Facies and depositional model of alluvial fan dominated by episodic flood events in arid conditions: An example from the Quaternary Poplar Fan,north-western China     

Chonglong Gao  Youliang Ji  Chenliang Wu  Jun Jin  Ying Ren  Zhao Yang  Dawei Liu  Zhijun Huan  Xiaobing Duan  Yuqi Zhou 《Sedimentology》2020,67(4):1750-1796

Alluvial fans are usually constructed through episodic flood events. Despite the significance of these ephemeral floods on the morphodynamics of alluvial fans, depositional responses to the variations in flood conditions are still poorly documented. This greatly limits the ability to interpret ancient sedimentary successions of fans and the associated flood hydrodynamics. The Quaternary Poplar Fan from endorheic Heshituoluogai Basin provides an optimal case for addressing this issue. Based on the variations in facies associations and flood conditions, three depositional stages – namely; lobe building stage, channel building stage and the abandonment stage – are identified. During the lobe building stage the Poplar Fan is predominately constructed through incised channel flood, sheetflood and unconfined streamflood, with coeval development of distal surficial ephemeral ponds. The channel building stage is characterized by the development of gravelly braided rivers. However, only scour pool fill deposits are preferentially preserved in the Poplar Fan. During the abandonment stage, erosional lags and aeolian sands randomly occur throughout the fan, while gully deposits can only be found in the distal fan. The distinctive facies architecture of the Poplar Fan is likely to be the result of periodicity of climate fluctuations between wetter and drier conditions during the Late Pleistocene to Holocene. The ephemeral floods formed under wetter conditions usually show high discharge and sediment concentrations which facilitate the lobe building processes. During the drier periods, only gravelly braided rivers can be developed through ephemeral floods as the intensity and frequency in precipitation, discharge and sediment concentrations of the flood flows significantly decrease. The abandonment stage of the fan may occur between recurring flood episodes or during the driest periods. Furthermore, the long-term (10⁵ to 10⁶ year) geomorphic evolution of the Poplar Fan shows the influence of tectonic activities. The ongoing thrust uplift tectonic activities have caused destruction of the fan but can also facilitate the fan-head trench/incision of the fan, which in turn facilitate the progradation of the fan. This study proposes a new depositional model for alluvial fans constructed through episodic flood events, which shows the character of both sheet-flood dominated and stream-flow dominated end members of alluvial fans. These findings supplement the understanding of the variability of the alluvial fans and provide means to characterize rock record of alluvial fans and their associated flood and climate conditions.  相似文献   

Discovery of Cosmic Spherules from the Mesoproterozoic Strata and its Significance—in Case of the Ming Tombs Area, Beijing     

SONG Tianrui  ZHENG Ning  LIU Yongqing  KUANG Hongwei  PENG Nan  LI Chao  TANG Jigang  YAN Qinggao  GAO Linzhi  ZHU Zhicai  XIA Xiaoxu  WANG Yuchong 《《地质学报》英文版》2020,94(1):38-56

This study covers cosmic spherules derived from the Mesoproterozoic Dahongyu Formation in the Ming Tombs area, Beijing. The cosmic spherules include iron oxide cosmic spherules, carbonaceous chondrites, and atomic iron “steely bead”-shaped cosmic spherules. The mineral assemblage of silicon carbide, forsterite, zircon, and glass spherules and fragments were picked from melt-silicified carbonate of the Mesoproterozoic Dahongyu Formation (ca. 1625 Ma). Cosmic spherule assemblages are solely discovered from sedimentary rocks in China. Platinum group elements (PGE) were determined for the first time in cosmic spherules and associated minerals. PGE comparative observation between meteorite and cosmic spherules is presented in this study. It is recognized that an extraterrestrial meteorite impact event might have occurred in the Dahongyu Stage. The main evidence is a large number of iron cosmic spherules in silicified oncolitic limestone, and associated cosmic silicon carbide, glass spherules, and fragments, as well as the presence of forsterite. The impact-volcanic crater is characteristic of a big black shale block dropped into the bended silicified limestone.  相似文献   

The Black Sea basins structure and history: New model based on new deep penetration regional seismic data. Part 1: Basins structure and fill     

《Marine and Petroleum Geology》2015

This work is based upon results of interpretation of about 8872 km-long regional seismic lines acquired in 2011 within the international project Geology Without Limits in the Black Sea. The seismic lines cover nearly the entire Black Sea Basins, including Russia, Turkey, Ukraine, Romania and Bulgaria sectors. A new map of acoustic basement relief and a new tectonic structure scheme are constructed for the Black Sea Basins. The basement of the Black Sea includes areas with oceanic crust and areas with highly rifted continental crust. A chain of buried seamounts, which were interpreted as submarine volcanoes of Late Cretaceous (Santonian to Campanian) age, has been identified to the north of the Turkish coast. On the Shatsky Ridge, probable volcanoes of Albian age have also been recognized. Synorogenic turbidite sequences of Paleocene, Eocene and Oligocene ages have been mapped. In the Cenozoic, numerous compressional and transpressional structures were formed in different parts of the Black Sea Basin. During the Pleistocene–Quaternary, turbidites, mass-transport deposits and leveed channels were formed in the distal part of the Danube Delta.  相似文献   

辽东地区国情监测套合整景正射影像更新变化图斑     

李萌 《测绘与空间地理信息》2021,44(1):82-85

主要针对2018年辽宁省地理国情监测项目影像数据源的获取及全色整景影像制作过程作以明确概述,实例验证整景纠正影像适用监测任务区内新增或已变化图斑要素进行内业解析判读与外业调查以及带来的直观性与便捷性。将整景影像用于国情图斑变化核查,极大程度上确保地表覆盖和国情要素成果在时间精度、逻辑一致性、位置精度、属性精度、表征质量等方面均符合国情监测阶段的技术指标要求。  相似文献   

淮北杨柳矿区煤系构造热演化对页岩气生成与保存的影响     

余坤  万志军  琚宜文  王朱亭  赵帅  乔鹏 《地质学报》2023,97(8):2690-2701

在“双碳”目标背景下,大力发展以页岩气为代表的低碳清洁能源是实现“碳减排”的重要途径。华北南部淮北地区蕴藏着丰富的煤系页岩气资源,但受复杂构造热演化影响,区域内页岩气生成与保存机理尚不清晰。因此,本文采用镜质组反射率、岩石热解、裂变径迹和盆地模拟技术研究了华北南部淮北地区晚古生代以来的构造热演化与生烃过程,讨论了复杂构造热作用下煤系页岩气的生成和保存机理。结果表明,淮北地区煤系页岩气生成过程受到燕山期构造热事件的显著控制,晚侏罗世基性岩浆侵入煤系使得下石盒子组和山西组页岩经历最高古温度达~172℃,对应热流峰值124 mW/m2。煤系页岩Ro值在0. 87%~1. 74%,最高热解温度（Tmax）在437~563 ℃,表明有机质进入轻质油—湿气生成阶段。研究区二叠系山西组砂岩磷灰石裂变径迹年龄（60~42 Ma）明显小于所在地层年龄（298~272 Ma）,部分锆石裂变径迹年龄略低于地层年龄,证实了研究区发生了强烈的岩浆热活动,导致地温梯度达到峰值~65 ℃/km。燕山期岩浆热效应促使区域煤系页岩高效生烃成藏,太平洋板块俯冲后撤引起的伸展断裂使得强构造变形区页岩气藏破坏逸散。因此,在淮北地区,弱构造变形区并伴有适度岩浆活动的区域具备页岩气保存的良好条件,具有良好的油气勘探前景。  相似文献   

Molecular characterization of dissolved black nitrogen via electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry     

《Organic Geochemistry》2015

Combustion produces a complex mixture of polycondensed aromatic compounds known as black carbon (BC). Such products can become remobilized from char and soil in the form of dissolved BC (DBC). Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (ESI–FT-ICRMS) analysis of a variety of soil and char leachates showed that a significant proportion of DBC compounds contained one or more nitrogen atoms. While the presence of black nitrogen (DBN) in dissolved organic matter (DOM) has been reported, its molecular features were uncharacterized. Here we present results of FT-ICRMS characterization of DBN, where assigned formulae were validated on the basis on their ¹³C isotope signatures and fragmentation patterns obtained via collision induced dissociation. Possible chemical structures were assigned for several DBN formulae and suggest that nitrogen was incorporated into the core ring system as a pyrrole-type moiety. Most DBN compounds existed as part of homologous series where homologs differed by a mass corresponding to CO₂, suggesting that they were polysubstituted with carboxylic acid groups. The environmental contribution of such novel, aromatic, combustion-derived nitrogen compounds with respect to global nitrogen cycling remains elusive. The biogeochemical implications of the input of such fire-derived products to aquatic ecosystems as part of climate change therefore need to be assessed.  相似文献   

燕山构造带北部喀喇沁地区晚古生代-中生代岩浆活动的构造背景分析   总被引：1，自引：0，他引：1       下载免费PDF全文

林少泽  朱光  赵田  宋利宏  刘备 《地质科学》2015,50(1):30-49

燕山构造带北缘喀喇沁地区发育了晚古生代一中生代多期岩浆活动,记录了多期构造变形事件,是认识该构造带大地构造演化的理想地区。本文通过对该地区岩浆岩的系统定年及各期构造变形事件的研究,结合区域地质资料,综合分析了晚古生代一中生代的大地构造演化历史。分析结果表明,燕山构造带在早石炭世晚期一早二叠世处于古亚洲洋俯冲背景下的活动陆缘环境,出现了弧岩浆活动。中二叠世古亚洲洋沿索伦克缝合线关闭,使得燕山构造带成为周缘前陆挤压变形带,并对应着岩浆活动的平静期。之后燕山构造带分别出现了晚二叠世一三叠纪、中侏罗世、晚侏罗世与早白垩世4期伸展背景下的岩浆活动。在这些岩浆活动之间的平静期,先后发生了早侏罗世、晚侏罗世初、早白垩世初3期挤压事件。这些现象还表明,岩浆活动与构造演化具有明显的耦合关系,板内环境下岩浆活动发生在伸展背景中,而岩浆活动平静期多对应区域挤压活动。  相似文献   

华北晚古生代陆表海盆地海侵事件微观沉积特征及成煤探讨   总被引：3，自引：0，他引：3  

吕大炜  李增学  王东东  刘海燕  贾强  王平丽  于得明  吴晓燕 《沉积学报》2015,33(4):633-640

采用沉积学、煤地质学、古生物学、地层学及地球化学等多技术手段,结合比较分析法的思路,分析了事件型海侵的特点和海侵事件沉积组合特征,研究发现:海侵事件沉积组合为区域对比性强、具沉积时间连续性与相序间断性的暴露沉积-煤层-灰岩组合,其关键沉积学特征是煤层底板的暴露沉积.海侵事件组合灰岩的古生化石个体小、破碎强烈等特征表现为高能量水体运动等环境,孢粉表现为低含量的单缝孢和裸子植物及高含量的三缝孢.地球化学分析表明暴露沉积为陆相环境,煤层中的微量元素表现为海相主要原因是由于泥炭沼泽覆于深水后受海水影响所致.海侵事件成煤与海侵过程成煤差异体现在两个方面:第一,盆地属性差异,即海侵事件成煤形成于陆表海盆地之中,而海侵过程成煤则形成于具有缓坡的边缘海盆地,第二,成煤原理存在着差异,海侵事件成煤强调的是成煤前海侵未发生前的碎屑体系废弃而发育大量泥炭沼泽且被后期突发性海侵终止,而海侵过程成煤则强调的是泥炭沼泽发育于滨海的活动碎屑体系并终止于后期的缓慢海平面上升.  相似文献   

藏南仲巴地区早白垩世日朗组物源分析及其构造意义     

张新毅  魏玉帅  王成善  张小龙  商咏梅 《岩石学报》2015,31(1):273-283

藏南仲巴地区早白垩世日朗组出露于特提斯喜马拉雅北亚带,整体为黄绿色火山岩屑砂岩,局部层位可见页岩与泥岩,分析为一套深海海底扇沉积组合。本文仔细分析了日朗组砂岩岩石学特征及鲍马序列和槽模沉积构造等沉积学特征,结果表明:日朗组砂岩成分成熟度和结构成熟度均不高,具有近源物源的特点;槽模构造古水流数据统计表明古流向由南向北,指示物质组分来源于南侧特提斯喜马拉雅和/或印度克拉通。砂岩碎屑组分统计结果表明日朗组的物源区构造背景属于克拉通内部及石英再旋回区。碎屑锆石U-Pb年龄频谱图对比进一步表明其物源区为印度稳定大陆边缘,外加一套早白垩世火山碎屑物质的输入。仲巴地区日朗组物源特征反映了印度大陆北缘早白垩世由深部断裂引起的一次强烈的火山事件,可能与印度大陆从澳大利亚-南极大陆裂解有关。  相似文献   

从扩充的威尔逊循回看中国大陆演化轨迹     

杨文采 《地质论评》2015,61(2):237-244

全球对比同类大地构造单元的壳幔结构,根据壳幔结构的差异和大地构造作用发生的时代把它们按演化阶段排序,可以找寻这类大地构造单元岩石圈演化的规律性。笔者在文中根据全球地学界实施的COCORP、BIRPS、DEKORP、LITHOPROBE、ICDP、ECORS和SINOPROBE等计划取得的成果,扩充了板块构造学中的威尔逊循回,即把原先主要描述大洋板块起源、发展和封闭的威尔逊循回,扩展到同时包括大陆和大洋板块演化的大循回中去。文中概述了扩充的威尔逊循回的内容,除经典的威尔逊循回的组元之外,扩充的组元包括洋陆转换、大陆汇聚拼合和大陆裂解等,为大陆岩石圈生成和演化作用提供了细节。根据扩充的威尔逊循回的大陆岩石圈演化规律,可以对中国地质学家已经发展的大陆构造演化的序列进行进一步的阐释,使构造演化的序列的属性和轨迹更加准确清晰。从寒武纪古亚洲洋扩张和冈瓦纳大陆裂解,到新生代印度次大陆与亚欧大陆碰撞拼合,中国大陆的大地构造事件序列说明扩充的威尔逊循回的是大陆岩石圈演化轨迹的大概率规律。  相似文献