Transgressive Eocene clastic–carbonate sediments from the Circum‐Rhodope belt,northeastern Greece: implications for a rocky shore palaeoenvironment

Locally exposed Middle to Upper Eocene conglomerates in the western part of the Cenozoic Thrace Basin are interpreted as products of continuous marine erosion of a rocky coast (consisting of Lower Cretaceous carbonates) and subsequent redeposition of the land‐derived limestone material in a wave‐dominated nearshore setting during a prolonged transgression. Contemporaneous biological activity in the warm‐temperate marine environment contributed to the accumulation of mixed coarse‐grained clastic–carbonate sediments on the upper shoreface. The formation of a relatively thick sedimentary succession was favoured by the interplay of several controlling factors as only shoreface deposits were preserved in the rock record. The results may help to elucidate the evolution of the hydrocarbon‐bearing Thrace Basin and to assist with the regional correlation of its basal deposits. Copyright © 2014 John Wiley & Sons, Ltd.     

Evolution of Cretaceous–Cenozoic quartz pebble conglomerate gold placers during basin formation and inversion, southern New Zealand

Numerous auriferous fluvial quartz pebble conglomerates (QPCs) are present within the Late Cretaceous–Recent sedimentary sequence in southern New Zealand. The QPCs formed in low-relief settings before, during, and after regional marine transgression, in alluvial fan and a variety of fluvial and near-shore depositional settings: In particular, during slow thermal subsidence associated with Late Cretaceous–early Cenozoic rifting, and during the early stages of orogenic uplift following mid Cenozoic marine regression. QPC maturity characteristics are complex and vary with sediment transport and recycling history, stratigraphic proximity to the transgressive Waipounamu Erosion Surface, and the amount of first-cycle detritus incorporated during recycling. For pre-marine QPCs, the amount of first cycle detritus varies with tectonic intensity and proximity of the depositional setting to remnant Cretaceous topography. For post-marine QPCs, it varies with tectonic intensity and proximity to Late Cenozoic uplift of basement ranges.QPCs do not form during a single bedrock erosion–sediment deposition cycle: Non-oxidised and/or oxidized groundwater alteration (kaolinisation) of labile minerals in immature sediment and the upper part of underlying basement, and repeated sedimentary recycling, are fundamental processes of QPC formation regardless of the tectonic or sedimentary settings. Altered immature rock disaggregates easily upon erosion, and alteration clays are winnowed to leave quartz-rich residues containing resistant heavy minerals such as zircon and gold. Detrital sulfide survives recycling if deposition and burial in saturated sediments are rapid. QPCs result only if sediment recycling is not accompanied by excessive erosion of fresh basement rock. Uplift of many parts of the Otago Schist belt since late Miocene has raised rocks above the water table, increased erosion rates, and inhibited groundwater alteration and QPC formation. QPC formation is still occurring in Southland, where the water table is high, sediments are saturated and undergoing alteration, and uplift and erosion rates, topography, and fluvial gradients are all low. The QPCs accumulate as residual gravel on the valley floors of low-competence streams that are slowly incising pervasively altered dominantly late Miocene–Pliocene immature conglomerates.QPCs formation essentially represents physical and chemical lagging of precursor strata. Accumulation of detrital gold and other heavy minerals is an inevitable consequence, and most QPCs contain some gold. Three types of significant gold placer have developed in the QPCs. Type 1 placers are essentially eluvial and/or colluvial in origin and form without significant fluvial transport, by residual accumulation in low-competence valleys during low-rate uplift, fluvial incision and QPC formation. Type 2 placers have formed during significant fluvial transport and subsequent fluvial incision, mainly in higher energy proximal and medial reaches of larger pre-marine (Eocene) and post-marine fluvial systems. Type 3 placers formed by wave-base and marine current winnowing in the shallow shelf setting during low-rate regional marine transgression, especially in the Eocene.     

砾岩隧洞的长期稳定性分析

本文首先研究某工程泥质砾岩扰动样的流变、渗透和浸水软化特性，然后，简要介绍泥质砾岩隧洞的施工方法和支护形式并根据材料特性，模拟施工过程，湿化饱和过程和钢筋混凝土瓦片形衬砌的结构形式，分析了围岩和衬砌的应力及变形，探讨了浸水软化对围岩长期稳定性的影响和失稳机制。     

砾质辫状河型冲积扇岩相类型、成因及分布规律 ——以准噶尔盆地西北缘现代白杨河冲积扇为例

冲积扇砂砾岩储层是准噶尔盆地一类重要的油气储层类型,由于其具岩相类型多、连续性差等特点,对冲积扇内部岩相成因解释一直是冲积扇相带认知的基础和难点。以准噶尔盆地西北缘现代白杨河冲积扇为例,在大量的野外露头资料和粒度分析数据的基础上,结合冲积扇源区母岩类型、水文资料以及冲积扇文献资料,对现代白杨河冲积扇岩相的类型、成因及分布规律进行探讨。按沉积机制,白杨河冲积扇属于辫状河型冲积扇,具有规模大(扇体总面积约327.6 km^2),坡度平缓(约1‰～7‰),沉积粒度粗等特征。在白杨河冲积扇内共可识别出16种岩相类型,并根据岩相形成的流体动力差异划归为5类成因,即重力流成因、高流态牵引流成因、低流态牵引流成因、静水沉积成因以及风成沉积成因。重力流以洪流沉积为主;高流态牵引流主要包括片流沉积和湍流沉积;低流态牵引流以砂(砾)质河道沉积为主;静水沉积以蓄水细粒沉积为主;风成沉积以风携细粒沉积为主。根据各岩相沉积构造、粒度特征及展布规模,可将岩相划分为四类:Ⅰ类岩相沉积构造特征明显并具有较大展布规模;Ⅱ类岩相沉积构造特征明显但展布规模局限;Ⅲ类岩相为不具层理构造但具有较大展布规模的岩相;Ⅳ类岩相不具层理构造并且展布规模局限。其中Ⅰ类和Ⅱ类岩相多为牵引流成因,多发育于洪水期扇体扇中、扇缘区域以及间洪期扇体的扇中区域,并可在地下继承性发育为较好的储集相带。     

砂砾岩储集体成岩差异性分析 ——以玛北斜坡带三叠系百口泉组为例

凭借着高产油气流,玛湖凹陷北斜坡带百口泉组砂砾岩储层成为近年来颇受储层沉积学家们关注的热点区域。层段内砂砾岩储层储集物性表现出明显的差异性,其控制机理一直尚未明确。本文按照流体成因差异,将层段内岩石相划分为4 种类型：牵引流成因的砂砾岩相、含砾砂岩相、砂岩相,以及重力流成因的砂砾岩相。在不断埋深过程中,重力流砂砾岩相的压实进程远远早于且明显强于牵引流砂砾岩相。而随后持续深埋过程中,重力流砂砾岩相孔隙度不再明显降低,渗透率却呈现明显增加,表明重力流砂砾岩相内的微裂缝开始发育。上述压实效应的差异造成了在储集空间上,牵引流砂砾岩相以原生粒间孔为主要类型,而重力流砂砾岩相则以粒内溶孔和微裂缝为主要类型。最终在宏观储集物性上,牵引流砂砾岩相储集性能明显优于重力流砂砾岩相,成为研究层段内有效的储集体。     

北京“洼里砾岩”的成因及时代探讨

关于北京“洼里砾岩”成因的争议由来已久,主要有构造成因和沉积成因两种不同的观点。在以往资料的基础上,结合近年来新的地热钻井资料,绘制了地质剖面图,进行了地层比对与构造分析,发现剖面中存在数条、多期、规模不一的逆断层,存在相互切割,这使得地层受到较大扰动,体现出八宝山断裂的逆冲作用非常强烈,且具有多期性;并在构造分析的基础上,结合砾岩的成分、结构、岩溶发育及出现层位等岩性特征,以及北京凹陷的形成过程,分析了其形成机制,提出“洼里砾岩”属于八宝山断裂带断层角砾岩雾迷山组内的部分,形成时代大约是在中生代中晚期。      

甘肃北山中泥盆统砾岩中放射虫的发现及其地质意义

笔者于甘肃北山地区墩墩山一带中泥盆统三个井群砾岩内的硅质岩砾石中发现放射虫,经鉴定主要为空滴虫类(Inaniguttids),有两个属:Inanigutta sp.(空滴虫)和Inanibigutta sp.(双壳空滴虫).这两个属在世界上主要见于奥陶—志留纪,我国华北地区主要产在奥陶纪.表明北山于泥盆纪碰撞造山时,墩墩山之北被抬升成山系,奥陶系含放射虫的硅质岩被剥蚀后向南搬运到墩墩山山前磨拉石盆地中沉积下来.结合区域地质特征,放射虫的发现为北山地区泥盆纪碰撞造山作用和磨拉石盆地的存在提供了佐证.     

大兴安岭北部绣峰组下部砾岩的形成时代及其大地构造意义

对漠河盆地南缘绣峰组下部砾岩的野外观察,发现其碎屑物除了主要来源于被前人置于新元古代的花岗岩外,还含有火山岩砾石;与上部砂岩之间被断层分隔而不是连续沉积。作为该砾岩主要源岩的花岗岩中的锆石蒸发法年龄为354～164Ma,锆石SHRIMP定年揭示其最后一次岩浆活动可能发生在早侏罗世(180～190Ma);全岩-长石-黑云母内部Rb-Sr等时线年龄为177～191Ma,黑云母Ar-Ar年龄为171～175Ma,表明该岩基在中侏罗世还深埋地下没有出露地表。其中的火山岩砾石的岩石学和岩石化学特征与区域上晚侏罗世塔木兰沟组火山岩类似。结合区域地质资料,推测该砾岩的形成时代不是中侏罗世,而可能是早白垩世;漠河盆地是与蒙古-鄂霍茨克造山带有关的前陆盆地,而不是侏罗纪陆内断陷盆地。     

祁连山老君山砾岩的碎屑组成和源区大地构造背景

老君山砾岩是一套由砾岩和杂砂岩组成的陆相粗碎屑岩。砾岩由来自下伏基底的超镁铁岩、中—基性火山岩、硅质岩、花岗岩等碎屑组成。杂砂岩中岩屑含量大于70％,石英约10％,长石约15％。岩屑以中基性火山岩和花岗岩为主;硅质岩屑是主要的沉积岩屑。锆石、磷灰石、磁铁矿是杂砂岩中最为丰富的重矿物,同时还有铬铁矿、石榴子石、电气石、金红石、黄铁矿。这些事实说明,老君山砾岩的源区曾出露有超镁铁岩、中基性火山岩、变质岩等类型的岩石。砂岩碎屑模式和粉砂岩、泥岩的地球化学成分均表明,老君山砾岩源区为大陆边缘弧和大洋岛弧,形成于活动大陆边缘与岛弧相关的沉积盆地中。     

基于岩性精细识别基础上的砂砾岩储层研究——以渤海CFD油田为例

砂砾岩体多位于陡坡带,具有纵向厚度大,粒径粗,泥岩不发育,岩相变化快,储层非均质强等特点。储层评价存在一定的困难,特别在海上油田探井较少、各项资料缺少、可类比油田较少的情况下,更增加了精细研究该类储层的难度。以渤海CFD油田的岩心、壁心、薄片、粒度、测井等资料为基础,通过岩矿与测井结合的研究,提出一套岩性判别模式,从而精确识别出储层段岩性。通过孔隙类型、孔隙结构、物性等微观特征描述,分析了沉积微相、岩性与物性的关系,指出本研究区储层物性的主控因素是岩性,从而确定了井点的优势储层。以层序地层格架为基础,井震结合,提取地震属性,在相控模式的指导下,预测出平面储层分布。这种由点到面的研究思路,为油田开发方案的合理编制提供了较为详实的地质基础。同时,为相似地质条件和资料基础的巨厚储层精细描述提供了技术和方法借鉴。