Browsing by Author "Culleton, Brendan J."

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Demographic Artifacts of the Radiocarbon Calibration Curve: Implications for Identifying Mechanisms of Social Transformation
    (2006-04) Culleton, Brendan J.; Kennett, Douglas J.; Erlandson, Jon M.
    Archaeologists working on the Northern Channel Islands of California have use changing frequency of radiocarbon-dated components through time as a proxy for demographic change (e.g., Arnold 1992; Erlandson et al. 2001; Glassow 1999). Fluctuations in the number of dated components have been interpreted as demographic changes in response to climatic instability, introduction of disease, or social transformation (Arnold 1992; Erlandson et al. 2001; Kennett and Kennett 2000; Kennett 2005), assuming a correlation between the number of dated components and population size (see Rick 1997). To what extent are these shifts caused by fluctuations in the calibration curve? Here we model the regular creation of datable archaeological carbon to explore the effect of variable atmospheric 14C production calibrated component frequencies, focusing on the last 2000 cal BP. We show that some periods are likely to systematically over- or underestimate the number components present when intercepts are used to organize 14C databases for demographic analyses.
  • Thumbnail Image
    ItemOpen Access
    Human Ecology, Agricultural Intensification and Landscape Transformation at the Ancient Maya Polity of Uxbenká, Southern Belize
    (University of Oregon, 2012) Culleton, Brendan J.; Culleton, Brendan J.; Kennett, Douglas J.
    Identifying connections between land use, population change, and natural and human-induced environmental change in ancient societies provides insights into the challenges we face today. This dissertation presents data from archaeological research at the ancient Maya center of Uxbenká, Belize, integrating chronological, geomorphological, and settlement data within an ecological framework to develop methodological and theoretical tools to explore connections between social and environmental change or stability during the Preclassic and Classic Period (~1000 BC to AD 900). High-precision AMS 14C dates from Uxbenká were integrated with stratigraphic information within a Bayesian framework to generate a high-resolution chronology of sociopolitical development and expansion in southern Belize. This chronology revises the previous understanding of settlement and development of Classic Maya society at Uxbenká and indicates specific areas of investigation to elucidate the Late and Terminal Classic periods (AD 600-900) when the polity appears to disintegrate. A geoarchaeological record of land use was developed and interpreted with respect to regional climatic and cultural histories to track landscape transformations associated with human-environment interactions at Uxbenká. The first documented episode of landscape instability (i.e., erosion) was associated with farmers colonizing the area. Later, landscape stability in the site core parallels Classic Period urbanization (AD 300-900) when swidden agriculture was likely restricted in the core. Another erosional event followed political disintegration as farmers resumed cultivation in and around the abandoned city. Maize yields derived from contemporary Maya farms in the area were used to estimate the maximum population size of Uxbenká during its Classic Period peak. The maximum sustainable population is estimated between 7500 and 13,000, including a potential population of ~525 elites in the core, assuming low levels of agricultural intensification. This accords well with the lack of archaeological evidence for intensive land management during the Classic Period (e.g., terraces). An ecological model developed using maize productivity and other environmental/social datasets largely predicts the settlement pattern surrounding Uxbenká. Settlements in marginal areas may be evidence of elite intra-polity competition during the Late Preclassic Period (ca. AD 1-300), though it is possible that marginal areas were settled early as garrisons to mediate travel into the site core.
  • Thumbnail Image
    ItemOpen Access
    Implications of a freshwater radiocarbon reservoir correction for the timing of late Holocene settlement of the Elk Hills, Kern County, California
    (Elsevier, 2006) Culleton, Brendan J.
    Uncertainties regarding the magnitude of freshwater radiocarbon reservoir effects can introduce random errors into dates on archaeological freshwater carbonates. As a result, many archaeologists avoid dating freshwater shells unless no other datable materials are available. The chronology of prehistoric occupation of the former Naval Petroleum Reserve No. 1 (NPR-1) at Elk Hills, Kern County, has been established with 50 radiocarbon dates on freshwater mussels (Gonidea and Anodonta sp.). Characterization of any freshwater radiocarbon reservoir effect is crucial for the accurate interpretation of inferred settlement and subsistence changes on the Elk Hills. Paired charcoal and freshwater mussels sampled from closely associated contexts were dated to identify a freshwater reservoir effect. Paired Anodonta and Gonidea sp. shells were dated to investigate interspecific differences in fractionation. Results indicate that a 340  20 14C yr correction should be applied to conventional 14C dates on freshwater carbonates in the Buena Vista Basin before calendar calibration. Evidence of interspecific differences is inconclusive. Dates recalibrated with the reservoir correction indicate that widespread occupation of the Elk Hills is correlated with increasing precipitation towards the end of the Medieval Climatic Anomaly and during the Little Ice Age, suggesting that slough resource exploitation may have been driven by regional population pressure rather than drought-related declines in aquatic productivity.
  • Thumbnail Image
    ItemOpen Access
    Intrashell Radiocarbon Variability in Marine Mollusks
    (Arizona Board of Regents, 2006) Culleton, Brendan J.; Kennett, Douglas J.; Ingram, B Lynn.; Erlandson, Jon M.; Southon, John R.
    We demonstrate variable radiocarbon content within 2 historic (AD 1936) and 2 prehistoric (about 8200 BP and 3500 BP) Mytilus californianus shells from the Santa Barbara Channel region, California, USA. Historic specimens from the mainland coast exhibit a greater range of intrashell variability (i.e. 180–240 14C yr) than archaeological specimens from Daisy Cave on San Miguel Island (i.e. 120 14C yr in both shells). δ13C and δ18O profiles are in general agreement with the upwelling of deep ocean water depleted in 14C as a determinant of local marine reservoir correction (ΔR) in the San Miguel Island samples. Upwelling cycles are difficult to identify in the mainland specimens, where intrashell variations in 14C content may be a complex product of oceanic mixing and periodic seasonal inputs of 14C-depeleted terrestrial runoff. Though the mechanisms controlling ΔR at subannual to annual scales are not entirely clear, the fluctuations represent significant sources of random dating error in marine environments, particularly if a small section of shell is selected for accelerator mass spectrometry (AMS) dating. For maximum precision and accuracy in AMS dating of marine shells, we recommend that archaeologists, paleontologists, and 14C lab personnel average out these variations by sampling across multiple increments of growth.