藻源性有机质对高原深水湖泊沉积物矿化作用的激发效应

湖泊营养水平提升,浮游植物快速增殖,大量藻类碎屑沉降到沉积物表面。藻屑作为新生不稳定有机质,对湖泊沉积物有机质(SOM)产生激发效应,影响湖泊沉积物碳循环过程。本文以深水湖泊抚仙湖南湖心沉积物为研究对象,采用优势种水华束丝藻(Aphanizomenon flos-aquae),进行不同浓度藻屑添加(×1倍组、×5倍组和×10倍组)的培养实验。应用碳同位素在线监测仪,探究藻屑添加对于SOM矿化作用的激发效应并预测可能产生的环境效应。结果表明：(1)添加的藻屑对上覆水和间隙水发光性溶解性有机质(CDOM)组成和性质产生影响,前期CDOM中类蛋白组分含量显著增加,但后期CDOM腐殖化程度升高。同时,藻屑的添加使二氧化碳(CO₂)释放量增大,蛋白酶活性和转化酶活性增强;(2)3个不同浓度的藻屑添加组均检测到不同程度激发效应,其中×1倍组和×5倍组对SOM矿化过程前期体现为正激发效应,最大值分别达到(12.18±0.65)和(26.60±9.14)μg/(mL ws),后期两个组别都转为负激发效应;×10倍组则在整个实验过程中均表现为负激发效应;(3)藻屑的添加使得间隙水易...     

From marine bands to hybrid flows: Sedimentology of a Mississippian black shale

Organic-rich mudstones have long been of interest as conventional and unconventional source rocks and are an important organic carbon sink. Yet the processes that deposited organic-rich muds in epicontinental seaways are poorly understood, partly because few modern analogues exist. This study investigates the processes that transported and deposited sediment and organic matter through part of the Bowland Shale Formation, from the Mississippian Rheic–Tethys seaway. Field to micron-scale sedimentological analysis reveals a heterogeneous succession of carbonate-rich, siliceous, and siliciclastic, argillaceous muds. Deposition of these facies at basinal and slope locations was moderated by progradation of the nearby Pendle delta system, fourth-order eustatic sea-level fluctuation and localized block and basin tectonism. Marine transgressions deposited bioclastic ‘marine band’ (hemi)pelagic packages. These include abundant euhaline macrofaunal tests, and phosphatic concretions of organic matter and radiolarian tests interpreted as faecal pellets sourced from a productive water column. Lens-rich (lenticular) mudstones, hybrid, debrite and turbidite beds successively overlie marine band packages and suggest reducing basin accommodation promoted sediment deposition via laminar and hybrid flows sourced from the basin margins. Mud lenses in lenticular mudstones lack organic linings and bioclasts and are equant in early-cemented lenses and in plan-view, and are largest and most abundant in mudstones overlying marine band packages. Thus, lenses likely represent partially consolidated mud clasts that were scoured and transported in bedload from the shelf or proximal slope, as a ‘shelf to basin’ conveyor, during periods of reduced basin accommodation. Candidate in situ microbial mats in strongly lenticular mudstones, and as rip-up fragments in the down-dip hybrid beds, suggest that these were potentially key biostabilizers of mud. Deltaic mud export was fast, despite the intrabasinal complexity, likely an order of magnitude higher than similar successions deposited in North America. Epicontinental basins remotely linked to delta systems were therefore capable of rapidly accumulating both sediment and organic matter.     

高压密闭消解技术在土壤有效态样品前处理中的应用

土壤样品经有机酸浸提后,浸提出的溶液中存在大量有机酸及有机质,如未进行破坏处理,进入电感耦合等离子体发射光谱仪(ICP-OES)进样系统后容易堵塞雾化器、中心管、矩管等,或有颗粒黏附于中心管壁和矩管壁上,造成测定结果精密度和准确度差、空白高等问题,进而影响土壤有效态的综合评价。本文将土壤样品用有机酸(DTPA、草酸-草酸铵、柠檬酸等)浸提后,过滤或离心,吸取上清液加入高压密闭消解罐中,经电热板上处理,再加2mL浓硝酸,于180℃烘箱中保温至少3h,采用ICP-OES测定有效态元素铜锌铁锰镉铅镍铬钼硅的含量。本方法采用高压密闭消解技术处理土壤样品,各元素测定结果的相对标准偏差(RSD)为2.5%～5.9%,相对误差为-2.1%～5.2%,回收率为90.1%～103.2%,方法检出限为0.32μg/kg～0.038mg/kg;而采用以往高温炉中灼烧法、硝酸-高氯酸(硫酸)敞开消解法等技术手段,回收率为89.2%～100.5%,方法检出限为0.50μg/kg～0.050mg/kg,两者相比,本方法的测定结果稳定、空白低,分析周期短,适合批量样品的连续分析。     

Nucleation and stabilization of Eocene dolomite in evaporative lacustrine deposits from central Tibetan plateau

In past decades, the formation of dolomite at low temperature has been widely studied in both natural systems and cultured experiments, yet the mechanism(s) involved in the nucleation and precipitation of dolomite remains unresolved. Late Eocene dolomitic deposits from core in the upper Niubao Formation (Lunpola Basin, central Tibetan Plateau, China) are selected as a case study to understand the dolomitization process(es) in the geological record. Dolomite formation in Lunpola Basin can be ascribed to a different mechanism forming the large quantities of replacive dolostones in the geological record; and provides a potential fossil analogue for primary dolomite precipitation at low temperature. This analogue consists of an alternation of laminated dolomitic beds, organic-rich and siliciclastic layers; formed in response to intense evaporation interpreted to take place in a continental shallow lake environment. Mineralogical, textural and stable isotopic evaluations suggest that the dolomite from those dense-clotted laminated beds is a primary precipitate. At the nanoscale, these dolomitic beds are composed of Ca–Mg carbonate globular nanocrystals (diameter 80 to 100 nm) embedded in an organic matrix and attached to clay flakes. Micro-infrared spectroscopy analyses have revealed the presence of aliphatic compounds in the organic matrix. Microscopic and elemental compositional studies suggest that clay surfaces may facilitate the nucleation of dolomite at low temperature in the same way as the organic matrix does. The dolomite laminae show values for δ¹⁸O_VPDB from −3.2 to −1.76‰ and for δ¹³C_VPDB from −2.62 to −3.78‰. Inferred δ¹⁸O_SMOW values of the lake water reveal typical evaporitic hydrological conditions. These findings provide a potential link to primary dolomite formation in ancient and modern sedimentary environments; and shed new light on the palaeoenvironmental conditions in central Tibet during the Eocene.     

Characteristics of Carbonate Reservoir and Its Forming Conditions in Continental Lake Basin of China

For decades of exploration, geologists have made great achievements in the exploration of lacustrine carbonate rocks. By dissecting four typical cases of lacustrine carbonate rocks, such as Lucaogou Formation of Permian in Junggar Basin, Da'anzhai Section of Jurassic in Sichuan Basin, Cretaceous in Yin'e Basin and Oligocene in Qaidam Basin, the reservoir characteristics, hydrocarbon generating capacity and reservoir forming model of source rocks were analyzed. The results show that: \mathrm{①} Lacustrine carbonate reservoirs are generally dense, with nano-micron reservoir space as the main reservoir space, including dolomite intergranular pore, organism cavity and accumulation pore, micro-fracture system and its corrosion expansion pore. Saline environment is beneficial to dolomitization and can improve the reservoir capacity of lacustrine carbonate rocks, but most of the permeability is less than 0.1 mD. \mathrm{②} Lacustrine carbonate rocks have not only reservoir capacity, but also can be used as source rocks. The abundance of organic matter is not high and the maturity is generally low. However, dispersed soluble organic matter in source rocks can generate and expel hydrocarbons in large quantities at low maturity stage, which has high liquid hydrocarbon yield. \mathrm{③} Oil and gas reservoirs are characterized by "high initial production, large reduction of production and long-term low and stable production", and are typical "fracture-pore" reservoirs. Fracture networks provide migration pathways in the process of primary migration and accumulation of oil and gas in geological history and oil and gas exploitation nowadays. \mathrm{④} Oil and gas reservoirs are "continuous" unconventional reservoirs, which often form regional oil and gas field groups together with conventional reservoirs in adjacent areas. The research results lay a theoretical foundation for re-evaluating the exploration potential of lacustrine carbonate rocks.     

Geochemical characterization of soil organic matter and variability of a postglacial detrital organic supply (chaillexon lake,france)

Geochemical analysis of sedimentary organic matter in recent lacustrine sediments appears to be a useful tool in providing information concerning past environmental conditions. However, such analysis is often made without knowing the geochemical characteristics of the organic matter derived from the watershed and, more explicitly, its soils. The present work deals with (i) a geochemical investigation (Rock-Eval pyrolysis) of soil organic matter sampled in a lake watershed, and (ii) the study of the sedimentary organic matter trapped in the lake deposits. The research was conducted on Chaillexon Lake which was created by a rock collapse that dammed the palaeovalley of the Doubs River about 12 000 years ago. Since this event, the sediment trap provides a continuous palaeoclimatic record for the Postglacial period. Results obtained lead to two main conclusions. First, the variability of Rock-Eval pyrolysis values observed in soils modifies the common interpretation given to these parameters in the characterization of sedimentary organic matter. Indeed, variations in these parameters point not only to varying proportions of terrestrial and lacustrine organic matter in a lacustrine infilling but also to variations of the terrestrial supply linked with the evolution of vegetal cover in the catchment. The second conclusion is that the story of the Chaillexon lacustrine system is marked by a rather sudden soil and forest development at the Preboreal–Boreal transition (9000 BP ). Copyright © 1998 John Wiley & Sons, Ltd.     

Non-synchronous records of Holocene aeolian sand deposition and landscape stability at adjacent lake-side sites in the Falkland Islands,South Atlantic: a caution

Lithostratigraphical interpretation and ¹⁴C dating of adjacent lake-side sedimentary sequences at the Sulivan House lakes, West Falkland, indicate between-site non-synchronous records of Holocene aeolian sand deposition and landscape stability. It is inferred that the sands are associated with deflation of exposed sandy shorelines at times of lower lake levels, whereas stability phases are characterised by peat formation and/or organic matter incorporation into sand horizons at times of ‘normal’ lake levels. The data imply that a cautious approach to interpretation of lake-side sediments may be warranted if the purpose is to use lake-level changes and aeolian — non-aeolian interbeds as proxy indicators of regional climatic signals. © 1998 John Wiley & Sons, Ltd.     

Genesis of Strata-bound Sulfide Orebodies in the Tongling Polymetallic Mineralization Cluster, SE China: Evidence from Colloform Pyrite

Colloform pyrite (CPy) is widely distributed in the Tongling mineralization cluster of the Middle–Lower Yangtze River Mineralization Belt (MLYRMB), China. There have many debates as to whether such CPy is associated with Late Mesozoic igneous or Carboniferous sedimentation. CPy from the Xinqiao deposit, a representative of the stratabound sulfide deposits in the MLYRMB, was studied by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (TEM). The results show that CPy mainly comprises pyrite, pyrrhotite, quartz, and illite. Pyrite in CPy shows cubic, globule, and xenomorphic morphologies. No octahedral or pyritohedron was observed. Most of the quartz crystals display xenomorphic morphology, where pyrite mold are popular on the surface. Organic matter (OM), which is usually bound to illite, is an important component in CPy. Morphological investigations which exhibit detrital features of quartz and clay minerals indicate that they were derived from continental weathering. Specially, some hexagonal pyrrhotite nanoparticles which show mackinawite morphology are coexisted with OM. The results indicate that the transformation process of sulfides possibly is mackinawite (the precursor)—hexagonal pyrrhotite—pyrite. Thus, compositional and micro-textural characteristics of CPy in Xinqiao deposit suggest it to be a sedimentary origin rather than a hydrothermal origin which is associated with Yanshanian magmatism. Moreover, the coexistence of CPy and stratabound sulfide orebodies in the MLYRMB suggests a causal link between the two. It is considered that CPy might have served as a Cu mineralization geochemical barrier for the Cu-bearing ore-forming fluids, which originated from the Mesozoic magma in the MLYRMB.     

气候变暖对多年冻土区土壤有机碳库的影响

多年冻土区存储了大量土壤有机碳。气候变暖、 多年冻土退化导致其长期封存的有机碳逐渐或快速释放, 进入大气圈或水系统, 改变原有多年冻土区碳循环, 并可能显著加速气候变暖。通过综述气候变暖对多年冻土区碳库的影响研究进展, 主要包括多年冻土碳库储量、 降解机理及变化预测, 研究表明： 北半球多年冻土区的碳储量巨大, 但不确定性很高, 尤其是海底多年冻土和水合物碳库储量的评估; 多年冻土碳库对气候变暖的响应速度受土壤水热特性、 土壤有机质C/N比、 有机碳含量和微生物群落特征等多种环境因素的控制或影响; 目前, 关于北半球多年冻土碳库对气候变暖响应模拟结果说明, 多年冻土退化短期内不会导致经济和生产方面的灾难性后果。但是, 无论是针对多年冻土碳库评估, 还是多年冻土有机碳库对气候变暖的响应模拟研究结果, 都有较大的不确定性。未来多年冻土碳库变化的模拟和预测研究应更多考虑多年冻土快速退化和多年冻土区水合物分解, 如中小尺度热喀斯特的生态环境和碳的源汇效应。准确的多年冻土区有机碳排放模拟可为未来多年冻土碳与气候反馈的预估提供重要支持。     

末次冰期以来南海东北部陆源有机碳埋藏通量演变:海平面和季风驱动

大陆边缘盆地是大陆风化剥蚀产物的主要沉积汇,其中有机碳的埋藏通量及其控制机制的研究对于理解全球碳循环具有重要科学意义。本研究基于南海东北部台西南盆地TWS-1岩芯的AMS14C测年、总有机碳、总氮含量和稳定碳同位素组成的分析,探讨了末次盛冰期23ka BP以来南海东北部陆源有机碳的来源、历史和影响机制。与潜在物源端元对比表明,台湾是研究站位沉积物陆源有机碳的主要物源,相对海源其贡献比例约为58%,陆源物质可能主要通过海底峡谷水道和低海平面时期陆架河流输入。重建的陆源有机碳通量在末次冰消期早期(19—13kaBP)和中全新世(7—4ka BP)期间有两个峰值,分别约0.16g/(cm2·ka)和0.09g/(cm2·ka)。综合分析表明,二者分别受控于冰期低海平面时期增强的陆架风化剥蚀和全新世季风强盛期降水驱动的古台湾岛剥蚀。我们的工作表明冰期-间冰期循环中海平面和季风分别驱动的大陆边缘有机碳埋藏可能对全球碳循环和大气CO2浓度演变有重要影响。