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1.
西沙礁相第四纪地层初步研究 总被引：5，自引：1，他引：5
本文根据西沙三个全取芯钻孔的纵向序列,结合部分年代学数据,开展了岩石地层学、生物地层学、碳、氧稳定同位素和地球化学地层学研究,对西沙礁相第四纪地层进行了划分。整个第四系称西沙群,下更新统称永兴组,中更新统称琛航组,上更新统仍沿用石岛组,全新统称为西沙洲组。这一新的系统划分,对海陆第四纪地层间的互相对比提供了一定的依据。 相似文献
2.
High‐resolution chirp sonar profiling in the northeastern Skagerrak shows acoustically stratified sediments draping a rough‐surfaced substratum. A 32 metre long sediment core retrieved from the survey area encompasses the entire Holocene and latest Pleistocene. The uppermost seismo‐acoustic units in the chirp profiles represent Holocene marine sediments. The lowermost unit is interpreted as ice‐proximal glacial‐marine sediments rapidly deposited during the last deglaciation. The end of ice‐proximal sedimentation is marked by a strong reflector, interpreted to have been formed during latest Pleistocene time as a consequence of rapid ice retreat and drastically lowered sedimentation rate. The subsequent distal glacial‐marine sediments were deposited with initially high sedimentation rates caused by an isostatic rebound‐associated sea‐level fall. Based on correlation between the core and the chirp sonar profiles using measured sediment physical properties and AMS 14C dating, we propose a revised position for the Pleistocene/Holocene boundary in the seismo‐acoustic stratigraphy of the investigated area. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
3.
We present results of study of Holocene and Late Pleistocene deposits recovered on the underwater Akademichesky Ridge in Lake Baikal. The change in mineral composition and grain size in the bottom sediment core is closely consistent with the change of major diatom complexes marking the Holocene–Late Pleistocene boundary. A high content of chloritoid (up to 14.6%) has been found among the heavy minerals of the sand fraction of Late Pleistocene clays. The concentration of chloritoid in Holocene mud is no higher than 1.2%. The source of chloritoid is chloritoid shales of the Anaya Formation (Upper Proterozoic), widespread in the watershed of the Primorsky Ridge in the upper reaches of the Lena and Anaya Rivers. Chloritoid was transported to the area of the Akademichesky Ridge by predominant western and northwestern winds, which is also evidenced from the absence of mechanical impacts on the surface of its grains. The high contents of chloritoid in the Late Pleistocene sediments are due to the more intense eolian transportation at that time as compared with the Holocene. 相似文献
4.
三万年前后太湖平原环境变化中的若干问题 总被引：8，自引：0，他引：8
根据近400个浅钻（30m）的岩性、岩相及其空间分布规律和14C年龄、矿物、粒度、微体、孢粉、软体动物化石分析,揭示了组成太湖基底及太湖平原的浅层第四系主要是23000—18000 aB.P.的褐黄色粘土、28000—23000 aB.P.前后的灰色粉砂和亚粘土以及大于33000 aB.P.的暗绿色粘土。上层和下层均属陆相,系海退过程中的泛滥沉积,示干冷环境;中层为海相,反映温湿的季风海洋性气候。区内全新统仅沉积于上层黄土侵蚀沟谷和洼地中,全新世海侵是局部的。 相似文献
5.
The boundary between the last two geological epochs, the Pleistocene and the Holocene, is placed at 'the date 10,000 B.P., measured in radiocarbon years'. In the European chronostratigraphy, this corresponds to the Younger Dryas/Preboreal boundary, the pollen zone III/IV boundary and the Late Glacial/Postglacial boundary. The stratal sequence in the Botanical Garden of Gothenburg is proposed as a suitable boundary-stratotype of the Pleistocene/Holocene that fulfils the stratigraphical rules of marine environment and accessibility. A core, labelled B 873, has been analyzed for multiple parameters by various authors. The suggested Pleistocene/Holocene boundary in Core B 873 is indicated by a lithologic boundary, a palynological change tentatively correlated with the pollen zone III/IV boundary, and a distinct palaeomagnetic intensity maximum, the 'Gålön Magnetic Intensity Maximum', identified in numerous other cores at the Younger Dryas/Preboreal boundary and at the drainage of the Baltic Ice Lake in varved clay sequences (with the peak dated at the drainage ±4 varves). This boundary is closely radiocarbon dated at 10,000 B.P. (10,000–9950 B.P.) in terrestrial-lacustrine sequences within the proposed type area in Gothenburg and in Southern Sweden, the established type region for the Pleistocene/Holocene boundary. The corresponding varve date is 9965 varves B.P. (De Geer's varve –1073). The various parameters directly and indirectly connected with the study of Core B 873 make global correlations possible. Because every region has its own local characteristics, however, it will be necessary to establish regional type sections, hypostratotypes. 相似文献
6.
中国第四纪地层 总被引：32，自引：0，他引：32
本文综述了中国第四纪沉积类型及第四系的划分,并与国际第四系划分进行了对比。指出中国第四纪沉积物分布广泛,种类繁多,以陆相沉积为主。按其成因主要有风成黄土堆积、河一湖相沉积、冲一洪积堆积、冰川沉积、洞穴堆积、风化壳残积（红土）、火山堆积和海相沉积等。各种沉积物都有很好的剖面,尤其是黄土和河一湖相沉积更为连续完整。按中国第四纪地层发育的实际情况,第四系的底界应置于松山一高斯极性转换界线（Ｍ／Ｇ,２．６ＭａＢ,Ｐ,）;第四系内部划分为更新统（Ｑｐ）和１４新统（Ｑｈ）,界线在１１０００ａＢ,Ｐ,。更新统进一步划分为下、中和上３个阶(Ｑｐ１, Ｑｐ２, Ｑｐ３), Ｑｐ２／Ｑｐ１的界线为布容一松山极性转换界线（Ｂ／Ｍ; ０．７８ＭａＢ,Ｐ,）;Ｑ(ｐ３／Ｑｐ２的界线为本次间冰期的起始时间（０．１２８ＭａＢ,Ｐ,）。 相似文献
7.
《Geodinamica Acta》2013,26(2):153-161
The Quaternary tectonic activity in the Gulf of Cadiz has considerably influenced the depositional regime and distribution of Holocene marine deposits. The aim of this work is to determine the nature of the recent sedimentary filling in the Bay of Cadiz sea bottom and adjacent continental shelf and to establish the main controlling factors on the Holocene marine sedimentation. The sedimentary record indicates siliciclastic sedimentation supplied from the continent, with alternating episodes of high and low sedimentation rates. The recent sedimentary evolution of this marine area was controlled by the Late Quaternary eustatic fluctuations. Bathymetric, geophysical and drilling data have been employed to prepare a detailed isopach map of the non-consolidated recent sedimentary cover. Thickness distribution shows significant variations related to the infilling of former fluvial palaeochannels incised during the Late Pleistocene lowstand, and highly controlled by the structural neotectonic trends of faults and joints: NNW-SSE, NNE-SSW and ENE-WSW. The general distribution of isopachs in this area is clearly influenced by these morphostructural lines, which controlled the sedimentary processes during the Holocene. These results are coherent with the main regional neotectonic structures previously described in the nearby continental area, and confirm their prolongation towards the marine domain. 相似文献
8.
渤海湾泥质海岸带国土资源大调查以其特有的方法、手段和要求,获得了一批带有地质调查特点的、关于全新世地层与近现代地质环境变化的阶段性成果,主要包括:1)该地区海岸带全新世地层具有4种沉积类型:(A)远离海岸的传统的"三分"型;(B)海相层与陆(海陆过渡)相层的多次交替;(C)末次冰期后期未接受沉积,全新统半咸水的海陆过渡相直接覆于历时约10～20ka的沉积间断面上,向上,进一步发育为海相层;(D)沿海低洼地区在末次盛冰期后的晚更新世晚期即已进入海侵阶段,晚更新世晚期与全新世早期的海陆过渡相沉积是连续的,向上继续发育海相层.2)从以海水影响为主的开放潮坪(及浅海区)环境转变为(陆源影响逐渐加强的)湖-盐沼环境,是研究区中晚全新世地质环境转变的重要特征,建立了表征这两种不同环境的非正式地层单位("灰色单元"与"黄色单元").3)牡蛎礁与贝壳堤的对比方案,以牡蛎礁对应潮坪的贝类繁盛期,牡蛎礁中的水平再搬运夹层和/或上覆泥质盖层(往往形成"岭地")对应贝壳堤成堤.4)大比例尺区调地质点(浅孔)揭示了中晚全新世(近现代)地质环境变化,编绘出约4500calB.P.以来小于1ka时段的二维、假三维环境系列图.一个实例是Ⅱ贝壳堤向陆侧的洼地甚至早于该堤的形成,推测洼地边缘的NNW向的埋藏线性凸起可能受同一方向的新构造活动控制.5)渤海湾沿海平原线性砂坝(障壁岛)-湖/盐沼成因假说.作为堆积贝壳堤正地形的补偿,堤前因"簸选"贝壳导致的潮坪负地形,同样可发育湖沉积.6)210pb/137Cs测年研究提供了该地区现代沉积速率的初步结果(＜0.1cm/a或＞3cm/a不等),据此将海岸带划分为不同的沉积类型区. 相似文献
9.
The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition. The first and the second episodes occurred in Late Pleistocene times. The second episode was followed by a soil forming interval (Early Holocene to Mid-Holocene times). The third episode took place at about 5000 yr BP, after the Holocene sea-level maximum when marine regression began. The fourth episode constitutes a historical event of only local significance.Loess shows a fairly constant granulometric and mineralogical composition. The modal fraction consists of very fine sand and coarse silt (3 to 5 phi). They are classified as sandy silts or silty sands. Three grain-size subpopulations are differentiated: coarse, medium and fine. The medium-size subpopulation, which is the most important, consists of most of the very fine sand and coarse silt. It is thought to be transported by modified saltation and short-term suspension during local dust-storms.The mineralogical composition of loess consists of a volcaniclastic assemblage derived mainly from reworked pyroclastic deposits, primary tephras and volcaniclastic sediments. The source area of these materials was located in the lower Colorado river valley about 400 km SW of the studied area. There was also a direct supply by volcanic ash falls. 相似文献
10.
《Boreas: An International Journal of Quaternary Research》2018,47(3):754-767
The Fehmarn Belt is a key area for the Late Pleistocene and Holocene development of the Baltic Sea as it was a passage for marine and fresh water during its different stages. The pre‐Holocene geological development of this area is presented based on the analysis of seismic profiles and sedimentary gravity cores. Late Pleistocene varve sediments of the initial Baltic Ice Lake were identified. An exceptionally thick varve layer, overlain by a section of thinner varves with convolute bedding in turn covered by undisturbed varves with decreasing thicknesses is found in the Fehmarn Belt. This succession, along with a change in varve geochemistry, represents a rapid ice‐sheet withdrawal and increasingly distal sedimentation in front of the ice margin. Two erosional unconformities are observed in the eastern Mecklenburg Bight, one marking the top of the initial Baltic Ice Lake deposits and the second one indicating the end of the final Baltic Ice Lake. These unconformities join in Fehmarn Belt, where deposits of the final Baltic Ice Lake are missing due to an erosional hiatus related to a lake‐level drop during its final drainage. After this lake‐level drop, a lowstand environment represented by river deposits developed. These deposits are covered by lake marls of Yoldia age. Tilting of the early glacial lake sediments indicates a period of vertical movements prior to the onset of the Holocene. Deposits of the earliest stages of the Baltic Sea have been exposed by ongoing erosion in the Fehmarn Belt at the transition to the Mecklenburg Bight. 相似文献
11.
S.J. MAZZULLO 《Sedimentology》2006,53(5):1015-1047
Lithostratigraphy, depositional facies architecture, and diagenesis of upper Pliocene to Holocene carbonates in northern Belize are evaluated based on a ca 290 m, continuous section of samples from a well drilled on Ambergris Caye that can be linked directly to outcrops of Pleistocene limestone, and of overlying Holocene sediments. Upper Pliocene outer‐ramp deposits are overlain unconformably by Pleistocene and Holocene reef‐rimmed platforms devoid of lowstand siliciclastics. Tectonism controlled the location of the oldest Pleistocene platform margin and coralgal barrier reef, and periodically affected deposition in the Holocene. A shallow, flat‐topped, mostly aggradational platform was maintained in the Holocene by alternating periods of highstand barrier‐reef growth and lowstand karstification, differential subsidence, and the low magnitude of accommodation space increases during highstands. Facies in Pleistocene rocks to the lee of the barrier reef include: (i) outer‐shelf coralgal sands with scattered coral patch reefs; (ii) a shoal–water transition zone comprising nearshore skeletal and oolitic sands amidst scattered islands and tidal flats; and (iii) micritic inner‐shelf deposits. Four glacio‐eustatically forced sequences are recognized in the Pleistocene section, and component subtidal cycles probably include forced cycles and autocycles. Excluding oolites, Holocene facies are similar to those in the Pleistocene and include mud‐mounds, foraminiferal sand shoals in the inner shelf, and within the interiors of Ambergris and surrounding cayes, mangrove swamps, shallow lagoons, and tidal and sea‐marginal flats. Meteoric diagenesis of Pliocene and Pleistocene rocks is indicated by variable degrees of mineralogic stabilization, generally depleted whole‐rock δ18O and δ13C values, and meniscus and whisker‐crystal cements. Differences in the mineralogy and geochemistry of the Pliocene and Pleistocene rocks are attributed to variable extent of meteoric alteration. Dolomitization in the Pliocene carbonates may have begun syndepositionally and continued into the marine shallow‐burial environment. Positive dolomite δ18O and δ13C values suggest precipitation from circulating, near‐normal marine fluids that probably were modified somewhat by methanogenesis. Sedimentologic and diagenetic attributes of the Pliocene–Pleistocene rocks in the study area are similar to those in the Bahamas with which they share a common history of sea‐level fluctuations and climate change. 相似文献
12.
High-resolution seismic data shed light on latest Pleistocene and Holocene sedimentation beneath the Büyükçekmece Bay, northern shelf area of the Marmara Sea, Turkey. Discontinuous fluvio-marine and marine deposits overlying the erosional truncation surface of Oligocene–Lower Miocene deposits are as thick as 30 m and preserved preferentially within the incised valleys that were controlled by some old faults. A series of prograding shoreline, laterally passing to the latest Pleistocene–Holocene valley-fill deposits, are thought to have accumulated mainly during times of shoreline transgression and sea-level rise. The overall morphology and stratigraphic setting observed in the Büyükçekmece Bay and at the southern outlet of the Bosphorus Strait have nearly same characteristics, implying that similar hydrodynamic conditions, erosional and depositional processes were mainly under the control of strong northerly flows during the Late Quaternary. These flows were less powerful in the Büyükçekmece region with decreased sediment input and smaller accommodation space. 相似文献
13.
《Quaternary Science Reviews》2007,26(7-8):876-893
The Quaternary sedimentary record of Sal Island includes marine and related aeolian and alluvial fan deposits. The substratum of the island is volcanic, with ages between 25 and 0.6 Ma. Quaternary marine units generally occur as raised marine terraces forming a broad staircase between elevations of 55–60 m and present sea level. Terraces include a basal conglomerate overlaid by calcarenite; both host corals, algae and molluscs.A chronostratigraphic framework for the Middle Pleistocene to Holocene units has been generated based on a geomorphologic map of the Quaternary landforms and associated deposits and morphosedimentary analysis, with support of laboratory dating: U-series by TIMS in corals, 14C analyses, palaeomagnetic measurements, and K/Ar ages from other literature. U-series dating of corals from marine terraces provides benchmarks for the Last Interglacial (Oxygen Isotope Substage 5e) and Holocene deposits. The present elevation of the marine terraces and their staircase arrangement suggest a change in vertical movement trend around 330 ka from an uplift to either subsidence or stabilization. 相似文献
14.
15.
大凌河河口地区LZK06孔40m以浅岩心的沉积学、古生物学和年代学等综合研究以及该地区LZK02- 04钻孔资料,揭示了研究区中更新世晚期以来经历了两次海侵- 海退旋回,依次形成了中更新世晚期湖相/河流相 SymbolnB@ 晚更新世海相- 湖相/河流相 SymbolnB@ 全新世海相- 河流相地层。全新世早中期由于物源供给很少,研究区处于长达约10ka的饥饿滞留相沉积环境,平均沉积速率仅约0. 02~0. 05cm/a。全新世晚期约1500a cal BP以来,由于人类活动导致水土流失,河流输砂量增加,研究区开始了快速加积过程,平均沉积速率约0. 9~1. 2cm/a,下辽河平原被快速充填,开始成陆。与全球海面变化时空分布特征的对比,推断辽东湾的第II海相层发育于MIS 5- MIS 3早期,第I海相层发育于MIS 1阶段高海面时期。晚更新世以来频繁的海面升降是辽东湾泥质海岸带地层和环境演化的主要控制因素。 相似文献
16.
Borings from the barrier island/lagoon system of the Eastern Shore of Virginia penetrated an unconformity which separates Pleistocene barrier island and offshore marine sediments from the overlying Holocene tidal delta and barrier island sediments. Offshore marine sediments and deposits within the flood-tidal delta (marsh, tidal flat-bay, inlet-mouth bar complex) are recognized on the basis of sediment color, composition, grain-size changes in the vertical sequence, presence of organic matter, and faunal suite. Subsurface data, historical records, and morphology of lateral accretion on barrier islands suggest that major inlets in the vicinity of Wachapreague have been relatively stable throughout Holocene time; they appear to be located where Pleistocene stream valleys previously existed. Holocene barrier islands apparently developed on drainage divide areas following post-Wisconsin transgression of the sea.
The initial phase of tidal delta development was characterized by vertically accreting, fan-shaped, inlet-mouth bars; tidal channels stabilized after bar crests had shoaled sufficiently for marsh to form. With landward progradation across the lagoon, sand-rich deposits graded laterally away from the inlets and vertically into clayey sand and silty clay of the tidal flat-bay and marsh environments.
Ebb inlet-mouth bars developed asymmetrically southward in response to littoral drift. Flood tidal deltas also built preferentially toward the south as indicated by: (1) sand distribution of the inlet-mouth bar complex; and (2) greater development of marsh south of the inlets. 相似文献
17.
With the exception of the south of the country, the Netherlands has a strong bipartite hydrogeology: the Holocene part with a coastal dune belt and confining top layer of clay and peat further inland, and the Pleistocene, where thick phreatic aquifers dominate. This research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions. Close to 6000 groundwater analyses were grouped and interpreted in terms of 1. salinity, 2. redox status, 3. acid/base and carbonate status and 4. natural nutrients NH4 and PO4. The a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians, even for geologically or geographically related data groups. The compound-specific interpretation indicates that there are geogenically controlled, systematic differences in groundwater composition at the regional scale. The imprint of the geological sediments on the groundwater composition decreases in the order marine/estuarine via limnological, fluvial to aeolian. The imprints with respect to pH and carbonate status, natural nutrients and redox status are not necessarily interrelated. The vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive Holocene, confining top layer or temporal changes in contamination. In the Holocene part, the salinity is controlled by the palaeoenvironmental conditions during the Holocene and by the recharge origin: the average Cl concentration decreases from estuarine via lagoonal to the former Zuider Sea (which was a bay). The most reduced states and also the highest nutrient concentrations and highest CO2 pressure are related to the presence of Holocene marine sediments in the confining top layer. Degradation of marine-derived organic matter as a nutrient source, is likely more intense in the Holocene deposits than that of peat and sedimentary remnants of terrestrial plants. A broad range in pH, carbonate status and redox status is encountered in the Pleistocene part. Here, the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in pH, calcite saturation and silicate weathering. One region with Late Pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the Holocene part of the Netherlands. Furthermore, reactive Fe is not abundant in all Pleistocene fluvial sediments nor is it maximally mobilised, as not all anoxic groundwater in these sediments is siderite-saturated. This leads to considerable intra- and inter-region variability. 相似文献
18.
The Moringa Cave within Pleistocene sediments in the En Gedi area of the Dead Sea Fault Escarpment contains a sequence of various Pleistocene lacustrine deposits associated with higher-than-today lake levels at the Dead Sea basin. In addition it contains Chalcolithic remains and 5th century BC burials attributed to the Persian period, cemented and covered by Late Holocene travertine flowstone. These deposits represent a chain of Late Pleistocene and Holocene interconnected environmental and human events, echoing broader scale regional and global climate events. A major shift between depositional environments is associated with the rapid fall of Lake Lisan level during the latest Pleistocene. This exposed the sediments, providing for cave formation processes sometime between the latest Pleistocene (ca. 15 ka) and the Middle Holocene (ca. 4500 BC), eventually leading to human use of the cave. The Chalcolithic use of the cave can be related to a relatively moist desert environment, probably related to a shift in the location of the northern boundary of the Saharo-Arabian desert belt. The travertine layer was U-Th dated 2.46 ± 0.10 to 2.10 ± 0.04 ka, in agreement with the archaeological finds from the Persian period. Together with the inner consistency of the dating results, this strongly supports the reliability of the radiometric ages. The 2.46-2.10 ka travertine deposition within the presently dry cave suggests a higher recharge of the Judean Desert aquifer, correlative to a rising Dead Sea towards the end of the 1st millennium BC. This suggests a relatively moist local and regional climate facilitating human habitation of the desert. 相似文献
19.
澧县凹陷内第四系厚度达200m左右,由早更新世-中更新世中期沉积和全新统组成。早更新世-中更新世中期沉积除顶部为粘土外,主体为砾石层,在凹陷中央夹粉砂、细砂和少量粘土。全新统分布于凹陷南部,为湖冲积粘土。早更新世澧县凹陷区断陷沉降,于河道和冲积扇环境下接受沉积;中更新世凹陷逐渐扩张,沉积范围扩展至凹陷外缘,凹陷主体部位自边缘向中央依次为冲积扇和扇前浅湖环境。中更新世中后期因盆地扩张,自凹陷中央至边缘地带均为静水湖泊环境。中更新世晚期至晚更新世,凹陷及周缘因构造抬升而遭受剥蚀而缺失沉积。全新世凹陷南部受澧水及区域湖面上升影响而发育湖冲积沉积。 相似文献
20.
第四纪洞庭盆地沅江凹陷东缘鹿角地区构造—沉积演化研究 总被引：7，自引：0，他引：7
沅江凹陷为第四纪洞庭盆地东部的一个次级凹陷。通过地表地质调查和钻孔资料,在沅江凹陷东缘北部鹿角地区第四纪构造、沉积及地貌特征研究基础上,探讨并提出其构造-沉积演化过程：早更新世早期洪湖-湘阴断裂和荣家湾断裂相继活动,断裂以西地区断陷沉降并沉积,以东地区则构造抬升而遭受风化剥蚀。早更新世末期凹陷区东部构造反转抬升并遭受侵蚀。中更新世早期和中期凹陷区断陷沉降并接受沉积。中更新世晚期研究区整体抬升而遭受剥蚀。晚更新世西部主凹陷区在稳定或弱沉降并形成泥质沉积,东部间歇性抬升。在上述中更新世晚期开始的构造抬升的同时,研究区东部产生了自东向西、自南向北的构造掀斜。全新世构造总体稳定,西部洞庭湖区形成湖冲积。区域上,第四纪洞庭盆地构造性质经历了早期断陷到晚期坳陷的转变。 相似文献