253 research outputs found

    A Precise Chronology of Middle to Late Holocene Bison Exploitation in the Far Southern Great Plains

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    In regions on the margins of the Great Plains grasslands, documenting the intermittent history of bison exploitation has presented challenges to archeologists. Chronologies based on archeological associations have long been useful in regional research, but can be imprecise and of inadequate resolution for constructing precise sequences of prehistoric events. Here, we present a record of directly dated bison from archeological contexts spanning the last 6000 years on the very southern extent of the Great Plains. This study includes 61 specimens from archeological contexts that were dated by XAD purified AMS radiocarbon, with reported errors of only 15-20 14C years for most dates. The resulting record of bison exploitation for this area defines four main periods (Calf Creek, Late Archaic 1 and 2, and early Toyah) during which bison were exploited. Several dates also indicate an early historic presence of bison; this period may represent a late facet of the Toyah horizon. This study adds significant chronological resolution to the regional record of bison in parts of Texas and begins to help correlate cultural chronologies with important climatic data. It also points to the research value of obtaining additional directly dated bison samples from temporally and geographically diverse archeological contexts in our study area and beyond

    Wildfire and Abrupt Ecosystem Disruption on California\u27s Northern Channel Islands at the Allerod-Younger Dryas Boundary (13.0-12.9 ka)

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    Sedimentary records from California\u27s Northern Channel Islands and the adjacent Santa Barbara Basin (SBB) indicate intense regional biomass burning (wildfire) at the Ållerþd–Younger Dryas boundary (~13.0–12.9 ka) (All age ranges in this paper are expressed in thousands of calendar years before present [ka]. Radiocarbon ages will be identified and clearly marked “14C years”.). Multiproxy records in SBB Ocean Drilling Project (ODP) Site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats. Abrupt ecosystem disruption is evident on the Northern Channel Islands at the Ållerþd–Younger Dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape. These wildfires coincide with the extinction of Mammuthus exilis [pygmy mammoth]. The earliest evidence for human presence on these islands at 13.1–12.9 ka (~11,000–10,900 14C years) is followed by an apparent 600–800 year gap in the archaeological record, which is followed by indications of a larger-scale colonization after 12.2 ka. Although a number of processes could have contributed to a post 18 ka decline in M. exilis populations (e.g., reduction of habitat due to sea-level rise and human exploitation of limited insular populations), we argue that the ultimate demise of M. exilis was more likely a result of continental scale ecosystem disruption that registered across North America at the onset of the Younger Dryas cooling episode, contemporaneous with the extinction of other megafaunal taxa. Evidence for ecosystem disruption at 13–12.9 ka on these offshore islands is consistent with the Younger Dryas boundary cosmic impact hypothesis [Firestone, R.B., West, A., Kennett, J.P., Becker, L., Bunch, T.E., Revay, Z.S., Schultz, P.H., Belgya, T., Kennett, D.J., Erlandson, J.M., Dickenson, O.J., Goodyear, A.A., Harris, R.S., Howard, G.A., Kloosterman, J.B., Lechler, P., Mayewski, P.A., Montgomery, J., Poreda, R., Darrah, T., Que Hee, S.S., Smith, A.R., Stich, A., Topping, W., Wittke, J.H. Wolbach, W.S., 2007. Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and Younger Dryas cooling. Proceedings of the National Academy of Sciences 104, 16016–16021.]

    Isolated deep earthquakes beneath the North Island of New Zealand

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    Seismicity shallows towards the south along the Tonga-Kermadec-Hikurangi margin, deep and intermediate seismicity being absent altogether in the South Island of New Zealand. Beneath the Taranaki region of the North Island the maximum depth of the main seismicity is 250 km, but very rare events occur directly below at 600 km. These could be associated with a detached slab or a vertical, aseismic continuation of the subducted Pacific Plate. Six small events that occurred in the 1990s were recorded extensively by digital instruments of the New Zealand National Network (NZNN) and temporary deployments. We relocate these events by a joint hypocentre determination (JHD) method and find their focal mechanisms using first motions and relative amplitudes of P and S arrivals. The earthquakes relocate to a remarkably uniform depth of 603 +/- 3 kmrelative error (+/- 10 km absolute error) in a line 30- km long orientated 40 NE, roughly parallel to the strike of the intermediate- depth seismicity. The only consistent component of the focal mechanisms is the tension axis: all lie close to horizontal and tend to align with the line of hypocentres. We interpret this deep seismic zone as a detached sliver of plate lying horizontally with the same orientation as the main subducted plate above. Volume change caused by a phase change controlled by the pressure at 600 km and temperature in the sliver produces a pattern of strain that places the sliver under tension along its lengt

    Persistent Early to Middle Holocene tropical foraging in southwestern Amazonia

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    The Amazon witnessed the emergence of complex societies after 2500 years ago that altered tropical landscapes through intensive agriculture and managed aquatic systems. However, very little is known about the context and conditions that preceded these social and environmental transformations. Here, we demonstrate that forest islands in the Llanos de Moxos of southwestern Amazonia contain human burials and represent the earliest settlements in the region between 10,600 and 4000 years ago. These archaeological sites and their contents represent the earliest evidence of communities that experienced conditions conducive to engaging with food production such as environmental stability, resource disturbance, and increased territoriality in the Amazonian tropical lowlands

    Discovery of a nanodiamond-rich layer in the Greenland ice sheet

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    We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5!106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9 0.1 ka. However, more investigation is needed to confirm this association

    New research at Teotihuacan’s Tlajinga district, 2012–2015

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    Teotihuacan's Tlajinga district is a cluster of neighborhoods on the southern periphery of the city best known for earlier investigations at Compound 33:S3W1. New research includes excavations at two other apartment compounds and along the southern extension of the Street of the Dead. Excavation contexts, major finds, chronology, and preliminary interpretations are the subject of this article. We highlight evidence attesting to a major obsidian-blade workshop at Compound 17:S3E1, offerings, and other features at that compound and Compound 18:S3E1, and the tempo and processes of urbanization viewed through well-recorded stratigraphic sequences of the compounds and the Street of the Dead. We conclude that significant occupation began in the Miccaotli phase, but it was not until some point in the Early Tlamimilolpa phase that the dominant housing type became apartment compounds; the continuation of the axis of Street of the Dead in the district was accomplished by excavating in the volcanic tuft substrate (tepetate) and could have been undertaken by the inhabitants of the district themselves; and the presence of items such as a sculpted stone face, marine shell, and polychrome pottery demonstrates that commoners at Teotihuacan enjoyed some access to finer items within the interregional economy.Accepted manuscrip

    Archaeological Central American maize genomes suggest ancient gene flow from South America

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    Maize (Zea mays ssp. mays) domestication began in southwestern Mexico ∌9,000 calendar years before present (cal. BP) and humans dispersed this important grain to South America by at least 7,000 cal. BP as a partial domesticate. South America served as a secondary improvement center where the domestication syndrome became fixed and new lineages emerged in parallel with similar processes in Mesoamerica. Later, Indigenous cultivators carried a second major wave of maize southward from Mesoamerica, but it has been unclear until now whether the deeply divergent maize lineages underwent any subsequent gene flow between these regions. Here we report ancient maize genomes (2,300–1,900 cal. BP) from El Gigante rock shelter, Honduras, that are closely related to ancient and modern maize from South America. Our findings suggest that the second wave of maize brought into South America hybridized with long-established landraces from the first wave, and that some of the resulting newly admixed lineages were then reintroduced to Central America. Direct radiocarbon dates and cob morphological data from the rock shelter suggest that more productive maize varieties developed between 4,300 and 2,500 cal. BP. We hypothesize that the influx of maize from South America into Central America may have been an important source of genetic diversity as maize was becoming a staple grain in Central and Mesoamerica

    An Anthropocene Without Archaeology—Should We Care?

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    For more than a decade, a movement has been gathering steam among geoscientists to designate an Anthropocene Epoch and formally recognize that we have entered a new geological age in which Earth’s systems are dominated by humans. Chemists, climatologists, and other scientists have entered the discussion, and there is a growing consensus that we are living in the Anthropocene. Nobel Prize-winning atmospheric chemist Paul Crutzen (2002a, 2002b; Crutzen and Stoermer 2000) coined the term, but the idea that humans are a driver of our planet’s climate and ecosystems has much deeper roots. Italian geologist Antonio Stoppani wrote of the “anthropozoic era” in 1873 (Crutzen 2002a), and many others have proposed similar ideas, including journalist Andrew Revkin’s (1992) reference to the “Anthrocene” and Vitousek and colleagues (1997) article about human domination of earth’s ecosystems. It was not until Crutzen (2002a, 2002b) proposed that the Anthropocene began with increased atmospheric carbon levels caused by the Industrial Revolution in the late eighteenth century (including the invention of the steam engine in A.D. 1784), however, that the concept began to gain serious traction among scientists and inspire debate