Jesse Ballenger

The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact

Some of the evidence for the recent hypothesis of an extraterrestrial impact that caused late Pleistocene megafaunal extinctions [Firestone et al. (2007) Proc Natl Acad Sci USA 104:16016–16021] was based upon samples collected at Murray Springs, a Clovis archaeological site in southeastern Arizona. Here we describe sampling and analyses of magnetic separates from within, above, and below the lower Younger Dryas boundary (LYDB) black mat at Murray Springs, as well as radiation measurements from the LYDB at Murray Springs and two other well-stratified Clovis sites. The main magnetic fraction at Murray Springs is maghemite. Magnetic microspherules have terrestrial origins but also occur as cosmic dust particles. We failed to find iridium or radiation anomalies. The evidence for massive biomass burning at Murray Springs is addressed and found to be lacking. We could not substantiate some of the claims by Firestone and others, but our findings do not preclude a terminal Pleistocene cosmic event.

Landscape Engineering and Organizational Complexity among Late Prehistoric Bison Hunters of the Northwestern Plains

Studies of hunter-gatherer sociopolitical organization consistently exclude terrestrial big-game hunters—pedestrian bison hunters, in particular—from discussions of emerging complexity. To an important extent, this exclusion stems both from the ethology of bison and its consequences for mobile hunters and from the character of their archaeological record, which lacks conventional indicators of organizational complexity such as high-status burials and long-term storage facilities. However, this record exhibits stone architecture of monumental proportions. We argue that evidence of emerging sociopolitical complexity is embodied in the hunters’ ability to (1) invest extensively on landscape engineering to amass communal bison wealth for consumption, storage, and exchange, and (2) produce and reproduce ritual wealth among individuals and restricted sectors of the group. Through a multiscalar research design that integrates thousands of surface stone features with data recovered from kill site excavation, ethnohistorical records, and Blackfoot traditions, we demonstrate that Late Prehistoric bison hunters of the northwestern Plains endeavored to create conditions for permanence in their hunting territory by strategically emplacing and maintaining hunting facilities. These, in turn, would be used by ensuing generations of culturally related groups for whom the communal hunt was a formal and ritually managed act.

Isotopic paleoecology of Clovis mammoths from Arizona

The causes of megafaunal extinctions in North America have been widely debated but remain poorly understood. Mammoths (Mammuthus spp.) in the American Southwest were hunted by Clovis people during a period of rapid climate change, just before the regional onset of Younger Dryas cooling and mammoth extirpation. Thus, these mammoths may provide key insights into late Pleistocene extinction processes. Here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the San Pedro Valley of Arizona, using the carbon (13C/12C) and oxygen (18O/16O) isotope compositions of tooth enamel. These records suggest that Clovis mammoths experienced a warm, dry climate with sufficient summer rainfall to support seasonal C4 plant growth. Monsoon intensity may have been reduced relative to the preceding time period, but there is no isotopic evidence for severe drought. However, it is possible that the “Clovis drought”, inferred from stratigraphic evidence, occurred suddenly at the end of the animals’ lives and thus was not recorded in the enamel isotopic compositions. Unlike mammoths that lived before the Last Glacial Maximum, Clovis mammoths regularly increased C4 grass consumption during summer, probably seeking seasonally green grasslands farther from the river valley. This predictable seasonal behavior may have made mammoths easier to locate by Clovis hunters. Furthermore, Clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction.

Implications from chemical, structural and mineralogical studies of magnetic microspherules from around the lower younger dryas boundary (New Mexico, Usa)

Abstract Hollow magnetic microspherules from along the lower Younger Dryas boundary (c. 12.9 ka bp) in New Mexico (USA) were studied using scanning electron microscopy, electron probe microanalysis, X‐ray diffraction, and laser‐ablation inductively coupled‐plasma mass spectrometry methods. The shell of the microspherules (10–15% of the spherules diameter) displays dendritic surface textures, which are likely due to quenching during rapid cooling of molten material. Structurally, multiple single‐magnetite crystals attached together form the bulk of the microspherules. Iron dominates the microspherules’ composition (∼90% FeOtot), Mn is the second most abundant element (up to 0.4% MnO), Al is detected in low concentrations (<0.30% of Al2O3). Among the trace elements, the rare earth elements display slightly fractionated patterns with concentrations of 0.1–1.0× CI chondrite. The microspherules contain elevated concentrations of Ni relative to detrital magnetite (up to 435 ppm) and very low concentrations of Ti (down to 5 ppm). Chemical, structural and mineralogical features of the microspherules do not contradict the existing models of the formation during ablation while a meteoroid goes through the Earths atmosphere. Elevated concentrations of the magnetic microspherules in sediments can be a stratigraphic marker for the lower Younger Dryas boundary in North America.

Non-agricultural Recurrence, Mobility, Adaptation, and Groundwater Variations on the Lower Bajada, Sonoran Desert, USA

The construction of a solar-power-array on Luke Air Force Base, Arizona, prompted the archaeological investigation of one of the most completely excavated Archaic period sites in the Sonoran Desert. Beginning with the Middle Archaic period and continuing to the early Historic period, people visited this location to gather and process wild plants, particularly mesquite. Despite the long occupational history, the plant-processing tools and techniques changed little over time. This paper focuses on the settlement location and history of Falcon Landing, a multicomponent site in the western Phoenix Basin. The excavation of Falcon Landing uncovered over 3,000 features representing over 5,000 years of intermittent human occupation. The results of this project offer a unique and intriguing look into Archaic period subsistence and settlement in a lower bajada landscape, and how this subsistence and settlement strategy persisted for millennia and became an integral part of human adaptation to the Sonoran Desert.