南流江河口水下三角洲表层沉积物端元分析及其沉积动力环境意义

沉积物粒度分布特征可揭示沉积动力环境。基于广西南流江河口水下三角洲的粒度分析数据,采用Folk分类法进行分类,应用端元分析对其粒度数据进行分解,探讨了南流江河口水下三角洲的物源和现代沉积动力环境。结果表明,研究区表层沉积物可划分为9类,其中含砾沉积物5类,不含砾沉积物4类,沉积物类型与河口环境动力特征相吻合。端元分析结果显示,研究区有5个不同类型的端元,分别代表着5种类型的沉积物动力环境:端元1反映了风浪和潮流对表层沉积物的动力作用;端元2指示了外海涌浪对表层沉积物的作用过程;端元3代表了南流江冲淡水引起的表层沉积物的输运;端元4代表了大陆架残留沉积物;端元5为干扰端元,可能是由于工程建设等人类活动所引起的。利用端元分析探讨复杂环境(如小型山溪性河口)下的沉积动力环境时,一方面需要综合考虑研究区域的物源与环境动力特征;另一方面可以结合参数拟合、粒径趋势分析等研究手段。     

河南晚更新世—全新世黄土记录的环境变化及物源特征

基于河南新郑县的一套完整晚更新世—全新世黄土古土壤剖面(格大张剖面),应用端元分析模型,对75个沉积样品的粒度分析数据进行分析,并对各端元组分在地层深度对应的时间尺度上做了小波变换。结果认为,从格大张剖面沉积物粒级组分中可以分离出三个沉积端元,端元1可能指示了东亚夏季风作用动力特征,夏季风的强弱引起的温湿变化造成相应时期内沉积物的古土壤化的强弱;端元2可能指示了东亚冬季风作用下沙尘暴沉积动力作用特征,代表了典型风成黄土的粗颗粒组分特征;端元3粒级组分更粗,代表了更强搬运动力条件,应属于东北风搬运黄泛平原粗颗粒而来的近源沉积物,距今3100 a以来尤为显著。根据小波分析结果,认为各端元组分在不同的时间尺度上具有周期性特点。端元分析法在指示沉积物沉积动力环境和物源特征上具有很好的效果,各端元组合特征能够敏感地反映出沉积动力组合特征,很好地反映晚更新世以来各动力变化特征。采用小波分析方法对识别各端元组的周期性特征以及根据目前状态推断未来可能的趋势具有参考意义。     

Neoproterozoic environmental change recorded in the Port Askaig Formation,Scotland: Climatic vs tectonic controls

The snowball Earth hypothesis suggests that the Neoproterozoic was characterized by several prolonged and severe global glaciations followed by very rapid climate change to ‘hot house’ conditions. The Neoproterozoic Port Askaig Formation of Scotland consists of a thick succession of diamictite, sandstone, conglomerate and mudstone. Sedimentological and stratigraphic analysis of Port Askaig deposits exposed on the Garvellach Islands was carried out to establish the nature of Neoproterozoic palaeoenvironmental change preserved in this thick succession. Particular emphasis was placed on identifying and distinguishing between climatic and tectonic controls on sedimentation.Port Askaig Formation diamictite units are attributed to deposition by sediment gravity flow processes or ‘rainout’ of fine-grained sediment and ice-rafted debris in a glacially influenced marine setting. Associated facies record various depositional processes ranging from sediment gravity flows (conglomerate, massive sandstone and laminated mudstone) to deposition under other unidirectional currents (cross-bedded and horizontally laminated sandstone). The Port Askaig Formation is also characterized by abundant soft sediment deformation features that occur at discrete intervals and are interpreted to record episodic seismic activity.Stratigraphic analysis of the Port Askaig Formation on the Garvellach Islands reveals three phases of deposition. Phase I was dominated by sediment gravity flow processes and sedimentation was primarily tectonically controlled. Phase II was a transitional phase characterized by continued tectonic-instability, an increased supply of sand to the basin and the preservation of current-generated facies. In the third and final phase of deposition, the interbedded units of sandstone and diamictite are interpreted to reflect development of large sandy bedforms and ice margin fluctuations in a tectonically stable marine setting.Sedimentological and stratigraphic analysis of the Port Askaig Formation demonstrates that tectonic activity had a significant influence on development of the lowermost parts of the succession. Climatic influences on sedimentation are difficult to identify during such phases of tectonic activity but are more easily discerned during episodes of tectonic quiescence (e.g.,, Phase III of the Port Askaig Formation). The thick succession of diamictite interbedded with current-deposited sandstone preserved within the Port Askaig Formation is not consistent with deep freeze conditions proposed by the snowball Earth hypothesis.     

岷江上游新磨村湖相沉积物粒度端元反演及其记录的构造和气候事件

应用沉积物粒度端元分析模型对岷江上游新磨村湖相沉积高分辨率粒度数据序列进行了反演,分离出2个端元。根据端元的频率分布曲线和沉积学分析,并结合岷江上游的地质构造背景,分析了各端元与研究区物源和古地震活动的对应关系。EM1为震间期的湖泊沉积,代表风力近源搬运的极细颗粒组分;EM2为极端灾变(地震等)期间的湖泊沉积,代表风力为主和部分水力近距离搬运的细颗粒组分。对新磨村剖面分离出的EM2百分含量与中值粒径、20~63μm、63~200μm粒径组分、磁化率值及地球化学比值(SiO2/Al2O3、TiO2/Al2O3、CaO/Al2O3、Sr/Al2O3、Rb/Sr,Na2O/Al2O3)进行对比分析,各指标的突变明显受粒度变化控制,指示可能的地震事件,进而识别出26次地震事件。为确定地震事件所代表的地震震级,基于震级与累积砂层厚度关系进行估算,共获得16次5~6级,5次6~7级,5次>7级地震。因此,采用粒度端元模拟不仅可以分离出不同的粒径组分和各组分百分含量,有效识别出不同动力组分和沉积动力环境,还可以较好地厘定出沉积记录的构造事件(地震等)等,更好地理解构造活动在地质、地貌演化中的作用。     

Facies Associations and Discontinuous Surfaces in the Syringothyris Limestone Formation of Tethyan Margin of Gondwana,Kashmir

The early Carboniferous sedimentation of the Tethyan Margin of Gondwana in the Kashmir Himalaya represents alternating siliciclastic - carbonate succession consisting of distinct stratigraphic sequences which are bounded by discontinuities. The discontinuities in the sedimentation are related to environmental changes in the form of subaerial exposure, subaqueous erosion, subaqueous omission or changes in texture and facies. These distinct surface zones or time significant boundaries can be correlated across the depositional platform. Low stand, high stand and transgressive sedimentation units in the lower and middle parts of early Carboniferous Syringothyris Limestone Formation in Banihal area have been recognised. This is explained by superposition of high frequency and low amplitude sea level fluctuations on a large-scale trend under greenhouse conditions during the early Carboniferous period. The facies associations present in the early Carboniferous succession of the Himalaya broadly represent intertidal (peritidal), shallow subtidal, deeper subtidal, off-shore-slope and deeper environments. Discontinuities that are interpreted as progradational, retrogradational and aggradational phases of sedimentation bound these facies associations. This formation represents continental margin depositional setting which is authenticated by deposition of siliciclastic sediments. This marginal depositional setting is greatly affected by numerous dynamic processes including tectonic and other active sea as well as continental processes. The records of all those processes in this formation reflect the eustatic changes in sea level. These periodic eustatic changes have generated the various discontinuities, stratigraphic sequences or systems tracts. Overall it appears that interplay of many processes such as sediment supply, thermal and tectonic activity, eustatic and climatic changes in the Kashmir Tethyan depositional basin generated these distinct depositional sequences during the early Carboniferous period.     

Characteristics of Holocene Loess-Palaeosol Particle Size Composition and Paleoclimatic Significance in East Guanzhong,Shaanxi Province

This paper made an end-member analysis of particle size data collected from 150 samples based on the continuous Holocene Loess-Paleosol profile (Yaohecun profile) in east Guanzhong, Shaanxi Province. Wavelet analysis was also performed for the EMs along the time scale of depth.The result shows that three end members can be separated from different sediment particle sizes. Based on comparative analysis of magnetic susceptibility and geochemical index, it was considered that the End-member 1 might indicate the weathering and pedogenic remoulding after sediment deposition under the east Asian summer monsoon. The End-member 2 might indicate dynamic effect of dust storm accumulation under the influence of northwest monsoon, representing typical component characteristics of aeolian loess.The End-member 3 indicated the stronger transporting force for coarse components, which should belong to the northeasterly winds for the coarse-grained near-source sediments from the Yellow River flood plain. Results of wavelet analysis show that each EM has different periodic characteristics at 1.5 ka, 3.0 ka and 4.5 ka scales.The End-element analysis method has a good effect in indicating the sedimentary environment and provenance characteristics of sediments. The combination characteristics of each End-member can reflect the characteristics of sedimentary dynamics combination and can well reflect the Holocene dynamic change course. At the same time, it hasreference significance to reconstruct the paleoclimate on the longer time scale.The wavelet analysis method provides significant results in terms of inversion cycles and trends of dynamics change of sedimentary particle size within each EM.     

Calibration of modelled mixing patterns in loess grain-size distributions: an example from the north-eastern margin of the Tibetan Plateau, China

Genetically meaningful decomposition (unmixing) of sediment grain-size distributions is accomplished with the end-member modelling algorithm. Unmixing of the loess grain-size distributions of a Late Quaternary loess–palaeosol succession from the north-eastern Tibetan Plateau indicates that the loess is a mixture of three end-members representing very fine sandy, coarse silty and medium silty loess. The unmixing approach potentially enables the unravelling of sediment fluxes from multiple dust sources, opening the way to significant advances in palaeoclimatic reconstructions from loess grain-size distribution data. However, as laser-diffraction size analysis is a volume-based technique, the proportional contributions of the modelled end-members might deviate (significantly) from weight proportions. Hence, calibration of the end-member volume proportions to weight proportions must be established before one can calculate the source-specific dust fluxes. This paper reports the findings of a sediment-mixing experiment which enables calibration of the modelled mixing patterns established for the Tibetan loess–palaeosol succession.     

Holocene climate vs. catchment forcing on a shallow,eutrophic lake in eastern Poland

This paper presents a sedimentary record from Lake ?ukie located in the southeastern part of the Central European Plain, beyond the reach of the maximum extent of the last glaciation. The lake has thermokarstic origin and developed during the last glacial termination due to subsidence of the sub‐Quaternary carbonate basement triggered by permafrost thawing. A sediment core was investigated to reconstruct water trophic state and lake depth changes during the Holocene. We aimed at showing the relationship between ecological and geochemical changes in the lake and regional/supraregional climatic and hydrological trends throughout the Holocene. Results of subfossil Cladocera analysis were combined with data on the geochemistry and stable C and O isotopes in sedimentary carbonates. Isotopic and geochemical proxies helped to detect sources of sedimentary particles in the lake and thus to reconstruct changes in the intensity of atmospheric and catchment processes (e.g. precipitation and surface runoff). The Cladocera analysis results indicated endogenic processes in the lake such as trophic changes. Our data revealed that Lake ?ukie has always been a rather eutrophic water body and the periods of particularly high productivity were in the lower Preboreal and upper Subatlantic. Periods of increased water depth were recorded in the lower Preboreal, lower Boreal and upper Subboreal, whereas low water stands were obtained during the late Preboreal, late Boreal, late Atlantic and Atlantic/Subboreal transition as well as during the lower Subboreal. The sediment succession from Lake ?ukie provides the first full Holocene record of carbon and oxygen stable isotopes in lacustrine carbonates from the eastern part of the Central European Lowland. The record is characterized by uncommonly high δ¹³C and δ¹⁸O values of the carbonates resulting from a combination of within‐lake processes and dissolution of the carbonate bedrock of Cretaceous age. The impact of the old carbonates on isotope values was helpful in the reconstruction of the catchment forcing on the lake.     

云南洱海沉积物粒度组成及其环境意义辨识

高原封闭,半封闭湖泊是气候和环境演化的敏感指示器,其沉积物记录具有连续性,敏感性和高分辩率的特点,在恢复和重塑各种短时间凡度的气候和环境演化序列上,具有其它自然历史记录无法替代的优势。     

Late Pleistocene and Holocene coastal palaeoeconomies: A reconsideration of the molluscan evidence from northern Spain

The worldwide increase in shell midden deposits on coastlines during the Holocene has been variously explained as the result of human population growth, economic intensification, changes in the visibility of midden deposits with changes in sea level, or climatic and environmental changes. Since coastlines are relatively unstable in geological and ecological terms, and since many archaeological sequences span periods of major climatic change, a critical issue is the ability to disentangle palaeoenvironmental from cultural and anthropogenic effects. We draw on a case study from the cave sequences of northern Spain to illustrate the problems and possibilities of palaeoeconomic and palaeoenvironmental interpretation, using studies of palaeogeographical context and analysis of abundance, taxonomic representation, ecological tolerances, size, growth structures, and other physical and chemical characteristics of the molluscs themselves. We demonstrate that the dominant, but by no means exclusive, factor in archaeologically visible long‐term changes in shell‐gathering behavior is environmental change rather than cultural change. © 2003 Wiley Periodicals, Inc.     

Petrography and major element geochemistry of the Permo-Triassic sandstones, central India: Implications for provenance in an intracratonic pull-apart basin

Detrital mode, composition of feldspars and heavy minerals, and major element chemistry of sandstones from the Permo-Triassic succession in the intracratonic Satpura Gondwana basin, central India have been used to investigate provenance. The Talchir Formation, the lowermost unit of the succession, comprises glacio-marine and glacio-fluvial deposits. The rest of the succession (base to top) comprising the Barakar, Motur, Bijori, Pachmarhi and Denwa formations, largely represent variety of fluvial depositional systems with minor fluvio-deltaic and fluvio-lacustrine sedimentation under a variety of climatic conditions including cold, warm, arid, sub-humid and semi-arid. QFL compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault-bounded basement uplift tectonic setting. Compositional maturity of sandstones gradually increases upwards from the Early Permian Talchir to the Middle Triassic Denwa but is punctuated by a sharp peak of increased maturity in the Barakar sandstones. This temporal change in maturity was primarily controlled by temporal variation in fault-induced basement uplift in the craton and was also influenced by climatic factors. Plots of different quartz types suggest plutonic source rocks for the Talchir sandstones and medium-to high-rank metamorphic plus plutonic source rocks for the younger sandstones. Composition of alkali feldspars in the Permo-Triassic sandstones and in different Precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks. Compositions of plagioclase in the Talchir and Bijori sandstones are comparable with those of granite, acid volcanic and metasedimentary rocks of the Precambrian basement suggesting the latter as possible source. Rare presence of high-K plagioclase in the Talchir sandstones, however, indicates minor contribution from volcanic source rock. Exclusively plagioclase-bearing metasedimentary rock, tonalite gneiss and mafic rocks are the probable sources of plagioclase in the Upper Denwa sandstones. Quartz-rich nature of the sandstones, predominance of K-feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic, pull-apart basin like the Satpura Gondwana basin. Composition of garnet and its comparison with that from the Precambrian basement rocks suggests mica-schist and amphibolite as possible sources. Predominance of dravite variety of tourmaline in the Permian sandstones suggests sediment supply from metasedimentary rocks. Presence of both dravite and schorl variety of tourmaline in subequal amount in the Triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks. However, schorl-bearing rocks are absent in the basement complex of the study area. A-CN-K plot suggests granites, acid volcanic rock and meta-sediments of the basement as possible sources of the Talchir sandstones and metasedimentary rocks for the Barakar to Pachmarhi sandstones. The Denwa sandstones were possibly derived from K-feldspar-free, plagioclase-bearing metasediments, mafic rocks and tonalite gneiss. Chemical Index of Alteration (CIA) values suggest low intensity source rock weathering for the Talchir sandstones and higher intensity source rock weathering for the others. Various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples.     

Sediment particle size distribution and its environmental significance in Lake Erhai, Yunnan Province

A closed or semi-closed plateau lake, whose sediment records can provide us with plenty of fine and high resolution information, is a sensitive indicator of climatic and environmental changes. During the reconstruction of various short-time-scale climatic and environmental changes, the geochemical records in plateau-lake sediments are superior to other natural files. Based on fine dissection of the vertical profile of sediment particle sizes, this paper reveals the quasi-periodical changes of sediment particle sizes, which indicates the quasi-periodical fluctuations of the regional climate. A synthetic analysis of multiple indexes shows that sediment particle size is a more sensitive and more effective index of climatic and environmental changes than other geochemical indexes. High content of >20μm sediment particles and low content of 2–10μm sediment particles indicate a warm-dry climate and conversely a cold-humid climate, and their ratio can be used as an effective index of climatic changes. The basic climate succession in the region of Lake Erhai is characterized as being alternatively warm-dry and cold-humid and it has been developing into a warm-dry climate as a whole. There exist at least 2 time-scale quasi-periodical fluctuations of the regional climate in Lake Erhai. At present, the region of Lake Erhai is at the end of the warm-dry period and at the beginning of a cold-humid period, so the temperature will go down and the water level will rise. This project was supported by the National Natural Science Foundation of China (Nos. 49894170, 49773207).     

青藏高原环境变化对全球变化的响应及其适应对策

青藏高原的环境变化对全球变化具有敏感响应和强烈影响。青藏高原的现代环境与地表过程相互作用,引起包括冰冻圈和水资源以及生态系统等方面的一系列变化,对高原本身以及周边地区的人类生存环境和经济社会发展产生重大影响。作为国际研究的热点地区,青藏高原环境变化研究目前出现三个新的科学动向：关注关键地区的关键科学问题的系统研究;关注以现代地表过程为核心的监测研究;关注全球变化影响下的圈层相互作用研究。本项目的研究对青藏高原环境变化科学的发展、国际科学前沿的贡献以及服务于社会经济发展,都具有十分重要的意义。通过项目的研究将揭示青藏高原隆升到现代地貌与环境格局过程中所出现的重大构造事件和环境事件;重建不同区域、不同时间尺度的气候环境变化序列并揭示其时空分布特征;阐明青藏高原冰冻圈、湖泊和主要生态系统与土地覆被在不同气候条件下的变化特征;揭示青藏高原环境变化与地表过程对全球变化的响应特点和高原热力与动力过程对不同气候系统变化的影响。本项目将在高原南北典型区域利用地貌学与沉积学手段,研究青藏高原现代地貌与环境格局的形成过程;利用湖芯、冰芯、树木年轮等手段,研究青藏高原过去环境变化的特征事件、区域分异及其与全球变化的联系;利用冰川、冻土、积雪的时空变化,结合对高原特殊大气边界层的观测,研究青藏高原冰冻圈变化与能量水分循环过程;从冰川、湖泊、大气的监测入手,结合模式方法,研究青藏高原环境变化的机制;利用生态系统碳的源—汇变化,研究青藏高原生态系统对环境变化的响应;综合研究全球变化背景下青藏高原环境变化与水资源变化所产生的区域效应和适应对策。     

现代河流沉积物碎屑及矿物组分研究新进展

现代河流沉积物忠实地记录了流域盆地内的母岩、风化、搬运和沉积过程中的化学、物理过程以及人类活动的改造作用,是探索和验证源- 汇系统等理论的重要媒介。本文以全球现代河流砂组分数据库为基础,总结了碎屑组分、重矿物组分在不同大陆的分布特征,探讨了其在物源识别、源区贡献率计算、沉积物产生及搬运过程中气候- 构造等影响因素的评估、对源- 汇系统的研究启示等方面的应用。今后建议加强基于大数据的沉积物组分对气候- 构造- 人类活动的响应、沉积物产生及通量、高时间分辨率的沉积物组分变异性、不同物源定量化方法的差异等方面的研究。     

Sediment geochemistry as a provenance indicator: Unravelling the cryptic signatures of polycyclic sources,climate change,tectonism and volcanism

Interpretation of bulk‐sediment geochemistry is one of several approaches for determining sediment provenance. This study investigates the value added by bulk‐sediment geochemical analysis in interpreting provenance in a passive margin clastic basin, the Upper Jurassic–Lower Cretaceous deltaic sediments of the Scotian Basin. Provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant. More than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements. Diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km, thus impacting principal component analysis and published weathering indices. However, multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the Tithonian and Barremian, and changes in supply from major tectonic events, such as the top‐Aptian uplift in the Labrador rift. Covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources. Geochemical analyses revealed a previously unsuspected Tithonian alkali volcanic sediment source, characterized by high niobium and tantalum. The lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance. Published discrimination diagrams are of limited value. Statistical analysis of geochemical data is strongly influenced by diagenetic processes, episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones. Single indicator elements for particular sources are generally lacking. Nevertheless, careful consideration of geochemical variability on a case by case basis, integrated with detrital mineral studies, provides new insights into palaeoclimate, sediment provenance and, hence, regional tectonics. Although there is no simple template for such analysis, this study demonstrates an approach that can be used for other basins.     

Lacustrine source rock deposition in response to co-evolution of environments and organisms controlled by tectonic subsidence and climate, Bohai Bay Basin, China

Three Paleogene syn-rift intervals from the Bohai Bay Basin, the most petroliferous basin in China, were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities, to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions. The third (Es₃) and first (Es₁) members of the Eocene Shahejie Formation and the Oligocene Dongying Formation (Ed) display widely variable total organic carbon contents, hydrogen indices and visual kerogen compositions, suggesting changes in organic facies from deep to marginal sediments. Carefully selected deep-lake facies samples from any interval, however, display fairly uniform biomarker composition. These three intervals have distinctly different biomarker assemblages, which indicate weakly alkaline, freshwater lakes with a moderately deep thermocline during Es₃ deposition, alkaline-saline lakes with shallow chemocline during Es₁ deposition and acidic, freshwater lakes with deep, unstable thermocline during the deposition of the Dongying Formation. Such environmental changes corresponded to changes in subsidence rate and paleoclimate, from rapid subsidence and wet climate during Es₃ deposition, through slow subsidence and arid climate during Es₁ deposition to rapid subsidence and wet climate during Ed deposition and resulted in synchronous changes in terrigenous organic matter input, phytoplankton community and primary productivity. The co-evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics. Most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn-rift evolutions. The models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins.     

Tectonically controlled sedimentation: impact on sediment supply and basin evolution of the Kashafrud Formation (Middle Jurassic,Kopeh-Dagh Basin,northeast Iran)

The Kashafrud Formation was deposited in the extensional Kopeh-Dagh Basin during the Late Bajocian to Bathonian (Middle Jurassic) and is potentially the most important siliciclastic unit from NE Iran for petroleum geology. This extensional setting allowed the accumulation of about 1,700 m of siliciclastic sediments during a limited period of time (Upper Bajocian–Bathonian). Here, we present a detailed facies analysis combined with magnetic susceptibility (MS) results focusing on the exceptional record of the Pol-e-Gazi section in the southeastern part of the basin. MS is classically interpreted as related to the amount of detrital input. The amount of these detrital inputs and then the MS being classically influenced by sea-level changes, climate changes and tectonic activity. Facies analysis reveals that the studied rocks were deposited in shallow marine, slope to pro-delta settings. A major transgressive–regressive cycle is recorded in this formation, including fluvial-dominated delta to turbiditic pro-delta settings (transgressive phase), followed by siliciclastic to mixed siliciclastic and carbonate shoreface rocks (regressive phase). During the transgressive phase, hyperpycnal currents were feeding the basin. These hyperpycnal currents are interpreted as related to important tectonic variations, in relation to significant uplift of the hinterland during opening of the basin. This tectonic activity was responsible for stronger erosion, providing a higher amount of siliciclastic input into the basin, leading to a high MS signal. During the regressive phase, the tectonic activity strongly decreased. Furthermore, the depositional setting changed to a wave- to tide-dominated, mixed carbonate–siliciclastic setting. Because of the absence of strong tectonic variations, bulk MS was controlled by other factors such as sea-level and climatic changes. Fluctuations in carbonate production, possibly related to sea-level variations, influenced the MS of the siliciclastic/carbonate cycles. Carbonate intervals are characterized by a strong decrease of MS values indicates a gradual reduction of detrital influx. Therefore, the intensity of tectonic movement is thought to be the dominant factor in controlling sediment supply, changes in accommodation space and modes of deposition throughout the Middle Jurassic sedimentary succession in the Pol-e-Gazi section and possibly in the Kopeh-Dagh Basin in general.     

Climate control on stacked paleosols in the Pleistocene of the Po Basin (northern Italy)

Paleosols are recurrent features in alluvial successions and provide information about past sedimentary dynamics and climate change. Through sedimentological analysis on six sediment cores, the mud-dominated succession beneath the medieval ‘Two Towers’ of Bologna was investigated down to 100 m depth. A succession of weakly developed paleosols (Inceptisols) was identified. Four paleosols (P1, P2, P3 and PH) were radiocarbon-dated to 40–10 cal ka bp . Organic matter and CaCO₃ determinations indicate low groundwater levels during soil development, which spanned periods < 5 ka. The development and burial of soils, which occurred synchronously in the Bologna region and in other sectors of the Po Plain, are interpreted to reflect climatic and eustatic variations. Climatic oscillations, at the scale of the Bond cycles, controlled soil development and burial during Marine Isotope Stage (MIS) 3 (P1 and P2). Rapid sea-level oscillations probably induced soil development at the MIS 3/2 transition (P3) and favored burial of PH after 10 ka bp . Weakly developed paleosols in alluvial successions can provide clues to millennial-scale climatic and environmental variations. In particular, the paleosol-bearing succession of the Po Plain represents an unprecedent record of environmental changes across the Late Pleistocene (MIS 3 and 2) in the Mediterranean region.     

长江沉积物源示踪研究进展

近期物源分析方法发展较快,包括稀土元素、同位素地球化学与单颗粒碎屑矿物微区分析方法的广泛运用,以及分不同粒级组分或根据需要选择特定粒级组分进行物源分析逐渐代替了全样分析法,物源示踪效果得到明显的提高。长江作为连接青藏高原与西太平洋边缘海的最重要水系,河流沉积物从源到汇的现代与历史过程备受关注。长江沉积物源示踪研究进展包括:①建立和运用河流入海沉积物示踪端元模型,定性或定量地分析长江沉积物在海域的扩散与沉积分布规律,倾向于运用细颗粒组分矿物学、元素与同位素地球化学等方法,研究程度较高,今后需注意各端元值的时空变化,及受沉积过程的分异作用与早期成岩作用的影响;②建立和运用不同支流的物源示踪模型,研究晚新生代以来长江水系的演化历史,倾向于运用粗颗粒组分的物源分析方法,尤其是单颗粒碎屑矿物微区分析。由于长江流域面积巨大、区域地质复杂,建立支流域的精细物源分析指纹特征尚处在探索阶段,需注意运用碎屑锆石U-Pb定年与稀土元素、Hf同位素组成的综合物源分析法。综合运用多种物源分析法于长江中下游和三角洲盆地若干钻孔地层的研究,已较好地限定长江贯通的时间约在上新世晚期—早更新世之间,但仍存在较大争议,今后需在一些关键区域开展更多的深钻研究,提高物源精细示踪的效果、晚新生代地层测年的精度,并加强钻孔间的的对比研究。     

Magnetic susceptibility studies of the upper Albian-Danian sediments of Cauvery basin,south India

The Cauvery basin of the Indian Peninsular shield, formed during the fragmentation of the Gondwana Supercontinent, continued to evolve until the end of Neogene through rift, pull-apart, shelf sag and tilt processes. The basin witnessed many cycles of transgression, regression, erosion and deposition. A more or less complete succession of upper Cretaceous–Paleocene sediments is exposed in the Ariyalur–Pondicherry depression of the basin. Anisotropy of magnetic susceptibility (AMS) technique is applied in an attempt to examine the depositional and eustatic conditions prevailed during the formation of these sedimentary sequences. AMS results point to the sedimentation history dominated by marked sea level changes with several phases of transgression and regression. The sedimentation occurred mainly in a shallow epicontinental sea which has been punctuated with terrigenous supply more often. Greater utility of magnetic fabrics is suggested as a tool to trace fluvial responses to tectonic and climatic changes.