AMS Dating on the Shell Bar Section from Qaidam Basin, Ne Tibetan Plateau, China

Abstract

ABSTRACT. Radiocarbon dating by accelerator mass spectrometry (AMS) of the shell bar section of Qaidam Basin, NE Tibetan Plateau, shows that this section was formed between ~39.7 and ~17.5 14 C kyr BP and represented the highest paleolake development period since the Late Pleistocene. It was difficult to obtain reliable dates due to the low organic carbon content, which was formed mainly by authochtonous algae-bacteria (Zhang et al. 2007a). In order to improve the dating, 14 C ages of both the alkali residual and acid-soluble components of the organic carbon were measured to check the consistency of the dating results. Total organic carbon (TOC) content and stable carbon isotopes (δ 13 C org ) might also be used as critical references for checking the reliability of dates. For example, in our study of the shell bar section from Qaidam Basin, we found that when the TOC content was higher than 0.15% and/or δ 13 C org was lower than -23‰, the AMS dates were reliable. AMS dating of fossil shells demonstrated that they could provide valuable age information. The ages given by fossil shells are comparable to those of bulk carbonate from a similar sampling site, and are about 15~18 kyr older than the ages given by organic matter. Due to the U/Th dating requirements and open nature of the system, we concluded that U/Th dating results are unreliable and that this technique is unsuitable for dating halite deposits from Qaidam Basin.

Climate variability recorded by n-alkanes of paleolake sediment in Qaidam Basin on the northeast Tibetan Plateau in late MIS3

“…The detailed dating study can be found in refs. [33,34]. For the sake of comparison, we use the online radiocarbon calibration program provided by University of Cologne (http://www.calpal-online.de) to calibrate the 14 C age data.…”

“…CPI h =oddΣ[C[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] ]/evenΣ [C[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36];ACL h =(Σ[C i ] ×i)/Σ[C i ] (22≤i≤37); P aq =(C 23 +C 25 )/(C 23 +C 25 +C 29 +C 31 ).…”

Geochemical fractionation of rare earth elements in lacustrine deposits from Qaidam Basin

“…Based on a detailed comparison and discussion on dating results, we identified the "true ages" from the "sample ages" and established the chronology of the Shell Bar section using the "true ages". These dates suggest that the studied section was formed between 39.7 (the bottom of the lacustrine deposits) and 17.5 14 C ka BP [7,10] . In addition the 14 C dates were calibrated to calendar years using the on-line program via website http://www.calpal-online.de.…”

Improvement of Strength and Ductility of Mg‐Zn‐Ca‐Mn Alloy by Equal Channel Angular Pressing

“…Alloying Mg with Ca increases the strength and corrosion resistance [7], while the presence of Zn in the binary Mg-Ca alloys enhances the precipitation hardening response [8], and Mn addition can improve the strength of Mg alloy effectively through grain refinement [9]. Recently, Mg-Zn-Ca alloys with high hardness and good creep resistance have been developed, due to the existence of fine stable precipitates in the alloys [10,11], which are considered as Ca 2 Mg6Zn3 [11,12].…”