Redox evolution of western Tianshan subduction zone and its effect on deep carbon cycle

Knowing the phase relations of carbon-bearing phases at high-pressure(HP) and high-temperature(HT) condition is essential for understanding the deep carbon cycle in the subduction zones.In particular,the phase relation of carbon-bearing phases is also strongly influenced by redox condition of subduction zones,which is poorly explored.Here we summarized the phase relations of carbon-bearing phases(calcite,aragonite,dolomite,magnesite,graphite,hydrocarbon) in HP metamorphic rocks(marble,metapelite,eclogite) from the Western Tianshan subduction zone and high-pressure experiments.During prograde progress of subduction,carbonates in altered oceanic crust change from Ca-carbonate(calcite) to Ca,Mg-carbonate(dolomite),then finally to Mgcarbonate(magnesite) via Mg-Ca cation exchange reaction between silicate and carbonate,while calcite in sedimentary calcareous ooze on oceanic crust directly transfers to high-pressure aragonite in marble or amorphous CaCO3 in subduction zones.Redox evolution also plays a significant effect on the carbon speciation in the Western Tianshan subduction zone.The prograde oxygen fugacity of the Western Tianshan subduction zone was constrained by mineral assemblage of garnet-omphacite from FMQ-1.9 to FMQ-2.5 at its metamorphic peak(maximum P-T) conditions.In comparison with redox conditions of other subduction zones,Western Tianshan has the lowest oxygen fugacity.Graphite and light hydrocarbon inclusions were ubiqutously identified in Western Tianshan HP metamorphic rocks and speculated to be formed from reduction of Fe-carbonate at low redox condition,which is also confirmed by high-pressure experimental simulation.Based on petrological observation and high-pressure simulation,a polarized redox model of reducing slab but oxidizing mantle wedge in subduction zone is proposed,and its effect on deep carbon cycle in subduction zones is further discussed.     

松辽盆地松科1井上白垩统烃源岩有机碳含量与沉积速率的关系*

与海相盆地相比,陆相湖盆沉积物TOC和沉积速率关系的研究尚处于探索阶段,尤其是在沉积作用对TOC的控制机理研究方面还有待深入。首先运用旋回地层学方法,识别了松科1井南孔上白垩统天文周期,并利用滑动窗口频谱分析方法计算了各窗口的沉积速率及对应的TOC值。以姥鲛烷和植烷(Pr/Ph)比值作为氧化还原条件的指标,以介形虫壳体的δ¹³C作为古生产力大小的指标,对不同环境和不同古生产力条件下TOC和沉积速率的关系进行了探讨。研究表明: 在还原环境下,TOC主要取决于古生产力高低,而沉积速率的影响相对较小,当古生产力较高时,TOC值一般大于1%;反之,TOC值小于1%。但在氧化环境、低古生产力条件下,TOC随着沉积速率先增大后减小,其临界值为11,cm/ka。     

浑善达克沙地地表沉积物有机碳同位素组成 与植被-气候的关系

研究现代地表沉积物有机碳同位素与植被-气候的关系,对于重建过去气候变化过程有重要意义。然而,对于气候变化幅度大、生态环境脆弱的浑善达克沙地,尚缺少相关的研究。本研究对浑善达克沙地进行了全面采样,对42个地表样品进行了有机碳同位素分析。结果表明,浑善达克沙地表土有机碳同位素(δ13C)介于-25.0 ‰ ~-19.4 ‰ 之间,平均为-22.2 ‰。通过两端元方法估算,研究区C4生物量介于0~46% 之间,平均为17.9%,与前人的C4植被调查结果有很好的可比性。相关分析表明,C4生物量与年降水量呈显著负相关关系,而与温度关系不大,这表明在该地区年均温差异较小的情况下,降水可能是控制C4植物生物量的主要因素; 另外,推测也可能是研究区C3生物量的变化主导地表有机碳同位素的变化。建立的δ13 C-年降水量转换函数,预期可用于重建浑善达克沙地全新世降水量的变化。     

Geomorphological controls on fluvial carbon storage in headwater peatlands

Geomorphological controls and catchment sediment characteristics control the formation of floodplains and affect their capacity to sequester carbon. Organic carbon stored in floodplains is typically a product of pedogenic development between periods of mineral sediment deposition. However, in organically-dominated upland catchments with a high sediment load, eroded particulate organics may also be fluvially deposited with potential for storage and/or oxidation. Understanding the redistribution of terrestrial carbon laterally, beyond the bounds of river channels is important, especially in eroding peatland systems where fluvial particulate organic carbon exports are often assumed to be oxidised. Floodplains have the potential to be both carbon cycling hotspots and areas of sequestration. Understanding of the interaction of carbon cycling and the sediment cascade through floodplain systems is limited. This paper examines the formation of highly organic floodplains downstream of heavily eroded peatlands in the Peak District, UK. Reconstruction of the history of the floodplains suggests that they have formed in response to periods of erosion of organic soils upstream. We present a novel approach to calculating a carbon stock within a floodplain, using XRF and radiograph data recorded during Itrax core scanning of sediment cores. This carbon stock is extrapolated to the catchment scale, to assess the importance of these floodplains in the storage and cycling of organic carbon in this area. The carbon stock estimate for the floodplains across the contributing catchments is between 3482-13460 tonnes, equating on an annualised basis to 0.8-4.5% of the modern-day POC flux. Radiocarbon analyses of bulk organic matter in floodplain sediments revealed that a substantial proportion of organic carbon was associated with re-deposited peat and has been used as a tool for organic matter source determination. The average age of these samples (3010 years BP) is substantially older than Infrared Stimulated Luminesence dating which demonstrated that the floodplains formed between 430 and 1060 years ago. Our data suggest that floodplains are an integral part of eroding peatland systems, acting as both significant stores of aged and eroded organic carbon and as hotspots of carbon turnover. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Determination of Total Organic Carbon Content and δ13C in Carbonate-Rich Detrital Sediments

The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (C_org) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble C_org respectively. In Himalayan and Amazon river sediments, the proportion of C_org solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the C_org content for the dissolved organic carbon content measured after decarbonation. Data presented here show that C_org dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment.     

全球链网下的欠发达地区产业集群化研究——以韶关汽车零部件产业为例

全球链网下的地方产业集群,已成为区域经济发展的重要组织形式。欠发达地区产业集群的形成与发展是特色资源、产业基础、创新文化、政策激励和市场驱动对地方化和全球化两股力量“粘滞—集聚—再粘滞—再集聚”的循环积累结果。针对韶关资源丰富、产业基础厚实,但空间粘滞作用不强、产业集群化程度低的现状,认为韶关汽车零部件产业应走“立足资源,一园三片;精细专工,错位发展”的特色集群化道路。     

广东凡口铅锌矿碳、氧同位素地球化学特征及其地质意义

广东凡口超大型铅锌矿床产于泥盆系台地碳酸盐岩中,矿床成因仍存在较大争议。通过含矿地层岩石以及矿石系统的碳、氧同位素分析研究,发现紫色砂岩的褪色蚀变和碳酸盐岩的白云石化与盆地卤水作用密切相关,褪色蚀变砂岩中的碳酸盐胶结物具有显著低的δ^13C和δ^18O值,与矿石中碳酸盐矿物相似,白云石化的碳酸盐岩之δ^13c和δ^18...     

广西涠洲岛滨海湿地潮下带海草、红树林与互花米草的分布和群落结构特征

系统报道了广西涠洲岛的潮下带海草、红树林以及互花米草的分布和群落结构特征.2019—2020年的调查结果表明,涠洲岛海草分布于南湾西侧,紧邻珊瑚礁区,面积4246 m2,为潮下带的生长形式,海草种类仅见卵叶喜盐草(Halophila ovalis);真红树植物有6种[红海榄(Rhizophora stylosa)、海漆...     

Carbon and oxygen isotopic composition of car- bonate cements of different phases in terrigenous siliciclastic reservoirs and significance for their origin： A case study from sandstones of the Triassic Yanchang Formation, southwestern Ordos Basin, China

Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope （their δ^18O values range from -0.3‰- -0.1‰） and lighter oxygen isotope （their δ^18O values range from -22.1‰- -19.5‰）. Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process.     

河南淅川龙山时代陶鼎炭化残留物的碳、氮稳定同位素分析

对河南淅川丹江沿岸龙山时代若干遗址出土陶鼎残片内壁残留的炭化物,开展了碳、氮稳定同位素分析,旨在揭示该类型器物所盛放或烹煮过的食物来源以及器物的用途。结果显示,δ 13 C值介于C3和C4类植物之间,表明大部分器物曾烹煮过C3和C4类食物,根据该地区当时为稻粟混作区的状况,推测稻、粟可能是食物的主要来源; 结合δ 13 C与 δ 15 N 值表明部分炭化物的生物来源包括豆科类植物、食肉类动物或鱼类资源,说明先民的蛋白质摄取来源较为丰富。因此,当时陶鼎加工的食物种类并不局限于肉类,这表明了陶鼎使用功能的广泛性以及当时人类食物来源的多样性,从而深化了对古代社会食物结构以及生存环境的认识。