BHVO-2 (hawaiite), STM-1 (syenite), QLO-1 (quartz latite), RGM-1 (obsidian), W-2 (diabase), BIR-1 (basalt), SDC-1 (mica schist), BCR-2 (basalt), TLM-1 (tonalite), SCO-1 (shale), all US Geological Survey standards, NBS-278 (obsidian) from the National Institute of Standards and Technology, BR-1 (basalt) from the Centre de Recherches Pétrographiques et Géochimiques in France, and JR-1 and JR-2 (obsidian) from the Geological Survey of Japan (Govindaraju 1994).
For the analysis of light elements (Na-Ca) a fundamental parameter (theoretical) method is employed using two separate conditions depending on atomic weight (Z). For the Low Za condition (Na, Mg, Al, Si) the tube is operated at 6 kV, auto current, with no tube filter in vacuum for 100 live seconds. For the Mid Zb condition (K, Ca, Ti, Mn, Fe) the tube is operated at 32 kV, auto current, with a thin (0.06 mm) Pd filter in vacuum at 100 live seconds. Five
USGS and Japanese standards (described above) are used in the theoretical calibration; RGM-1, JR-1, AGV-2, BHVO-2, BIR-1, and one Corning Glass standard D. Multiple conditions are designed to ameliorate peak overlap identified with digital filter background removal, least squares empirical peak deconvolution, gross peak intensities and net peak intensities above background.
The data from the WinTrace software were translated directly into Excel for Windows and into SPSS for statistical manipulation (Tables 1 and 2). In order to evaluate these quantitative determinations, machine data were compared to measurements of known standards during each run (Table 1). RGM-1 is analyzed during each sample run for obsidian artifacts to check machine calibration (Table 1). Bivariate plots of the trace element data indicate the similar magmatic relationship between the two localities (Figures 1-4). Field structural geological survey will confirm the analytical hypothesis.
REFERENCES CITEDDavis, M.K., T.L. Jackson, M.S. Shackley, T. Teague, and J. Hampel 2011 Factors Affecting the Energy-Dispersive X-Ray Fluorescence (EDXRF) Analysis of Archaeological Obsidian. In X-ray Fluorescence Spectrometry (XRF) in Geoarchaeology, edited by M.S. Shackley, pp. 45-64. Springer, New York.
1994 1994 Compilation of Working Values and Sample Description for 383 Geostandards. Geostandards Newsletter 18 (special issue).
Hampel, Joachim H.
1984 Technical Considerations in X-ray Fluorescence Analysis of Obsidian. In Obsidian Studies in the Great Basin, edited by R.E. Hughes, pp. 21-25. Contributions of the University of California Archaeological Research Facility 45. Berkeley.
1981 Gradients in Silicic Magma Chambers: Implications for Lithospheric Magmatism.
Journal of Geophysical Research 86:10153-10192.
Hughes, Richard E., and Robert L. Smith 1993 Archaeology, Geology, and Geochemistry in Obsidian Provenance Studies. In Scale on Archaeological and Geoscientific Perspectives, edited by J.K. Stein and A.R.
Linse, pp. 79-91. Geological Society of America Special Paper 283.
Mahood, Gail A., and James A. Stimac 1990 Trace-Element Partitioning in Pantellerites and Trachytes. Geochemica et Cosmochimica Acta 54:2257-2276.
McCarthy, J.J., and F.H. Schamber 1981 Least-Squares Fit with Digital Filter: A Status Report. In Energy Dispersive X-ray Spectrometry, edited by K.F.J. Heinrich, D.E. Newbury, R.L. Myklebust, and C.E. Fiori, pp. 273-296. National Bureau of Standards Special Publication 604, Washington, D.C.
1977 A Modification of the Linear Least-Squares Fitting Method which Provides Continuum Suppression. In X-ray Fluorescence Analysis of Environmental Samples, edited by T.G.
Dzubay, pp. 241-257. Ann Arbor Science Publishers.
Shackley, M. Steven 1988 Sources of Archaeological Obsidian in the Southwest: An Archaeological, Petrological, and Geochemical Study. American Antiquity 53(4):752-772.
1990 Early Hunter-Gatherer Procurement Ranges in the Southwest: Evidence from Obsidian Geochemistry and Lithic Technology. Ph.D. dissertation, Arizona State University, Tempe.
1995 Sources of Archaeological Obsidian in the Greater American Southwest: An Update and Quantitative Analysis. American Antiquity 60(3):531-551.
2005 Obsidian: Geology and Archaeology in the North American Southwest. University of Arizona Press, Tucson.
Shackley, M.S. and C. Henrickson 2009 From the Unknown to Known: the State of Obsidian Source Provenance Studies in Baja California. Paper presented at the Annual Meeting of the Society for American Archaeology, Atlanta, Georgia.
Table 1. Major oxides for one sample from Ciruelo and one from Toris.
APPENDIX IV: CUEVA SANTA RITA PROFILE DESCRIPTIONS______________________________________________________________________________
Figure 1 and Table 1. Trench A, Unit 1, east wall profile description Figure 1. Photograph of Unit 1, south wall. *
*Profile destroyed during tropical storm Julio. Unable to clean profile. A white line is visible along the walls of Unit 1. This line shows the highest level of perched water, leaving precipitates behind after it evaporated.
Figure 2 and Table 2. Trench A, Unit 2, east wall Figure 2. Northern half of east 2X2 meter wall profile.
Figure 4 and Table 5. Trench A, Unit 3, north wall.
Figure 4. North wall, Unit 3. Circles indicate rocks.