Exploring the spatial distribution patterns of South African Cape hakes using generalised additive models

We developed delta generalised additive models (GAMs) to predict the spatial distribution of different size classes of South African hakes, Merluccius capensis and M. paradoxus, using demersal trawl survey data and geographical (latitude and longitude) and environmental features (depth, temperature, bottom dissolved oxygen and sediment type). Our approach consists of fitting, for each hake size class, two independent models, a binomial GAM and a quasi-Poisson GAM, whose predictions are then combined using the delta method. Delta GAMs were validated using an iterative cross-validation procedure, and their predictions were then employed to produce distribution maps for the southern Benguela. Delta GAM predictions confirmed existing knowledge about the spatial distribution patterns of South African hakes, and brought new insights into the factors influencing the presence/absence and abundance of these species. Our GAM approach can be used to produce distribution maps for spatially explicit ecosystem models of the southern Benguela in a rigorous and objective way. Ecosystem models are critical features of the ecosystem approach to fisheries, and distribution maps constructed using our GAM approach will enable a reliable allocation of species biomasses in spatially explicit ecosystem models, which will increase trust in the spatial overlaps and, therefore, the trophic interactions predicted by these models.     

Isotope Geochronologic and Geochemical Constraints on the Magmatic Associations of the Collisional Orogenic Zone in the West Kunlun Orogen,China

The Jiajiwaxi pluton in the southern portion of the West Kunlun Range can be divided into two collision–related intrusive rock series, i.e., a gabbro–quartz diorite–granodiorite series that formed at 224±2.0 Ma and a monzonitic granite–syenogranite series that formed at 222±2.0 Ma. The systematic analysis of zircon U-Pb geochronology and bulk geochemistry is used to discuss the magmatic origin(material source and thermal source), tectonic setting, genesis and geotectonic implications of these rocks. The results of this analysis indicate that the parent magma of the first series, representing a transition from I-type to S-type granites, formed from thermally triggered partial melting of deep crustal components in an early island–arc–type igneous complex, similar to an I-type granite, during the continental collision orogenic stage. The parent magma of the second series, corresponding to an S-type granite, formed from the partial melting of forearc accretionary wedge sediments in a subduction zone in the late Palaeozoic–Triassic. During continued collision, the second series magma was emplaced into the first series pluton along a central fault zone in the original island arc region, forming an immiscible puncture-type complex. The deep tectonothermal events associated with the continent–continent collision during the orogenic cycle are constrained by the compositions and origins of the two series. The new information provided by this paper will aid in future research into the dynamic mechanisms affecting magmatic evolution in the West Kunlun orogenic belt.     

Sequence stratigraphy of the Berriassian-Lower Aptian deposits of West Siberia

The geological structure and conditions of formation of a Lower Cretaceous clinoform complex in West Siberia are examined based on sequence stratigraphy. The regional Berriasian-Hauterivian clinoforms are interpreted as third-order sequences, and their formation should be considered in terms of the Depositional Sequence III model. Productive beds of both shallow and deep marine as well as continental genesis formed mostly in a regressive basin and belong to the highstand systems tracts.     

Geologic structure and correlation of the Berriasian-Lower Aptian productive beds of the Gydan Peninsula (Russian Arctic)

We discuss the geologic structure of the Berriasian-Lower Aptian deposits of the Gydan Peninsula. Eight seismic sequences have been distinguished; most of them are associated with Lower Cretaceous regional clinoforms of West Siberia, their characteristics are given. A correlation of productive beds was based on the stratotype sections of the Yamal and Gydan Peninsulas as well as seismic and well data. A sequence stratigraphic model of the Berriasian-Lower Aptian complex is proposed.     

A new record and a new ichnospecies of Arachnostega from the Middle Miocene of Egypt

The ichnogenus Arachnostega Bertling, 1992 is recorded for the first time from a bioeroded, coral-rich, Middle Miocene limestone bed in the middle Siwa Escarpment Member (Marmarica Formation) at Siwa Oasis, northern Western Desert of Egypt. These burrowing traces are preserved on the surface of a few internal moulds of bivalves and gastropods. Until now, the ichnogenus Arachnostega included a single ichnospecies, A. gastrochaenae Bertling, 1992. In the material studied herein, two ichnospecies are identified, described, illustrated and compared with other, similar traces. One of these is a new ichnospecies of Arachnostega; this is here named A. siwaensis ichnosp. nov. It is distinguished from A. gastrochaenae in the possession of tunnels that usually branch in a V-pattern; intervals of ramification are longest in the main branch and decrease in second- and third-order branches. Arachnostega traces were produced in a warm, low-energy, shallow-marine (<10?m water depth) environment. Polychaetes are the most likely producers of marine Arachnostega, which are commonly occurred in the same studied bed. This new occurrence is significant in extending the known stratigraphical and geographical ranges of Arachnostega into the Middle Miocene of Egypt.     

Spatial and temporal geochemical variability in lacustrine sedimentation in the East African Rift System: Evidence from the Kenya Rift and regional analyses

Many previous studies on lacustrine basins in the East African Rift System have directed their attention to climatic controls on contemporary sedimentation or climate change as part of palaeoenvironmental reconstruction. In contrast, this research focuses on the impact of tectonism and volcanism on rift deposition and develops models that help to explain their roles and relative importance. The study focuses on the spatial and temporal variability in bulk sediment geochemistry from a diverse range of modern and ancient rift sediments through an analysis of 519 samples and 50 major and trace elements. The basins examined variously include, or have contained, wetlands and/or shallow to deep, fresh to hypersaline lakes. Substantial spatial variability is documented for Holocene to modern deposits in lakes Turkana, Baringo, Bogoria, Magadi and Malawi. Mio‐Pleistocene sediments in the Central Kenya Rift and Quaternary deposits of the southern Kenya Rift illustrate temporal variability. Tectonic and volcanic controls on geochemical variability are explained in terms of: (i) primary controlling factors (faulting, subsidence, uplift, volcanism, magma evolution and antecedent lithologies and landscapes); (ii) secondary controls (bedrock types, rift shoulder and axis elevations, accommodation space, meteoric and hydrothermal fluids and mantle CO ₂); and (iii) response factors (catchment area size, orographic rains, rain shadows, vegetation densities, erosion and weathering rates, and spring/runoff ratios). The models developed have, in turn, important implications for palaeoenvironmental interpretation in other depositional basins.     

西秦岭阳山金矿带控矿因素、找矿标志及深部成矿预测

目前对西秦岭阳山金矿带勘查评价正在加速进行,为了进一步查明该矿带成矿规律和找矿潜力,指导矿田深部勘查找矿工作,武警黄金第十二支队在矿区开展了深部矿产调查和研究。文章在前人研究的基础上,通过最新的地质、地球物理勘查和室内综合研究,分析和总结了阳山金矿带主要控矿因素和找矿标志以及各因素的控矿机制。研究显示:区内的北东东向、近东西向断裂系统多沿葛条湾-草坪梁复背斜南翼层间褶皱岩层薄弱面或不同岩性接触面发育,在成矿过程中起到通道作用,限定了矿体的展布,为主要控矿因素。在明确找矿标志的基础上,以安坝矿段为研究对象,采用三维地质建模找矿信息量法进行了定量成矿预测,共圈定出深部找矿靶区4处,为矿区下一步的勘查指明了方向。     

新疆西昆仑汗铁热克一带侏罗纪沉积相与沉积环境分析

新疆西昆仑汗铁热克一带地处塔里木盆地西南缘,构造上属塔里木盆地与西昆仑造山带的结合部位,侏罗纪地层包括积莎里塔什组、康苏组、扬叶组、塔尔尕组和库孜贡苏组。根据岩性、颜色、粒度分析及沉积相标志等方法,将汗铁热克一带侏罗纪沉积环境与沉积相划分为冲积扇、扇三角洲和湖泊相,其沉积特征为侏罗纪早期快速充填,中期稳定沉降,晚期短暂的沉积间断后充填,并系统分析了研究区在整个侏罗纪沉积环境演化规律。     

滇西芦子园远程矽卡岩Pb-Zn-Fe(Cu)多金属矿床流体包裹体初探及矿床成因探讨

滇西镇康芦子园是"三江"成矿带保山地块内迄今发现的唯一超大型Pb-Zn-Fe(Cu)多金属矿床,是区内系列同类层控热液铅锌矿床的典型代表。矿体呈似层状、脉状及透镜状产于寒武系碳酸盐岩建造的矽卡岩和大理岩层间破碎带,矿石构造以条带状、浸染状和脉状-网脉状为主要特征;围岩蚀变复杂、分带明显,由下至上依次为石榴子石-透辉石-透闪石-阳起石化带→绿泥石-绿帘石-阳起石-蔷薇辉石化带→碳酸盐-大理岩化带。矿床成矿流体从早期到晚期经历了多个矿化阶段。本文选取了该矿床早矽卡岩阶段、晚矽卡岩阶段、石英硫化物阶段和石英碳酸盐阶段的多种脉石矿物及闪锌矿进行了系统的流体包裹体研究。结果显示,早矽卡岩阶段发育微溶CO_2富液相和纯液相水溶液包裹体,并含大量K~+、Na~+、Ca~(2+)、F~-和Cl~-和少量SO_4~(2-),气相成分主要为H_2O、CO_2及少量CH_4和N_2,包裹体均一温度为233.6~315.6℃,盐度为10.6%~17.6%NaCleqv;晚矽卡岩阶段发育含CO_2和子矿物三相包裹体,均一温度214.9~388.0℃,盐度5.9%~16.4%NaCleqv;石英硫化物阶段发育含CO_2的水溶液包裹体,气相成分为CH_4、H_2O和少量CO_2,均一温度150.0~285.0℃,盐度为2.5%~13.8%NaCleqv;石英碳酸盐阶段为单一成分的水溶液包裹体,均一温度为105.0~187.5℃,盐度为0.5%~12.3%NaCleqv。结合H-O同位素研究表明,成矿流体最初来源于具中高温、中高盐度、高K、Na,富CO_2、Cl、F等特征的深部岩浆热液,在石英硫化物阶段开始有大气降水混入,演化为中阶段中低温、低盐度、贫CO_2的热液流体,至成矿晚阶段转化为以大气降水占主导。该矿床成矿环境的改变、流体混合以及流体的沸腾作用可能是导致成矿物质富集沉淀的重要机制。综合矿床地质特征、成矿流体包裹体和HO同位素研究认为,该矿床为与陆陆碰撞造山和深部隐伏岩体有关的远程矽卡岩成矿系统。     

甘肃祁连山西段金矿分布特征及控矿因素分析

祁连西段是甘肃省重要的金成矿带,分布有鹰嘴山、寒山、阳凹大泉、车路沟、金湾子等金矿床,近年又新发现豹子沟南、滴水山、牛毛泉、积阴功台金矿,显示出较大的区域找矿潜力。本文通过典型金矿床和新发现金矿成矿地质条件分析,总结了甘肃祁连山西段金矿的空间分布特征、控矿因素。初步研究认为祁连山西段主要的金矿床呈带状分布于阿尔金走滑断裂与北祁连褶皱断裂构造带交汇部位,明显受不同规模、不同序次的韧、脆性断裂构造破碎带控制;成矿与区域内不同规模中酸性—中基性岩体及岩脉有关;古生代火山碎屑岩、浅变质碎屑岩为主要容矿岩性及含矿建造;矿体普遍具有延深大于延长、深部明显富集的特征。新发现金矿多以化探异常查证为重点,不断浓缩异常源,实现找矿突破。本文对祁连山西段的金矿勘查具有指导意义,对该地区的金矿研究也提供了重要的基础资料。