• Digital Humanities and Cultural Heritage
• Publications close
• TW close
• Quaternary Geochronology close

Abstract Authigenic carbonates from cold seep systems, such as chimney and crust carbonate deposits, are important archives of biogeochemical processes associated with the migration and seepage of methane-rich fluids and seepages on the seafloor. Here we use a new U–Th dating method to precisely determine the ages of the authigenic carbonates of a chimney in the Okinawa Trough (OT), East China Sea. The method uses a series of heavy liquids (HL, a mixture of tribromomethane and alcohol with a density of 2.71–2.80 g/cm3) to separate subsamples of carbonate contaminated by detrital material. The contents of relevant elements (Al, Rb, Zr, Nb, and rare earth elements) of the subsamples reveal that the separation of the mineral phase was successful. Five samples from along the radius of a well-structured chimney (PES-1) from station D2-5 in the OT were analyzed and yielded U–Th ages of 28.8 ± 0.4 ka, 26.1 ± 0.5 ka, 24.4 ± 0.7 ka, 22.5 ± 0.6 ka and 20.1 ± 0.6 ka, from the exterior to the interior of the chimney section, and AMS 14C dating of the same samples produced the similar results. The agreement between the 230Th/U and AMS 14C ages suggests that the application of heavy liquid methods in U–Th dating can be very successful, and it reduces the influence of detrital contamination. Therefore, the approach has a great potential space for studying the evolutionary history of authigenic carbonates in cold seep systems. Moreover, the new 230Th/U ages show that the carbonate chimney was formed during the Last Glacial Maximum (LGM), which corresponding to the large sea-level fall in the East China Sea. Together with information on biogeochemical processes, the results will provide valuable geochronological information for the future study of active fluid venting on continental margins.

Abstract In the absence of reliable charcoal, wood or plant macrofossils, organic matter in loess-paleosols is often used for 14C dating. However, organic matter can be contaminated by a variety of carbon sources within the sediments, and this may affect the radiocarbon dating results. Specific chemical pretreatments can be applied to minimize such effects, and comparisons with optically stimulated luminescence (OSL) dates from the same sediments allows us to assess potential open system effects on organic matter. Here we present comparisons of the two geochronometers from loess-paleosol deposits in the Chinese Loess Plateau. Our results show that loess -paleosol samples from the past 25 cal kyr BP generally yield reliable 14C dates, however, beyond this range, specifically ~25–59 cal kyr BP, we observe a steady increase in OSL ages with depth, but no consistent increase in corresponding AMS 14C ages. We suggest that relatively old samples from loess-paleosols should be studied using techniques such as compound-specific radiocarbon dating, ramped pyrolysis or stepped-temperature combustion.

Abstract Multiple-collector inductively coupled plasma mass spectrometric (MC-ICPMS) techniques, with high-precision and high-throughput capabilities, have been applied to 230Th/U geochronology since the late 1990s. Significant effort has been dedicated to refining such techniques, but few studies have emphasized the development of data processing schemes. This study presents a convenient data-processing protocol that allows users to easily transform measured MC-ICPMS data to accurate 230Th/U ages, accounting for most sources of analytical uncertainty. This protocol comprises two interactive programs UTh_Review and UTh_Reduction, written with the MATLAB programming language. UTh_Review is designed to graphically present raw data of ion beam intensities and filter out outliers. UTh_Reduction enables data reduction, age calculations and data storage. This newly-developed protocol was validated by long-term measurement of δ234U in the Harwell uraninite isotope reference solution (HU-1) and an inter-laboratory comparison of 230Th/U dating of stalagmite. This methodology of data processing can easily be modified to fit previously published U Th data acquisition strategies.

A precisely 230Th-dated stalagmite oxygen isotope (δ18O) record from Dragon Cave,Shanxi Province, northern China, is proposed to reconstruct the millennial-scale changes of the East Asian Summer monsoon (EASM) during the period 53.2-1.3 ka BP (before 1950 AD). Our record shows significant millennial-scale oscillations that match in timing, characteristic, and duration with the Dansgaard/Oeschger (DO)30 events 14-8 and the Heinrich events 5, 4, 2, and 1 (hereafter H5, H4, H2 and H1) in high-latitude regions of the Northern Hemisphere. Especially, the H5 event is well\ud constrained from 48.1 to 46.9 ka BP with ten 230Th dates. Our chronology supports the NGRIP GICC05 timescale from 50 to 38 ka BP. A comprehensive comparison of the Chinese speleothem records from different regions along a north-south transect shows a unique trend towards more negative δ\ud 18O values from 48.0 to 38.0 ka BP, suggesting that an intensified Asian summer monsoon (ASM) across the whole monsoonal China during the interval. We speculate that the joint effect, from both the cooling of the Southern Hemisphere and the enhanced land-sea temperature contrast\ud due to the rising summer insolation, is capable to regulate the low-latitude large-scale atmospheric circulation patterns and exert significant influences on the long-term\ud ASM variations during the middle of Marine Isotope Stage 3.

Abstract Radiocarbon has been widely used in determining the age of various geological materials and events. The validity of ages, particularly for sediments, has often been questioned due to the incorporation of carbon-bearing components with different abundances of 13 C and 14 C. This study examines carbon contained in clay minerals (kaolinite, illite and illite-smectite) extracted by temperature-stepped combustion experiments, ranging from 350 °C to 1100 °C. Distinct carbon components were identified in the samples using both their 13 C and 14 C contents. Two carbon end-members were observed for all of the clay minerals: a low temperature component ( 13 C and enriched in 14 C; and a high temperature component (>550 °C), relatively enriched in 13 C and depleted in 14 C. The high temperature carbon component is relatively old and not released until the clay is completely oxidized. This observation suggests that this carbon was incorporated into the clay mineral when it first formed by weathering. We applied the same procedure to sediments collected from terraces along the Kueichung River, in southwestern Taiwan, sieved to

Abstract Optically stimulated luminescence (OSL) thermochronometry is an emerging application, whose capability to record sub-Million-year thermal histories is of increasing interest to a growing number of subdisciplines of Quaternary research. However, several recent studies have encountered difficulties both in extraction of OSL signals from bedrock quartz, and in their thermochronometric interpretation, thus highlighting the need for a methodological benchmark. Here, we investigate the characteristic OSL signals from quartz samples across all major types of bedrock and covering a wide range of chemical purities. High ratios of infrared to blue stimulated luminescence (IRSL/BLSL), an insensitive ‘fast’ OSL component, and anomalously short recombination lifetimes seen in time-resolved luminescence (TR-OSL), are often encountered in quartz from crystalline (magmatic and metamorphic) bedrock, and may hamper successful OSL dating. Furthermore, even when the desirable signal is present, its concentration might be indistinguishable from its environmental steady-state prediction, thus preventing its conversion to a cooling or heating history. We explore the saturation properties and the thermal activation parameters of various OSL signals in quartz to outline the capabilities and limitations for their use in low-temperature thermochronometry.

Lake Manas, located in northwestern China, has been formed in a structure depression since early Quaternary. Optically stimulated luminescence (OSL) dating is applied to the lacustrine and aeolian deposits collected from the lake to construct a chronological frame for lake level fluctuations since the last inter-glacial period. The results yielded two stages of high lake stands (∼20 m above the present lake bed) occurred before 66 ka and 38-27 ka ago. No evidence for Holocene high lake level was found in the studying area. © 2012 Elsevier B.V. link_to_subscribed_fulltext

Abstract Thermal ages (e.g. fission track, Ar/Ar and U–Th/He ages) are important to understand mountain building activities within the upper crust. In order to understand the uplift history of Taiwan, researchers are looking for the applicability of thermal ages from fairly low cooling temperatures by using luminescence dating methods. The low-temperature-involved recent past is an area of great interest. Since the reliability of the luminescence dating method is sample dependent, this ongoing study starts with checking relevant characteristics of the luminescence properties from appropriate minerals (e.g. quartz). The samples for this study were collected from the Central Range in Taiwan. Sampling locations were chosen to cover various altitudes across the Central Range from two different rock types: 1) cherty-marble and 2) meta-sandstone. This sampling strategy is intended to decipher rock dependent variation because cherty-marble has not undergone as much stress as meta-sandstone. We compare luminescence behaviors of quartz between samples from cherty-marble and meta-sandstone. The equivalent doses were determined by conventional single aliquot regenerative-dose (SAR) protocol and SAR isothermal thermoluminescence (ITL) protocol. Results suggest that the preheat process may not be applicable for quartz from both cherty-marble and meta-sandstone of Taiwan. The SAR ITL protocol without preheat processes was applied successfully on the sample for such an approach. Although our current results of ITL seem promising, further and detailed luminescence characteristics of ITL should be examined before the feasibility is finally proposed.

The direct and feedback relationships between tectonics, climate and denudation are a matter of debate.