Dryland continental mudstones: Deciphering environmental changes in problematic mudstones from the Upper Triassic (Carnian to Norian) Mercia Mudstone Group,south‐west Britain     

Paul Milroy  V. Paul Wright  Michael J. Simms 《Sedimentology》2019,66(7):2557-2589

The sedimentology, petrography and mineralogy of the seemingly monotonous Late Triassic Mercia Mudstone Group across the Severn Basin and Bristol Channel region reveals a bipartite division of mudrock facies above and below the Arden Sandstone Formation. Frequently cryptic sedimentary and pedogenic features reveal diverse alluvial, aeolian, playa‐lacustrine and pedogenic processes operating at different times, locations and scales probably in response to climate change. The current study found no evidence of significant marine influence in either of the two mudrock facies associations that are described here. Blocky claystones dominate the lower Mercia Mudstone Group (Sidmouth Mudstone Formation), with pedogenic features such as slickensides, mottling, tubules and carbonate/sulphate nodules common and widespread. The claystones are of alluvial/lacustrine origin with subordinate sheet sandstones, themselves overprinted by pedogenic features, reflecting occasional high intensity rainfall events. These facies reflect a seasonal (wet/dry) semi‐arid climate favouring development of transformed/neoformed (smectite‐rich) clay minerals of intrabasinal origin. Massive to weakly stratified silty mudstones dominate the upper Mercia Mudstone Group (Branscombe Mudstone Formation). Commonly conchoidally weathered, locally gypsiferous, but with distinct sedimentary structures scarce, they alternate with subordinate blue‐grey laminated silty mudstones. Together they reflect fluctuating hydrological conditions within extensive saline mudflats and ephemeral playa lakes, with laminated facies deposited under subaqueous conditions during more humid phases whereas massive mudstones reflect modification through interstitial growth/dissolution of sulphates and deflation of surface sediments during drier episodes. These facies reflect increased aridity during deposition of the upper Mercia Mudstone Group compared with the lower Mercia Mudstone Group, favouring development of detrital/transformed (illite–chlorite) clay minerals of extrabasinal origin. The described facies associations and the sedimentary fabrics and structures that characterize them, occur widely in the Mercia Mudstone Group across the United Kingdom and comparable facies associations may be anticipated in other fine‐grained red bed successions. Recognition of these facies may aid palaeoenvironmental interpretation of such sequences on Earth and, potentially, on Mars also.  相似文献   

基于激光U-Pb定年的埋藏白云岩形成过程——以塔里木盆地永安坝剖面下奥陶统蓬莱坝组为例     

乔占峰  张哨楠  沈安江  胡安平  梁峰  罗宪婴  佘敏  吕学菊 《岩石学报》2020,36(11):3493-3509

埋藏白云石化作用是形成厚层块状白云岩的主要机制之一,但其形成过程一直存在争议。本文以塔里木盆地永安坝剖面蓬莱坝组为例进行解剖,在露头和薄片岩石学研究的基础上,利用激光U-Pb定年和同位素分析,剖析了蓬莱坝组白云岩形成时期及演化过程,取得三个方面的认识：（1）蓬莱坝组发育四种类型白云岩：藻纹层白云岩、自形-半自形细中晶白云岩、雾心亮边自形中晶白云岩和他形粗晶白云岩,不同类型白云岩垂向互层发育;（2）U-Pb定年结果显示蓬莱坝组受三期云化作用改造,分别为准同生期云化作用、晚奥陶世到志留纪浅埋藏云化作用（464±12Ma到433±22Ma）及泥盆纪埋藏云化作用（382±29Ma）,浅埋藏云化作用会对准同生白云石造成重结晶,而埋藏云化作用表现为白云石次生加大,存在寒武系云化流体卷入,影响U-Pb定年;（3）规模白云岩的发育为沉积环境和构造埋藏演化史共同作用的结果,提出塔中北斜坡和塔北南缘为规模白云岩发育区,这对本区油气勘探具有重要的指导意义。  相似文献   

Gold in the Brunswick No. 12 volcanogenic massive sulfide deposit,Bathurst Mining Camp,Canada: Evidence from bulk ore analysis and laser ablation ICP─MS data on sulfide phases     

Sean H. McClenaghan  David R. Lentz  Jillian Martin  Wilfredo G. Diegor 《Mineralium Deposita》2009,44(5):523-557

The 329-Mt Brunswick No. 12 volcanogenic massive sulfide deposit (total resource of 163 Mt at 10.4% Zn, 4.2% Pb, 0.34% Cu, and 115 g/t Ag) is hosted within a Middle Ordovician bimodal volcanic and sedimentary sequence. Massive sulfides are for the most part syngenetic, and the bulk of the sulfide ore occurs as a Zn–Pb-rich banded sulfide facies that forms an intimate relationship with a laterally extensive Algoma-type iron formation and defines the Brunswick Horizon. Zone refining of stratiform sulfides is considered to have resulted in the development of a large replacement-style Cu-rich basal sulfide facies, which is generally confined between the banded sulfide facies and an underlying stringer sulfide zone. Complex polyphase deformation and associated lower- to upper-greenschist facies regional metamorphism is responsible for the present geometry of the deposit. Textural modification has resulted in a general increase in grain size through the development of pyrite and arsenopyrite porphyroblasts, which tend to overprint primary mineral assemblages. Despite the heterogeneous ductile deformation, primary features have locally been preserved, such as fine-grained colloform pyrite and base and precious metal zonation within the Main Zone. Base metal and trace element abundances in massive sulfides from the Brunswick No. 12 deposit indicate two distinct geochemical associations. The basal sulfide facies, characterized by a proximal high-temperature hydrothermal signature (Cu–Co–Bi–Se), contains generally low Au contents averaging 0.39 ppm (n = 34). Conversely, Au is enriched in the banded sulfide facies, averaging 1.1 ppm Au (n = 21), and is associated with an exhalative suite of elements (Zn–Pb–As–Sb–Ag–Sn). Finely laminated sulfide lenses hosted by iron formation at the north end of the Main Zone are further enriched in Au, averaging 1.7 ppm (n = 41) and ranging up to 8.2 ppm. Laser ablation inductively coupled plasma-mass spectrometry (ICP-MS) analyses of pyrite (n = 97) from the north end of the Main Zone average 2.6 ppm Au and range from the detection limit (0.015 ppm) to 21 ppm. Overall, these analyses reveal a distinct Au–Sb–As–Ag–Hg–Mn association within pyrite grains. Gold is strongly enriched in large pseudo-primary masses of pyrite that exhibit relict banding and fine-grained cores; smaller euhedral pyrite porphyroblasts, and euhedral rims of metamorphic origin surrounding the pyrite masses, contain much less Au, Sb, Ag, As, and Sn. Arsenopyrite, occurring chiefly as late porphyroblasts, contains less Au, averaging 1.0 ppm and ranging from the detection limit (0.027 ppm) to 6.9 ppm. Depth profiles for single-spot laser ablation ICP-MS analyses of pyrite and arsenopyrite display uniform values of Au and an absence of discrete microscopic inclusions of Au-bearing minerals, which is consistent with chemically bonded Au in the sulfide structure. The pervasive correlation of Au with Sn in the Zn–Pb-rich banded sulfide facies suggests similar hydrothermal behavior during the waxing stages of deposition on the seafloor. Under high temperature (>350oC) and moderate- to low-pH conditions, Au and Sn in hydrothermal fluids would be transported as chlorocomplexes. An abrupt decrease in temperature and aH₂S, accompanied by an increase in fO₂ and pH during mixing with seawater, would lead to the simultaneous destabilization of both Au and Sn chlorocomplexes. The enrichment of Au in fine-grained laminated sulfides on the periphery of the deposit, accompanied by sporadic occurrences of barite and Fe-poor sphalerite, supports lower hydrothermal fluid temperatures analogous to white smoker activity on the flanks of a large volcanogenic massive sulfide system. In lower temperature (<350oC) and mildly acidic hydrothermal fluids, Au would be transported by thiocomplexes, which exhibit multifunctional (retrograde–prograde) solubility and a capacity to mobilize Au to the outer parts of the sulfide mound. The sluggish nature of this low-temperature venting together with larger variations in ambient fO₂ could lead to a sharp enrichment of Au towards the stratigraphic hanging wall of massive sulfide deposits. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Hazard assessment and runout analysis for an unstable rock slope above an industrial site in the Riviera valley, Switzerland   总被引：2，自引：1，他引：1  

Heike Willenberg  Erik Eberhardt  Simon Loew  Scott McDougall  Oldrich Hungr 《Landslides》2009,6(2):111-119

This paper presents a detailed field investigation and hazard assessment for an unstable rock slope above an industrial site in the Riviera valley in the Canton of Ticino in southern Switzerland. An integrated framework was used to counter issues of geological complexity and uncertainty, linking geological mapping and numerical modeling to develop an understanding of the acting instability mechanism to 2-D and 3-D dynamic runout simulations to predict the travel path and reach in the event of a large volume rockslide. The results from the numerical stability analysis provided a means to constrain failure volume estimates, whereas a series of calibration simulations were used to constrain the input parameters required by the rheological model used for the runout analysis. Results from this assessment suggest that current protection measures in place may not be sufficient, helping local authorities to define hazard zones and aid further development plans for the region.  相似文献   

短期大规模人口流动对上海市城市热岛效应的影响   总被引：1，自引：0，他引：1  

黄群芳  陆玉麒 《气候与环境研究》2017,22(6):708-716

城市热岛效应是一种非常重要的局地气候现象,随着全球变暖和城市化快速发展,城市热岛效应受到越来越多的关注和研究。以往的研究表明人口聚集和人口数量对城市热岛效应和区域城市气候会产生显著的影响。但是,人口短期的快速迁移流动对城市气候是否存在影响以及影响的程度多大尚不清楚。本文利用世界上每年最大规模的人类迁徙——春节人口流动来探讨人口短期快速流动对国际化大都市上海城市热岛效应的影响。研究结果表明,2000~2015年上海市春节周日最高温、日均温和日最低温城市热岛强度分别为0.35℃、0.90℃和1.53℃,相对于背景场(春节前2~4周和春节后2~4周的平均值),分别低了0.16℃、0.11℃和0.15℃,相对变化分别为31.4%、10.9%和8.9%。由此可见,人口短期快速迁移流动是影响热岛效应和城市气候一个重要因素,但是人口流动对城市热岛效应的影响是复杂的,其效应与气候背景、天气状况、城市规模、城市人口流动特征及分布甚至城市烟花爆竹燃放(通过影响气溶胶、云量及废热影响城市热岛效应)等因素交织在一起,未来仍需开展进一步的深入研究。  相似文献   

Mineral assemblages of the Francisco I. Madero Zn–Cu–Pb–(Ag) deposit, Zacatecas, Mexico: Implications for ore deposit genesis     

Carles Canet  Antoni Camprubí  Eduardo Gonzlez-Partida  Carlos Linares  Pura Alfonso  Fernando Pieiro-Fernndez  Rosa María Prol-Ledesma 《Ore Geology Reviews》2009,35(3-4):423-435

The Francisco I. Madero deposit, central Mexico, occurs in the Mesozoic Guerrero Terrane, which hosts many ore deposits, both Cretaceous (volcanogenic massive sulfides) and Tertiary (epithermal and skarn deposits). It is hosted by a 600 m-thick calcareous-pelitic unit, of Lower Cretaceous age, crosscut by porphyritic dikes that strike NW–SE. A thick felsic volcanic Tertiary sequence, consisting of andesites and rhyolitic ignimbrites, unconformably overlies the Cretaceous series. At the base, the mineralization consists of several mantos developed within calcareous beds. They are dominantly composed of sphalerite, pyrrhotite and pyrite with minor chalcopyrite, arsenopyrite and galena. At the top of the orebody, there are calcic skarns formed through prograde and retrograde stages. The resulting mineral assemblages are rich in manganoan hedenbergite (Hd_75–28Di_40–4Jh_40–20), andraditic garnets (Adr_100–62Grs_38–0), epidote (Ep_95–36Czo_60–5Pie_8–0), chamosite, calcite and quartz. The temperature of ore deposition, estimated by chlorite and arsenopyrite geothermometry, ranges from 243° to 277 °C and from 300° to 340 °C, respectively. The pressure estimated from sphalerite geobarometry averages 2.1 kbar. This value corresponds to a moderately deep skarn and agrees with the high Cu content of the deposit. Paragenesis, P–T conditions and geological characteristics are compatible with a distal, dike-related, Zn skarn deposit. Its style of mineralization is similar to that of many high-temperature carbonate replacement skarn deposits in the Southern Cordillera.  相似文献   

五台山新太古代块状硫化物矿床成矿作用研究——海底喷流沉积成因显微构造证据     

牛向龙  李江海  冯军 《地球科学进展》2009,24(9):1009-1014

在五台山金岗库新太古代块状硫化物矿床发现了一些多孔状黄铁矿石标本,经过详细的显微构造鉴别和相关的电子探针分析,发现其中保留的一些特征性显微结构(胶状结构、通道构造、分带构造及淬火构造等)与现代海底硫化物黑烟囱结构构造非常类似,初步得出这些标本为新太古代海底黑烟囱的残片,显示了该矿床黑烟囱模式的海底喷流成因机制。  相似文献   

红太平多金属矿床地质特征及区域找矿意义   总被引：1，自引：0，他引：1  

宋群 《吉林地质》1991,10(4):22-28

红太平多金属矿床产于延边古生代地槽区二叠系海相火山岩中及其与碎屑沉积岩的过渡带上。矿体呈层状,矿石具典型的沉积构造,矿石硫同位素组成与国内变质火山岩铜矿床相似,气液包裹体氢氧同位素组成介于大气循环水和变质水之间。因此,初步认为矿床属与火山热液或热泉活动有关的块状硫化物型矿床。  相似文献   

基于NGAS的多点观测数据存储与同步方法     

石聪明  邓辉  戴伟  卫守林  王锋 《天文研究与技术》2019,(2):204-210

平方千米阵列(Square Kilometre Array, SKA)望远镜建成后将具有超高的灵敏度、超快的巡天速度以及宽视场,进而产生超海量的观测数据。SKA天文台与各国区域数据中心间的海量数据同步传输是当前SKA建设中的一个难点。SKA先导项目使用的下一代归档存储系统(Next Generation Archive System, NGAS)在应用测试中存在效率低下,性能不足等问题。提出了一种基于ZeroMQ的数据存储与同步方法,通过采用更加高效的异步消息机制实现同步传输数据,回避了NGAS原有的采用HTTP协议的局限。实验结果表明,新方法在平均数据归档存储效率方面比原有方法快了近40倍,能够基本满足10 GB带宽的全速传输需要,取得了较好的使用效果。  相似文献   

用中子星限制暗物质粒子散射截面          下载免费PDF全文

王弋尘  缪雪丽  邵立晶 《天文学报》2021,62(5):54

中子星可以通过重子物质和暗物质的相互作用吸积暗物质,且在一定条件下, 中子星吸积的暗物质粒子可以引发自引力塌缩形成小型黑洞, 生成的黑洞可能会进一步吞噬中子星.依据文献已有模型, 基于以上物理过程给出了在暗物质粒子不同质量下对暗物质粒子--中子的散射截面的限制.使用弱相互作用大质量粒子(Weakly Interacting Massive Particle, WIMP)模型, 并考虑暗物质粒子是玻色子的情形, 讨论了暗物质粒子有无自相互作用以及有无湮灭等条件下对限制暗物质参数的影响.既考虑了已发现的两个中子星系统来给出对暗物质参数空间的限制,也考虑了两个可能存在的年老中子星来预测未来观测可能对暗物质参数空间的限制.对于考虑玻色--爱因斯坦凝聚(Bose-Einstein Condensate, BEC)的玻色子暗物质, 在无自相互作用或有弱自相互作用, 无湮灭或有很小湮灭截面的条件下,中子星给出的间接观测对暗物质粒子-中子散射截面的限制的强度比XENON1T直接探测实验来得更强.未来, 如果在银心附近能观测到年老中子星, 其观测结果可以提升模型给出的对暗物质粒子--中子散射截面的限制, 从而帮助人们进一步理解暗物质.  相似文献