Growth patterns of a proximal terrigenous margin offshore the Guadalfeo River, northern Alboran Sea (SW Mediterranean Sea): glacio-eustatic control and disturbing tectonic factors     

F. J. Lobo  A. Maldonado  F. J. Hernández-Molina  L. M. Fernández-Salas  G. Ercilla  B. Alonso 《Marine Geophysical Researches》2008,29(3):195-216

The shelf-upper slope stratigraphy offshore and around the Guadalfeo River on the northern continental margin of the Alboran Sea, Western Mediterranean Basin, has been defined through the interpretation of a grid of Sparker seismic profiles. We tried to identify evolutionary trends in shelf growth, as well as to determine the regional/local factors that may modify the influence of glacio-eustatic fluctuations. Four major depositional sequences are identified in the sedimentary record by a detailed seismic interpretation, which defines three significant intervals of shelf-upper slope progradation, dominated by deposition of shelf-margin wedges, which resulted in uniform patterns of shelf-margin growth in response to significant sea-level falls. In contrast, the record of transgressive intervals is more variable, mainly as the result of distinct patterns of regressive-to-transgressive transitions. Major progradational wedges are internally composed of seaward-prograding, landward-thinning wedges, interpreted to represent shelf-margin deltaic deposits. In contrast, the last aggradational interval is composed of shelf-prograding wedges that show distinct characteristics, in terms of seismic facies, morphology and distribution when compared with previous shelf-margin wedges. These shelf wedges are thought to represent the particular case of Regressive Systems or Shelf Margin Systems Tracts, and their development seems to be controlled by a drastic change in main depocenter location, which moved from the upper slope to the shelf during the Pleistocene. The stacking pattern of seismic units, the shallowness of the acoustic basement and the migration of the shelf break are used to infer spatial and temporal changes in tectonic subsidence-uplift rates, which interact with low-order glacio-eustatic changes. For much of the Pliocene-Quaternary, uplifted sectors alternated laterally with sectors experiencing more subsidence. Subsequently, a significant change from lateral outgrowth to vertical accretion is recognised. This stratigraphic change could be related to the combined influence of increased subsidence rates on the shelf and the onset of higher-frequency glacio-eustatic cyclicity after the Mid Pleistocene Revolution that occurred around 1 Ma.  相似文献   

上新世热带海道变化影响东亚气候的模拟研究     

谭宁  张仲石  郭正堂  王会军 《地学前缘》2022,29(5):310-321

上新世早—中期是巴拿马海道关闭及印度尼西亚海道收缩的关键时期。目前,针对这两个海道关闭的气候效应已有不少研究,但多数研究关注巴拿马海道、洋流变化及其与北半球高纬冰盖发育的联系,缺乏两大热带海道关闭/收缩对东亚气候影响及机理的研究。我们基于挪威地球系统模型(NorESM-L)探讨了印尼海道收缩及巴拿马海道的浅关闭对东亚气候的影响。结果表明,热带海道的关闭/收缩加强了北太平洋的经向梯度,进一步导致夏季近地表气温在东亚北部降低,东亚南部升高;降水在长江流域至中国东海一线显著增加,但在东亚南部至西南部显著减少。冬季,近地表气温在东亚大陆地区升高,降水减少。上述变化主要由印尼海道的收缩导致,除冬季温度外,巴拿马海道浅关闭对东亚气候的影响较弱。此外,结合定性的记录-模拟对比,我们进一步揭示出热带海道的关闭/收缩可在一定程度上影响东亚气候在中上新世的转型,但不是主要驱动力。  相似文献   

南沙海区晚上新世海水上层结构变化     

李建如  汪品先 《海洋地质与第四纪地质》2004,24(4):67-71

对南沙海区水深2772m的ODP1143站100～150m井段共101块沉积样品进行了浮游有孔虫分析，结果表明，从3．27Ma到2．55Ma该区表层海水温度逐步降低，温跃层逐步加深，推测是晚上新世北半球冰盖形成过程中，东亚季风相应加强的结果。与此同时，南沙与南海北部的温跃层深度差值不断加大，可能是西太平洋暖池最终形成或加强的表现。3．2Ma前后，表层海水温度和海水温跃层深度都发生了急剧变化，反映出北半球冰盖和西太平洋暖池的发育可能存在一定的相关性。  相似文献   

中国北方上新世晚期-更新世早期风成沉积物磁化率各向异性初探          下载免费PDF全文

朱艳明  周力平  张世红 《第四纪研究》2007,27(6):1009-1015

前人对中国黄土高原晚更新世黄土沉积物的磁化率各向异性的研究表明,磁化率椭球体最大轴(Kmax)偏角的方向能够指示黄土沉积时期的搬运动力方向,即古风向,并可以通过这种途径进行古季风的重建.本研究试图通过对中国黄土高原晚上新世-早更新世转折时期的风成沉积磁化率各向异性研究进一步检验其在古风向重建方面的应用潜力.选择分别地处黄土高原中部、南部和东部地区的灵台、渭南和保德3个剖面,对红粘土向黄土过渡时期4个不同地层单元古土壤层(S32)、黄土层(L33)、过渡层(TU)以及红粘土沉积(RC)的样品进行了磁化率各向异性测量,结果表明磁线理L值很小,而磁面理F较为发育,这与前人对晚更新世黄土沉积磁化率各向异性的研究结果一致;同时,4个不同地层单元的磁面理F、各向异性度P和形状因子T在3个剖面上均表现出随土壤发育程度增强而减小的变化趋势,说明后期的成壤作用能够不同程度地降低磁面理、磁化率各向异性度以及形状因子的大小.与前人对于晚更新世黄土沉积磁化率各向异性的研究结果不同的是3个剖面的S32,L33,TU以及RC的Kmax的偏角似乎并不能反映出当时的搬运动力方向,即古风向,而长期的压实作用以及不同程度的后期土壤化作用是造成这一时期黄土和红粘土沉积物磁化率各向异性最大轴偏角方向未能反映出当时搬运动力方向(古风向)的原因之一.  相似文献   

Pliocene to Holocene geomorphic evolution and paleogeography of the El’gygytgyn Lake region,NE Russia     

O. Yu. Glushkova  V. N. Smirnov 《Journal of Paleolimnology》2007,37(1):37-47

Geomorphic, lithologhic, and stratigraphic field studies as well as pollen data and mineralogical study have been used to propose Pliocene and Pleistocene paleogeographic reconstructions of the El’gygytgyn meteorite crater area. The moment of impact is recorded above the early Pliocene hill denudation plain as a “chaotic horizon” consisting of fragments of impactite rocks. This chaotic horizon lies between layers of late Pliocene alluvial sediments. During the second half of the late Pliocene, the region was tectonically active, when the Anadyr lowland was uplifted causing alluvial sediments to accumulate in the basins to the south of the crater. Regional climatic cooling, which supported the spread of tundra and the formation of permafrost is characteristically to late Pliocene. The 35–40 m high terrace that roughly follows the 530 m contour interval along the Enmyvaam River formed during the middle Pleistocene. This terrace represents the maximum lake level. Erosion and incision of the upper Enmyvaam River increased due to another wave of uplift. Additionally, El’gygytgyn Lake discharge increased causing lake level to begin to drop in the Middle Pleistocene. Cooling continued, which led to the development of herb-dominated arctic tundra. middle and late Pleistocene glaciations did not reach the El’gygytgyn lake region. The 9–11 m high lacustrine terrace was formed around the lake during the late Pleistocene and the 2–3 m high lacustrine terrace formed later during the Holocene. During the last 5000 years, the lake level has continued to drop as the modern coastline developed. This is the third in a series of eleven papers published in this special issue dedicated to initial studies of El’gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献   

Polycyclic aromatic hydrocarbons as evidence of hydrocarbon migration in marine and lagoon sediments of a recent rift zone (Skjálfandi and Öxarfjörður), Iceland     

Alfred R. Geptner  Bjarni Richter  Yurii I. Pikovskii  Sergey S. Chernyansky  Tatiana A. Alexeeva 《Chemie der Erde / Geochemistry》2006,66(3):213-225

Polycyclic aromatic hydrocarbons (PAHs) content and distribution was studied in the northern part of modern rift zone. All samples analysed represent slightly altered clastic deposits and hot water discharging in springs and from wells. To study PAH in present-day gas emission traps with diatomite absorbent were installed in the Skógalón geothermal field. All samples were analysed by the method of Shpol'sky spectroscopy. Hydrothermally altered deposits show the highest amount of PAH. Data obtained allow to believe that the distribution of PAH is closely associated with the dynamics of the hydrothermal environment. The fissure formation and temperature fluctuation in hydrothermal systems can govern both the processes of PAH synthesis and sorption. The evidences of PAH migration up through the Skjálfandi and Öxarfjörður sedimentary basins show that hydrocarbons associate mainly with hydrothermal minerals and deep ground waters. Studying PAH associations can be used as an indicator of hydrocarbons distribution, ways of migration and possible zones of accumulation in the land and marine sedimentary basins in active and ancient rift zones of Iceland.  相似文献   

Late Pliocene to Holocene platform evolution in northern Belize, and comparison with coeval deposits in southern Belize and the Bahamas     

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   

云南上新世杜鹃属和松属化石木研究及其古气候意义          下载免费PDF全文

扆铁梅  李承森  姜笑梅  王宇飞 《古地理学报》2002,4(4):90-98

研究了云南西部龙陵县上新世的化石木。鉴定出两种木材类型。杜鹃花科杜鹃属的似腋花杜鹃Rhododendron cf. racemosum Franchet，其主要木材特征有散孔材，生长轮略明显，导管具多角形轮廓，螺纹加厚出现在整个导管壁上，梯状穿孔板，射线异形II型。松科华山松Pinus armandii Franchet的主要特征有交叉场纹孔窗格状，具正常轴向和纵向树脂道，且泌脂细胞壁薄，射线管胞内壁平滑或具稀疏的微锯齿。两种类型的化石木在我国均属首次报道。根据化石木结构和现代相应树种和植被的生境范围，当时植物生长于亚热带温凉湿润的山地环境，其海拔大约在1800米左右。  相似文献   

上新世～早更新世云杉属和冷杉属在华北地区的发展及其气候指示意义          下载免费PDF全文

石宁 《第四纪研究》1996,16(4):319-328

华北地区的云杉属和冷杉属在早上新世就有大量的发展。榆社盆地在4.4MaBP.时，云杉属在孢粉植物群中的含量达50%一70%,与云杉属同时发现的还有一些喜暖植物。根据化石和孢粉学证据、沉积条件、古地形及欧洲的旁证材料推测，上新世云杉属和冷杉属的生态习性与现代生活在寒冷地带的云杉、冷杉不同，它们是一些可以生长在相对暖湿气候条件下的种类。上新世以森林为主的植被在2.3MaB.P.时转变为疏林草原，亚热带植物基本迁离榆社盆地。云杉属和冷杉属不仅在孢粉植物群中大量减少，在木本植物中也降为次要组分。古植物的演化和迁移历史反映了冰期气候和东亚季风气候发展的历程。  相似文献   

云南元谋上新世秋枫化石的首次发现及古气候分析?   总被引：2，自引：0，他引：2       下载免费PDF全文

程业明  王宇飞  李承森  姜础 《古地理学报》2005,7(1):107-112

云南元谋盆地西部物茂盆地的湾堡土林和虎跳滩土林的晚上新世沙沟组地层大戟科秋枫属的秋枫（Bischofia javanica BL.）化石木。化石木木材由导管、纤维、射线组成。生长轮不明显。散孔材。径列复管孔（2~6，多2~4）甚多，单管孔较少，管孔团稀见。导管端壁具单穿孔。管间纹孔式互列。导管内侵填体丰富。轴向薄壁组织未见。木纤维壁薄，分隔。射线组织异形Ⅰ及Ⅱ。射线与导管间纹孔式为横列梯形及大圆形。孢粉分析表明元谋盆地晚上新世可能存在包括大戟科草本植物，而当前秋枫化石木的发现清楚地表明大戟科乔木植物的存在。秋枫为热带和亚热带常绿季雨林中的主要树种。秋枫化石木的发现指示元谋盆地当时的环境较现今湿润。  相似文献