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1. Resolving time among non-stratified short-duration contexts on a radiocarbon plateau: possibilities and challenges from the AD 1480–1630 example and northeastern North America

   https://doi.org/doi:10.1017/RDC.2020.51  

   Manning, Sturt W. ; Birch, Jennifer ; Conger, Megan Anne ; Sanft, Samantha ( January 2020 , Radiocarbon)

   null (Ed.)

   Reversals and plateaus in the radiocarbon (14C) calibration curve lead to similar 14C ages applying to a wide range of calendar dates, creating imprecision, ambiguity, and challenges for archaeological dating. Even with Bayesian chronological modeling, such periods remain a problem when no known order—e.g., a stratigraphic sequence—exists, and especially if site durations are relatively short. Using the reversal/plateau AD 1480–1630 and the archaeology of northeastern North America as our example, we consider possible strategies to improve chronological resolution across such reversal/plateau periods in the absence of stratigraphic sequences, including uses of wood-charcoal TPQs from even very short wiggle-matches, and site phase duration constraints based on ethnohistoric and archaeological evidence. 

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2. A CENTENNIAL AMBIGUITY: THE CHALLENGE OF RESOLVING THE DATE OF THE JEAN-BAPTISTE LAINÉ (MANTLE), ONTARIO, SITE—AROUND AD 1500 OR AD 1600?—AND THE CASE FOR WOOD-CHARCOAL AS A TERMINUS POST QUEM

   https://doi.org/10.1017/RDC.2022.23  

   Manning, Sturt W ; Birch, Jennifer ( April 2022 , Radiocarbon)

   ABSTRACT Considered in isolation, the radiocarbon ( 14 C) dates on short-lived plant remains from the Jean-Baptiste Lainé (formerly Mantle) site, Ontario, yield an ambiguous result: more or less similar probability around AD 1500 or alternatively around AD 1600. This village site, likely of no more than ca. 20–30 years total duration, illustrates the challenges of high-resolution dating across periods with a reversal/plateau in the 14 C calibration curve. Another problem we identify is the tendency for dating probability for short-duration sites to sometimes be overly compressed as dating intensity increases under analysis with OxCal, and for probability to shift away from the real age range especially during reversal/plateau episodes. To address both issues additional constraints are necessary. While a tree-ring sequenced 14 C “wiggle-match” is the best option where available, we investigate how, in the absence of such an option, use of the in-built age in wood-charcoal samples can be used to distinguish the likely correct date range. This approach can resolve ambiguities in dating, e.g., for shorter-duration Late Woodland village sites in northeastern North America, but also other short-duration cases corresponding with reversal/plateau episodes on the 14 C calibration curve. We place the Jean-Baptiste Lainé site most likely in a range between ca. AD 1595–1626 (95.4% probability). 

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3. Geoarchaeology and Coastal Morphodynamics of Harbor Key (8MA15): Indigenous Persistence at a Partially Inundated Native Shell Mound Complex in Tampa Bay, Florida

   https://doi.org/10.1017/aaq.2023.45  

   Jackson, Kendal ; Pluckhahn, Thomas J. ; Rogers, Jaime A. ; Wang, Ping ; Thompson, Victor D. ( September 2023 , American Antiquity)

   Applying a coastal-geoarchaeological approach, we synthesize stratigraphic, sedimentological, mollusk-zooarchaeological, and radiometric datasets from recent excavations and sediment coring at Harbor Key (8MA15)—a shell-terraformed Native mound complex within Tampa Bay, on the central peninsular Gulf Coast of Florida. We significantly revise the chronological understanding of the site and place it among the relatively few early civic-ceremonial centers in the region. Analyses of submound contexts revealed that the early first millennium mound center was constructed atop a platform of sand and ex situ cultural shell deposits that were reworked during ancient storm landfalls around 2000 BP. We situate Harbor Key within a seascape-scale stratigraphic and paleoenvironmental framework and show that the shellworks comprise an artificial barrier protecting the leeward estuary basin (and productive inshore wetlands) from high-energy conditions of the open bay and swells from the Gulf of Mexico. The sedimentary and archaeological records attest to the long-term history of morphodynamic interaction between coastal processes and Indigenous shell terraforming in the region and suggest that early first millennium mound building in Tampa Bay was tied to the recognition and reuse of antecedent shellworks and the persistent management of encompassing cultural seascapes. 

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4. Multitechnique dating of earthen irrigation canals at the La Playa site, Sonora, Mexico

   https://doi.org/10.1002/gea.21800  

   Cajigas, Rachel ; Quade, Jay ; Rittenour, Tammy ( June 2020 , Geoarchaeology)

   La Playa (SON:F:10:3) is an archaeological site in Sonora, Mexico that contains the remains of an extensive preceramic earthen irrigation canal system. Modern floodplain erosion has destroyed the majority of these canals, but geoarchaeological investigations on areas of the system that remain reveal much about this early agricultural technology. Comprehensive dating using accelerator mass spectrometry¹⁴C on gastropods, charcoal, and soil humates and single‐grain optically stimulated luminescence (OSL) dating on canal sediments revealed that multiple irrigation systems were used at La Playa during at least two periods during the Early Agricultural period (~750–350 B.C. and ~ A.D. 50–250).¹⁴C and OSL age estimates from canals are in agreement with the earliest direct dates on maize from La Playa (A.D. 20–240), indicating that the introduction of maize corresponds to a significant investment in the modification of the floodplain environment for canal irrigation. The late phase of canal use (~A.D. 50–250) occurs before destructive floodplain erosion at the site. This is contemporaneous with local cultural changes, including the development of a new ceramic tradition, changes in burial practices, and changing subsistence strategies. These results demonstrate the utility of the combined¹⁴C and OSL approach for dating ancient earthen canals.

    

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5. Scale of time-averaging in archaeological shell middens from the Canary Islands

   https://doi.org/10.1177/0959683619883020  

   Parker, Wesley G ; Yanes, Yurena ; Mesa Hernández, Eduardo ; Hernández Marrero, Juan Carlos ; Pais, Jorge ; Surge, Donna ( February 2020 , The Holocene)

   Characterizing the degree of disturbance in archaeological deposits is critically important for archaeologists assessing foraging strategies, environmental conditions, or behavior patterns of ancient human groups. Qualitative techniques (e.g. micromorphology analysis) have previously been applied to assess the degree of disturbance (age-mixing) in archaeological sites; however, quantitative dating of material in the sites provides a more robust assessment of potential age-mixing. Unfortunately, because of budget constraints, archaeologists are frequently forced to rely on few quantitative age dates for an assemblage, thus obfuscating the signal of age-mixing of the deposit. The development of an affordable and rapid carbonate-target accelerator mass spectrometry (AMS) radiocarbon ( 14 C) dating method provides a cost-effective way to retrieve more quantitative dates from carbonate material in archaeological assemblages to assess the degree of age-mixing in the deposit. This study tests this new technique and dates numerous harvested marine limpet shells from archaeological sites in the Canary Islands to determine whether there is multidecadal to multicentennial age-mixing. A total of 58 shells retrieved from six sites and three islands yielded uncalibrated radiocarbon ages ranging from 2265 ± 40 to 765 ± 35 BP, coinciding with the time of prehistoric human occupation in these islands. While most shells from the same stratum showed statistically equivalent ages, in some cases we detected age ranges that exceeded the imprecisions from analytical errors. This investigation is one of the first to quantitatively illustrate that shells retrieved from depth intervals without evident stratigraphic disturbance do not always contain contemporaneous remains and, therefore, dating each specimen is valuable for developing further paleoclimatic and paleoanthropological inferences. This study presents the first report of carbonate-target 14 C ages from archaeological shell middens, and suggests that this novel radiocarbon methodology can be applied to these sites, thus allowing the generation of a more comprehensive chronology. 

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