Facies character and geochemical signature in the late Quaternary meteoric diagenetic carbonate succession at the Xisha Islands,South China Sea

The late Quaternary shallow-water carbonates have been altered by a variety of diagenetic processes, and further influenced by high-amplitude global and regional sea level changes. This study utilizes a new borehole drilled on the Yongxing Island, Xisha Islands to investigate meteoric diagenetic alteration in the late Quaternary shallowwater carbonates. Petrographic, mineralogical, stable isotopic and elemental data provide new insights into the meteoric diagenetic processes of the reef limestone. The results show the variation in the distribution of aragonite,high-Mg calcite(HMC) and low-Mg calcite(LMC) divides the shallow-water carbonates in Core SSZK1 into three intervals, which are Unit I(31.20–55.92 m, LMC), Unit II(18.39–31.20 m, aragonite and LMC) and Unit III(upper 18.39 m of core, aragonite, LMC and HMC). Various degrees of meteoric diagenesis exist in the identified three units. The lowermost Unit I has suffered almost complete freshwater diagenesis, whereas the overlying Units II and III have undergone incompletely meteoric diagenesis. The amount of time that limestone has been in the freshwater diagenetic environment has the largest impact on the degree of meteoric diagenesis. Approximately four intact facies/water depth cycles are recognized. The cumulative depletion of elements such as strontium(Sr),sodium(Na) and sulphur(S) caused by duplicated meteoric diagenesis in the older reef sequences are distinguished from the younger reef sequences. This study provides a new record of meteoric diagenesis, which is well reflected by whole-rock mineralogy and geochemistry.     

Seismic reflection evidence of crustal duplexing and lithospheric underthrusting beneath the western Qilian Mountains,northeastern margin of the Tibetan Plateau

The geological processes responsible for outward growth of the Tibetan Plateau are debated.The Qilian Mountains on the northeastern margin of the plateau comprise one of the youngest structural components of the plateau whose understanding is key to deciphering the broader geological evolution of the region.Here,based on a reprocessed deep seismic profile which was originally collected during the 1990 s across the northeast margin of the western Qilian Mountains and previous geological and geophysical data,we find evidence for decoupled crustal deformation that was partitioned by a decollement,in which lowercrustal deformation featured by local duplexing preceded upper-crustal deformation featured by imbricate thrusts.Furthermore,we propose that the Asian lithospheric mantle is being underthrust beneath the western Qilian Mountains,as inferred from patterns of lower crustal deformation which is marked by the Moho geometry.Integrating these results yields a better understanding of lithospheric deformation of western Qilian Mountains,northeastern margin of the plateau during the Cenozoic.     

Comparison of ecophysiological characteristics between introduced and indigenous mangrove species in China

Due to its rapid growth, the introduced mangrove species Sonneratia apetala from Bangladesh has been widely used in mangrove restoration in southeastern China since 1985. As an indigenous mangrove species in Hainan, China, Sonneratia caseolaris was also planted in Guangdong Province for afforestation purposes. Both species have developed well in their new habitats, but their ecophysiological differences with the native mangrove species have not been studied. In this study, leaf gas exchange, water and nitrogen use efficiencies of two Sonneratia species were compared with those of selected native mangrove species (Avicennia marina, Aegiceras corniculatum, Kandelia candel, and Excoecaria agallocha) in Hainan and Shenzhen. The introduced S. apetala maintained lower carbon assimilation rate (A) and photosynthetic nitrogen use efficiency (PNUE) than the indigenous S. caseolaris. In Shenzhen, the two introduced Sonneratia had comparable photosynthetic rates and water use efficiency (WUE) with the native mangrove species, except that PNUE in S. caseolaris was significantly higher than in the native mangrove species. The two Sonneratia species showed significant overlap in PNUE and long-term WUE. Photosynthetic parameters derived from leaf photosynthetic light–response curves and A–C_i curves also suggested lower carbon assimilation capacities for the introduced Sonneratia than for the native mangrove species in both study sites. The lower light compensation point (LCP) of two introduced Sonneratia in both study sites also indicated a better adaptation to a low light regime than the native mangrove species. The results of photosynthetic capacities indicated that the introduced mangrove species have little competitive advantage over local native mangrove species in their respective new habitats.     

Evidence for the 8,200 a <Emphasis Type="SmallCaps">b</Emphasis>.<Emphasis Type="SmallCaps">p</Emphasis>. cooling event in the middle Okinawa Trough

Based on new and existing data on oxygen isotopes, alkenone-surface seawater temperature trends, planktonic foraminifers, lithology, and clay mineral composition of piston cores, a distinct cooling event has been identified around 8,200 cal a b.p. in the middle Okinawa Trough, northwest Pacific. This corresponds to the 8,200 a b.p. cooling event recorded in many places of the Northern Hemisphere. During this event, the local temperature decreased by 1°C, and the δ¹⁸O value increased by 0.6‰. A strengthened Asian winter monsoon is the most probable cause for this event, which thus adds further credibility to the contention that we are dealing here with a global phenomenon.     

Micromorphological features of Paleo-Stagnic-Anthrosols at archaeological site of Sanxingdui,China

The archaeological site of the Sanxingdui may date back as far as 5,000 years ago. The typical profiles of Palaeo-Stagnic-Anthrosols near the ancient site were selected, which aimed to identify diagnostic horizons employing methodology of soil taxonomic classification and to reveal the micromorphological properties of the paleosols. Under long-term anthropogenic mellowing, the discernible differentiation between anthrostagnic epipedon and its subhorizons as well as hydragric horizon and its subhorizons occurred in Paleo-Stagnie-Anthrosols at the archaeological site of the Sanxingdui. The mieromorphological properties diversified among each specific diagnostic subhorizon, e.g., the developed microstructure in cultivated subhorizon within anthrostagnic epipedon, closely arranged particles and considerable micropores beneficial to both of water conservation and filtration in plow subhorizon within anthrostagnic epipedon, and automorphic optical-orientation clays and calcareous corrosion in hydragric horizons. The findings above of micromorphological features related with diagnostic horizons are significant for soil taxonomic classification.     

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关于测量标志保护与管理的思考

针对测量标志出现大量毁坏的原因,联系当前测量标志新形势的要求,提出了现阶段测量标志维护与管理的想法和建议.     

数字高程模型对DOM的精度影响

DOM的数字微分纠正通常要用到DEM来实现地形的纠正,DEM的精度会在多大程度上影响DOM的纠正精度,是很多技术人员所关心的问题之一.本文通过详实的论证得出了一些结论,为航空摄影各项技术指标的确定、合理有效地选取DEM数据源等问题作了科学的回答.