A comparison of the sedimentary records of the 1960 and 2010 great Chilean earthquakes in 17 lakes: Implications for quantitative lacustrine palaeoseismology

Seismically‐induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions. Recent, well‐documented, great megathrust earthquakes provide an ideal opportunity to calibrate seismically‐induced event deposits for lakes with different characteristics and located in different settings. This study used 107 short sediment cores to investigate the sedimentary impact of the 1960 M_w 9·5 Valdivia and the 2010 M_w 8·8 Maule earthquakes in 17 lakes in South‐Central Chile (i.e. lakes Negra, Lo Encañado, Aculeo, Vichuquén, Laja, Villarrica, Calafquén, Pullinque, Pellaifa, Panguipulli, Neltume, Riñihue, Ranco, Maihue, Puyehue, Rupanco and Llanquihue). A combination of image analysis, magnetic susceptibility and grain‐size analysis allows identification of five types of seismically‐induced event deposits: (i) mass‐transport deposits; (ii) in situ deformations; (iii) lacustrine turbidites with a composition similar to the hemipelagic background sediments (lacustrine turbidites type 1); (iv) lacustrine turbidites with a composition different from the background sediments (lacustrine turbidites type 2) and (v) megaturbidites. These seismically‐induced event deposits were compared to local seismic intensities of the causative earthquakes, eyewitness reports, post‐earthquake observations, and vegetation and geomorphology of the catchment and the lake. Megaturbidites occur where lake seiches took place. Lacustrine turbidites type 2 can be the result of: (i) local near‐shore mass wasting; (ii) delta collapse; (iii) onshore landslides; (iv) debris flows or mudflows; or (v) fluvial reworking of landslide debris. On the contrary, lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments. Due to their more constrained origin, lacustrine turbidites type 1 are the most reliable type of seismically‐induced event deposits in quantitative palaeoseismology, because they are almost exclusively triggered by earthquake shaking. Moreover, they most sensitively record varying seismic shaking intensities. The number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity, starting with no lacustrine turbidites type 1 at intensities between V½ and VI and reaching 100% when intensities are higher than VII½. Combining different types of seismically‐induced event deposits allows the reconstruction of the complete impact of an earthquake.     

牛庄洼陷沙三中亚段浊积岩储层成岩作用及主控因素分析

东营凹陷牛庄洼陷沙三中亚段浊积岩储层以长石细砂岩、岩屑细砂岩及粉砂岩为主,结构成熟度及成分成熟度均较低.浊积岩样品的显微特征及成岩矿物的组合关系分析结果表明:该区的浊积岩储层目前主要处于晚成岩A期到B期的过渡阶段,成岩现象包括压实压溶作用、石英的次生加大作用、碳酸盐矿物胶结作用、溶解作用和粘土矿物转化作用等,这些作用过程受矿物与孔隙流体之间的相互作用控制.影响成岩作用的主要因素是岩石性质、沉积微相、水介质的性质、超压、高温以及烃类的早期注入.     

混合钻头在涪陵页岩气田的应用

涪陵页岩气田是中国第一个正式投入商业开采的海相页岩气田,历经2013年的开发评价试验阶段及2014-2015年的一期产能建设阶段,通过攻关研究与现场试验应用,创新形成了适合涪陵页岩气田勘探开发的钻完井技术系列,二期产建推进以来,由于埋深的增加、地层的不确定性,对钻井提速提效造成了巨大的阻碍,其中部分复杂层系的钻头选型显得尤为困难,主要体现在常规钻头行程钻速低、起下钻趟次多、定向困难等几个方面。通过对岩石可钻性及定向难点分析,针对平桥区块小河坝组地层研磨性强、砂泥岩交错的特点,优选了121/4 in高研磨性混合钻头;针对二开深层大三维井定向托压严重的问题,优选了121/4 in高效定向混合钻头;针对三开龙马溪组（含浊积砂岩）定向段高造斜率及研磨性强的特点,优选了81/2 in硬地层定向混合钻头。截止2019年2月,3种型号混合钻头在涪陵工区累计使用200余井次,平均减少起下钻4～5趟次,缩短钻井周期6～7 d。混合钻头的优选应用,为二期产建的钻井提速提效提供了技术保障,为下步页岩气田的高效开发提供了钻头选型方案。     

北部湾盆地福山凹陷深湖重力流成因分类、发育机制及沉积模式

福山凹陷为北部湾盆地南缘海南隆起斜坡上的一个新生代断陷湖盆。本文充分利用岩心、测井以及覆盖整个研究区的高分辨率三维地震资料,以层序地层学、沉积学等多种理论为指导,结合沉积岩石学、地震沉积学等相关技术,于古近系流沙港组SQEls₂EST+LST时期,在福山凹陷识别出4种深湖重力流沉积岩相类型;通过岩相组合及其转换特征、砂分散体系、地震相分析,对该时期沉积体系展布特征进行细致剖析,进而建立福山凹陷深湖重力流发育机制和沉积模式：西部地区发育以浊流为主、具有典型浊积水道的湖底扇沉积;而东部地区则以砂质碎屑流沉积形成的远端孤立朵体为主。     

Turbidite Events Recorded in Deep-sea Core IR-GC1 off Western Sumatra: Evidence from Grain-size Distribution

Sediment core IR-GC1, from the abyssal basin of the Indian Ocean off Sumatra, may provide important information on depositional events related to earthquakes and tsunamis. In this study, based on a combination of grain-size analysis with lithological studies and oxygen isotope stratigraphy, seven deep-sea turbidite layers were identified, corresponding to seven turbidity events that occurred at 128–130, 105–107, 98–100, 86–87, 50–53, 37–41 and 20–29 ka. The sediments of the turbidite deposits are characterized by coarse grain sizes, poor sorting, wide kurtosis, bimodal frequency distributions and clear depositional variations. Particle size grading is also an important signature of deep-sea turbidite deposits and can be used as an indicator to identify turbidite layers. Possible triggering mechanisms for the turbidite events include tsunamis, earthquakes, volcanic eruptions and sea-level changes.     

广西丹池盆地泥盆系浊积岩和硅质岩的特征及构造意义

对广西丹池地区泥盆系浊积岩和硅质岩的沉积特征、岩石化学成分和形成机制的研究表明,它们是在受同生断裂控制的深水拗陷盆地中,由浊流和热水沉积而形成的沉积岩石。相同类型岩石的分布特征表现南盘江晚古生代沉积盆地呈浅海“台地”和深海“槽沟”相间排列的构造格局,其形成和演化与滇黔桂地体和云开地体的碰撞拼贴造山作用以及造山后地壳的蠕散拉伸作用有关。     

鄂尔多斯盆地富县—黄陵县地区上三叠统 延长组长6、长7浊积岩成岩作用

根据砂岩薄片、铸体薄片、扫描电镜、压汞等分析,对富县—黄陵县地区上三叠统延长组长6及长7油层组的浊积岩岩石学特征、成岩作用类型及其对孔隙的影响进行了研究.研究结果表明,该区长6及长7浊积岩主要为细粒长石砂岩.压实作用、胶结作用、交代作用和溶解作用是控制浊积岩储层物性演化的主要成岩作用,其中压实作用和胶结作用强烈破坏了浊积岩的原生孔隙,它们造成的平均孔隙度丧失分别为23.1％和6.5％,但早成岩阶段绿泥石薄膜的形成使浊积岩的一些原生孔隙得以保存.溶解作用和交代作用有效地改善了浊积岩的孔隙结构,从而提高了浊积岩储层的孔渗条件.     

Turbidite deposition in the Cambrian Kanmantoo Group,South Australia

The Kanmantoo Group of South Australia is a thick (～7–8 km) succession of predominantly clastic marine sedimentary and metasedimentary rocks that were deposited very rapidly in a localised basin (Kanmantoo Trough) during the Early Cambrian. Despite structural complexity and varying grades of metamorphism, a surprising amount of primary sedimentological information is still available. Although a variety of depositional facies are represented, the group is dominated by parallel, sharp‐based, mineralogically immature sandstone interbedded with mudstone. The sandstone beds are most commonly fine to medium grained, massive and lacking in obvious grading except at the top. Single beds often reach several metres in thickness and amalgamation of beds is not uncommon. We argue that these sandstone beds could be the products of sustained high‐density turbidity currents. Triggering mechanisms for such turbidity currents remain uncertain, but they may have been initiated as hyperpycnal flows during catastrophic flood events at the mouths of high‐load‐capacity rivers, or from the failure of unstable buildups of sediment on delta slopes. Palaeocurrent studies from sole marks suggest a southerly source, which was probably an active orogenic terrain in formerly contiguous Antarctica. It is likely that a major delta complex lay at the southern end of the basin.     

灾变事件地层斜坡滑塌（带）堆积的特征——以滇西保山地区上三叠统南梳坝组为例

保山地块保山地区三叠系上统南梳坝组研究程度较差,以往的资料多侧重于岩石地层、生物地层的研究,沉积环境资料甚少。通过1∶5万保山幅等8幅区域地质调查,在南梳坝组中发现了灰岩滑塌岩块、下超面、饥饿沉积、水道砾岩、粒序层理、复理石韵律及槽模、沟模等一系列非常重要的沉积相资料,认为其沉积环境为斜坡-盆地环境,总体为一套浊积岩,其中的同沉积＂褶皱＂、同沉积断层、大量的滑塌面、各种类型的滑塌褶皱组成了3条较大规模的滑塌带,是斜坡环境的沉积物在地震作用触发下形成的,剖面结构＂不合理＂,明显具有灾变事件地层的特征。灰岩滑塌岩块有极浓的油气味,显示出生储存油气的良好环境。因此,重塑三叠系上统南梳坝组的古地理环境,不仅对发展沉积学、地层学有重要意义,而且对于寻找烃源岩也有重要的现实意义。