Stratigraphy of washover deposits in Florida: implications for recognition in the stratigraphic record

Twelve washover deposits were cored on the west-central Gulf Coast of Florida to provide data to permit development of a model to help identify washover facies in the stratigraphic record. Typical modern washover stratigraphy displays landward-dipping plane beds comprised of well-sorted sand with distinct laminae of shells and heavy minerals. Five subfacies are delineated which show variations in composition, texture, and bioturbation throughout the washover facies. These subfacies represent differences in flow conditions during overwash, position relative to sea level, and variable degrees of reworking after deposition. Three shell assemblages aid in identification of washover deposits. Backbarrier sediments composed of shoreface/open water species or mixed shoreface/backbarrier species may potentially be washover in origin. Sediments with purely backbarrier/quiet water shell species are likely to have been deposited independently of washover activity. Examination of washover deposits of differing ages reveals that preservation of washover stratigraphy is not exclusively a function of time. Reworking of small-scale stratification can occur in as short as a decade; however, this same stratification was found to be preserved in deposits several hundred years old. Destruction of original washover signatures is related to the position of the deposits relative to sea level, and the rate and depth of burial. Even after the destruction of small-scale stratigraphic features, washover deposits may still be identified as such due to their texture, composition, and shell assemblages. Key features in recognizing the facies after bioturbation and reworking are: (1) the presence of clean sand in otherwise muddy backbarrier sediments, (2) the landward thinning of the facies, and (3) the presence of shoreface shells or mixed shoreface/backbarrier shells on landward portions of the barrier island system. If reworking is severe and/or there are limited subsurface data, distinguishing washovers from genetically similar deposits (e.g. flood tidal deltas and spillover deposits) in the stratigraphic record is difficult and when considered out of stratigraphic context may not be recognizable.     

A Metamorphic Core Complex Model for the Host of Uranium Mineralization in the Khoshoumi Mountain,Central Iran

A metamorphic core complex model is proposed for Khoshoumi Mountain uranium mineralization located in the Bafq–Saghand metallogenic zone of central Iran. Uranium mineralization occurred in the Chapedoni metamorphic complex. Detailed structural analysis of the complex leads to the interpretation that the mineralization is spatially concentrated in a low angle shear zone of mylonitized migmatite, the lower ductile part of the Chapedoni metamorphic complex. The shear zone that has top to the NE sense of shear in the northeastern and southeastern parts of the mountain and top to the WNW sense of shear in the southwestern part is a detachment zone to the Chapedoni Metamorphic Core Complex (CMCC). The Eocene granite is the plutonic core to the CMCC. The shear zone is cut by several NE‐trending left‐lateral strike‐slip faults. This later faulting is interpreted to account for the significant enrichment of uranium in the southern part of the mountain. The bimodal distribution of radiometric data gathered from exploratory drill holes in this part of the mountain constrains this interpretation. That is, the lower value is from the shear zone across the area but the higher value is from the places that the shear zone is cut by the transverse faults.     

黑色页岩容矿型Ni-Co矿床: 研究进展与展望

Ni和Co都是重要的战略性矿产资源, 其中黑色页岩容矿型Ni-Co矿床是沉积岩容矿型Ni-Co矿床的重要组成部分, 具有非常重要的工业价值和科学研究意义。本文按照形成时代的先后顺序综述了芬兰Talvivaara组、英国Gwna群、中国华南牛蹄塘组、瑞典Alum Shale组、加拿大Canol组以及中欧Kupferschiefer组等全球范围内几个重要黑色页岩层位赋存的Ni-Co矿床。这些矿床的矿石具有纹层状构造、多金属共生富集、富有机质和硫等共同特征。矿床中多金属的初始来源可能为陆源风化的产物或者海底热液, 而导致溶解于海水中的金属发生沉淀的机制则是极端条件下海洋环境的变化。Ni-Co的共生分异受到同沉积期海水氧化还原环境和后期改造过程的共同控制。全球范围内几个重要的含Ni-Co黑色页岩层位均发育在第一次全球大氧化事件、新元古代大氧化事件和显生宙的地球表生环境突变期, 显示了地球表生环境对该类型矿床的形成具有控制作用。此外, 后期改造过程则有利于金属的进一步富集形成工业矿体。前人针对黑色页岩容矿型Ni-Co矿床的研究极大的推动了人们对这类矿床的认识, 然而, 对这类矿床中Ni-Co共生-分异机制、同沉积过程中多金属的共生关系以及后期改造过程仍需要更深入的探索。以现代分析技术为手段, 开展成矿学、沉积学、地质生物学、地球化学等多学科交叉研究, 将有助于深入理解黑色页岩容矿型Ni-Co矿床的成矿过程以及与地球多圈层协同演化(尤其是表生环境演化)的关系, 从而推动黑色页岩容矿型Ni-Co矿床成矿理论的发展。

     

Non-linear methods for event location in a global context

Directed search methods in four-dimensional hypocentre space do not require the differentiation of travel times and are particularly suitable for the use of information from multiple seismic phases including joint use of primary and depth phases (e.g. pP) for a reference model such as a k135. These approaches can be used with a wide range of measures of misfit between observed and estimated times. A very effective method of this class is the use of the neighbourhood algorithm that allows all previous hypocentre estimates to be employed to estimate the shape of the misfit surface. When used with a robust measure of misfit such as the sum of the absolute values of the residuals (L1 norm), the neighbourhood algorithm provides rapid convergence, and a measure of the uncertainty in the hypocentral estimate from the concentration of the points with low misfit in four-space. Such a procedure is well suited to the first pass analysis of observations since it is not distracted by occasional readings associated with other events. Phase association can then be improved and a more conventional procedure used to provide error ellipsoids around a well-defined depth.     

Petrogenesis and tectonic implications of early Palaeozoic igneous rocks of the western South Qilian Belt,central China

Early Palaeozoic granitoids in the South Qilian Belt, central China, record details of the tectonic evolution and crustal growth of the Qilian orogenic belt. Five representative granitoids from the western South Qilian Belt were sampled for zircon LA-ICPMS U–Pb dating, Lu–Hf isotopes, and whole-rock geochemical analyses. Zircon U–Pb dating of two porphyritic granodiorites and a porphyritic monzogranite yielded ages of 442.7 ± 3.5, 441.8 ± 4.3, and 435.4 ± 3.5 Ma, respectively. These granitoids exhibit a geochemical affinity to I-type granite, are metaluminous with a low aluminium saturation index (A/CNK = 0.75–1.15), have moderate Al₂O₃ and low MgO contents, high La/Yb and low Sr/Y ratios, and are depleted in Nb, Ta, P, and Ti, which suggests a subduction zone magmatic arc affinity, with mixing between a primary mantle-derived magma with lesser continental crustal material. The syenogranite and monzogranite from the South Qilian Belt, which yield U–Pb zircon ages of 440.4 ± 9.0 and 442.3 ± 1.2 Ma, respectively, have pronounced S-type geochemical affinities, are peraluminous with A/CNK values of 1.07–1.16, have relatively high SiO₂, Al₂O₃, K₂O, and Rb contents, low Y and Yb, low Sr/Y and La/Yb ratios, positive Th, U, and light Rare Earth Element (REE) anomalies, and depletions in Nb, Ta, Sr, and Ti. Their geochemical signature suggests derivation from partial melting of continental crust in a syn-collisional setting. The Hf isotopic data of zircons from the granitoids show a significant input of Paleoproterozoic crust in the crustal formation of the western South Qilian Belt in Palaeozoic. Compare the ε_Hf(t) value of S-type granite with that of I-type granite, the former may have a comparatively homogeneous source. Together with regional evidence, it is proposed that a collisional event occurred between the South Qilian Belt and the Central Qilian Belt at ca. 442–435 Ma.     

西双版纳国防铁矿控矿条件及矿体分布规律

铁矿体赋存于中元古界大勐龙群疆峰旋回第二、四段。含矿岩石为变中基性熔岩、角闪(阳起)斜长变粒岩、透辉钠长(斜长)变粒岩,分为上(Ⅰ)和下(Ⅱ)矿层。上矿层不稳定,下矿层由4个矿体组成复式矿。铁质就地运移、聚集、变质,典型的受变质火山汽液磁铁矿床。     

Variable character and diverse origin of hybrid event beds in a sandy submarine fan system,Pennsylvanian Ross Sandstone Formation,western Ireland

Hybrid event beds comprising both clean and mud‐rich sandstone are important components of many deep‐water systems and reflect the passage of turbulent sediment gravity flows with zones of clay‐damped or suppressed turbulence. ‘Behind‐outcrop’ cores from the Pennsylvanian deep‐water Ross Sandstone Formation reveal hybrid event beds with a wide range of expression in terms of relative abundance, character and inferred origin. Muddy hybrid event beds first appear in the underlying Clare Shale Formation where they are interpreted as the distal run‐out of the wakes to flows which deposited most of their sand up‐dip before transforming to fluid mud. These are overlain by unusually thick (up to 4·4 m), coarse sandy hybrid event beds (89% of the lowermost Ross Formation by thickness) that record deposition from outsized flows in which transformations were driven by both substrate entrainment in the body of the flow and clay fractionation in the wake. A switch to dominantly fine‐grained sand was accompanied initially by the arrest of turbulence‐damped, mud‐rich flows with evidence for transitional flow conditions and thick fluid mud caps. The mid and upper Ross Formation contain metre‐scale bed sets of hybrid event beds (21 to 14%, respectively) in (i) upward‐sandying bed set associations immediately beneath amalgamated sheet or channel elements; (ii) stacked thick‐bedded and thin‐bedded hybrid event bed‐dominated bed sets; (iii) associations of hybrid event bed‐dominated bed sets alternating with conventional turbidites; and (iv) rare outsized hybrid event beds. Hybrid event bed dominance in the lower Ross Formation may reflect significant initial disequilibrium, a bias towards large‐volume flows in distal sectors of the basin, extensive mud‐draped slopes and greater drop heights promoting erosion. Higher in the formation, hybrid event beds record local perturbations related to channel switching, lobe relocations and extension of channels across the fan surface. The Ross Sandstone Formation confirms that hybrid event beds can form in a variety of ways, even in the same system, and that different flow transformation mechanisms may operate even during the passage of a single flow.     

宁镇及宜溧地区全新世中晚期典型沉积相与5 700 a B.P.前后的气候突变事件

分析宁镇及宜溧地区中晚全新世典型剖面的地层划分与特征,采用R-Q型因子分析方法估算气候变化值,揭示5700a B.P.前后发生在本区的干燥降温异常气候突变事件。气候曲线与沉积相序列的对比分析表明,宝华山浅棕黄色砂土夹角砾层洪-坡积相是该突变事件背景下的产物,且该突变事件还具有全球变化区域响应的征候,林峰桥同期淤泥质层中Fe³⁺/Fe²⁺比和粘土百分含量异常值进一步印证了这一论断。     

面向新浪微博签到数据的时空热点事件检测方法

传统面向文本数据的事件检测方法在处理以微博为代表的社交媒体数据时面临着效率和准确性的挑战。同时,社交媒体数据中富含的位置信息常常不能被有效地识别和利用,这无疑会影响到事件检测的效果。本文基于对已有研究的总结归纳,定义了一类面向微博签到数据的时空热点事件,并提出了一种新的微博时空热点事件检测方法对其进行识别。通过两组实际数据的实验,证明该方法能够有效地从海量的微博数据中挖掘出具有时空特征的热点事件。