The formation age and evolution of Kumtagh Desert

The ancient aeolian sand has been regarded as an indicator for the formation and evolution of a desert in the past.Kumtagh Desert is located at the northern fringe of Qinghai-Tibet Plateau.The first integrated scientific investigation to the desert was carried out during the period of 2004-2006.Kumtagh Desert is an ideal natural model for studying the formation and evolution of the desert because the Quaternary strata containing ancient aeolian sands are widely distributed.The integrated field investigation and studies on sedimentary,chronology and palynology of typical profiles named Suosuo gully,Xiaoquan gully and gravel body with ancient aeolian sand layers showed that Kumtagh Desert was probably formed as early as 2,097.7±314.7 ka BP.During the period of 386.9±58.0 ka BP to 285.9±42.9 ka BP,the desert largely expanded and formed its modern distribution pattern.The desert was originally developed in the southwest,subsequently,expanded to the north and northeast.The sedimentary facies of Suosuo gully profile revealed that the desert experienced at least 19 cycles of advance and inverse processes of desertification with an average period of 110 ka in the Quaternary.The neotectonic movements played an important role in the formation,development and geomorphology of the desert.On one hand,the movements caused the formation of intermontane fault basin,which was further developed towards the closed drought basin,and caused the formation of natural environment.On the other hand,under the control of surrounding faults,the unique broom-shaped desert landscape was formed,and the gullies and sand ridges in this region experienced an abrupt directional change from north by west to north by east at the location of 39°45＇-39°55＇N.The unique landscape of gravel body that occurred widely in the northern desert was formed after 285.9±42.9 ka BP.The results in this paper provide the scientific basis for studying the formation age and evolutionary process under the dry climate and environment in the northwestern China,and the uplifting of Qinghai-Tibet Plateau as well as its responses to the global climate changes.

Rock Assemblages and Formation Ages of the Baishuijiang Group in the Southwest Qinling Orogenic Belt, Northwest China

The Baishuijiang Group, located in the southwest Qinling orogenic belt, is divided into three belts according to the characteristic of the matrix and rock blocks based on the large scale geological mapping. The north belt and south belt are composed of abyssal mudstone and siltstone, and limestone, chert and basic and ultrabasic rock blocks. The middle belt consists of a few limestone blocks and turbidites, which were formed in the trench environment. At present, in the Baishuijiang Group, many fossils were found in matrix and rock blocks, the fossils contain the Cambrian small shell fossils(Xiao, 1992;Tao et al., 1992), Silurian chitinozoas, scolecodonts and spores, and Ordovician graptolites, and middle Devonian Coral and conodonts in limestone and chert blocks(Wang et al., 2011a), and Permian radiolarians in the matrix(Wang et al., 2007). The volcanic rock blocks have undergone different degree of metamorphism. Their geochemical characteristics indicate that the rocks are similar to oceanic island arc and seamount(Wang et al., 2009), and SHRIMP U-Pb dating yielded ages from Neoproterozoic to early Paleozoic(Yan et al., 2007;Wang et al., 2009, 2011b). Therefore, comprehensive analysis of regional data, the Baishuijiang group is an accretionary complex which was consisted of matrix and blocks, and was finally formed during Permian-Triassic.

Redefining the Age of the Cenozoic Shanwang Formation in Shanwang Basin

The Shanwang Basin is a small Cenozoic sedimentary basin located in Linqu county, Shandong province.The Shanwang Formation, especially the diatomaceous shale member, contains diverse and finely preserved flora and fauna fossils （Fig. 1）. Previous paleontological study and radiometric dating show that it was formed in the Miocene. However, on the precise age of the formation, there are such different opinions as Late Miocene, Middle Miocene, Early stage of Middle Miocene, etc.

Zircon U-Pb Age of the Lamenzi Formation Volcanic Rocks in the Liuhe Basin of Southern Jilin Province, China

Objective A large number of Mesozoic volcano-sedimentary basins is distributed in southern Jilin Province,China,and filled with a great set of coal-bearing strata.According to the petroleum resources evaluation by previous researchers,these basins have decent exploration potential(Wang Dandan et al.,2017).The Liuhe Basin is one of the

Latest Zircon U-Pb Age of the Baiyingaolao Formation Volcanic Rocks in the Keyihe Area of North-Central Da Hinggan Mountains

Objective Mesozoic volcanic rocks are mainly distributed in the Da Hinggan Mountains.The Baiyingaolao Formation is the main stratum in this area and has been considered to be formed in the Late Jurassic.Many scholars have researched these Mesozoic volcanic rocks in this area,which have been much debatable（Zhang Xiangxin et al.,2017）.A series of studies focusing on the Baiyingaolao Formation volcanic rocks in the middle-south section of

On the Age of the Dongtang Formation in the Hengyang Basin of Hunan and the Cretaceous and Tertiary Boundary

Since the coexistence of the Cretaceous and Palaeocene was ascertained in the Hengyang Basin of Hunan in the middle of the 1960's, the Cretaceous and Tertiary boundary has been discussed in several papers, but it still remains controversal. The points at issue are the connotation, stratigraphical position and lateral correlation of the Dongtang (or Chejiang) Formation.

New Zircon SHRIMP U-Pb Ages of the Langjiu Formation Volcanic Rocks in the Shiquanhe Area,Western Lhasa Terrane and their Implications

Objective The potassic and ultrapotassic rocks relating to the India-Eurasia collision and continual plate convergence are widely distributed in the Lhasa terrane. These rocks are very important to understand the deep processes of the India-Eurasia collision and the uplift and evolution of the Tibetan Plateau. Although high-potassic volcanic rocks are also exposed in the western Lhasa terrane, their formation time is still uncertain for the lack of reliable dating. We carried out zircon U-Pb geochronological study on the Langjiu Formation volcanic rocks, which are part of the Early Cretaceous Zenong group volcanic rocks based on 1：250000 scale Shiquanhe regional geological survey report, in the Shiquanhe area of the western Lhasa terrane. These new age data not only offer chronological basis for the regional stratigraphic correlation and classification, but also provide an essential opportunity for revealing signatures of magmatic pulses hidden in the deep crust of the Lhasa terrane.

The reliability of age measurements for Young Stellar Objects from Hertzsprung-Russell or color-magnitude diagrams

The possibility to estimate ages and masses of Young Stellar Objects （YSOs） from their location in the Hertzsprnng-Russell diagram （HRD） or a color- magnitude diagram provides a very important tool for the investigation of fundamen- tal questions related to the processes of star formation and early stellar evolution. Age estimates are essential for studies of the temporal evolution of circumstellar material around YSOs and the conditions for planet formation. The characterization of the age distribution of the YSOs in a star forming region allows researchers to reconstruct the star formation history and provides important information on the fundamental ques- tion of whether star formation is a slow or a fast process. However, the reliability of these age measurements and the ability to detect possible age spreads in the stellar population of star forming regions are fundamentally limited by several factors. The variability of YSOs, unresolved binary components, and uncertainties in the calibra- tions of the stellar parameters cause uncertainties in the derived luminosities that are usually much larger than the typical photometry errors. Furthermore, the pre-main se- quence evolution track of a YSO depends to some degree on the initial conditions and the details of its individual accretion history. I discuss how these observational and model uncertainties affect the derived isochronal ages, and demonstrate how neglect- ing or underestimating these uncertainties can easily lead to severe misinterpretations, gross overestimates of the age spread, and ill-based conclusions about the star for- marion history. These effects are illustrated by means of Monte-Carlo simulations of observed star clusters with realistic observational uncertainties. The most important points are as follows. First, the observed scatter in the HRD must not be confused with a genuine age spread, but is always just an upper limit to the true age spread. Second, histograms of isochronal ages naturally show a decreasing number of stars for ages above the median, a pattern that can be misinterpreted as an accelerating star formation rate. Third, it is emphasized that many star forming regions consist of sev- eral sub-groups, which often have different ages. If these distinct stellar populations cannot be disentangled （e.g., due to projection effects） and the HRD of all stars in the region is used for an age analysis, it is very difficult （often impossible） to discern between the scenario of an extended period of star formation （i.e. a large age spread） and the alternative concept of a temporal sequence of several discrete star formation episodes. Considering these factors, most observations of star forming regions suggest that age spreads are usually smaller than the corresponding crossing times, supporting the scenario of fast and dynamic star formation.

Antiglycation,antioxidant,antiacne,and photoprotective activities of crude extracts and triterpene saponin fraction of Sapindus saponaria L.fruits:An in vitro study

Objective:To evaluate the photoprotective,antioxidant,antiglycation,and antiacne activities of crude extract(CESs)and triterpene saponin fraction(TSSs)of Sapindus saponaria.Methods:HPLC-MS purification was performed on a Symmetry TM C18 column.The saponins were identified by a UV detector.Antioxidant activity was evaluated by DPPH and O_(2)^(−)radicals scavenging,and FRAP and TBARS assays.Glycation activity was assessed by relative electrophoretic mobility and inhibition of advanced glycation end products(AGEs)formation.Additionally,antiacne activity was determined by inhibition of Cutibacterium acnes,and photoprotective effect was evaluated by Mansur’s method.Results:Most of the triterpene saponins detected in the fraction by HPLC-MS analysis were hederagenin as the aglycon.CESs and TSSs presented varying antioxidant activity in DPPH(CESs:75.69%and TSSs:83.65%),FRAP(CESs:425.39μM TE/g DW and TSSs:649.36μM TE/g DW),TBARS(CESs:42.96%and TSSs:52.16%)and O_(2)^(−)radicals scavenging(CESs:61.33%and TSSs:86.69%)tests.CESs and TSSs also exhibited antiglycation activity comparable to bovine serum albumin treated with aminoguanidine.In addition,CESs and TSSs showed inhibition of AGE formation(34.48%and 61.85%,respectively).Antiacne activity against Cutibacterium acnes was observed with a minimum inhibitory concentration equal to minimum bactericidal concentration(CESs:36.11µg/mL and TSSs:18.34µg/mL).In photoprotective assays,CESs and TSSs showed maximum absorbance of 1.42 to 0.20 and 2.80 to 1.30,respectively,in the wavelength range of 260 to 400 nm.Furthermore,CESs and TSSs showed sun protection factors of 8.89 and 14.89,respectively.Conclusions:Sapindus saponaria fruit extracts show strong antioxidant potential and antiglycation activity against bovine serum albumin glycation and AGE formation.Besides,they presented antibacterial activity against Cutibacterium acnes and photoprotective effect against UV-A and UV-B.