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  • Articles  (2)
  • Cambridge University Press  (2)
  • American Chemical Society
  • American Institute of Physics (AIP)
  • Cell Press
  • Springer Nature
  • 2000-2004  (1)
  • 1995-1999  (1)
  • 1970-1974
  • Archaeology  (2)
  • 1
    Publication Date: 2002-01-01
    Description: 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 B P. 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 B P. 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 B P. 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.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 2
    Publication Date: 1999-01-01
    Description: Twenty-two radiocarbon activity measurements were made by accelerator mass spectrometry (AMS) on 2 Holocene stalagmites from Belgium (Han-stm1b) and from southwest France (Vil-stm1b). Sixteen thermal ionization mass spectrometric (TIMS) U/Th measurements were performed parallel to AMS analyses. The past dead carbon proportion (dcp) due to limestone dissolution and old soil organic matter (SOM) degradation is calculated with U/Th ages, measured calcite 14C activity and atmospheric 14C activity from the dendrochronological calibration curves. Results show that the dcp is different for the 2 stalagmites: between 10,800 and 4780 yr from present dcp=17.5% (σ=2.4; n=10) for Han-stm1b and dcp=9.4% (σ=1.6; n=6) between 3070 and 520 yr for Vil-stm1b. Despite a broad stability of the dcp during the time ranges covered by each sample, a slight dcp increase of about 5.0% is observed in the Han-stm1b sample between 8500 and 5200 yr. This change is synchronous with a calcite δ13C increase, which could be due to variation in limestone dissolution processes possibly linked with a vegetation change. The dcp and δ13C of the 2 studied samples are compared with 5 other modern stalagmites from Europe. Results show that several factors intervene, among them: the vegetation type, and the soil saturation leading to variable dissolution process systems (open/closed). The good correlation (R2=0.98) between the U/Th ages and the calibrated 14C ages corrected with a constant dcp validates the 14C method. However, the dcp error leads to large 14C age errors (i.e. 250–500 yr for the period studied), which is an obstacle for both a high-resolution chronology and the improvement of the 14C calibration curves, at least for the Holocene.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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