• AMS Dating of Human Bone from Palau: New Evidence for a Pre-2000 BP Settlement

      Fitzpatrick, Scott M. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Direct dating of a human bone fragment from the Chelechol ra Orrak site (western Micronesia) has yielded one of the earliest dates for Palau thus far. This date compares well with recently collected paleoenvironmental evidence and radiocarbon dates on Babeldaob Island suggesting that settlement of the Palauan archipelago took place much earlier than previously thought.
    • AMS-14C Chronology of a Lacustrine Sequence from Lake Langano (Main Ethiopian Rift): Correction and Validation Steps in Relation with Volcanism, Lake Water and Carbon Balances

      Gibert, Elisabeth; Travi, Yves; Massault, Marc; Tiercelin, Jean-Jacques; Chernet, Tesfaye (Department of Geosciences, The University of Arizona, 2002-01-01)
      Located in the Ziway-Shala Basin of the Main Ethiopian Rift, Lake Langano is part of an asymmetric half-graben, defined by a series of north-northeast-trending faults in the tectonically active zone of the rift. A 15-m deep succession of organic homogeneous muds, silts, bioclastic sands, and pyroclastic layers was cored in 1994. The definition of a certified radiocarbon chronology on these deposits required the indispensable establishment of modern hydrological and geochemical balances. The isotopic contents of the total dissolved inorganic carbon (TDIC) of surface water clearly show the influence of a deep CO2 rising along the main fault crossing the lake basin. The 5.8 pMC disequilibrium existing in 1994 with the atmosphere likely produces the aging of authigenic materials developing at the lake surface. However, with a mean residence time of approximately 15 years, this apparent 14C aging of Lake Langano water still integrates the 14C produced by the nuclear tests in the 1960s. Reconstructing the natural 14C activity of the lake TDIC allows for the quantification of the deep CO2 influence, and for the correction of AMS-14C datings performed along the core. The correction of the AMS14C chronology defined on Lake Langano allows for a better understanding of paleohydrological changes at a regional scale for at least the last 12,700 cal BP.
    • Are the 14C Dates of the Dead Sea Scrolls Affected by Castor Oil Contamination?

      Carmi, Israel (Department of Geosciences, The University of Arizona, 2002-01-01)
      The paper "The effects of possible contamination on the radiocarbon dates of the Dead Sea Scrolls I: castor oil" by Rasmussen et al. (2001) is discussed. Detailed analysis of the extant dates of the Dead Sea Scrolls suggests that the pretreatment of the samples was adequate. Errors and omissions in the paper are discussed and the implications of the experiment of Rasmussen et al. (2001) are questioned.
    • Challenges in Radiocarbon Dating Organic Carbon in Opal-Rich Marine Sediments

      Zheng, Yan; Anderson, Robert F.; Froelich, Philip N.; Beck, Warren; McNichol, Ann P.; Guilderson, Thomas (Department of Geosciences, The University of Arizona, 2002-01-01)
      We explored the reliability of radiocarbon ages obtained on organic carbon phases in opal-rich Southern Ocean sediments. Paired biogenic carbonate and total organic carbon (TOC) 14C analyses for three Southern Ocean cores showed that the TOC ages were systematically younger than the carbonate ages. Carbonate ages were consistent with oxygen isotopic and bio-stratigraphy, indicating error in TOC ages that could be explained by 5-24% of modern carbon contamination of TOC samples. Two possible sources of contamination are: 1) adsorption of atmospheric CO2 or volatile organic compounds to reactive opal surface sites, and 2) fixation of atmospheric CO2 by chemosynthetic bacteria during core storage. In an effort to reduce the modern carbon contamination, diatoms were separated from sediments, purified, and pre-oxidized by concentrated nitric and perchloric acids to permit dating of opal-intrinsic organic carbon (approximately 0.1-0.3% by weight). 14C ages of chemically pre-oxidized opal showed a significant amount of modern carbon contamination, from 11 to 32%, indicating adsorption from the atmosphere of modern carbon onto opal surfaces that were previously cleaned by acid oxidation. Several experiments designed to eliminate the modern C contamination were attempted, but so far we have not been able to obtain a radiocarbon age on 14C-dead Southern Ocean opal-rich sediments, either bulk TOC or purified diatom opal samples, as old as our procedural blank.
    • Coastal Response to Changes in Sea Level since the Last 4500 BP on the East Coast of Tamil Nadu, India

      Achyuthan, Hema; Baker, V. R. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Geomorphology, clay mineral composition, and radiocarbon dates from Muttukadu to Marakkanam estuaries and the tidal zone along the east coast of Tamil Nadu, India, have been used to reconstruct coastal evolution between approximately 4500 and 1100 BP. Formation of alternate oyster beds with intervening tidal clay units indicate fluctuation in the sea level may be a consequence of changes in the Mid-Holocene sedimentation pattern and coastal configuration. 14C dates from Muttukadu indicate a rapid relative sea-level rise (RSL) subsequent to 3500 BP and tidal flat sedimentation between 3475 and 3145 BP. Marine conditions along the east coast area returned around 1900 BP. Comparison of dates with other sites, e.g. Muttukadu, Mammallapuram, and Marakkanam, points toward short removal of marine conditions, ample sediment supplies in the tidal zones, and neotectonic activity. Reactivation of the north-south trending fault line occurred not earlier than approximately 1050 BP. Our study indicates that Middle to Late Holocene coastal sedimentation and the chronology of the tidal zone formation have been strongly influenced by local factors. These have provided considerable scope for internal reorganization with changing coastal processes.
    • Differences in 14C Age Between Stratigraphically Associated Charcoal and Marine Shell from the Archaic Period Site of Kilometer 4, Southern Peru: Old Wood or Old Water?

      Kennett, Douglas J.; Ingram, B. Lynn; Southon, John R.; Wise, Karen (Department of Geosciences, The University of Arizona, 2002-01-01)
      Consistently large differences occur in the calibrated 14C ages of stratigraphically associated shell and charcoal samples from Kilometer 4, an Archaic Period archaeological site located on the extreme south coast of Peru. A series of nine shell and charcoal samples were collected from a Late Archaic Period (approximately 6000-4000 BP) sector of the site. After calibration, the intercepts of the charcoal dates were approximately 100-750 years older than the paired shell samples. Due to the hyper-arid conditions in this region that promote long-term preservation of organic material, we argue that the older charcoal dates are best explained by people using old wood for fuel during the Middle Holocene. Given this "old wood" problem, marine shell may actually be preferable to wood charcoal for dating archaeological sites in coastal desert environments as in southern Peru and Northern Chile.
    • Late Quaternary Chronology and Stratigraphy of Twelve Sites on Kaua'i

      Burney, David A. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Twelve new sites on Kaua'i provide an island-wide view of late Quaternary (near time) environments on the oldest of the major Hawaiian Islands. Radiocarbon-dated lithologies are compared for estuarine sites on windward and leeward coasts, interior peat bogs ranging from 169 to 1220 m in elevation, prehistoric fishponds, and a sinkhole paleolake in the Maha'ulepu cave system. Terrestrial sedimentation begins in many coastal sites about 6000 cal BP, as sea level approached modern levels. Prehuman sedimentation rates were quite low in all these sites, generally <2 mm/yr, although coastal sites in the late Holocene were subject to major episodic sediment influx from extreme events, including tsunamis, hurricanes, and floods. Interior sites are generally older, having accumulated humic clay and peat layers at least since the late Pleistocene. Since the arrival of humans less than two millennia ago, sedimentation rates have increased in some coastal sites, and further local increases (as much as two orders of magnitude) have occurred since European arrival. Evidence from sites containing fossils of extinct terrestrial snails is consistent with the hypothesis that human-caused extinctions have proceeded in three phases, corresponding to losses (generally the largest species) occurring soon after the arrival of the first humans, followed by a second wave of extinction in late prehistoric times, and a third after European colonization. Dating of sediments from fishponds constructed or enhanced by prehistoric Polynesians suggests that this early form of aquaculture was initiated on Kaua'i by about 830 +/50 BP. The most elaborate example of fishpond construction in the Hawaiian Islands, the Alekoko or Menehune fishpond on Kaua) i's southeast coast, was probably undertaken by 580 +/30 BP.
    • Radiocarbon and Stable Isotope Analyses of Archaeological Bone Consolidated with Hide Glue

      Takahashi, C. M.; Nelson, D. E.; Southon, J. S. (Department of Geosciences, The University of Arizona, 2002-01-01)
      We tested a simple method for removing a collagen-based glue preservative from bone destined for radiocarbon and stable isotope analyses. The method is sufficient for bone samples from which only stable isotope measurements are required. For 14C dating, such samples of age less than about 10 ka can be adequately dated, but for older samples, the circumstances must be carefully evaluated.
    • Radiocarbon Dating of Buried Holocene Soils in Siberia

      Orlova, Lyubov A.; Zykina, Valentina S. (Department of Geosciences, The University of Arizona, 2002-01-01)
      We have constructed a detailed chronological description of soil formation and its environments with data obtained on radiocarbon ages, palynology, and pedology of the Holocene buried soils in the forest steppe of western and central Siberia. We studied a number of Holocene sections, which were located in different geomorphic situations. Radiocarbon dating of materials from several soil horizons, including soil organic matter (SOM), wood, peat, charcoal, and carbonates, revealed three climatic periods and five stages of soil formation in the second part of the Holocene. 14C ages of approximately 6355 BP, 6020 BP, and 5930 BP showed that the longest and most active stage is associated with the Holocene Climatic Optimum, when dark-grey soils were formed in the forest environment. The conditions of birch forest steppe favored formation of chernozem and associated meadow-chernozem and meadow soils. Subboreal time includes two stages of soil formation corresponding to lake regressions, which were less intense than those of the Holocene Optimum. The soils of that time are chernozem, grassland-chernozem, and saline types, interbedded with thin peat layers 14C dated to around 4555 BP, 4240 BP and 3480 BP, and 3170 BP. Subatlantic time includes two poorly developed hydromorphic paleosols formed within inshore parts of lakes and chernozem-type automorphic paleosol. The older horizon was formed during approximately 2500-1770 BP, and the younger one during approximately 1640-400 BP. The buried soils of the Subatlantic time period also attest to short episodes of lake regression. The climate changes show an evident trend: in the second part of the Atlantic time period it was warmer and drier than at present, and in the Subboreal and Subatlantic time periods the climate was cool and humid.
    • Reservoir Corrections for Marine Samples from the South Atlantic Coast, Santa Catarina State, Brazil

      Eastoe, C. J.; Fish, S.; Fish, P.; Gaspar, M. Dulce; Long, A. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Coeval shell and charcoal from Santa Catarina State, Brazil, differ systematically in 14C content, indicating a reservoir effect in marine samples. For modern samples (AD 1939-2000) and archeological samples (2500-1595 BP), the mean 14C age difference between marine and atmospheric carbon is 220 +/20 years, the marine carbon being older. For three samples dated AD 1939-1944, a distinct reservoir correction of 510 +/10 years is also observed. The ages of archeological shell samples from Jabuticabeira may be corrected by subtracting 220 years from the apparent 14C ages.