Lateglacial climate change and coastal evolution in western Jura,Scottish Inner Hebrides

The geomorphic and sedimentological evidence for former sea-level changes in the exposed coastline of western Jura shows a clear coastal response to past changes in climate. In particular the rapid and high-magnitude climate changes associated with the onset and termination of the Younger Dryas appear to have been accompanied by major changes in coastal response. In western Jura, the temperate climate of the Lateglacial Interstadial was associated with beach-ridge deposition, with the earlier part of this period being associated with larger ridges than the latter. By contrast, the cold climate during the Younger Dryas appears to have been dominated by frost processes, sea-ice development and rapid rates of coastal erosion of bedrock. Cold-climate shore erosion of bedrock appears to have ended suddenly at the close of the Younger Dryas.     

The lateglacial lakes of Glens Roy,Spean and vicinity (Lochaber district,Scottish Highlands)

This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue.     

Late Quaternary landscape development along the Rancho Marino coastal range front (south‐central Pacific Coast Ranges,California, USA)

Late Quaternary landscape development along the Rancho Marino coastal range front in the central‐southern Pacific Coast Ranges of California has been documented using field mapping, surveying, sedimentary facies analysis and a luminescence age determination. Late Quaternary sediments along the base of the range front form a single composite marine terrace buried by alluvial fans. Marine terrace sediments overlie two palaeoshore platforms at 5 m and 0 m altitude. Correlation with the nearby Cayucos and San Simeon sites links platform and marine terrace development to the 125 ka and 105 ka sea‐level highstands. Uplift rate estimates based on the 125 ka shoreline angle are 0.01–0.09 m ka^?1 (mean 0.04 m ka^?1), and suggest an increase in regional uplift along the coast towards the NW where the San Simeon fault zone intersects the coastline. Furthermore, such low rates suggest that pre‐125 ka uplift was responsible for most of the relief generation at Rancho Marino. The coastal range front landscape development is, thus, primarily controlled by post 125 ka climatic and sea‐level changes. Post 125 ka sea‐level lowering expanded the range front piedmont area to a width of 7.5 km by the 18 ka Last Glacial Maximum lowstand. This sea‐level lowering created space for alluvial fan building along the range front. A 45 ± 3 ka optically stimulated luminescence (OSL) age provides a basal age for alluvial fan building or marks the time by which distal alluvial fan sedimentation has reached 300 m from the range front slope. Fan sedimentation is related to climatic change, with increased sediment supply to the range front occurring during (1) glacial period cold stage maxima and/or (2) the Late Pleistocene–Holocene transition, when respective increases in precipitation and/or storminess resulted in hillslope erosion. Sea‐level rise after the 18 ka lowstand resulted in range front erosion, with elevated localised erosion linked to the higher relief and steeper slopes in the SE. This study demonstrates that late Quaternary coastal range front landscape development is driven by interplay of tectonics, climatic and sea‐level change. In areas of low tectonic activity, climatic and sea‐level changes dominate coastal landscape development. When the sea‐level controlled shoreline is in close proximity to the coastal range front, localised patterns of sedimentation and erosion are passively influenced by the pre‐125 ka topography. Copyright © 2008 John Wiley & Sons, Ltd.     

Late-glacial sedimentological and morphological changes in a lowland river in response to climatic change: the Maas,southern Netherlands

The late Pleniglacial and Late-glacial Maas valley, south of Nijmegen, contains four terraces. Three river systems are described based on the morphology of channel scars on these terrace surfaces and by sediment characteristics. The River Maas reacted to climatic warming at the start of the Weichselian Late-glacial by changing its river system slowly, from a braided system to a transitional phase between braiding and meandering and finally to a highly sinuous meandering system. The Maas reacted rapidly to the Younger Dryas climate deterioration by again establishing a braiding system. At the onset of the Holocene, the river changed abruptly to a meandering river without a transitional phase. The triggering factor for change in the Maas river pattern is almost certainly the changing climate in the Late Glacial. Gradient lines on the terrace surfaces show that tectonic activity did not modify the morphology of the channels. A division of the terraces is shown, the morphological, sedimentological and petrographical characteristics are presented and the linking of changing fluvial patterns with climatic changes or tectonic movements is discussed. © 1997 John Wiley & Sons, Ltd.     

Geochemistry of Late Cretaceous (60-67 Ma) igneous activities in the Hebrides Terrace seamount (guyot) area, Scotland

1Introduction Seamountsarethewell knownfeaturesinthe world’soceans,beingmostcommoninthePacific (Smith,1988;Pringleetal.,1991;Hasse,1991). Recentvolcanicactivityoccursinthezonesondi vergentorconvergentplatemarginsorintheintraplate regimes.Seamountsexisteitherasisolatedvolcanic edifices(Gardneretal.,1984;MertzandRenne, 1995)or,sometimes,formlinearchainstogetherwith oceanislands.Anumberofgeochronologicalinvestiga tionsonoceanislands(DuncanandMcDougall,1974; Dymond,1975;McDougall,1979…     

西昆仑飞云山地区第四纪火山岩地质地球化学及成因

飞云山地区位于东西昆仑结合部及华北与华南板块结合带。区内第四纪火山岩较发育,为陆相中心式火山岩,分两次喷发,呈平缓的熔岩被覆盖于古近纪阿克塔什组(E3a)等地层之上。全岩KAr法同位素年龄2.97Ma,为第四纪更新世的产物。火山岩主要为粗安岩类,富碱,K2O+Na2O6.92%～8.25%,SiO253.73%～61.76%,MgO,CaO较低,属高钾钙碱性系列。大离子亲石元素(LILE)Cs,K,U,Th明显富集,高场强元素(HFSE)Nb,Ta,Ti,Y相对亏损,稀土元素∑REE274.61×10-6～719.01×10-6,LREE/HREE18.93～28.68,属LREE富集型,δEu0.80～0.99。局部见深源包体。综合研究表明,岩石主要来源于壳幔过渡带分离结晶岩浆,形成于碰撞后板内构造环境。     

四川红原日干乔泥炭剖面记录的古气候古环境演变

利用14C测年及孢粉分析方法对四川省红原县日干乔地区泥炭剖面进行了系统研究,建立了4个孢粉组合带。孢粉记录反应了红原县日干乔地区经历了潮湿一干燥一潮湿的气候变化过程。     

Quaternary coastal lithofacies,sequence development and stratigraphy in a passive margin setting,North Carolina and Virginia,USA

Lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea‐level fluctuations. These successions and their timing are often poorly understood. This report defines lithofacies encountered within the north‐eastern North Carolina and south‐eastern Virginia Quaternary section, interprets their depositional environments, presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and Quaternary evolutionary history of the region. Data were obtained from numerous drill cores and outcrops. Chronology was based on age estimates acquired using optically stimulated luminescence, amino acid racemization, Uranium series and radiocarbon dating techniques. Geomorphic patterns were identified and interpreted using light detection and ranging imagery. Since lithofacies occurrence, distribution and stratigraphic patterns are different on interfluves than in palaeo‐valleys, this study focused on interfluves to obtain a record of highstand sea‐level cycles with minimal alteration by fluvial processes during subsequent lowstands. Nine primary lithofacies and four diagenetic facies were identified in outcrops and cores. The uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface. Older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces. Portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle Pleistocene to present. Erosional processes associated with each successive depositional sequence removed portions of older depositional sequences. The stratigraphic record of the most recent sea‐level highstands (Marine Isotope Stage 5a and Marine Isotope Stage 3) is best preserved. Glacio‐isostatic adjustment has influenced depositional patterns so that deposits associated with late Quaternary sea‐level highstands (Marine Isotope Stages 5c, 5a and 3), which did not reach as high as present sea‐level according to equatorial eustatic records, are uplifted and emergent within the study area.     

Tectonic, eustatic and environmental controls on mid-Cretaceous carbonate platform deposition, south-central Pyrenees, Spain

Cenomanian–Turonian strata of the south‐central Pyrenees in northern Spain contain three prograding carbonate sequences that record interactions among tectonics, sea level, environment and sediment fabric in controlling sequence development. Sequence UK‐1 (Lower to Upper Cenomanian) contains distinct lagoonal, back‐margin, margin, slope and basin facies, and was deposited on a broad, flat shelf adjacent to a deep basin. The lack of reef‐constructing organisms resulted in a gently dipping ramp morphology for the margin and slope. Sequence UK‐2 (Upper Cenomanian) contains similar shallow‐water facies belts, but syndepositional tectonic modification of the margin resulted in a steep slope and deposition of carbonate megabreccias. Sequence UK‐3 (Lower to Middle Turonian) records a shift from benthic to pelagic deposition, as the shallow platform was drowned in response to a eustatic sea‐level rise, coupled with increased organic productivity. Sequences UK‐1 to UK‐3 are subdivided into lowstand, transgressive and highstand systems tracts based on stratal geometries and facies distribution patterns. The same lithologies (e.g. megabreccias) commonly occur in more than one systems tract, indicating that: (1) the depositional system responded to more than just sea‐level fluctuations; and (2) similar processes occurred during different times throughout sequence development. These sequences illustrate the complexity of carbonate platform dynamics that influence sequence architecture. Rift tectonics and flexural subsidence played a major role in controlling the location of the platform margin, maintaining a steep slope gradient through syndepositional faulting, enhancing slope instability and erosion, and influencing depositional processes, stratal relationships and lithofacies distribution on the slope. Sea‐level variations (eustatic and relative) strongly influenced the timing of sequence and parasequence boundary formation, controlled changes in accommodation and promoted platform drowning (in conjunction with other factors). Physico‐chemical and climatic conditions were responsible for reducing carbonate production rates and inducing platform drowning. Finally, a mud‐rich sediment fabric affected platform morphology, growth geometries (aggradation vs. progradation) and facies distribution patterns.     

瓮安县北斗山磷矿三号坑围岩应力分析及支护经验

通过对巷道中开挖岩体前后的应力关系及岩体开挖的破坏模式分析,充分证实了支护与围岩相互作用关系的重要性,鉴于这种相互作用关系,简述一些在采场地压变化及顶板管理中所采取的一些措施及经验。     

Late Quaternary sediments from Nal Sarovar, Gujarat, India: Distribution and provenance

A 54-m long core was raised from the bed of the Nal Sarovar, a large shallow lake located in the middle of the low-lying region linking the Gulfs of Kachchh and Khambhat, in western India. A three-layer sequence comprising: Zone-1 (top 3 m), predominantly silty-clay/clayey; Zone-2 (3–18 m), sandy; and Zone-3 (18–54 m), dominated by sticky silty-clay/clayey-silt with occasional thin sand layers and basalt fragments was identified. Smectite and illite are the dominant clay minerals with minor amounts of kaolinite and chlorite. Very high content of smectite (53–97%) in the clays of the lowermost zone (18–54 m) and the geomorphic features of the surrounding region suggested that the sediments were derived from the basaltic terrain of Saurashtra and/or via the Gulf of Khambhat. The clay content in the middle zone (3–18 m), dominantly sandy, is very low. Therefore, provenance for this zone was derived using heavy minerals in the sand fraction. The heavy mineral species in this zone suggested the mixed metamorphic and igneous terrain of Aravallis as the major source. The grain-size distribution of this zone closely matched with the sediments underlying the modern Sabarmati riverbed at Ahmedabad, suggesting fluvial depositional environment. Clays also dominate sediments of the topmost (0–3 m) zone with illite as the dominant (74–81%) specie followed by smectite suggesting derivation from the mixed metamorphic and igneous terrain of Aravallis.     

Late Quaternary cycles of mangrove development and decline on the north Australian continental shelf

Mangrove communities in the Australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered, muddy coasts. Palynological data from continental-shelf and deep-sea cores indicate a long-term cyclical component of mangrove development and decline at a regional scale, which can be linked to specific phases of late Quaternary sea-level change. Extensive mangrove development, relative to today, occurs during periods of marine transgression, whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea-level stability. Episodes of flourishing mangrove cannot be linked to phases of humid climate, as has been suggested in studies elsewhere. Rather, the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental-shelf coasts during transgressive and regressive phases, in particular by the existence, or lack, of well-developed tidal estuaries. Copyright © 1999 John Wiley & Sons, Ltd.     

第四纪华容隆起构造活动、成因及动力机制

第四纪华容隆起位于江汉—洞庭盆地中部。通过地表观察和第四系钻孔对华容隆起及周缘地貌、第四纪断裂和沉积进行调查,恢复华容隆起构造升降特征与过程,进而探讨华容隆起的成因及其构造活动的动力机制。研究表明:早更新世-中更新世中期华容隆起与周缘凹陷一道沉降,同时前者受周边正断裂控制相对后者有抬升,中更新世晚期一道抬升,晚更新世—全新世构造稳定或弱沉降。第四纪期间华容隆起总体表现为明显的构造沉降。以上表明第四纪华容隆起主要由前第四纪盆—山地貌分异造成,其次与第四纪期间相对周缘凹陷抬升有关。上述地质特征以及区域第四纪地质资料,表明早更新世-中更新世中期江汉—洞庭盆地为断陷盆地,中更新世晚期—全新世转变为坳陷盆地。就华容隆起第四纪构造活动的动力机制进行了探讨并提出:1)早更新世-中更新世中期江汉—洞庭盆地断陷沉降与地幔上隆背景下的深部物质迁出有关。2)中更新世晚期以来的构造活动可能与深部物质蠕移运动的回返以及板块尺度的物质运动和挤压作用有关。3)江汉—洞庭盆地的整体性沉降导致盆地中部的华容隆起以沉降为主;华容隆起特殊的地壳物质结构可能导致深部物质更难向外迁移,使其相对周缘凹陷有抬升。     

柴达木盆地三湖地区第四系生物气源岩中可溶有机质丰度及地质意义

柴达木盆地东部第四系生物气源岩有机质丰度是控制该区生物气资源的关键因素。通过重新设计实验流程,建立了针对未成熟生物气源岩的有机质丰度评价方法。柴达木盆地第四系生物气源岩可溶有机质含量约是不溶有机质含量的2.6倍,有机质大部分以可溶的形式存在。鉴于未成熟生物气源岩有机质赋存形式的特殊性,提出了柴达木盆地东部第四系生物气源岩的有机质丰度评价标准。大量存在的可溶有机质揭示柴达木盆地东部地区第四系仍处于生物甲烷生成阶段,较高的气源岩有机质丰度为生物气勘探提供了重要的资源保障。     

大兴安岭诺敏河第四纪火山岩分期:岩石学、年代学与火山地质特征

大兴安岭北段诺敏河第四纪火山24座,分布于诺敏河及其支流毕拉河和甘河支流奎勒河,火山岩分布面积约600km2。诺敏河火山岩均属于钾质系列火山岩(K2O含量2%～4%,且K2O>Na2O-2%),类似于邻区五大连池-科洛钾质火山岩,具有来自类似的富钾地幔源区。但诺敏河火山岩的K2O含量明显低于五大连池-科洛火山岩的K2O含量(一般4%～6%)。东北地区和内蒙东部处于中亚造山带东段,从古生代到新生代,多重构造-岩浆活动导致火山岩源区地球化学非均一性和火山岩的多样性。根据本文提出的火山岩K-Ar年龄(2.3～0.128Ma)及火山地质特征,可将诺敏河第四纪火山岩分为四期。早期(早更新世)火山活动主要沿诺敏河和奎勒河流域分布,火山产物多被晚期沉积物或火山产物所覆盖。中更新世保留的火山锥体及熔岩流是诺敏河第四纪火山产物的主体,表明是第四纪火山活动的高潮期。晚更新世-全新世火山活动限于毕拉河流域,典型的四方山火山和马鞍山火山是该时期火山活动的代表作,保留了较完好的火山地质地貌特征。从火山产物的时空展布,推测诺敏河第四纪火山活动有从东向西发展的趋势。     

古昆虫学的发展、存在问题与展望

对国际古昆虫学的发展作了回顾,大体上将其分为两个大的发展阶段;开始与积累阶段,发展和繁荣阶段。这两个阶段又可分为8个时期。在古昆虫学的发展史上曾有过3次历史性的重要总结。即Handlirsch A(1906-1908）的《Die Fossil Insketen und die Phylogenie der rezenten Formen》,Rohdemdorf b.b.et al(1962)的《Foundamentals of Paleonentomology》,Carpenter F.A(1992)的《Hexapoda》,以及各国区域性昆虫化石研究和以分类为核心的总结,等等。通过国际古昆虫工作者的共同努力。一部分类为核心的古昆虫学专著基本完成。在国际古昆虫学及中国古昆虫学研究新成就的基础上,提出了古昆虫学研究中还存在的一些问题;如加强基础研究工作,包括化石采集、分类、描述;古昆虫学研究与地质学、地质背景相结合;化石昆虫群的演化及其发展史的建立：昆虫的起源;加强国际合作与交流,崇尚科学精神,促进学科发展等。     

黔中降起的油气勘探壁垒——兼论海相碳酸盐岩烃源岩

黔中隆起在地质构造上属于扬子地块的滇黔隆褶带．南华纪晚期初现雏形，震旦纪—奥陶纪为水下隆起，燕山运动使其整体抬高，喜马拉雅运动时急剧隆升，构造地貌长期相对隆起。地表油苗油样分析结果显示，在红外吸收谱图中缩合芳烃结构及含氧基团吸收明显，有机质热成熟度高，且遭受了氧化蚀变：震旦系以上地层大量暴露，地表水溶蚀下渗深度在黔西南地区可达3000-4000m；作为长期存在的古隆起，经历了多次抬升，直至挽近仍处于严重剥蚀阶段。地腹可能存在酸性岩浆热源使有机质过度热演化、保存条件不佳以及缺少勘探目的层，是黔中隆起油气勘探的三大壁垒。兼谈了碳酸盐岩烃源岩问题．认为形成大油气田的烃源岩主要是泥质岩系，“碳酸盐岩烃源岩”只是从属性的．分布在泥质烃源岩系的边缘或局部范围。     

黔中隆起的油气勘探壁垒——兼论海相碳酸盐岩烃源岩

黔中隆起在地质构造上属于扬子地块的滇黔隆褶带,南华纪晚期初现雏形,震旦纪—奥陶纪为水下隆起,燕山运动使其整体抬高,喜马拉雅运动时急剧隆升,构造地貌长期相对隆起。地表油苗油样分析结果显示,在红外吸收谱图中缩合芳烃结构及含氧基团吸收明显,有机质热成熟度高,且遭受了氧化蚀变;震旦系以上地层大量暴露,地表水溶蚀下渗深度在黔西南地区可达3000～4000m;作为长期存在的古隆起,经历了多次抬升,直至挽近仍处于严重剥蚀阶段。地腹可能存在酸性岩浆热源使有机质过度热演化、保存条件不佳以及缺少勘探目的层,是黔中隆起油气勘探的三大壁垒。兼谈了碳酸盐岩烃源岩问题,认为形成大油气田的烃源岩主要是泥质岩系,“碳酸盐岩烃源岩”只是从属性的,分布在泥质烃源岩系的边缘或局部范围。     

第四纪冰川年代学以及新技术研究的现状、问题与趋势

一百多年来,新技术的运用和认识水平的不断提高,给第四纪冰川研究带来重大变化,研究方法和内容大致经历了两个阶段：早期的研究者采用野外地质地貌调查方法,定性描述冰川地貌和冰碛物沉积特征及其分布,根据冰川遗迹的相对位置和风化程度划分了4~6次经典冰期;20世纪80年代开始到21世纪初的近30年间,采用放射性碳、光释光和电子自旋共振、宇宙成因核素暴露年代,以及火山灰钾氩法/裂变径迹等测年技术测定冰川地貌及其相关沉积物的数值年代。其他新技术的不断涌现,定量化描述冰川遗迹,解决了许多以往第四纪冰川研究不能解决的问题,还发现了不少新的科学问题。结果表明：1）相当于深海氧同位素3阶段的大规模冰进、末次冰盛期（Last Glacial Maximum,简称LGM）、末次冰期早阶段的时代和倒数第二冰期的时代在全球范围内可以对比;北美洲、南美洲和青藏高原最老的冰期时代大约1 Ma。2）采用3S技术（GPS、GIS和RS）并结合野外调查,发现海洋性冰川作用区冰下磨蚀量与冰流速成2次方的定量关系,定量描述古冰川分布和平衡线的空间变化,最近和未来将采用数值模型并结合野外调查模拟山地冰川的面积、体积和平衡线等对气候变化的响应和反馈作用,并进一步提高实验室测年水平,对冰碛物精细测年,以利全球冰期对比和古冰川气候模拟。