Nano-scale pore structure and fractal dimension of organic-rich Wufeng-Longmaxi shale from Jiaoshiba area,Sichuan Basin: Investigations using FE-SEM,gas adsorption and helium pycnometry

Much attention have been recently paid to the upper Ordovician Wufeng shale (O₃w) and lower Silurian Longmaxi shale (S₁l) in the Jiaoshiba area of Sichuan Basin, which is now the largest producing shale gas field in China. Field emission scanning electron microscopy (FE-SEM), low pressure gas (N₂ and CO₂) adsorption, helium pycnometry, X-ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in O₃w-S₁l shale formation in the Jiaoshiba area. FE-SEM images show that organic matter (OM) pores are dominant in the organic-rich samples and these pores are often irregular, bubble-like, elliptical and faveolate in shape, while in organic-poor samples, limited and isolated interparticle (interP), intraparticle (intraP) and OM pores are observed. Reversed S-shaped isotherms obtained from nitrogen adsorption are type Ⅱ, and hysteresis loops indicate that the shape of micropore in the samples is slit-or plate-like. BET surface areas and total pore volume vary from 12.2 to 27.1 m²/g and from 1.8 × 10⁻² to 2.9 × 10⁻² cm³/g, with an average of 19.5 m²/g and 2.3 × 10⁻² cm³/g, respectively. Adsorption volume from both N₂ and CO₂ adsorption increases with respect to TOC contents. Porosities obtained from helium porosimetry are comparable with these from gas (CO₂ and N₂) adsorption in O₃w-S₁l shale. However, porosity determined by quantitative FE-SEM analysis is much smaller, which is mainly related to limited resolution and the small areas of investigation.Based on the Frenkel-Halsey-Hill (FHH) model of low-pressure N₂ adsorption, fractal dimensions of the pores varied from 2.737 to 2.823. Relationships between pore structure parameters and TOC content, mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores. Samples with higher TOC content, higher quartz content and lower clay content tend to contain more heterogeneous micropores, resulting in higher fractal dimensions and more complicated pore structure in shales. Therefore, fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in O₃w-S₁l shale.     

西藏拉萨地体西北部革吉地区两期早白垩世岩浆作用——锆石U-Pb年龄、Hf同位素和地球化学特征

邦巴岩体位于拉萨地块西部革吉地区,由主体花岗岩、花岗闪长岩、闪长质包体及一系列近平行、南北向展布的花岗斑岩脉体组成。野外地质调查和LA-MC-ICP-MS锆石U-Pb定年表明,革吉地区白垩纪的两期岩浆活动分别发生在131~132Ma和127Ma。早期岩浆作用形成主体花岗岩、花岗闪长岩及闪长质包体,具有以下特征:(1)明显富集K、Cs等大离子亲石元素,亏损Nb、Ti、Zr等高场强元素;(2)具有明显的负Eu异常(Eu/Eu*=0.49~0.61)及负Ce异常;(3)具负εHf(t)值(-3.2~-0.3)及古老的地壳模式年龄(1.210~1.399Ga);(4)初始Sr同位素比值为0.70424~0.71472,εHf(t)值为-5.70~-5.54。晚期岩浆作用形成花岗斑岩脉体,具有以下特征:(1)富集K、Cs等大离子亲石元素,强烈亏损Nb、Ta、Ti等高场强元素;(2)基本不具有负Eu异常或具有轻微的负Eu异常(Eu/Eu*=0.74~0.87);(3)具有更老的Hf同位素地壳模式年龄(1.226~1.576Ga)及更负的大范围变化的εHf(t)值(-6.1~-0.7)。晚期岩浆作用锆饱和温度(777~796℃)及轻稀土元素不饱和温度(794~812℃)均高于早期岩浆的锆饱和温度(661~762℃)及轻稀土元素不饱和温度(750~769℃)。上述特征表明,两期岩浆作用均为中拉萨地块古老基底部分与地幔物质混染部分熔融的产物,随着岩浆作用的持续进行,岩浆中的古老地壳组分增加,熔体温度也增加,可能与南向俯冲的班公-怒江洋壳回转驱动的地幔岩浆活动向北迁移有关。     

Provenance Study of Fe–Ti Oxide Minerals in the Quaternary Sediments in Yichang Area and Its Implication of Formation Time of the Yangtze Three Gorges, China

The Three Gorges are considered to be critical to understand the formation of Yangtze River. Recent research results suggest that the Yangtze Three Gorges was created during the Quaternary but the exact time is debatable. Fe–Ti oxide minerals are seldom used to study sediment provenance, expecially using scanning electron microscopy(SEM), and energy dispersive spectrometer(EDS). In this study, the provenance of Quaternary sediments in Yichang area, which is located to the east of the Yangtze Three Gorges, was investigated by using SEM and EDS to research Fe–Ti oxides. The Panzhihua vanadium titanomagnetite and Emeishan basalt outcrop are located to the west of the Three Gorges. Further, the materials from them are observed in the Quaternary sediments of Yichang area. Fe–Ti oxide minerals from the Huangling granite are observed in the Yunchi and Shanxiyao Formations, which were formed before 0.75 Ma B.P., whereas Fe–Ti oxide minerals from the Huangling granite, Panzhihua vanadium titanomagnetite, and Emeishan basalt are observed in the riverbed and fifth-terrace sediments of the Yangtze River, which were formed after 0.73 Ma B.P.. Thus, we can infer that the Three Gorges formed after the deposition of the Shanxi Formation and before the fifth-terrace; i.e., 0.75–0.73 Ma B.P..     

Discussion on the dextral movement and its effect in continental China and adjacent areas since Cenozoic

Continental China has moved dextral Eastward since Cenozoic time, driven by the collision of the Indian with the Eurasian plate. Evidence for this comes from landscape evolution, the distribution of earthquake epicenters, Cenozoic sedimentary and volcanic rocks, and the measurement of GPS velocity vectors, the distribution of crustal stress, paleomagnetic data, and deep mantle structure, among others. This movement commenced around 40 Ma, coupled with thickened lithosphere and widespread stress release along strike-slip faults that bound the continental Chinese block. Because of continued Northward subduction of the Indian plate, manifestation of the dextral movement has intensified since 25 Ma. Far-reaching effects include extensive strike-slip movement on the Tan-Lu fault in Eastern China, formation of the Dabie ultrahigh pressure metamorphic terrane, extensive thrust faults in East China, delamination and thickening of the lithosphere of South China, a possible tectonic doubling of the Middle-Lower Yangtze Valley metallogenic belt, and the formation of the Japan, Huanghai (East China), and South China Sea.     

扬子地台东南缘下寒武统清虚洞组风暴沉积特征及其重要意义

在扬子地台东南缘,下寒武统龙王庙阶清虚洞组主要由浅水碳酸盐岩组成。在野外露头剖面实测和室内镜下薄片观察的基础上,大量风暴沉积被发现于不同剖面清虚洞组的不同层位中,同时大量风暴诱发形成的沉积构造被识别出来,包括侵蚀基底、粗粒滞留沉积、粒序层理、平行层理、丘状交错层理(少见并且值得怀疑)以及沙纹层理,组成了多种类型的风暴沉积序列。结合更靠扬子东南缘的深水剖面中重力流沉积的缺乏,可以推断早寒武世龙王庙期扬子地台的沉积模式为碳酸盐缓坡。结合风暴的形成机制以及清虚洞组风暴沉积的发育特征(尤其是粗粒滞留砾屑的定向排列和典型丘状交错层理的缺乏),可以推断研究区风暴沉积形成于强烈的冬季风暴作用,并且早寒武世龙王庙期华南的古地理位置应当位于中纬度地区,这一结论对一些著名的全球古地理重建方案提出了质疑。同时中纬度地区大规模发育蒸发岩和碳酸盐岩还佐证了寒武纪地球处于热室(Hothouse)时期。     

基于支持向量机的喀斯特山区土壤环境质量评价——以贵州北部一茶叶园区为例

以贵州北部一茶叶园区80个表层土壤样品为研究对象,对其Hg、As、Cd、Pb、Cr和Cu含量进行测定,在MATLAB中应用支持向量机构建土壤环境质量评价模型,并与模糊综合评价法和内梅罗综合污染指数法的评价结果对比分析,探究支持向量机模型在喀斯特山区土壤环境质量评价中的适用性,其结果表明:研究区土壤质量Ⅰ类与Ⅱ类样品比例为33∶7,土壤环境质量大多数为I类;支持向量机方法的评价结果与模糊综合评价法和内梅罗综合污染指数法结果的相同率分别达到82.5%和80.0%,并分析结果有差异的样品,发现支持向量机评价结果更符合实际情况,这说明该模型适用于土壤环境质量的评价。      

1980年以来中国农地利用变化的区域差异

依托1980~2002年的中国农产品成本收益资料与中国农业统计年鉴等基础数据,从集约度、播种面积与耕地撂荒变化三个方面,对中国1980年以来农地利用变化的区域差异进行了研究。结果表明：① 西部地区农地利用的集约度具有强劲的上升态势,而东、中部地区在1992~1993年时集约度下降显著,在1997年以后,集约度具有明显的持续下降趋势;② 东部地区农地利用的总播种面积显著下降,而西部地区却有相当稳定的扩大趋势;③ 东部、中部与西部地区三种粮食作物的播种面积变化均经历了一个“三缩二扩”的变化过程：“缩小 (1980~1985)-扩大 (1985~1991)-缩小 (1991~1994)-扩大 (1994~1999)-再缩小 (1999~ 2002)”;但在变化幅度与发展态势上,三个区域之间差异明显。东部地区的播种面积有显著的下降态势,而中部与西部地区在1999年以前,其总的态势是播种面积有所扩大,此后播种面积明显下降,但其下降幅度小于东部地区;④ 中部地区耕地撂荒案例最多,涉及地域最广,东部地区次之,西部地区相对较少;东部地区的耕地撂荒现象主要出现在1992~1995年,而中部地区高度集中在1998~2002年,西部地区耕地撂荒的时间分布较为均匀,没有高度集中出现的特点。     

上海市城乡实体地域的划分

正确的城乡划分,并以此为依据统计城镇人口,是社会经济统计的重要组成部分,城乡划分方法的研究在理论和现实两方面都具有重要的意义。利用上海市2000年的航空遥感影像和人口普查地理信息系统,作了实验性的城乡实体地域划分。特别对上海市主城区、郊区青浦区、远郊金山区张堰镇三种类型的城镇实体地域,作了较详细的划分方法探讨,以此来分别模拟国内大城市、中小城市和小城镇的实体地域划分。 本文分步骤介绍了各类型城乡实体地域划分的基本过程,同时对每种类型实体地域的多种精度的结果进行比较研究,分别探讨大城市、中小城市和城镇三种类型的实体地域划分在近远期分别应达到的精度。精度合适、操作简便,是本次研究的重点,目的是为了将城镇实体地域划分工作在大范围内推广。     

干旱生态系统净初级生产力估算及变化探测

针对中国西部干旱区特有的气候-植被特征,利用卫星遥感混合像元分解技术对干旱区植被进行了光合作用植被和非光合作用植被区分和组分解析,尝试通过对干旱覆被植被灌层结构进行解析而解决因植被区系差异和环境背景干扰的问题,并参考国际上遥感-生态模型GLO-PEM和CASA,借助遥感生态反演的物理分析,初步构建起基于遥感与生态过程的干旱区适用的光能利用率模型NPP-PEM,并以中国西部干旱区喀什地区叶尔羌-喀什噶尔河流域山地-绿洲-荒漠生态系统为案例,利用AVHRR/NOAA气象卫星遥感数据和气候资料估算了1992年和1998年中国西部喀什地区叶尔羌-喀什噶尔河流域山地-绿洲-荒漠生态系统1 km分辨率年净第一性生产力,并进行了变化探测分析。模拟检验结果精度较好,生态系统碳吸收的空间异质性特征明显。结果表明,考虑了干旱植被生理特征和灌层结构的光能利用模型,模拟结果较为合理,也为引入其他生态模型应用到干旱区生态系统研究提供了借鉴,从而为干旱区陆地生态系统碳循环研究开辟了途径。     

渤海湾北部滨外沙坝演变的遥感分析

通过多时相航空遥感影像和MSS、TM、ETM卫星遥感影像的解译、对比,分析渤海湾北部滨外沙坝近50年来的演变过程。结果表明:在波浪、潮汐、潮流和河流等动力因素的作用下,滨外沙坝的动态变化较为明显,在整体西向漂移、向海侧边线蚀退的背景下,个体沙坝的变化表现为陆向蚀退、侵蚀消亡、西南向漂移与端点蚀退、西向漂移与端点延展和海向淤进与陆向蚀退交替等多种态势。