Thresholds of intrabed flow and other interactions of turbidity currents with soft muddy substrates          下载免费PDF全文

Jaco H. Baas  Rafael Manica  Eduardo Puhl  Ana Luiza de Oliveira Borges 《Sedimentology》2016,63(7):2002-2036

Controlled laboratory experiments reveal that the lower part of turbidity currents has the ability to enter fluid mud substrates, if the bed shear stress is higher than the yield stress of the fluid mud and the density of the turbidity current is higher than the density of the substrate. Upon entering the substrate, the turbidity current either induces mixing between flow‐derived sediment and substrate sediment, or it forms a stable horizontal flow front inside the fluid mud. Such ‘intrabed’ flow is surrounded by plastically deformed mud; otherwise it resembles the front of a ‘bottom‐hugging’ turbidity current. The ‘suprabed’ portion of the turbidity current, i.e. the upper part of the flow that does not enter the substrate, is typically separated from the intrabed flow by a long horizontal layer of mud which originates from the mud that is swept over the top of the intrabed flow and then incorporated into the flow. The intrabed flow and the mixing mechanism are specific types of interaction between turbidity currents and muddy substrates that are part of a larger group of interactions, which also include bypass, deposition, erosion and soft sediment deformation. A classification scheme for these types of interactions is proposed, based on an excess bed shear stress parameter, which includes the difference in the bed shear stress imposed by the flow and the yield stress of the substrate and an excess density parameter, which relies on the density difference between the flow and the substrate. Based on this classification scheme, as well as on the sedimentological properties of the laboratory deposits, an existing facies model for intrabed turbidites is extended to the other types of interaction involving soft muddy substrates. The physical threshold of flow‐substrate mixing versus stable intrabed flow is defined using the gradient Richardson number, and this method is validated successfully with the laboratory data. The gradient Richardson number is also used to verify that stable intrabed flow is possible in natural turbidity currents, and to determine under which conditions intrabed flow is likely to be unstable. It appears that intrabed flow is likely only in natural turbidity currents with flow velocities well below ca 3·5 m s^?1, although a wider range of flows is capable of entering fluid muds. Below this threshold velocity, intrabed flow is stable only at high‐density gradients and low‐velocity gradients across the upper boundary of the turbidity current. Finally, the gradient Richardson number is used as a scaling parameter to set the flow velocity limits of a natural turbidity current that formed an inferred intrabed turbidite in the deep‐marine Aberystwyth Grits Group, West Wales, United Kingdom.  相似文献   

Planktonic foraminifera and calcareous nannofossils record in the upper Campanian-Maastrichtian pelagic deposits of the Malatya Basin in the Hekimhan area (NW Malatya,eastern Anatolia)     

《Cretaceous Research》2016

The uppermost Cretaceous (upper Campanian-Maastrichtian) pelagic successions from the Malatya Basin (NW Malatya, eastern Anatolia) were studied by 688 samples, which were collected from five stratigraphic sections in the Hekimhan area. The pelagic deposits conformably overlie rudist bearing shallow-water limestones and are overlain conformably by Maastrichtian dolomites and unconformably by Paleocene-Eocene deposits, respectively.The pelagic successions in the Hekimhan area comprise the Kösehasan Formation at the base and the Zorbehan Formation at the top and reach up to 1100 m in thickness. The Kösehasan Formation rests over the neritic rudist-bearing limestones of the Güzelyurt Formation along a sharp contact and consists mainly of flysch-type sandstone-mudstone alternation with complete and partial Bouma sequences. The carbonate content of abundant planktonic foraminifera and nannoplankton-bearing 980-m-thick succession increases upwards and the formation passes gradually to the clayey limestones and marlstones of the Zorbehan Formation to the top. Occurrences of nannoplankton Lithraphidites quadratus Bramlette and Martini and Micula praemurus (Bukry) in the first beds of the Kösehasan Formation indicate that the age of the Kösehasan Formation and overlying Zorbehan Formation is of late Maasthrichtian. Another late Maastrichtian taxa Cribrosphaerella daniae Perch-Nielsen and Arkhangelskiella maastrichtiana Burnett are observed from the lowermost part of the succession. Maastrichtian planktonic foraminifera such as Contusotruncana walfischensis (Todd) and Globotruncanita pettersi (Gandolfi) were recorded through the successions. Although planktonic foraminifera are diverse and abundant particularly in the Kösehesan Formation, index late Maasthrichtian species were not encountered. Campanian and Santonian-Campanian planktonic foraminifera, e.g. Radotruncana calcarata (Cushman) and Globotruncanita elevata (Brotzen), obtained particularly from the lower part of the succession and calcareous nannofossils such as Broinsonia parca parca Bukry, Reinhardtites anthophorus (Deflanre) and Eiffellithus eximius (Stover) are interpreted as reworked from older strata. Trace fossils are common throughout the succession.Rareness of planktonic foraminifera and nannoplankton in the uppermost part of the succession (Zorbehan Formation) indicates maximum shallowing of the latest Maastrichtian sea in this part of the basin. Rare echinoids, bivalves and ammonites are observed in that part of the sequence.The obtained data indicate that sediment accumulation rate of the pelagic deposits is rather high and about 27.5 cm/ky for this part of the basin. Changes in thickness of the formations along short distances in the five stratigraphic sections analysed in this study should be related to the diachroneity of the depositional and erosional events.  相似文献   

内蒙古巴拉格歹地区构造混杂岩带中浊积岩、震积岩特征及意义——以内蒙古哈拉黑等八幅1:5万区域地质调查为例     

张庆奎  杨宾  邵学峰  陈树良  赵明远  吕凤祥 《地质通报》2018,37(9):1731-1735

浊积岩为具有鲍马序列的古海沟沉积,其部分沉积物与古海沟地震密切相关,由于岛弧外弧海沟地质构造复杂,洋板块俯冲及火山岩的喷发,地震活动强烈、频繁,沉积岩在成岩过程不断受到地震扰动,形成具有地震活动特点的震积岩。通过对巴拉格歹地区构造混杂岩带中浊积岩、震积岩的研究,识别出浊积岩系的具递变层理的槽模、沟模等冲刷铸模,包卷层理构造及最顶部黑色粉砂质泥岩段;识别出震积岩系的液化脉、地震震碎角砾岩、滑塌角砾岩、震褶岩-卷曲、纹层状、阶梯状断层构造等,建立并确认浊积岩、地震岩识别标志,恢复古地理构造环境,认为原划分的大石寨组应该解体,应为一套弧前盆地古海沟浊积岩沉积。结合浊积岩中的火山岩、基性岩及区域上化石山发现的超基性岩,初步确认,在测区浊积岩与岛弧火山岩、洋壳沉积物受板块碰撞拼接作用,由一系列逆冲断裂将上述各种块体构造就位在一起,形成构造混杂岩,为二连-贺根山缝合带在本区东延问题提供了资料。  相似文献   

Biotic response to the latest Cenomanian drowning and OAE2: A case study from the Eastern Desert of Egypt     

Emad Nagm  Sreepat Jain  Kamel Mahfouz  Ahmed El-Sabbagh  Aziz Abu Shama 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):70-92

The changes in macrofauna and microfauna, before, during and after the latest Cenomanian global Oceanic Anoxic Event (OAE2), from the Eastern Desert of Egypt are documented, along with an inferred paleoenvironment. The age of the studied OAE2 interval is constrained by the last occurrence of the marker calcareous nannofossils species Axopodorhabdus albianus along with the previously identified positive δ¹³C excursion from the coeval ammonite Vascoceras cauvini Zone (= Neocardioceras juddii Zone), enabling correlation with the peak ‘b’ of the OAE2. Based on the studied microfaunal assemblages, a warm shallow restricted lagoonal environment with mesotrophic conditions and strong seasonality is inferred. The presence of a rare ammonite (and ostracods) attest to the intermittent introduction of marine waters within this inner ramp setting. In terms of sequence stratigraphy, two 3rd order depositional sequences are recorded. The top surface of the first depositional sequence, at the sequence boundary, SB Ce 5 (the start of the OAE2), is marked by an abrupt faunal change with reduced abundances of the macrofaunal elements. This is in tune with other Egyptian records of relatively smaller loss (10 %) at the Cenomanian-Turonian boundary, as compared to much higher numbers (53–79% of species), globally. This faunal (biotic bottleneck) and lithological change (from siliciclastic-dominated deposits to a largely carbonate-dominated one) at the SB Ce 5 is attributed as a response to the latest Cenomanian drowning (the highest sea-level during the Phanerozoic), that also resulted in the formation of carbonate platform.  相似文献   

花垣县李梅地区早寒武世清虚洞期碳酸盐岩中的风暴沉积   总被引：4，自引：0，他引：4  

劳可通 《湖南地质》1989,8(3):10-16

扬子地台东南缘的花垣李梅地区,早寒武世晚期清虚洞组钙质风暴岩分布广泛,表现为层数众多,剖面类型丰富,识别标志清楚,颇具特色。风暴作用强度和侵蚀力按地层层序自下而上有由弱到强的规律性变化,与本区清虚洞期陆棚浅滩化演变过程相对应。早寒武世晚期的风暴事件与本区岩相、岩性的分布,均有密切联系。  相似文献   

Siliceous microfossils of the Upper Cretaceous Mishash Formation,Central Negev,Israel     

S. Moshkovitz  A. Ehrlich  D. Soudry 《Cretaceous Research》1983,4(2):173-194

New finds of siliceous microfossils, mainly diatoms, are reported from hard limestone levels in the Campanian cherty Mishash Formation, Negev, Israel. Twenty taxa were recognized, of which Melosira campaniensis and Trinacria negeviensis are new species. Representatives of Ebridians are reported for the first time from Cretaceous sediments. Calcareous nannofossils are usually few and poorly preserved. The diversity of the micro- and nannofossil assemblages vary through the succession and points to fluctuations in the palaeoenvironmental conditions from restricted to more normal marine. The moderate preservation of the opaline microfossils within the limestones is probably the result of early diagenetic lithification.  相似文献   

The deep-lake deposit in the Upper Triassic Yanchang Formation in Ordos Basin, China and its significance for oil-gas accumulation     

CHEN QuanHong  LI WenHou  GAO YongXiang  GUO YanQin  FENG JuanPing  ZHANG DaoFeng  CAO HongXia  LIANG JiWei 《中国科学D辑(英文版)》2007,50(Z2):47-58

The deep-lake facies of the Yanchang Formation represents a large outflowing lake basin in the Ordos area. Its deposition can be divided into four stages lake genetic and expanding stage, peak stage, inversion stage and dying stage. All the stages are obviously consistent with the evolution of depositional environment and the paleoclimate in the region. The study indicates that the lake basin has evolution fluctuations from highstand to lowstand for four times in its evolution history, and the deposition center of the lake has not obviously moved, staying along the Huachi-Yijun belt. The deep lake sedimentary system mainly consists of deep water deltas and turbidite fans during the entire evolution course of the lake basin in the Late Triassic. The former mainly developed on the slope of steep shore of the delta in the early period of the deep-water expansion and gradually experienced a big shift from deep-water deltas to shallow-water platform delta. And the latter appeared almost in all the above stages and had two types of turbidite fans, slope-moving turbidite fans and slump turbidite fans. The slope-moving turbidite fans have relatively complete facies belts overlapping one another vertically and consist of the slope channel of inter fans, the turbidite channel, inter turbidite channel and turbidite channel front of middle fans and outer fans (or lakebottom plain). However, the slide-moving turbidity fans are formed in the deep lake with their microfacies difficult to be distinguished, and only the center microfacies and edge microfacies can be determined. The two types of the turbidity fans are similarly distributing in the near-root-slope and far-root-slope regions. The deep-lake deposition governs the distribution of the hydrocarbon and reservoir, while the slope-moving turbidite fans are excellent reservoirs for oil-gas exploration due to their great thickness, widespread distribution and accumulation properties.  相似文献   

广西金牙金矿床百逢组沉积特征及其与金矿的关系   总被引：2，自引：2，他引：2  

肖建新  杨建民  林畅松  刘景颜 《现代地质》2001,15(3):269-274

广西金牙金矿产于中三叠统百逢组中 ,矿区的百逢组为一套陆源碎屑浊积岩 ,既有阵发性高密度浊流引起的浊积扇体系 ,又有稳定低密度浊流引起的鲍马序列。百逢组下段为浊积扇体系 ,中段及上段为鲍马序列 ,一般不全 ,其中d、e段最发育 ,其次为c、b段。金矿化出现在砂泥混积的百逢组中段。矿体位于鲍马序列段 ,尤其是de和cde组合段 ,岩石为富含有机质的泥质与粉砂的混积岩 ,属远端浊积岩。其中 ,钙质泥岩和粉砂质泥岩是最有利的矿化围岩。主要载金矿物毒砂和黄铁矿呈自形晶出现。矿体的有机碳含量高于相邻围岩的有机碳含量 ,与运移烃类的叠加有关。金品位随有机碳含量的增加而增加 ,有机质也是有用的金的载体。富含有机质的浊积岩是浊积岩型金矿床形成的有利条件。  相似文献   

深水浊积砂体的成因机理及特征   总被引：1，自引：0，他引：1  

陈海洲  李瑞军 《上海国土资源》2007,4(3):10-13

深水浊积砂体及其体系域以其重要的理论意义和作为油气储集层的经济价值始终是沉积地质学研究的主要领域之一。深水浊积砂体是在深水环境下在重力作用下所形成的一个连续过程的组成部分。这个连续部分可以分为五类:泥石流、颗粒流、流体化沉积物流、浊流和滑塌。由浊流过程形成的深水环境下的浊积砂体,具有海相浊积体和湖相浊积体的特征,与海(湖)平面的下隆低水位有关。  相似文献   

浊积岩型金矿简介     

王尚彦  张立新  王睿 《贵州地质》2007,24(1):32-35

本文简要介绍了浊积岩型金矿的概念、特征、成因和2个浊积岩型金矿的矿床实例,并对浊积岩型金矿概念和应用作了讨论。  相似文献