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This study assesses the impact of fold-thrust belt driven deformation on the topographic evolution, bedrock exhumation and basin formation in the southeastern Peruvian Andes. We do this through a flexural and thermokinematically modelled balanced cross-section. In addition, published thermochronology samples from low-elevation (river canyons) and high-elevation (interfluves) and Cenozoic sedimentary basin datasets along the balanced cross-section were used to evaluate the age, location, and geometry of fault-driven uplift, as well as potential relationships to the timing of ∼2 km of canyon incision. The integrated structural, thermochronologic, and basin data were used to test the sensitivity of model results to various shortening rates and durations, a range of thermophysical parameters, and different magnitudes and timing of canyon incision. Results indicate that young apatite (U-Th)/He (AHe) canyon samples from ∼2 km in elevation or lower are consistent with river incision occurring between ∼8–2 Ma and are independent of the timing of ramp-driven uplift and accompanying erosion. In contrast, replicating the young AHe canyon samples located at >2.7 km elevation requires ongoing ramp-driven uplift. Replicating older interfluve cooling ages concurrent with young canyon ages necessitates slow shortening rates (0.25–0.6 mm/y) from ∼10 Ma to Present, potentially reflecting a decrease in upper plate compression during slab steepening. The best-fit model that reproduces basin ages and depositional contacts requires a background shortening rate of 3–4 mm/y with a marked decrease in rates to ≤0.5 mm/y at ∼10 Ma. Canyon incision occurred during this period of slow shortening, potentially enhanced by Pliocene climate change.
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Refining Potential Source Regions via Combined Maize Niche Modeling and Isotopes: a Case Study from Chaco Canyon, NM, USA
The application of geochemical sourcing methods to archaeological questions continues to grow, as does the need for innovation in applying these methods. The process of sourcing materials is to rule out potential areas in favor of the most likely origin. It will foreseeably remain true that additional data could reveal other potential sources for an artifact. However, the use of multiple methods to further refine potential sources should not be neglected. In this paper, we use maize niche modeling in tandem with isotopic data to refine possible source regions of archaeological deer from Chaco Canyon, NM, USA (ca. AD 800–1250). Previous research on this prehistoric community demonstrated an extensive non-local procurement system where small mammals were garden-hunted in plots lying > 40 km from the canyon and the procurement of deer from upper elevations at > 90 km. The upper elevation procurement of deer will be tested by adding carbon isotopes and maize niche modeling to previously published strontium and oxygen isotopic data. As browsers with an affinity for maize, deer harvested in low to mid elevations within the maize farming niche should have carbon isotope ratios reflecting C4 plant consumption. Growing degree days in this region place the most salient limits on the elevation of maize production and define the region corresponding to a maize-free diet. Analyses of archaeofaunal deer from Pueblo Bonito indicate that hunting occurred at a higher elevation than the maize farming niche. These results demonstrate the utility of combining geochemical sourcing methods with paleoenvironmental modeling.
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- Award ID(s):
- 1637171
- PAR ID:
- 10074698
- Date Published:
- Journal Name:
- Journal of archaeological method and theory
- ISSN:
- 1573-7764
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Laguna Santa Elena (8.9290° N, 82.9257° W, 1055 m a.s.l.) is a small lake in the Diquís archaeological sub-region of southern Pacific Costa Rica. Previous analyses of pollen and charcoal in a sediment core from Santa Elena revealed a nearly 2,000 year history of vegetation change, maize cultivation and site occupation that is consistent with the archaeological record from the lake basin and surrounding area. Here we present the results of new loss-on-ignition, geochemical and bulk stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of the Santa Elena sediments that supplement and refine the previous reconstruction. Like many lakes in Central America and the Caribbean, Laguna Santa Elena was a magnet for humans throughout its history. As a result, the lake experienced vegetation modification by humans and maize cultivation at varying intensities over a long duration. The Santa Elena sediments provide a record of palaeoenvironmental change during times of major culture change and increasing cultural complexity in the Diquís region, which occurred during intervals of broader changes driven by external forcing mechanisms, including the Terminal Classic Drought (TCD), the Little Ice Age (LIA) and the Spanish Conquest. Our high resolution lake sediment study from Santa Elena reveals details of these events at the local scale that are unobtainable by other means, including the timing of the initial intensification of maize cultivation at ca. 1,570 cal BP (AD 380) and two intervals of population decline coinciding with the TCD at ca. 1,085 cal BP (AD 865) and near the start of the LIA at ca. 683 cal BP (AD 1267).more » « less
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McLeester, Madeleine; Casana, Jesse (Ed.)Archaeologists have developed tools to reconstruct the locations of farming and animal herding using ecological and digital modeling of ancient landscapes. The determination of where on a landscape farming and herding took place, however, can remain elusive in environments with evidence for substantial geomorphological and/or ecological change since the period of occupation. Archaeobotanical and geoarchaeological evidence from the site of Gordion, in central Anatolia, indicates substantial landscape change over the last 4000 years, including deforestation, overgrazing, erosion, and alluviation. These have been inferred to be the result of past agricultural practices, but no firm evidence has pointed to specific locations (geographic and temporal) where ancient farming and herding may have caused these changes. Integrating extant archaeobotanical, zooarchaeological, and geoarchaeological evidence with new isotopic data provides a more detailed reconstruction of the sequence of agricultural practices that shaped the present landscape and ecology of the region, offering a model for future archaeological research within substantially transformed landscapes.more » « less
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Social learning is a primary mechanism for information acquisition in social species. Despite many benefits, social learning may be disadvantageous when independent learning is more efficient. For example, searching independently may be more advantageous when food sources are ephemeral and unpredictable. Individual differences in cognitive abilities can also be expected to influence social information use. Specifically, better spatial memory can make a given environment more predictable for an individual by allowing it to better track food sources. We investigated how resident food-caching chickadees discovered multiple novel food sources in both harsher, less predictable high elevation and milder, more predictable low elevation winter environments. Chickadees at high elevation were faster at discovering multiple novel food sources and discovered more food sources than birds at low elevation. While birds at both elevations used social information, the contribution of social learning to food discovery was significantly lower at high elevation. At both elevations, chickadees with better spatial cognitive flexibility were slower at discovering food sources, likely because birds with lower spatial cognitive flexibility are worse at tracking natural resources and therefore spend more time exploring. Overall, our study supported the prediction that harsh environments should favour less reliance on social learning.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10816-017-9359-
