Search

Founding populations of the first Americans likely occupied parts of Beringia during the Last Glacial Maximum (LGM). The timing, pathways, and modes of their southward transit remain unknown, but blockage of the interior route by North American ice sheets between ~26 and 14 cal kyr BP (ka) favors a coastal route during this period. Using models and paleoceanographic data from the North Pacific, we identify climatically favorable intervals when humans could have plausibly traversed the Cordilleran coastal corridor during the terminal Pleistocene. Model simulations suggest that northward coastal currents strengthened during the LGM and at times of enhanced freshwater input, making southward transit by boat more difficult. Repeated Cordilleran glacial-calving events would have further challenged coastal transit on land and at sea. Following these events, ice-free coastal areas opened and seasonal sea ice was present along the Alaskan margin until at least 15 ka. Given evidence for humans south of the ice sheets by 16 ka and possibly earlier, we posit that early people may have taken advantage of winter sea ice that connected islands and coastal refugia. Marine ice-edge habitats offer a rich food supply and traversing coastal sea ice could have mitigated the difficulty of traveling southward in watercraft or on land over glaciers. We identify 24.5 to 22 ka and 16.4 to 14.8 ka as environmentally favorable time periods for coastal migration, when climate conditions provided both winter sea ice and ice-free summer conditions that facilitated year-round marine resource diversity and multiple modes of mobility along the North Pacific coast.

Sea level rise and marine erosion threaten coastal archaeological sites around the world, forcing difficult decisions about how to prioritize which sites to document and analyze. Here we present the results of research at a heavily eroded Late Holocene shell midden at CA-SRI-26, Santa Rosa Island, California. Systematic surface collection and radiocarbon dating of the site revealed an assemblage that is about 1400 years old and contains a variety of shellfish, bird, fish, and mammal remains, stone and bone tools, and matted sea grass (Phyllospadix sp.). Of the more remarkable finds is a humerus from a subadult Guadalupe fur seal (Arctocephalis towndsendi) with a projectile point tip lodged in the bone. This rare archaeological example of direct marine mammal hunting and other evidence for diverse marine foraging activities demonstrate the research value of eroded sites threatened by rising seas around the world. [ABSTRACT FROM AUTHOR]

Part 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed ∼10 million km2 of Earth’s surface, or ∼9% of Earth’s biomass, considerably more than for the K-Pg impact. Bayesian analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and of the YDB impact event (12,835–12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an “impact winter.” This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes.

In America’s Far West, chipped stone crescents dating between approximately 12,000 to 8000 cal BP are often found associated with Western Stemmed Tradition points. Crescent function is debated, but scholars have suggested that they are closely associated with wetland habitats, an association that has never been systematically investigated. Using a geographic information system-based Euclidean distance analysis, we compared a sample of 100 geolocated crescent-bearing sites in Washington, Oregon, Idaho, Nevada, Utah, and California with reconstructed paleoshorelines. We confirmed a strong association of crescents with wetlands—94 of the 100 sites and approximately 99% of crescents themselves were located within 10 km of reconstructed paleoshorelines. Our results provide quantitative and region-wide support for a strong association of crescents with terminal Pleistocene and early Holocene wetland habitats. The diversity of aquatic habitats crescents are associated with, along with their morphology, suggests an association with faunal rather than plant resources, possibly birds of the Pacific Flyway.

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼ 100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

Lithic technologies have been an important part of Native American lifeways on California’s Channel Islands for more than 12,000 years. However, little is known about stone tool technologies on Anacapa, the second smallest and closest island to California’s mainland. To broaden our understanding of stone tool technologies on the Channel Islands and assess the availability of toolstone on Anacapa, we classified 859 lithic artifacts recovered from three ~3,000-year-old shell middens. Each artifact was classified by material, artifact type, and visually inspected for thermal damage. One hundred and forty three of the larger artifacts were examined using a glossmeter. Our results suggest that prehistoric Anacapa Islanders were heat-treating and using local Anayapax polychromatic green cherts and chalcedony to manufacture a variety of core and flake tools. Some of these cherts may overlap in color and quality with polychromatic cherts documented on eastern Santa Cruz Island, but the polychromatic green cherts appear to have been of local Anacapa origin. Our study sheds light on lithic resource use on Anacapa Island, demonstrates that cherts were available and procured on all the Northern Channel Islands, and adds to the growing challenges of identifying specific sources of chipped stone artifacts.

A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ± 150 years before present, forming the YD Boundary (YDB) layer, distributed over 150 million km2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs.We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust.

A survey on San Nicolas Island found a cluster of over 4,200 shell beads associated with Middle Holocene archaeological deposits eroded from a coastal dune at CA-SNI-12. Among the 12 bead types recovered were more than 146 Olivella Grooved Rectangle (OGR) beads, including a previously unknown subtype with diagonal grooves, >3,000 Olivella cap beads, and nearly 400 Olivella spire-removed beads. Direct AMS radiocarbon dates (~5,000 cal B.P.) on two bead fragments con rm the Middle Holocene age of the feature. Between approximately 5,400 and 4,400 cal B.P., California’s southern Channel Islands appear to have been the focal point of OGR bead production and use, though these beads have been found in a variety of archaeological contexts across western North America. The broad distribution but short temporal duration of these beads makes them an important Middle Holocene indicator of bead production and exchange in California and the Great Basin.

The Channel Islands Barbed point type occurs on the three larger northern Channel Islands off the coast of southern California. The points are small, unusually thin, and carefully knapped, and occur in archaeological assemblages dating between 12,100 and 7,800 cal B.P. Based on points of this type in museum collections compiled during the late nineteenth and early twentieth century and a lesser number from recent investigations, we present a typology of Channel Islands Barbed points consisting of seven subtypes, with the objective of facilitating investigation into their spatio­temporal patterning. The delicate character of the points implies that the spears or darts on which they were hafted were used to acquire fauna in aquatic environments or were thrust rather than thrown, given that they would be highly vulnerable to breakage if thrown on land. Although having a very limited geographic distribution, the Channel Islands Barbed point type is comparable in quality of knapping to other Paleoindian and early Archaic types found elsewhere in North America.

Excavations at CA­SMI­161 provide insight into Middle Holocene human subsistence strategies and exploitation of kelp forest and rocky intertidal habitats on San Miguel Island. Faunal data from two red abalone (Haliotis rufescens) middens dated to ca. 4,400 cal B.P. and an earlier deposit dominated by sea urchin (Strongylocentrotus spp.) dated to 5,800 cal B.P. demonstrate variability in the use and availability of different marine shell sh through time. Some of these data come from one of the youngest red abalone middens reported on the Northern Channel Islands and suggest that by 4,400 cal B.P. red abalone was still highly abundant (approximately 48 –73% by weight) in some San Miguel Island middens, but declined to 24% by 4,000 cal B.P. at CA­SMI­603 and to just 7% by 3,600 cal B.P. at CA­SMI­261. When compared to Late Holocene sites from Cuyler Harbor, the CA­SMI­161 data document a broader decline in red abalone, with n sh and California mussels (Mytilus californianus) dominating subsistence resources after about 3,000 cal B.P.These trends may relate to growing Late Holocene human population densities and the higher biomass provided by n shes.

Despite dramatic growth in the number of Terminal Pleistocene and Early Holocene sites known from California’s Northern Channel Islands, two substantial chronological gaps have remained for which no early sites had been found—one between ~10,000 and 11,400 cal B.P. and another between ~12,200 and 12,900 cal B.P. These gaps have led some scholars to propose that the Northern Channel Islands may have been abandoned by Paleocoastal peoples for substantial periods, while others have suggested that the number of early sites is too limited San Miguel Island Santa Rosa Island to be con dent that the gaps are not due to sampling or preservation issues. Here we summarize what is known about CA-SMI-274, a San Miguel Island shell midden recently dated to ~10,500 cal B.P. The site lls a portion of the later gap and sheds some light on a previously unknown period in the deep archaeological history of the islands.