Geological evolution of Mount Etna volcano (Italy) from earliest products until the first central volcanism (between 500 and 100 ka ago) inferred from geochronological and stratigraphic data

We present an updated geological evolution of Mount Etna volcano based on new ⁴⁰Ar/³⁹Ar age determinations and stratigraphic data integrating the previous K/Ar ages. Volcanism began at about 500 ka ago through submarine eruptions on the Gela–Catania Foredeep basin. About 300 ka ago fissure-type eruptions occurred on the ancient alluvial plain of the Simeto River forming a lava plateau. From about 220 ka ago the eruptive activity was localised mainly along the Ionian coast where fissure-type eruptions built a shield volcano. Between 129 and 126 ka ago volcanism shifted westward toward the central portion of the present volcano (Val Calanna–Moscarello area). Furthermore, scattered effusive eruptions on the southern periphery of Etna edifice occurred until about 121 ka ago. The stabilization of the plumbing system on the Valle del Bove area is marked by the building of two small polygenic edifices, Tarderia and Rocche volcanoes. Their eruptive activity was rather coeval ending 106 and 102 ka ago, respectively. During the investigated time-span volcanism in Etna region was controlled by a main E–W extensional tectonic related to the reactivation of Malta Escarpment fault system in eastern Sicily. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

The unconformity-related palaeokarst in the uppermost Ediacaran carbonate rocks in the northwestern Tarim Block,NW China: implication for sedimentary evolution during the Ediacaran–Cambrian transition

ABSTRACT

The unconformity between the Ediacaran and Cambrian and its associated palaeokarst was well preserved within the Aksu area of the northwestern margin of the Tarim Block and provides new insights into the sedimentary evolution of the Tarim Basin during the Ediacaran–Cambrian transition. In this contribution, the typical palaeokarst features in the uppermost Ediacaran dolostones at nine outcrops in the Aksu area were documented, including palaeocaves, cave-sediment infills, solution vugs, and pores. Large-scale collapsed breccia assemblages in palaeocaves indicate that strong karstification had occurred in the south belt from the Xiaoerburak to Kule sections. Karst characterized by small-scale caves and solution vugs at the Chigebrak and Kakebashi sections suggests that the karstification in the north belt was not stronger than that in the south belt. Whereas sparse solution pores and small vugs can only be observed at the Sugetbrak and Yuermeinak sections, demonstrating that the karstification was weak in the middle belt. Combined with the thickness of sediments in the base of the Cambrian which subsequently overlay on the Ediacaran–Cambrian unconformity, it is speculated that the palaeo-upland was probably located in the middle belt from the Sugetbrak to Yuermeinak sections and the slope was developed in the south and north belts during the Ediacaran–Cambrian transition. The palaeokarst documented in the uppermost Ediacaran dolostones in the Aksu area illustrates an important sedimentary hiatus of the Tarim Block during the Ediacaran–Cambrian transition, which might be due to the sea-level fall at the end of the Ediacaran.     

西天山备战铁矿一带大哈拉军山组火山岩岩石地球化学特征与地质意义

新疆西天山备战铁矿位于阿吾拉勒铁铜成矿带,其铁矿资源丰富,成因类型复杂.对研究区大哈拉军山组火山岩样品进行主量元素、微量元素及稀土元素等测试分析认为,区内岩石化学类型属陆内拉斑玄武岩系列及钙碱性系列,与成矿关系密切.岩性主要为一套滨海相中基性火山熔岩,次为酸性火山熔岩夹少量火山碎屑岩、正常沉积岩.通过对西天山备战铁矿一带大哈拉军山组火山岩岩石地球化学特征及构造环境研究,对分析矿床成因指导找矿具重大意义.     

港西北坡西南缘沙三段油气藏勘探研究

港西北坡位于大港探区北大港潜山构造带东北翼,沙三段沉积前与其沉积时期,受断裂活动迁移性控制,发生多次构造掀斜与构造反转,沙三段遭受多期剥蚀,在其顶、底及内部存在不整合界面.不整合面对油气运移和富集有重要作用,其附近存在地层削截与地层超覆现象,在港西岛物源控制下形成地层圈闭.在港西北坡西南缘沙三段寻找地层不整合油气藏,以构造背景为基础,开展层序地层学研究,追踪有利砂体分布范围,建立油气成藏模式.     

准噶尔盆地不整合结构模式及半风化岩石的再成岩作用

由于风化剥蚀程度的不均一性及后期水进形成上覆岩石使得不整合纵向可分为三层结构:不整合面之上岩石、风化粘土层和半风化岩石。准噶尔盆地不整合面之上岩石类型主要包括底砾岩、水进砂体与煤层,它们的发育受控于构造运动强度、古气候、古地形及暴露时间,其中底砾岩分布最为广泛,而且孔渗性好,构成流体的良好运移通道。风化粘土层在上覆沉积物压实作用下岩性较致密,是一套良好的封盖层。半风化岩石类型有砂质岩类、泥质岩类和火山岩类,它们均能形成风化淋滤带,改善其孔隙结构,增大储集空间,其中火山岩岩溶作用较强,次生孔隙发育带最厚,砂质岩类次之,泥质岩类较差。     

辽河坳陷滩海月东油田新近系馆陶组底界研究

辽河坳陷南部滩海地区馆陶组底界的确定长期以来缺乏划分的依据,因靠近南部中央低凸起及其两侧的馆陶组巨厚块状砂砾岩层与下伏东营组之间发育一套厚50～100m不等的砂砾岩与砂泥岩的正粒序沉积,其时代归属有不同意见。本文首次在这套有争议的地层的岩心中发现了属新近纪的孢粉化石组合以及属于古近纪沙河街组和东营组中-下部的藻类再沉积化石,为本套地层归属新近纪馆陶组提供了可靠的生物化石对比依据。渤海湾盆地的新近系与下伏古近系间普遍为角度不整合接触,因风化侵蚀面起伏不平而馆陶组与下伏东营组的岩性变化可分为突变型、渐变型和“三明治”型3种。正确认识馆陶组底界对合理划分和对比油气层组有重要的勘探意义。     

塔里木盆地震旦系—寒武系不整合面特征及油气勘探意义

塔里木盆地震旦系—寒武系不整合面在盆地内部及周边露头区广泛发育。通过地震资料追踪及露头地质剖面研究,认为震旦系—寒武系不整合面主要有两种类型:平行不整合和角度不整合。平行不整合主要分布在库鲁克塔格、柯坪露头区及盆地北部坳陷及其以北的广大地区;角度不整合分布在中央隆起带(英东构造带—塔东低凸起—塔中低凸起—巴楚断隆)的北翼附近,自东向西地震剖面结构表现清晰。震旦系白云岩受该期不整合面影响,遭受大气淡水溶蚀作用,形成古岩溶型储层,中央隆起带北翼角度不整合分布区为震旦系白云岩古岩溶型储层的有利勘探部位。     

米苍山东河地质大剖面的构造几何学与运动学及其对上扬子北部陆内俯冲机制的约束

米苍山位于四川盆地北缘,受秦岭造山带由北向南挤压作用的影响,构造变形特征复杂,深入研究米苍山地区构造变形特征对陆内造山作用以及山前冲断带油气勘探具有积极作用。本文通过对米苍山地区的野外地质考察,对地表产状进行详细观测,建立了米苍山地区东河地表地质大剖面,并且利用等倾角区划与轴面分析,对东河剖面进行构造解析,建立了米苍山造山带构造几何学模型,通过构造楔模型分析了米苍山扇形隆升机制,通过不整合面分析,对四川盆地北部米苍山构造变形时间进行了研究。米苍山南缘基底发育4个构造楔,是影响米苍山南部地层抬升的主要原因,其顶部滑脱层为震旦系,底部滑脱层为元古界变质岩,前缘单斜带由嘉陵江-雷口坡组膏岩层作为滑脱层产生的反冲断层控制,寒武系滑脱层与震旦系滑脱层共同影响了大两会背斜的形成,而米苍山北缘则发育单个构造楔,其顶部滑脱层为震旦系,元古界变质岩为底部滑脱层; 通过对米苍山地区不整合面研究,米苍山造山带自中生代以来,至少经历了印支期与燕山期两次大规模的隆升。因此,米苍山前表现为多期次多层滑脱的构造特征。     

Stratigraphy and structure of the southeastern Garona Dome

Abstract

North-facing recumbent folds in the Palaeozoic rocks of the Garona Dome have been recognized, and a modified pre-Silurian stratigraphic sequence is suggested. The gradual disappearance of part of this sequence may be interpreted as a result of truncation by an unconformable late Ordovician conglomeratic unit.