Biogenic Sedimentary Structures of the Yellow River Delta in China and Their Composition and Distribution Characters

The biogenic sedimentary structures （i.e., the morphology and trace makers of burrows, tracks, trails and traces made by extant organisms） and their composition and distribution characters in different micro environments and sub environments of the Yellow River delta in China are described. Three ichnocoenosis can be recognized： （1） Steinichnus-like ichnocoenosis, includes F, Y-shaped traces, birds＇ footprints on bedding plane, and Y, U-shaped burrows in intrastratal bedding, produced by Coleoptera （Heteroceridae）, Orthoptera （Gryllotalpidae） and birds. It is majorly found at the delta plain point bar deposits, denoting the fresh water-related terrestrial environments. （2） Steinichnus-Psilonichnus-like ichnocoenosis, consitsis of Steinichnus-like traces on the bedding plane and Psilonichnus-like burrow which a vertical, irregularly J-, Y-, or U-shaped burrows, some of them with bulbous basal cells burrows in the intrastratal bedding, created by Coleoptera （Heteroceridae）, Orthoptera （Gryllotalpidae） and crabs. It is observed in the delta plain abandoned distributary channels, and the delta front tidal creek and subaquous distributary channels, indicating the brackish water environment. （3） Palaeophycus-like ichnocoenosis, includes the round entrance burrows or with craters-shaped loop-protrusionsand and the parallel forked trails on the bedding plane, and the U, J or vertical shaped feeding burrows are in the intrastratal bedding, majorly produced by the clam （bivalve molluscs）, gastropods and Nereis. It is present in the subaqueous interdistributary bay, reflecting the intertidal related environment.

The magnetic properties of sediment and sedimentary environment in the Huanghe Delta area after the last glacial maximum

On the basis of measuring the magnetic parameters of sediment in Core YDZ1, combined with a grain size analysis and Carbon-14 dating, the magnetic properties of sediment and sedimentary environment in the Huanghe（Yellow River） Delta area after the last glacial maximum have been studied. The results show that the ferrimagnetic minerals of a pseudo single domain and multi domain particles dominate the magnetic properties of sediment in Core YDZ1. The imperfect anti ferrimagnetic minerals have more contribution on sediment in a depth of 24.0–22.1 m, and more stable-single domain and pseudo single domain particles exist. The susceptibility of anhysteretic remanent magnetization and the ratio of the susceptibility of anhysteretic remanent magnetization to saturation isothermal remanent magnetization show a decrease trend below depth of 24 m, a marked increase trend in a depth of 24.0–13.5 m, and a rapid decrease at depth of 13.5 m, then a fluctuation trend upward. The above two magnetic parameters and the ratio of the susceptibility of anhysteretic remanent magnetization to the mass susceptibility can be regarded as the proxy indicators for the content of clay（〈4 μm）and the fine-grained size（〈32 μm）. The sedimentary environment after the last glacial maximum in the Huanghe Delta area has experienced the fluvial facies, the tidal flat facies, the neritic facies, the pro delta facies, the delta front facies and the floodplain facies. Thickness of the Holocene transgression layer is 10.5 m and the depth of substrate is about 24 m according to the YDZ1 core. The sedimentary dynamic has a variation trend with strongweak-strong, which has been proved by the Flemming triangular schema.

Introduction to the China-Vietnam Cooperation Project: A Comparative Study of the Holocene Sedimentary Evolution of the Yangtze and Red River Deltas

Both China and Vietnam confront the challenges of natural geohazards and environmental changes in their deltas and coastal zones due to rapid urbanization, economic development, and the impacts of global climate change. China and Vietnam initiated a comparative study of the Holocene sedimentary evolution of the Yangtze River Delta(YRD) and Red River Delta(RRD) for the period 2015–2018 in order to improve the understanding of the two delta evolution histories in the Holocene. Previous investigative data of the two rivers, onshore delta plains, and offshore subaqueous deltas have been explored and reinterpreted. New data gleaned from boreholes, piston cores, shallow seismic and hydrodynamic sources have been collected from the offshore YRD and the East China Sea inner shelf, and surface sediments and short cores have been collected from the RRD near-shore areas. Six focal areas of the joint project have been defined for comparative studies of the two deltas, including morphological development, sequential stratigraphy, coastline shifting, sedimentary characteristics, sedimentary dynamics, and correlation with anthropogenic global climate change. The results of these study areas are presented herein. The joint project also includes cooperative capacity building; exchanges of young scientists have been organized during the project period, and hands-on training in laboratory geochemical analysis, numerical modeling, and seismic data processing and interpretation have been provided by China and its Vietnamese geoscientist partners. Joint field excursions were organized to the upstream of the Yangtze and Red Rivers in Yunan Province, China, all the way downstream along the Vietnamese portion of the Red River. These joint studies have, over the past three years, improved understanding of the evolutionary history of these two major rivers and their mechanisms of source to sink. Joint project results of these two major deltas are not limited to the geosciences; the cooperative mechanical and operational experiences have been helpful for future cooperation in the field of marine geoscience between China and Vietnam, as well for cooperative activities with other ASEAN member countries.

Distribution of diatoms and silicoflagellates in surface sediments of the Yellow Sea and offshore from the Changjiang River, China

The spatial distribution of siliceous microfossils （diatoms and silicoflagellates） in the surface sediments was mapped at 113 sites in the Yellow Sea and sea areas adjacent to the Chang^iang （Yangtze） River, China. In total, 267 diatom taxa and two silicoflagellate species were identified from the sediments. The spatial variations in abundance and diversity were classified into three distinct geographic patterns using Q mode clustering： a south-north geographic pattern, a coastal-offshore pattern and a unique pattern in the Changjiang River mouth. The south-north geographic pattern was related to the spatial variations in sea temperature. Coscinodiscus oculatus, a warm-water species, indicated these variations by a gradual decrease in abundance from the south to the north. The coastal-offshore pattern was in response to the spatiaJ variations in salinity. Cyclotella stylorum, Actinocyclus ehrenbergii and Dictyocha messanensis, the dominant brackish species in coastal waters, significantly decreased at the isobaths of approximately 30 m, where the salinity was higher than 31. Paralia sulcata and Podosira stelliger indicated the impact of the Yellow Sea Warm Current in the central Yellow Sea. The unique pattern in the Changjiang River mouth showed the highest species diversity but lower abundance, apparently because： freshwater input can significantly increase the proportion of brackish species; nutrients can supply the growth ofphytoplankton; and high sedimentation rates can dilute the mierofossil abundance in the sediments. Our results show that an integration of environmental factors （e.g., nutrient levels, sedimentation rate, sea temperature, salinity and water depth） determined the spatial characteristics of the siliceous micro fossils in the surface sediments.

Foraminiferal Changes and Response to the Channel Diversion and Discharge Fluctuation of the Yellow River in the North Yellow Sea During the Past Century

Diversion of the Yellow River is a unique geological event in offshore China,causing changes of the sedimentary environment in eastern China Seas.The last diversion took place in AD 1855,with the estuary diverted from the Yellow Sea into the Bohai Sea.The identification of the river diversion events in the shelf sediments would not only provide the definite ages for the sediments,but also give a clue for better understanding of the sedimentation in that area.In this study,210 Pb,grain size,geochemical element,and foraminiferal data in core H205 from the north Yellow Sea were systematically investigated.A high-resolution sedimentary record was established,which was coupled with the Yellow River diversion and runoff changes.The results show that the foraminiferal composition and foraminiferal abundance of the sediments from the north Yellow Sea had good response to the Yellow River diversion in 1855.Before the change,shallow water assemblages dominated the foraminifera,and the abundance of each foraminiferal species was very low.After the diversion event,the abundance of most foraminifera increased sharply,with a maximum increase of 16 times,and the assemblage was still dominated by shallow water species.Furthermore,the changes in foraminiferal abundance in the core sediments corresponded well with the discharge fluctuation of the Yellow River since 1855.When the Yellow River began entering the Bohai Sea,the Yellow River water,which is rich in nutrients,along with the coastal currents affected the north Yellow Sea,increased the primary productivity in the north Yellow Sea,which is the main reason for the abrupt increase and fluctuation of foraminiferal abundance in this area.At the meantime,the East Asian winter monsoon could also promote the development of nearshore foraminiferal species by enhancing the coastal currents.

准噶尔盆地二叠系上乌尔禾组退覆式扇(辫状河)三角洲前缘-滩坝复合砂砾岩沉积特征及控制因素

近年来准噶尔盆地的油气勘探从源外常规圈闭逐渐走向源内岩性圈闭,二叠系上乌尔禾组是该盆地增储上产的主力层系,沉积体系展布对上乌尔禾组岩性油气藏分布具有控制作用。利用岩心数据、薄片资料等,并结合地震数据和钻测井资料,对准噶尔盆地二叠系上乌尔禾组的沉积相类型及沉积体系分布特征进行了识别和刻画,总结了大型退覆式扇(辫状河)三角洲-滩坝复合砂砾岩体的沉积模式,并分析了其控制因素。研究表明:(1)研究区发育扇三角洲、辫状河三角洲、滨浅湖滩坝等沉积相类型,扇三角洲平原亚相和扇三角洲前缘亚相主要发育在盆地西部,辫状河三角洲平原亚相和辫状河三角洲前缘亚相主要发育在盆地东部和北部,滩坝相叠置在扇三角洲和辫状河三角洲前缘之上或在其前端独立分布;(2)准噶尔盆地上乌尔禾组各段沉积体系是在整体湖侵的背景下发育的,乌一段沉积时期湖盆面积较小,沉积的砂体较厚,延伸距离近,靠近凹陷的中央;乌二段沉积时期物源持续供应,湖盆水体加深,湖盆面积增加,沉积砂体厚度薄,分布广;乌三段沉积时期湖侵作用增强,湖盆面积进一步扩大,湖盆内广泛发育湖泛泥岩;(3)扇三角洲与辫状河三角洲前缘在湖平面不断变化与湖浪的改造下,形成了扇(辫状河)三角洲前缘-滩坝复合砂砾岩体;(4)准噶尔盆地上乌尔禾组沉积时期,沉积体系的主要控制因素为气候、物源供给、湖平面变化和沉积时的古地形坡度和古地貌。该研究为上乌尔禾组油气勘探提供了地质依据。

古黄河三角洲典型钻孔XJ01第四纪沉积物地球化学特征

江苏古黄河三角洲为全球海陆相互作用研究的典型地区,研究其第四纪沉积环境演化有助于进一步认识和理解海陆变迁、气候变化特征。本文基于XJ01典型钻孔第四纪沉积物的常量、微量元素地球化学,开展了沉积环境示踪。常量元素Al_(2)O_(3)、Fe_(2)O_(3)、FeO、MgO、CaO、MnO、P_(2)O_(5)、TiO_(2)总体上与SiO_(2)呈负相关关系。钻孔中地球化学元素曲线中,CIA、SiO_(2)/Al_(2)O_(3)、SiO_(2)/(Al_(2)O_(3)+Fe_(2)O_(3))、SiO_(2)/(K_(2)O+Na_(2)O+CaO+MgO)等变化趋势基本一致,微量元素Be、Rb、Cr、Cu与Rb/Sr变化趋势基本一致。地球化学元素曲线钻孔中沉积物分为10个带,分带反映该孔第四纪沉积环境由还原到氧化、水环境由深水到浅水、沉积相由陆相到海相、古气候由湿热到干冷频繁交替的特征。该研究成果为恢复古黄河三角洲地区第四纪地质演化过程提供了基础地质资料。

安塞油田黑山梁区长6油层组单砂体构型分析及平面展布特征

安塞油田黑山梁区块位于延安市安塞区,三叠系延长组长6油层组是其主力产油层。目前该区已进入注水开发阶段,但砂体展布、非均质性、砂体叠置规律等认识不清,导致开发过程中存在注水受效程度不均衡,整体水驱效果差等问题。为此,本次研究依托丰富的测井、录井资料,以及岩心、镜下薄片资料和分析测试数据,开展地层精细刻画、沉积微相、砂体平面分布及单砂体叠置规律的综合研究。结果表明:黑山梁地区长6时期主要发育三角洲前缘亚相,岩性以细粒长石砂岩为主,分选性中等-好,磨圆度中等,水下分流河道和分流间湾微相较为多见,河口坝微相发育较少;水下分流河道为优势相,砂岩分布广、厚度大,沿河道方向延伸,早期形成的河口坝由于波浪作用和分流河道侵蚀作用被破坏,河口坝无法保存完整,仅有部分痕迹。砂体类型包括水下分流河道砂和河口坝砂两种,单砂体垂向叠置可分为孤立型、叠加型和切叠型3种;侧向拼接样式可分为孤立式、对接式和侧切式3种。研究区内砂体沿北东-南西方向呈长条状展布,由于河道频繁摆动和分叉,砂体切叠现象明显,顺物源方向砂体连通性较好,垂直物源方向砂体被分流间湾泥隔开,砂体连通性较差,并结合生产动态数据,认为砂体连通程度越高,水驱动用效果越好。基于该研究成果建立了研究区曲流河三角洲沉积模式,为后期油藏完善注采井网、分层注水开发方案调整提供地质依据。

台风“杜苏芮”远端影响下黄河三角洲沉积特征变化

通过原位观测、无人机遥测、野外调查取样和室内测试分析等多种手段,探讨了2023年台风“杜苏芮”外围风圈对黄河三角洲沉积环境的影响。研究结果表明:①台风外围风圈引起黄河三角洲区域风场特征出现快速调整,河口动力增强,导致沉积物再悬浮;②受海洋动力变化影响,河口三角洲不同断面整体呈现出近海一侧高程降低、向陆一侧潮沟增加的特征,受沿海人为工程影响,垦东12附近台风后淤积明显,废弃清水沟河道断面靠海部分侵蚀,靠岸部分淤积;③除高程外,三角洲不同断面位置沉积物粒度发生显著变化,粒度变化受到潮沟侵蚀、河流输沙、河口侵蚀和废弃河道充填等不同因素的影响,呈现出空间差异性。研究结果揭示了未直接过境的台风依然可能通过外围风圈影响三角洲沉积演化过程,在未来三角洲沉积演化研究与防灾减灾应对过程中应予以重视。

河控浅水三角洲平原亚相沉积模式探讨——以鄂尔多斯盆地S59区块山西组一段为例

鄂尔多斯盆地S59区块山一段,整体具有构造稳定、地势平坦、古水深较浅、湖平面频繁升降、物源充足等特点,发育浅水三角洲沉积体系。本文在前人研究的基础上,通过对取心井岩心分析及侧井相分析,探讨了浅水三角洲的沉积特征,建立了浅水三角洲平原亚相沉积模式。研究结果表明,山西组山一段为河控浅水三角洲沉积,浅水三角洲的陆上部分沉积过程与曲流河沉积具有一致性,发育边滩、“渐弃型”废弃河道、决口扇和洪泛平原等微相,平面上河道在凹岸不断侵蚀,凸岸不断堆积形成边滩微相。此外在凹岸发育一定规模的废弃河道,河道砂体呈南北向分布,发育少量的决口扇沉积,在河道间发育细粒沉积洪泛平原亚相。三角洲平原亚相沉积模式的建立为预测优质砂体发育位置提供地质依据。

川东北元坝西部须二段—须三段沉积相及其对储层控制作用

川东北元坝西部须二段—须三段是重要的油气产层。本文利用钻井岩心、测井资料和三维地震资料对川东北元坝西部上三叠统须二段—须三段沉积相类型、沉积特征、沉积模式及其对储层发育控制作用开展详细的研究,以指导该地区的油气勘探部署。结果表明,川东北元坝西部须二段—须三段主要为辫状河三角洲相和湖泊相沉积,能够识别出三角洲平原、三角洲前缘、前三角洲和浅湖4种亚相,可进一步划分出9种微相。须二段—须三段沉积时期发育两种沉积模式,须二段为缓坡型宽河道辫状河三角洲沉积模式,主要发育宽河道,砂体叠置连片;须三段为陡坡型窄河道辫状河三角洲沉积模式,主要发育窄河道,砂体沿河道呈条带状分布。须二段主要发育中粒长石岩屑砂岩和中粒石英砂岩两种有利储集岩类型,主要分布于三角洲前缘水下分流河道砂体中;须三段发育中粗粒钙屑砂岩和砂质细砾岩两种有利储集岩类型,主要分布于三角洲平原辫状河道—三角洲前缘水下分流河道过渡带砂体中。缓坡型宽河道辫状河三角洲中发育的中粒长石岩屑砂岩和中粒石英砂岩储层物性和孔隙结构明显好于陡坡型窄河道辫状河三角洲中发育的中粗粒钙屑砂岩和砂质细砾岩。

闽江河口水下三角洲及周边海域现代沉积环境演化及其对人类活动的响应

【目的】河口三角洲是陆海相互作用的敏感地带,也是人类活动最为频繁的地区,研究人类活动对河口三角洲演化的影响,一直以来都是国际沉积学的研究重点和热点。【方法】以福建闽江河口水下三角洲为研究对象,通过水动力模拟和表层沉积物粒度分析,探讨了闽江河口水下三角洲及周边海域现代沉积环境演化。【结果与结论】研究区河口内潮流以往复流为主,在口外海域逐渐转变为旋转流,水下三角洲地区流速大,外海流速较小;沉积物类型以砂、粉砂和砂质粉砂为主,平均粒径平均值分别为1.57Φ、6.78Φ和5.62Φ,并且由河口向口外陆架方向沉积物粗颗粒组分含量逐渐减少,细颗粒组分含量逐渐增大;沉积物输运趋势显示,在闽江河口水下三角洲内,沉积物输运呈现向东、东南和东北方向,在口外海域沉积物呈现朝东南和东北离岸方向,以及向西北朝岸方向输运;基于粒度组成、粒度参数及站位水深多元统计分析,综合地理位置、沉积物源和水动力条件,将研究区现代沉积环境划分为4个沉积区;通过探讨不同控制因素下的河口水下三角洲沉积环境差异,揭示了不同沉积区的沉积环境对人类活动的响应。该研究结果可为河口资源开发和生态环境保护提供科学依据。

苏里格气田S区块山西组山1段沉积微相特征研究

上古生界山西组山1段为鄂尔多斯盆地苏里格气田S区块的主力产气层,厘清其沉积相特征,对指导该地区的天然气勘探具有一定意义。运用沉积学基础原理和方法,综合岩心观察、测井曲线、微量元素特征、沉积构造及古生物化石等资料,对苏里格气田S区块山1段进行系统研究。并结合单井相、沉积相连井剖面及砂地比特征,刻画山1段沉积微相展布特征。研究结果表明,研究区岩性主要为中-细砂岩,总体表现出牵引流的沉积特征,沉积环境为气候较湿润的弱还原-还原的水下沉积环境。岩心上见冲刷面、板状交错层理、平行层理和水平层理等沉积构造,古生物化石以碳化植物茎杆化石或植物叶片化石印模为主。山1段为曲流河三角洲前缘沉积,划分为水下分流河道、水下分流间湾、席状砂沉积微相,主要发育近北南向的水下分流河道砂体,为研究区最主要的储集体。

Magnetic properties of sediments from the Pearl River Delta,South China:Paleoenvironmental implications

Magnetic parameters and their environmental implications of sediments in a core (PD) from the Pearl River Delta, South China, indicate that ferrimagnetic minerals with low coercivity, such as magnetite, dominate the magnetic properties although small amounts of Fe-sulphides occur. The fraction of Fe-sulphides increases and becomes the dominant minerals determining the magnetic characteristics in grey-black organic-rich clay horizons, indicating an anoxic, sulphate-reducing swamp environment resulting from a marine regression. In the "Huaban clay" , hard magnetic minerals, such as hematite and goethite, largely control the magnetic properties of the sediments and imply a long period of exposure and weathering. Where magnetite is the main magnetic mineral, its fraction and grain size determine properties such as magnetic susceptibility (κ ) and saturation isothermal remanent magnetization (SIRM). Ratios of SIRM/κ and χarm/SIRM reflect changes in sea level with high SIRM/κ and χarm/SIRM correlating with a smaller magnetic mineral grain size and rising sea level. Based on downcore variations of these environmental magnetic parameters along with sediment characteristics and microfauna, the sedimentary environment of the Pearl River Delta area can be divided into two main cycles of transgression and regression during the late Pleistocene and Holocene with more sub-cycles of sea level fluctuation during each transgression.

准噶尔盆地腹部上二叠统-下三叠统浅水辫状河三角洲沉积特征与模式

准噶尔盆地下组合油气资源规模巨大,是最重要的战略接替领域;腹部四大凹陷二叠系—三叠系发育规模三角洲砂体,并在其中连获油气新发现。为了揭示腹部凹陷区沉积特征、沉积模式和砂体展布规律,基于大量新钻井岩心、测录井和地球物理资料,系统开展了盆地原型、层序格架、古地貌恢复和沉积体系研究。准噶尔盆地腹部上二叠统—下三叠统浅水辫状河三角洲发育期具有大型坳陷湖盆发育背景,沉积时期地形平缓,坡度小,物源供给充足,水体极浅且频繁动荡,氧化和还原环境交替出现,且整体以氧化环境为主;浅水辫状河三角洲具有粒度较粗、低杂基含量、中等结构成熟度、较长距离搬运、强水动力淘洗、发育交错层理和平行层理等沉积特征;腹部地区上乌尔禾组—百口泉组沉积时期优势水系主要来自西北和东北方向,整体自北向南延伸,发育乌尔禾、克拉玛依及克拉美丽3大物源体系。盆内地形分带性明显,形成扇三角洲区、辫状河三角洲平原区、前缘区和湖区4个相带,由此在腹部地区形成了“大平原、小前缘”的浅水辫状河三角洲沉积格局,其中平原区和前缘区均为有利砂体发育地带。

黄河下游原阳段沉积物粒度特征与沉积环境分析

为探究现代黄河下游沉积环境演化,在原阳段钻取了两个钻孔岩芯(YHX-1、YHX-2),通过对钻孔沉积物粒度测试与分析,运用沉积物粒度参数、频率曲线与概率累积曲线,结合沉积物岩性及周边钻孔年代信息,划分研究区钻孔地质年代,揭示研究区沉积水动力条件及环境演化历史。结果表明:YHX-1分为7个沉积段,YHX-2钻孔为11个阶段,中更新世时期,两根钻孔以中细砂为主,沉积相以河床亚相为主;晚更新世时期,钻孔经历短暂河漫滩微相,进入漫长的河床相沉积;全新世早期,YHX-1钻孔由湖泊沼泽沉积转变为河漫滩沉积,YHX-2钻孔为河漫滩沉积;全新世晚期,黄河改道流入当今河道,两根钻孔河床沉积相对比分析表明,改道后黄河主河道经历由北向南的变迁过程。

黄河三角洲潮坪环境现代生物遗迹与物化条件的响应关系

黄河三角洲潮坪在沉积过程中长期受各种物理化学环境因素的影响,而其中生物遗迹特征可以高精度高灵敏度地反映环境的变化。运用沉积学和遗迹学方法,全面系统地研究遗迹的分布、分异度、行为生态学、形态变化及扰动率等特征,分析其与三角洲潮坪沉积过程中受波浪和潮汐作用影响下物理化学因素之间的响应关系。结果表明:1)黄河三角洲潮坪沉积中生物遗迹的分异度、丰度与沉积物的粒度、沉积速率、水动力和总有机碳(TOC)含量分布基本一致,但盐度和浑浊度影响了生物遗迹分布的种类。造迹生物种类相同的情况下,盐度影响了生物的潜穴直径和扰动率,盐度相同的情况下,浑浊度影响生物潜穴的数量;2)潮上带生物遗迹分异度整体呈对称均衡分布,但在粉砂质底层区域和多条潮道的汇聚处,生物遗迹的丰度和分异度最高;3)潮间带整体生物遗迹分异度和丰度与粒度变化不大,但在TOC含量相对较高、水动力相对较弱、沉积速率低、盐度降低的几条潮道汇聚处,生物遗迹丰度和分异度达到最高;4)潮下带生物遗迹丰度和分异度整体呈对称均衡分布。该研究将补充、完善和修正已有的三角洲潮坪遗迹学和现代潮坪沉积学资料,并对高精度地解释、修正古潮坪环境起到一定的作用。

若尔盖盆地黄河出口段一级阶地沉积序列及其环境变化研究

对若尔盖盆地进行实地考察,选取盆地西端黄河出口段典型的一级阶地沉积序列为研究对象。通过沉积物粒度和端元特征分析及OSL测年断代,对若尔盖盆地出口段的环境变化进行研究。研究结果表明:阶地底部的河床相砂卵石与河漫滩沙层构成了二元结构沉积层,其中河漫滩沙层夹有5.0—4.2 ka B.P.期间堆积形成的浅洼地泥沼土透镜状层,表明该河段黄河一级阶地从5.0 ka B.P.开始形成。河漫滩上为高原强劲风力改造成的风沙层,夹有古洪水滞流沉积层组,表明4.2—4.0 ka B.P.期间气候恶化,黄河源曾发生多期特大洪水事件。4.0—2.8 ka B.P.期间气候湿润,阶地面浅洼地有淤泥质沼泽形成。其后沙尘暴搬运堆积的粗粉沙覆盖阶地面,形成了风成黄土,其上部经生物风化成壤改造,发育成为具有团粒构造的现代亚高山草甸黑土土壤层。

准噶尔盆地南安集海河剖面中侏罗统头屯河组浅水三角洲沉积特征

准噶尔盆地南缘中侏罗统头屯河组是重要的油气勘探目的层系。通过对准噶尔盆地南缘南安集海河剖面实地丈量,结合岩石样品的薄片鉴定资料和地球化学分析测试资料,对该剖面头屯河组的岩性和沉积构造进行了描述,分析了其沉积环境、沉积相类型及其演化规律。研究结果表明:(1)准噶尔盆地南缘南安集海地区中侏罗世头屯河组沉积期经历了半干旱—干旱—湿润的气候演化,湖盆水体较浅,湖底地形平缓,发育浅水三角洲沉积。(2)在剖面上识别出了分流河道、分流间洼地、水下分流河道、水下分流间湾、席状砂、滩坝等6种沉积微相类型。头屯河组浅水三角洲受河流和湖浪共同作用,在湖盆水体稳定期形成了河控浅水三角洲;在高频振荡期发育了浪控浅水三角洲。(3)从头屯河组沉积早期到晚期,湖平面先下降后上升。头屯河组一段发育河控浅水三角洲,分流河道水动力较强,河流频繁改道分叉,不断向湖盆方向进积,多期河道呈拼接式,此时分流河道和水下分流河道占据主导地位。随着气候进一步干旱,头屯河组二段发育浪控浅水三角洲,河流作用减弱,波浪改造作用增强,三角洲平原以发育切叠式分流河道为主,三角洲前缘水下分流河道砂体被波浪冲刷改造,形成带状展布的席状砂。头屯河组三段,由于准噶尔盆地持续沉降和三角洲朵体侧向迁移作用,浅水湖盆的三角洲朵体表面被湖水覆盖,浅水三角洲前缘的部分碎屑物质受风浪改造,形成平行于湖岸的滩坝沉积。

珠江三角洲晚第四纪沉积序列及其对海侵过程的响应

地处南海北部的珠江三角洲在晚第四纪以来经历了数次海面升降过程,沉积了多套海相、陆相及海陆交互相地层,为研究河口海岸带地区的沉积模式及古环境演变过程提供了良好的研究材料。以江门GC088孔岩芯为主要研究材料,通过岩相分析、粒度分析、磁化率、微体古生物学及年代测试分析等手段,结合区域内其他第四系钻孔剖面资料,综合揭示了珠江三角洲江门新会地区晚更新世以来地层沉积序列及沉积环境演变过程,主要得出如下结论:(1)新会地区第四系存在河床相、潮控河流相、河口湾相、三角洲前缘相、潮坪相、三角洲平原相6种沉积相及风化形成的花斑黏土层;(2)通过本文新获取的14C和OSL年代测试结果并综合对比区域内其他钻孔的测年结果建立了新会地区晚第四纪以来的年代框架,认为珠江三角洲普遍存在2次海侵-海退旋回过程,且下海侵旋回的年代应归属于MIS 5;(3) GC088孔多指标分析结果呈现出较好的周期性,与海平面变化曲线变化较一致;结合区域内部分钻孔沉积相变化及其他各类指标结果(如元素比值、孢粉、有孔虫等),揭示了珠江三角洲MIS 5阶段可能存在次一级海平面波动。本研究结果表明珠江三角洲晚更新世的沉积环境演化过程主要受到全球海平面变化及冰期-间冰期旋回时岸线移动的影响。