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BACKGROUND Detrital zircon U-Pb geochronology is an important tool for identifying sedimentary provenance and determining the maximum depositional age. The numbers of grains for detrital zircon provenance investigations using laser-ablation inductively coupled-plasma mass spectrometer (LA-ICP-MS) typically range from 60 to 120. In this range, age components are commonly not identified from the sample aliquot. In order to improve the reliability of provenance investigation, analysis of more grains (n≥300) or even the large-n aliquot with more than 1000 grains (n > 1000) are required. The emergence of large-n detrital zircon U-Pb geochronology is challenging the methods of data measurement, reduction and evaluation. OBJECTIVES To summarize the progress of measurement, data reduction and data evaluation of large-n detrital zircon U-Pb geochronology. METHODS By summarizing the method innovation of domestic and foreign literature. RESULTS Firstly, each measurement requires rapid acquisition of U and Pb isotope signals, which can be conducted by improving the transmission efficiency of aerosol. The "flat" signal acquisition time can be shortened or transformed to a "peak" signal mode for rapid measurement. Secondly, large-n data require efficient data reduction protocol or powerful software (e.g. iolite) to improve visualization and reduce the variability between inter-laboratory comparisons. For U-Pb data processing flow, several optimized methods are introduced for fractionation correction and propagating uncertainty. In addition, total integrated counts and linear regression correction are introduced to specially process "peak" signals. Thirdly, the new calculation method of U-Pb and Pb-Pb age discordance, such as using Aitchison concordia distance, makes data filtering more reasonable. Based on recent research progress, the future of automation and standardization of large-n detrital zircon U-Pb geochronology is discussed and advice on the selection of instruments and reduction software is provided. CONCLUSIONS In the future, the development of large-n detrital zircon U-Pb geochronology has great prospects, and will play a greater role in the study of provenance tracing and stratigraphic dating.

Characterized as a climatologically sensitive region, the southeastern Tibetan Plateau (STP) is an ideal location for dendrochronological research. Here, five tree-ring width (TRW) chronologies were developed: three for Picea likiangensis along altitudinal gradients from 3600 to 4400 m a.s.l. and two for Sabina saltuaria and Abies squamata from 4200 m a.s.l. Significant differences in the growth rates and age composition of Picea likiangensis were observed at various elevation gradients. The chronology statistics (mean sensitivity, etc.) fluctuated with the elevation gradient. Picea likiangensis showed distinct growth patterns in response to climatic variability along the altitude gradient: the minimum temperature influenced tree growth at lower and middle altitudes, while higher altitudes were affected by precipitation. The radial growth of different tree species growing in the same region is controlled by the same climatic factors. Sabina saltuaria and Abies squamata exhibited similar growth responses to Picea likiangensis. Stand conditions (wind speeds, slope, and elevation) and biotic factors (the depth of root, forest type, tree age, and sensitivity) can partially explain why the ring width–climate relationships change with altitude. [ABSTRACT FROM AUTHOR]

The Hengduan Mountains is in the transitional zone between the Qinghai-Tibet Plateau (QTP) and the Yunnan-Guizhou Plateau in China, and a key area for elucidating the Quaternary environmental changes in Asia. The paleo-Daocheng ice cap was located on the Shaluli Hilly Plateau in the northeastern Hengduan Mountains, the oldest moraines in the Hengduan Mountains region were found in the ice cap area. Such glacial landforms provide key evidence to study the timing when this area entered the cryosphere with the uplift of the QTP. However, it is difficult to collect suitable glacial boulders from these moraines for traditional terrestrial in-situ cosmogenic nuclide (TCN) exposure dating because of long-term severe moraine degradation. Here, we collected clast samples from the moraine surface and depth profile to constrain the age of the oldest moraine in Kuzhaori (moraine E) using TCN 10Be dating technique. The minimum 10Be ages of five clast samples from the moraine surface range from 187.4±1.5 to 576.8±4.3 ka, implying that the moraine has been seriously degraded since deposition. Based on the TCN 10Be concentrations of the samples from a depth profile and simulations, the exposure-erosion-inheritance history of the profile was obtained. By fitting to the profile 10Be concentrations using the chi-square test, the simulations yielded a reliable age of 626.0±52.5 ka for the moraine. Therefore, the oldest moraine (moraine E) in Kuzhaori was most likely formed at about 0.63 Ma ago, corresponding to the marine isotope stage (MIS) 16. This glaciation represents the maximum Quaternary glaciation after the QTP was elevated into the cryosphere by the Kunlun-Yellow River Tectonic Movement. [ABSTRACT FROM AUTHOR]

Author(s): Xianfeng Wang (corresponding author) [1, 2]; R. Lawrence Edwards [3]; Augusto S. Auler [4]; Hai Cheng [3, 5]; Xinggong Kong [6]; Yongjin Wang [6]; Francisco W. Cruz [7]; Jeffrey [...]

Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,00o years. The record's length and temporal precision allow us to test the idea that insolation changes caused by the Earth's precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record's timing, the terminations are separated by four or five precession cycles, supporting the idea that the '100,000-year' ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and 'unfinished terminations'., The seasonal cycle of solar heating over Asia gives rise to the Asian monsoon (AM), a vast system of overturning atmospheric circulation that transports heat and moisture during boreal summer [...]

[sup.230]Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric C[O.sub.2] and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing C[O.sub.2] and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and C[O.sub.2]. 10.1126/science.1177840