Robert J. Speakman

Fracturing of the Panamanian Isthmus during initial collision with South America

Tectonic collision between South America and Panama began at 23–25 Ma. The collision is significant because it ultimately led to development of the Panamanian Isthmus, which in turn had wide-ranging oceanic, climatic, biologic, and tectonic implications. Within the Panama Canal Zone, volcanic activity transitioned from hydrous mantle-wedge−derived arc magmatism to localized extensional arc magmatism at 24 Ma, and overall marks a permanent change in arc evolution. We interpret the arc geochemical change to result from fracturing of the Panama block during initial collision with South America. Fracturing of the Panama block led to localized crustal extension, normal faulting, sedimentary basin formation, and extensional magmatism in the Canal Basin and Bocas del Toro. Synchronous with this change, both Panama and inboard South America experienced a broad episode of exhumation indicated by (U-Th)/He and fission-track thermochronology coupled with changing geographic patterns of sedimentary deposition in the Colombian Eastern Cordillera and Llanos Basin. Such observations allow for construction of a new tectonic model of the South America–Panama collision, northern Andes uplift and Panama orocline formation. Finally, synchroneity of Panama arc chemical changes and linked uplift indicates that onset of collision and Isthmus formation began earlier than commonly assumed.

Temporal Variability of Tungsten and Cobalt in Fallon, Nevada

Background Since 1997, Fallon, Nevada, has experienced a cluster of childhood leukemia that has been declared “one of the most unique clusters of childhood cancer ever reported.” Multiple environmental studies have shown airborne tungsten and cobalt to be elevated within Fallon, but the question remains: Have these metals changed through time in correspondence with the onset of the leukemia cluster? Methods We used dendrochemistry, the study of element concentrations through time in tree rings, in Fallon to assess temporal variability of airborne tungsten and cobalt since the late 1980s. The techniques used in Fallon were also tested in a different town (Sweet Home, OR) that has airborne tungsten from a known source. Results The Sweet Home test case confirms the accuracy of dendrochemistry for showing temporal variability of environmental tungsten. Given that dendrochemistry works for tungsten, tree-ring chemistry shows that tungsten increased in Fallon relative to nearby comparison towns beginning by the mid-1990s, slightly before the onset of the cluster, and cobalt has been high throughout the last ~ 15 years. Other metals do not show trends through time in Fallon. Discussion Results in Fallon suggest a temporal correspondence between the onset of excessive childhood leukemia and elevated levels of tungsten and cobalt. Although environmental data alone cannot directly link childhood leukemia with exposure to metals, research by others has shown that combined exposure to tungsten and cobalt can be carcinogenic to humans. Conclusion Continued biomedical research is warranted to directly test for linkage between childhood leukemia and tungsten and cobalt.

Four-thousand-year-old gold artifacts from the Lake Titicaca basin, southern Peru

Artifacts of cold-hammered native gold have been discovered in a secure and undisturbed Terminal Archaic burial context at Jiskairumoko, a multicomponent Late Archaic–Early Formative period site in the southwestern Lake Titicaca basin, Peru. The burial dates to 3776 to 3690 carbon-14 years before the present (2155 to 1936 calendar years B.C.), making this the earliest worked gold recovered to date not only from the Andes, but from the Americas as well. This discovery lends support to the hypothesis that the earliest metalworking in the Andes was experimentation with native gold. The presence of gold in a society of low-level food producers undergoing social and economic transformations coincident with the onset of sedentary life is an indicator of possible early social inequality and aggrandizing behavior and further shows that hereditary elites and a societal capacity to create significant agricultural surpluses are not requisite for the emergence of metalworking traditions.

Multiple Dendrochronological Signals Indicate The Eruption Of Parícutin Volcano, Michoacán, Mexico

Abstract The eruption of Parícutin (1943–1952), a cinder cone volcano in Michoacán, Mexico, caused dendrochronological and dendrochemical responses that might be useful as general dating tools for eruptions. For the eruption period, pines near Parícutin have slightly suppressed ring widths plus high inter-annual variability of width. Wood anatomy changes include traumatic resin ducts and thin bands of false latewood. Dendrochemistry of tree rings shows little temporal variation in most elements, but beginning in 1943 sulfur content increased in rings of four trees and phosphorus content increased in rings of two trees. Hypotheses for increased S and P include new availability of pre-existing soil S and P and/or new input of S and P from the tephra itself. Pines at Parícutin also show suppressed ring widths for five years beginning in 1970, and had the eruption date not been known, the most likely conclusion from ring-width data alone would have been an eruption from 1970 to 1974. However, the 1970s suppression was in response to defoliation by a pine sawfly outbreak, not an eruption. For dendrochronological dating of cinder-cone eruptions, a combination of multiple characteristics (width, chemistry, and anatomy) would be more reliable than depending on any one characteristic alone.

Characterization of maya pottery by INAA and ICP-MS

A total of 81 pottery and 25 clay samples from the archaeological site and hinterland areas of Blue Creek in northwest Belize were analyzed by instrumental neutron activation analysis and inductively-coupled-plasma mass-spectrometry at the University of Missouri Research Reactor. Data generated for this study offers insight into local clay-resource variability and movement of pottery in the transition from Early (A.D. 250–600) to Late Classic (A.D. 600–850) occupation. Comparison of data generated by the two analytical techniques demonstrates the relative strengths and weaknesses of each method.

New Evidence for a Possible Paleolithic Occupation of the Eastern North American Continental Shelf at the Last Glacial Maximum

Mastodon remains dated to 22,760 RCYBP were recovered with a bifacial laurel leaf knife from 250 ft below sea level on the outer continental shelf of Virginia. This chapter reports the results of our research concerning this find and an on-going survey of the extensive archaeological collections of the Smithsonian and other repositories including large private collections that are representative of the Chesapeake Bay drainage system. We located additional laurel leaf specimens recovered by watermen working on the continental shelf. The study indicates that these bifaces are not part of the post last glacial maximum (LGM) technologies and, therefore, support an LGM occupation of the continental shelf of North America.

Obsidian Subsources Utilized at Sites in Southern Sardinia (Italy)

While geochemical analysis of obsidian artifacts is now widely applied around the world, both new instrumental methods and new research questions continue to be applied in archaeology. In the Mediterranean, many analytical methods have been employed and proven successful in distinguishing all of the island sources. In this study, results are presented from the virtually non-destructive, LA-ICP-MS multi-element analysis of 95 carefully selected obsidian artifacts from four neolithic period sites in southwestern Sardinia. The patterns of exploitation of specific Monte Arci obsidian subsources revealed in this study support a down-the-line model of obsidian trade during the neolithic period, but with chronological changes that are best explained by increased socioeconomic complexity.

Major, minor and trace element mass fractions determined using ED-XRF, WD-XRF and INAA for five certified clay reference materials: NCS DC 60102–60105; NCS DC 61101 (GBW 03101A, 03102A, 03103, and 03115)

Major, minor and trace element mass fractions were determined using wavelength dispersive and energy dispersive X-ray fluorescence and instrumental neutron activation analysis for five clay certified reference materials (NCS DC 60102–60105, 61101) distributed by the National Research Center for Certified Reference Materials in China. We report mass fractions for 10 major and the following 29 minor and trace elements: As, Ba, Ce, Co, Cr, Cs, Cu, Eu, Hf, La, Lu, Nb, Nd, Ni, Pb, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, U, V, Y, Yb, Zn, and Zr.

Source Analysis of Central Plains Tradition Pottery Using Neutron Activation Analysis: Feasibility and First Results

Abstract We report the results of a study applying instrumental neutron activation analysis (NAA) to pottery from eight sites assigned to the western part of the Central Plains tradition (Upper Republican and Smoky Hill phases) and six components identified as High Plains Upper Republican. Our purpose is to test the feasibility of using NAA to trace interactions among people of the Central Plains tradition and between the Central Plains tradition people and their counterparts on the High Plains. Results of the statistical analysis, which was performed using the chemical data for both newly sampled sites and previously studied sites (as reported by Cobry), suggest that NAA is a usable method for evaluating the movement of pottery for at least parts of the Central Plains tradition. Samples from four sites on Medicine Creek as well as the Albert Bell and LeBeau sites formed a single homogeneous group referred to as the Central Plains Reference Group. Samples from the other sites, however, formed distinct groups for each site and also reflected some interaction with their contemporaries. We discuss the implications of these results, some of the questions that remain, and the need for continued sampling.

Pottery in the Mormon Economy: An Historical, Archaeological, and Archaeometric Study

Pottery production was important to Latter-day Saint communities and distinguished these towns from their non-Mormon neighbors. The potters and workers left scant records that reveal how their wares fit into Utah’s theocratically organized economy. Potters and potteries of 19th-century Utah and the Mormon Domain were part of an archaeological survey conducted between 1999 and 2000. The research project yielded examples of kiln wasters that could be subjected to instrumental neutron activation analysis (INAA). The results demonstrate the utility of integrating primary records and archaeometric tools in the study of historical era economic processes. Data also indicate the applicability of the approach for potteries in close geographic proximity and to determine patterns of variation within site assemblages. The authors propose an anthropological research program to explore the economics of religion in Mormon Utah, combining the analytical power of archaeometry with the contextualized questioning possible in historical archaeology.