中国含煤岩系古地理及古环境演化研究进展*

随着含煤岩系沉积学从最初的旋回层理论到沉积模式,再到现阶段层序地层学理论的发展,中国学者已经在含煤岩系沉积学研究领域取得了显著的成果。(1)层序地层格架下基于可容空间增加速率与泥炭堆积速率之间平衡关系的厚煤层聚集模式受到重视,层序地层学提供了等时性地层单元,用于中国六大聚煤区等时性层序地层格架下岩相古地理的重建,为预测各聚煤期聚煤中心及富煤带的分布起到指导性作用。随着层序地层学理论的深入研究,煤相及沉积有机相的发育特征、研究方法以及划分方案也取得了新的进展。(2)近年来,煤系共伴生矿产已经成为当今煤地质学研究的热点问题之一,含煤盆地的煤层气、页岩气、天然气水合物、铀矿、三稀矿产、石墨等矿产资源具有重要的经济价值,部分共伴生矿产潜在的价值甚至超过煤炭本身。古地理作为研究煤系矿产资源的先决条件,与之联系密切,为这些矿产的研究和勘探提供极大的帮助。(3)煤作为泥炭地的产物和重要的沉积载体,其中蕴藏着丰富的“深时”古气候信息。以米兰科维奇旋回作为地层时间的“度量”工具,可以通过分析煤中碳的聚集速率,进而分析泥炭地的碳聚集速率、净初级生产力以及大气CO₂的变化趋势;而随着对煤中惰质组成因的重新认识,蕴含在煤中的古野火信息越来越受到重视,基于煤中惰质组的含量对地质历史中古泥炭地野火事件以及大气氧含量的估算也成为古环境研究的新方向。中国聚煤模式及聚煤古地理今后的研究需进一步加强对不同构造背景下含煤盆地的层序地层模式、各聚煤期的聚煤古地理及聚煤规律、有益煤系共伴生矿产的古地理重建、含煤岩系“深时”古气候信息以及大数据驱动下的含煤岩系古地理定量化研究等方面的探索。     

西藏果芒错蛇绿混杂岩中硅质岩的地球化学特征及其形成环境

果芒错蛇绿混杂岩位于狮泉河—永珠—嘉黎蛇绿混杂岩带中段,是该带中保存较好的一套蛇绿混杂岩,其形成环境是确定狮泉河—永珠—嘉黎蛇绿混杂岩带构造属性的重要依据。对果芒错蛇绿混杂岩中的硅质岩进行了地球化学分析,为判断蛇绿混杂岩的形成环境提供新的约束条件。硅质岩通常呈几十厘米夹层产于玄武岩中,含有大量晚三叠世—白垩纪放射虫化石。硅质岩SiO2含量为71.38%～77.67%,Al2O3含量为8.62%～11.51%,MnO/TiO2值为0.28～0.35,（Ce/Ce＊）SN值为0.92～0.94,（La/Ce）SN值为1.13～1.17,反映了陆源物质的影响,而V、Ni、Cu和V/Y值高于大陆边缘硅质岩,与洋中脊和大洋盆地硅质岩相似,说明果芒错硅质岩可能形成于受陆源物质影响且与大陆边缘有一定距离的环境中。结合变质橄榄岩、镁铁质岩墙和玄武岩的地球化学特征,初步认为果芒错蛇绿混杂岩的形成环境为靠近大陆边缘的弧后盆地。     

遥感卫星数据产品分类分级规则研究

随着遥感卫星应用的发展,多源、多时相、多尺度以及不同类型遥感卫星的数据综合集成应用以及与地面观测信息集成,对遥感信息产品进行深度开发利用正在成为遥感应用的重要趋势。目前不同国家和地区、不同系列的遥感卫星数据产品分别采用不同的分类分级方案,难以适应多源、多系列地理空间信息整合应用的需求。本文从遥感应用对遥感卫星数据产品分类分级的需求出发,分析了目前主要遥感卫星的产品系列及其数据产品分类分级规则,参考了正在研究的相关国际标准,遵循系统性、科学性、完整性、兼容性、可操作性和可扩充性原则,研究提出了中国遥感卫星数据产品分类分级的规则。该规则以卫星载荷采用的遥感探测光谱特征及其数据获取方式作为分类依据,以卫星遥感数据的处理水平作为分级依据,建立统一的遥感卫星数据产品的分类分级体系。该规则与正在研究制订的相关国际标准保持一致,不但覆盖目前广泛应用的各类遥感卫星数据产品,而且能方便地建立与现有遥感卫星数据产品分类分级方案的映射关系,并且对未来的数据产品的分类分级留有比较充分的可扩充性,为遥感卫星数据产品分类分级指标体系的研究和相关国家标准的研制提供了依据。     

Assessment of the hydrological status of Doñana dune ponds: a natural World Heritage Site under threat

ABSTRACT

The hydrological response of shallow ponds to groundwater withdrawal has been of growing concern in the Doñana National Park (southern Spain) in recent decades. This study examines the role of groundwater in maintaining the hydroperiod (i.e. the hydrological regime) in the park’s main dune ponds, by quantifying the groundwater fluxes to/from them. The hydrological characterization was performed by applying different methodologies. Daily hydrological balances registered in the ponds revealed groundwater contributions ranging from 80% of the total water inflows (i.e. groundwater discharge) to a net groundwater recharge from the ponds to the aquifer, and enabled the studied water bodies to be classified as discharge or recharge systems. The recharge systems must have been influenced by the lowering of piezometric levels due to groundwater extraction for urban supply in a nearby coastal resort.     

会宁县城镇土地分等定级的研究

文章运用定量和定性相结合的方法,对影响会宁县城镇土地质量的经济、社会、自然等各项因素进行综合分析,评定城镇等级,揭示城镇之间以及城镇内部的地域差异.根据会宁县城镇土地的自然、社会、经济属性,结合城镇土地分等规程,运用特尔菲法确定研究区域的因素因子及其权重,收集分等定级所需资料,计算了分等定级因素的综合分值,土地等级进行初步划分,最终取得会宁县城镇土地分等定级的成果,把会宁县的城镇土地分为4等,并确定会宁县城区的土地级别,可进一步摸清各镇区的基本情况,掌握各城镇之间的差异原因.     

南天山齐齐加纳克蛇绿混杂岩的SHRIMP年龄及其构造意义

齐齐加纳克蛇绿混杂岩位于中国新疆西南天山阔克萨彦岭地区,主要由辉石橄榄岩,橄榄辉石岩,橄榄玄武岩,辉长岩,辉绿岩,基性熔岩等组成。它们以一系列构造碎片近东西向产出,断续沿长约5km,宽约500m。本文应用SHRIMP方法对该蛇绿混杂岩中玄武岩中的锆石进行SHRIMP锆石U-Pb测年,获得了399±4Ma的加权平均年龄,说明该蛇绿混杂岩形成于早泥盆世。结合前人的研究成果,我们推测齐齐加纳克蛇绿混杂岩与吉根蛇绿岩残片均为中亚造山带南天山蛇绿岩带的延伸,可能代表了一个多岛窄洋盆演化的产物,为南天山洋北向俯冲及其后的塔里木微板块与哈萨克斯坦-准噶尔板块陆陆碰撞形成的最后缝合带。     

Relations quantitatives entre les craies à silex et les formations résiduelles à silex de l’ouest du bassin de Paris

Résumé

Depuis plus d’un siècle, l’origine autochtone ou allochtone des formations résiduelles à silex (en abrégé RS : résidus à silex) par rapport aux craies a fait l’objet de multiples discussions. Pour répondre à ce problème, un bilan d’altération entre ces deux formations a été effectué. Il repose sur une connaissance précise des âges des craies-mères des RS et sur des comparaisons granulométrique et chimique entre craie et RS. Ces comparaisons s’appuient sur les quantités de silex contenues dans les craies et les RS, sachant que les silex sont reconnus comme autochtones et que leur degré de dissolution est calculé. Les résultats apportent des informations sur l’évolution crétacée du Bassin anglo-parisien, avec la mise en évidence de la craie du Maastrichtien dans le bassin de Paris et la reconstitution des épaisseurs de craie dissoutes. De plus, ils indiquent que la stratigraphie des craies est conservée dans les profils de RS. Ils montrent également que les silex, éléments autochtones des RS, sont faiblement altérés. Les matrices des RS sont, quant à elles, en grande partie allochtones, notamment dans les dix mètres supérieurs de la formation. L’allochtonie diminue avec la profondeur, avec des RS pouvant être considérés comme des résidus d’altération de la craie au sens strict à partir de 20 mètres de profondeur. © Elsevier, Paris     

Ordovician backarc‐basin metadolerite and metabasalt of the South Kitakami Terrane,Northeast Japan

Basement rocks that occur along the northern margin of the South Kitakami Terrane in Japan consist of Ordovician ultramafic rocks (Hayachine ultramafic complex), gneissose amphibolite (Kuromoriyama amphibolite), and mafic rocks (Kagura igneous rocks, KIR). The KIR are composed of metagabbro, metadolerite, metabasalt, and minor felsic–intermediate dikes. Although the KIR contain green hornblende due to metamorphism of greenschist to epidote–amphibolite facies, they rarely retain primary brown hornblende. Approximately 30% of the metabasalt shows porphyritic textures, with phenocrysts of saussuritized plagioclase and/or altered mafic minerals. The geochemistry of the common metadolerite and metabasalt of the KIR shows a tholeiite trend, a low TiO₂ content, and high Th/Nb and Ti/V ratios. The KIR are therefore indicative of a supra‐subduction zone tectonic setting, which implies a backarc origin (as also indicated by discrimination diagrams). Trace element patterns of the KIR resemble those of the backarc‐basin basalt of the Japan and Yamato basins in the Japan Sea. We propose that the KIR formed during backarc spreading from the Ordovician to Early Silurian. This view is supported by the geochemical data, the tectonic setting of the Hayachine ultramafic rocks, and the provenance of clastics within Silurian sedimentary rocks.     

Late Holocene record of environmental changes,cyclones and tsunamis in a coastal lake,Mangaia, Cook Islands

A 4.3 m‐long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long‐ and short‐term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X‐Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp.), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short‐term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine‐dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis.     

Zircon U–Pb ages of plutonic rocks in the southern Abukuma Mountains: Implications for Cretaceous geotectonic evolution of the Abukuma Belt

Plutonic rocks in the southern Abukuma Mountains include gabbro and diorite, fine‐grained diorite, hornblende–biotite granodiorite (Ishikawa, Samegawa, main part of Miyamoto and Tabito, Kamikimita and Irishiken Plutons), biotite granodiorite (the main part of Hanawa Pluton and the Torisone Pluton), medium‐ to coarse‐grained biotite granodiorite and leucogranite, based on the lithologies and geological relations. Zircon U–Pb ages of gabbroic rocks are 112.4 ±1.0 Ma (hornblende gabbro, Miyamoto Pluton), 109.0 ±1.1 Ma (hornblende gabbro, the Hanawa Pluton), 102.7 ±0.8 Ma (gabbronorite, Tabito Pluton) and 101.0 ±0.6 Ma (fine‐grained diorite). As for the hornblende–biotite granodiorite, zircon U–Pb ages are 104.2 ±0.7 Ma (Ishikawa Pluton), 112.6 ±1.0 Ma (Tabito Pluton), 105.2 ±0.8 Ma (Kamikimita Pluton) and 105.3±0.8 Ma (Irishiken Pluton). Also for the medium‐ to fine‐grained biotite granodiorite, zircon U–Pb ages are 106.5±0.9 Ma (Miyamoto Pluton), 105.1 ±1.0 Ma (Hanawa Pluton) and the medium‐ to coarse‐grained biotite granodiorite has zircon U–Pb age of 104.5 ±0.8 Ma. In the case of the leucogranite, U–Pb age of zircon is 100.6 ±0.9 Ma. These data indicate that the intrusion ages of gabbroic rocks and surrounding granitic rocks ranges from 113 to 101 Ma. Furthermore, K–Ar ages of biotite and or hornblende in the same rock samples were dated. Accordingly, it is clear that these rocks cooled down rapidly to 300 °C (Ar blocking temperature of biotite for K–Ar system) after their intrusion. These chronological data suggest that the Abukuma plutonic rocks in the southern Abukuma Mountains region uplifted rapidly around 107 to 100 Ma after their intrusion.