Palaeoclimatic implications of the growth history and stable isotope (delta O-18 and delta C-13) geochemistry of a Middle to Late Pleistocene stalagmite from central-western Italy

The age structure and, stable isotope composition of a stalagmite (CC I) from an upland cave in central-western Italy were studied to investigate regional response to global climatic changes. Four growth phases are constrained by 28 thermal ionization and multi-collector inductively coupled plasma mass spectrometry Th-U ages and reveal intermittent deposition through the period between Marine isotope Stage (MIS) 11 and 3 (similar to380 and similar to43 kyr). Most of the growth took place between similar to380 and similar to280 kyr, a period punctuated briefly by a hiatus in deposition through the glacial maximum of MIS 10. Growth was terminated abruptly at 280 kyr just prior to the MIS 8 glacial maximum. With a present-day chamber temperature of 7.5 degreesC, the timing of hiatuses close to these glacial maxima point to freezing conditions at the time. No deposition was recorded through the entirety of MIS 7 and most of MIS 6, whilst two minor growth phases occurred at similar to141-125 and similar to43 kyr. Growth at 141 kyr indicates temperatures >0 degreesC at a time when MIS 6 ice volumes were close to their maximum. High stable carbon isotope (delta(13)C) values (similar to2.8parts per thousand to +3.1parts per thousand) throughout the stalagmite's growth reflect a persistently low input of biogenic CO2, indicating that the steep, barren and alpine-like recharge area of today ha's been in existence for at least the last similar to380 kyr. During MIS 9, the lowest delta(13)C values occur well after maximum interglacial conditions, suggesting a lag in the development of post-glacial soils in this high-altitude karst. The stable oxygen isotope (delta(18)O) trends match the main structural features of the major climate proxy records (SPECMAP, Vostok and Devils Hole), suggesting that the delta(18)O of CC1 has responded to global-scale climate changes, whilst remarkable similarity exists between CC1 delta(18)O and regional sea-surface temperature reconstructions from North Atlantic core ODP980 and southwest Pacific marine core MD97-2120 through the most detailed part of the CC1 record, MIS 9-8. The results suggest that CC1 and other stalagmites from the cave have the potential to capture a long record of regional temperature trends, particularly in regards to the relative severity of Pleistocene glacial stages. (C) 2004 Elsevier B.V. All rights reserved.

AMS dating of rock art in the Laura Region, Cape York Peninsula, Australia - protocols and results of recent research

The authors describe rock art dating research in Australia using the oxalate method While the array of dates obtained (which range from c. 1200 to c. 25000 BP) show a satisfactory correlation with other archaeological data, there are mismatches which suggest that some motifs were often imitated by later artists, and/or that the mineral accretions continued to form periodically, perhaps continuously, as a regional phenomenon over a long period of time.

Weathering geochronology by (U-Th)/He dating of goethite

Nine samples of supergene goethite (FeOOH) from Brazil and Australia were selected to rest the suitability of this mineral for (U-Th)/He dating. Measured He ages ranged from 61 to 8 Ma and were reproducible to better than a few percent despite very large Variations in [U] and [Th]. In all Samples with internal stratigraphy or independent age constraints, the He ages corroborated the expected relationship's. These data demonstrate that internally consistent He ages can be obtained on goethite. but do not prove quantitative 4 He retention. To assess possible diffusive He loss, stepped-heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic He-3. The He-3 release pattern indicates the presence of at least two diffusion domains, one with high helium retentivity and the other with very low retentivity at Earth surface conditions. The low retentivity domain, which accounts for similar to 5% of He-3, contains no natural He-4 and may represent poorly crystalline or intergranular material which has lost all radiogenic He-4 by diffusion in nature. Diffusive loss of He-3 from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate, so probably represents diffusion from individual micrometer-size goethite crystals. The He-2/He-3 evolution during the incremental heating experiments shows that the high retentivity domain has retained 90%-95% of its radiogenic helium. This degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to Earth surface temperature and held for the appropriate duration. Considering both the high and low retentivity domains, these data indicate that one of the samples retained 90% of its radiogenic He-4 over 47.5 Ma and the other retained 86% over 12.3 Ma. Thus while diffusive-loss corrections to supergene goethite He ages are required. these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton-irradiation He-4/He-3 method. Copyright (C) 2005 Elsevier Ltd.

High-precision TIMS U-series and AMS C-14 dating of a coral reef lagoon sediment core from southern South China Sea

Accurate dating of lagoon sediments has been a difficult problem, although lagoon profiles, usually with high deposition rates, have a great potential for high-resolution climate reconstruction. We report 26 high-precision TIMS U-series dates (on 25 coral branches) and five AMS C-14 dates (on foraminifera) for a 15.4-m long lagoon core from Yongshu Reef, Nansha area, southern South China Sea. All the dates are in the correct stratigraphical sequence, providing the best chronology so far reported for lagoon deposits. The results reveal a similar to 4000-a continuous depositional history, with sedimentation rates varying from 0.8 to 24.6 mm a(-1), with an average of 3.85 mm a(-1), which corresponds to an average net carbonate accumulation rate of similar to 2700 g CaCO3 m(-2) a(-1), significantly higher than the mean value (800 +/- 400 g CaCO3 m(-2) a(-1)) used for lagoons in general in previous studies of global carbonate budget. Episodes of accelerated depositions within the last 1000 years correlate well with strong storm events identified by U-series dates of storm-transported coral blocks in the area. However, in the longer term, the sedimentation rates during the past 1000 years were much higher than earlier on, probably due to more vigorous wave-reef interaction as a result of relative sea-level fall since 500 AD and expansion of reef flat area, supplying more sediments. The coral TIMS U-series ages and foraminifera AMS 14C dates reveal intriguing apparent radiocarbon reservoir ages (R) from 572 to 1052 years, which are much higher than global mean values of similar to 400 years. (c) 2006 Elsevier Ltd. All rights reserved.