Neotectonic state of stress in the Jura Mountains

Abstract

For the determination of the tectonic stress field in the region of the Jura Mountains, three different relief techniques have been used in 18 test sites. In six test sites measurements have been carried out in horizontal boreholes using the doorstopper method. In the remaining test sites measurements were made in vertical boreholes by the doorstopper method (8), triaxial strain cell method (3) and borehole slotter (1). Additionally, analyses of borehole breakouts from six deep wells are presented.

Orientation of maximum horizontal stress clearly deviates from the uniform NW-SE orientated central and western European stress field. Local stress sources, which are probably related to active decollement tectonics in the Jura Mountains, may explain the deviation in stress orientations in comparison to the foreland. Normal stress magnitudes perpendicular to the trend of compressional structures in the Folded Jura are largest in the southeastern Upper Rhine Graben and its southwards prolongation into the Jura Mountains. Low stress magnitudes are characteristic for the eastern termination, intermediate ones for the southern foreland of the Jura Mountains.     

Astronomical time scale for the Middle Oxfordian to Late Kimmeridgian in the Swiss and French Jura Mountains

Detailed investigation of facies and sedimentary structures reveals that, during the Middle Oxfordian to Late Kimmeridgian, the shallow carbonate platform of the Swiss and French Jura Mountains recorded high-frequency sea-level fluctuations quite faithfully. The cyclostratigraphic analysis within the established biostratigraphic and sequence-chronostratigraphic framework implies that the resulting hierarchically stacked depositional sequences formed in tune with the orbital cycles of precession (20 kyr) and eccentricity (100 and 400 kyr). The astronomical time scale presented here is based on the correlation of 19 platform sections and 4 hemipelagic sections from south-eastern France where good biostratigraphic control is available. The cyclostratigraphic interpretation suggests that the interval between sequence boundaries Ox4 and Kim1 (early Middle Oxfordian to earliest Kimmeridgian) lasted 3.2 myr and that the Kimmeridgian sensu gallico has a duration of 3.2 to 3.3 myr. The astronomical time scale proposed here is compared to time scales established by other authors in other regions and the discrepancies are discussed. Despite these discrepancies, there is a potential to estimate the durations of ammonite zones and depositional sequences more precisely and to better evaluate the rates of sedimentary, ecological and diagenetic processes. Editorial handling: Hanspeter Funk, Helmut Weissert, Stefan Bucher     

The ups and downs of “Tectonic Quiescence”—recognizing differential subsidence in the epicontinental sea of the Oxfordian in the Swiss Jura Mountains

Recent studies in northern Switzerland have shown that epicontinental areas thought to have been tectonically stable during the Mesozoic were not necessarily as rigid as presumed. By comparing Oxfordian facies boundaries and depocenters in their palinspastic position with known faults in the basement, a direct relationship between the two can be demonstrated. Previously, the lack of obvious synsedimentary tectonic features has lulled scientists into believing that the realm of the Swiss Jura was tectonically stable during the Mesozoic. However, it can be shown that facies and sedimentary structures are largely influenced by tectonics. Subsurface data provide evidence for the presence of Paleozoic troughs in the basement which, apparently, were prone to reactivation during the Pan-European stress-field reorganization taking place in the Late Jurassic. This led to differential subsidence along pre-existing lineaments within the study area, which can be recognized in the distribution of Oxfordian epicontinental basins and their coeval shallow-water counterparts. Eustatic sea-level fluctuations played an important role in the development of shallow-water facies patterns, but a subordinate role in the control of accommodation space in basins.

While tectonic activity is often recorded in the sedimentary record in the form of platform break-ups and associated sedimentary debris, more subtle indicators may be overlooked or even misinterpreted. Sedimentary structures and isopach maps, as well as subsurface data in the study area suggest that subtle synsedimentary tectonic movements led to the formation of two shallow, diachronous epicontinental basins during the Late Jurassic. It becomes possible to recognize and differentiate the combined effects of local and regional tectonism, eustasy and sedimentation.     

半干旱岩溶区油松林显著促进碳酸盐岩溶蚀

植被覆盖通过促进碳酸盐岩风化吸收大气CO2, 在实现碳中和中具有重要作用, 但不同植被类型的影响强度仍不清楚。为揭示半干旱区植被类型对碳酸盐岩风化的影响规律, 以一个典型岩溶小流域为研究区, 通过系统的植被调查和野外溶蚀试片试验, 详细对比了不同植物群系的碳酸盐岩溶蚀率及其影响因素, 并探讨了不同分类层次植被的溶蚀率的差异。结果表明, 半干旱岩溶区碳酸盐岩溶蚀率在植被型组层次为森林>草地>灌丛, 在演替的早期减弱、后期促进溶蚀; 群系层次的对比发现油松(Pinus tabuliformis)林内碳酸盐岩溶蚀率最高, 是其它群系的5倍至近30倍; 不同群系对溶蚀率的影响强度的大小得以明确; 溶蚀率与土壤CO2浓度(pCO2)、土壤温度和土壤含水量任何单一因素无相关性, 而与三者匹配性有较好的对应关系, 与湿润区明显不同; 植被演替通过增强对溶蚀环境因子匹配性的调控能力, 促进碳酸盐岩的溶蚀。半干旱区油松林显著促进碳酸盐岩溶蚀, 进行群系层次的广泛对比研究可以更好揭示植被类型与碳酸盐岩溶蚀之间的关系, 为提高岩溶生态系统恢复的碳汇量提供有效指导。     

Facies, cycles, and controls on the evolution of a keep-up carbonate platform (Kimmeridgian, Swiss Jura)

During the Late Jurassic, accelerated ocean-floor spreading and associated sea-level rise were responsible for a worldwide transgression, which reached its maximum in the Late Kimmeridgian. In many Western European basins, this major sea-level rise led to the formation of marly and condensed sections. In the Swiss Jura, however, a shallow carbonate platform kept growing and only subtle changes in the stratigraphic record suggest an increasingly open-marine influence. Field observations and thin-section analyses reveal that the central Swiss Jura was at that time occupied by tidal flats and by more or less open marine lagoons where shoals and bioherms developed. The evolution through time of sedimentary facies and bed thicknesses permits the definition of small-, medium-, and large-scale depositional sequences. The diagnostic features of these sequences are independent of scale and seem largely controlled by the Kimmeridgian second-order transgression. A high-resolution sequence-stratigraphic correlation with biostratigraphically well-dated hemipelagic and pelagic sections in the Vocontian Basin in France reveals that: (i) The most important increase in accommodation recorded in the Kimmeridgian of the central Swiss Jura occurs in the Eudoxus ammonite zone (Late Kimmeridgian) and corresponds to the second-order maximum flooding recognized in many sedimentary basins. (ii) The small- and medium-scale sequences have time durations corresponding to the first and second orbital eccentricity cycle (i.e. 100 and 400 ka, respectively), suggesting that sedimentation on the platform and in the basin was at least partly controlled by cyclic environmental changes induced by insolation variations in the Milankovitch frequency band. The comparison of the high-resolution temporal framework defined in the Swiss Jura and Vocontian Basin with the sequence-stratigraphic interpretation realized in other Western European basins shows that the large-scale sequence boundaries defined in the Kimmeridgian of the Swiss Jura appear in comparable biostratigraphic positions in most Western European basins. Discrepancies that occur are probably because of local or regional tectonics.     

Chemical Weathering in the Batura Glacier Basin, Karakoram Mountains

CHEMICAL WEATHERING IN THE BATURA GLACIER BASIN, KARAKORAM MOUNTAINStheChineseNationalBasicResearchProgramme(GrantG 19980 4 0 80 0 )andChineseNationalScienceFoundation (NSFgrant 4 980 10 0 4 )     

Water Geochemistry of Three Mountain Streams from Carbonate Watersheds in the Southern French Alps

The chemical composition of water from three streamsflowing through a carbonate watershed wasinvestigated. Although the study area is not spatiallyvery large (a few km²), local inhomogeneitieswithin the lithology appreciably affect the chemicalcomposition of the water and the geochemical gradientas a function of elevation. The main chemical processwhich leads to the observed water chemistry is thedissolution of calcium carbonate by atmospheric andmetabolic CO₂. In the stream La Sigouste, thewater dissolves nearly pure calcite and this reactionproceeds until an equilibrium with respect to calciteis reached. In Le Lauzon stream, local inhomogeneitiesin the lithologic composition prevent theestablishment of an unambiguous weathering budgetwhile, for Le Rif de l'Arc a stoichiometric modelshows that the weathering process is adequatelyrepresented by the dissolution of calcite associatedwith a minor incongruent dissolution of chloritepresent in marls. For the two last streamssupersaturation with respect to calcite is observed.For both streams, supersaturation with respect toatmospheric CO₂ is nearly permanent. The observedaltitudinal gradients of sulfate are interpretedthrough a set of biogeochemical redox reactions.     

阿尔泰山西北山区寒冻湿润条件下土壤的风化特征

通过阿尔泰山西北山区不同海拔的６个土壤剖面,从土壤的机械组成、底土层矿物、粘土矿物类型和粘粒的化学全量等,分析了其风化特征。研究结果表明,整个山区总体上风化较弱,在粘土矿物类型和粘粒的硅铝铁率比值方面无明显差异。粘土矿物都以水云母为主,粘粒的硅铝铁率为２．７８￣３．３７。风化程度的一定差异只表现在山区不同的高度带其土壤表层粘粒含量、Ｘ射线衍射峰的高度以及底土层矿物组成等方面。在高山带寒冻湿润的条件     

A study of erosion rates on salt diapir surfaces in the Zagros Mountains, SE Iran

Salt exposures and weathering residuum on several salt diapirs in different geographic/climatic settings were studied. Anhydrite, gypsum, hematite, calcite, dolomite, quartz, and clay minerals are the main constituents of the weathering residuum covering the salt diapirs in various thicknesses. Erosion rates of residuum as well as of rock salt exposures were measured at selected sites for a period of 5 years by plastic pegs as benchmarks. Recorded data were standardized to a horizontal surface and to long-term mean precipitation. For the rock salt exposures the following long-term denudation rates were determined of 30–40 mm a⁻¹ for coastal diapirs and up to 120 mm a⁻¹ for mountain salt diapirs. Long-term mean superficial denudation rate measured on weathering residuum of low thickness reached 3.5 mm a⁻¹ on coastal diapirs. The total denudation rate estimated for the thin residuum is close to 4–7 mm a⁻¹ based on apparent correlation with the uplift rate on Hormoz and Namakdan diapirs. Denudation of rock salt exposures is much faster compared to parts of diapirs covered by weathering residuum. The extent of salt exposures is an important factor in the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir. Salt exposures produce huge amounts of dissolved and clastic load, thus affecting the surrounding of the diapir.     

青藏高原东部长江流域盆地地表化学剥蚀通量剥蚀速率大气CO2净消耗率研究

2000~2002年期间,笔者对青藏高原东部长江流域溶质载荷分别进行了取样分析并对流域盆地化学剥蚀通量、剥蚀速率和大气CO₂净消耗率进行了计算。结果表明,流域盆地化学剥蚀速率以河源区楚玛尔河最高为2.34×10⁶mol/a/km²,沱沱河最低为1.40×10⁶mol/a/km²,四大支流雅砻江为1.69×10⁶mol/a/km²,金沙江为1.74×10⁶mol/a/km²,大渡河为1.57×10⁶mol/a/km²,岷江为1.88×10⁶mol/a/km²;流域盆地ФCO₂估算结果以大渡河最高为101.81×10³mol/a/km²,楚玛尔河最低为7.55×10³mol/a/km²,金沙江为44.38×10³mol/a/km²,雅砻江为69.64×10³mol/a/km²,岷江为81.90×10³mol/a/km²,沱沱河为21.90×10³mol/a/km²。并对长江流域地表化学剥蚀速率主要控制因素进行了讨论。     

青藏高原流域岩石风化速率及其控制机制——以贡嘎山地区典型地质背景小流域研究为例

以青藏高原东缘贡嘎山地区30余个典型地质背景小流域为研究对象,在河流水体物质来源定量辨识的基础上,估算了流域岩石风化速率,并系统分析了高原流域风化速率与物理剥蚀速率、径流量和温度之间的关系。雅家河西岸、加则拉、雅家河东岸以及大渡河东岸流域的硅酸盐岩风化速率（SWRcat）平均值（范围）分别为2.49（0.40~6.93）t/km2/a、3.20（2.20~3.90）t/km2/a、0.74（0.50~0.90）t/km2/a以及2.63（0.70~9.40）t/km2/a;TDR的平均值（范围）分别为332.85（31.03~2231.23）t/km2/a、66.92（38.5~167.7）t/km2/a、10.82（8.49~13.79）t/km2/a以及36.27（8.49~176.50）t/km2/a。研究区SWRcat流域面积加权平均值为2.1 t/km2/a。研究表明,硅酸盐岩风化速率受物理剥蚀和气候等多种因素的共同影响,这些小流域岩石风化控制机制可分为"运移限制（transport-limited）"和"风化限制（weathering-limited）"。在"运移限制"下的小流域,其化学风化速率取决于物理剥蚀速率,化学风化主要受流域的物理剥蚀所控制;而在"风化限制"下,其化学风化速率主要受风化反应动力学所控制,与温度、径流量等气候因子有关。     

祁连山黑河上游多年冻土区不同植被类型土壤有机碳密度分布特征

山地多年冻土的异质性影响其植被类型的分布特征,且对有机碳的分布也具有重要影响。通过采集黑河上游多年冻土区三种典型植被类型（高寒沼泽草甸、高寒草甸、高寒草原）8个活动层的土壤样品,测定其土壤有机碳密度及其理化性质。结果表明：高寒沼泽草甸土壤有机碳密度最高（49.50 kg·m^-2）,高寒草甸次之（11.22 kg·m^-2）,高寒草原最低（7.30 kg·m^-2）。土壤有机碳密度的剖面垂直分布特征具有差异性,高寒沼泽草甸土壤有机碳密度随深度变化不明显,高寒草原和高寒草甸土壤有机碳密度随深度逐渐减小,存在显著的表层聚集性。有机碳密度与土壤含水率和细粒含量呈显著正相关,与pH值呈显著负相关关系。一般线性模型结果表明土壤含水率、pH值和土壤颗粒组成解释了96.39%的有机碳密度变异,其中土壤含水率贡献了81.53%,pH值和土壤粒度分别贡献了9.33%和4.75%。研究表明多年冻土区不同植被类型土壤有机碳密度分布特征具有明显差异,山地多年冻土土壤含水率是控制有机碳密度分布特征的重要影响因素。     

模拟不同气候条件下碳酸盐岩风化作用的淋溶实验研究

通过模拟干热、湿热与干冷3种气候条件,以饱和CO2水作为淋溶液,对黔中岩溶区3条碳酸盐岩风化壳岩-土界面的岩粉层试样进行了淋溶实验(其中干热、湿热条件下淋溶到残余酸不溶物阶段),对淋出液的pH值以及主要造岩元素的浓度进行了动态分析。结果表明,碳酸盐岩风化壳岩-土界面由岩到土的转变过程中,伴随碳酸盐的溶蚀,酸不溶物已表现出明显的风化倾向。碳酸盐的溶蚀强度表现为干冷>干热>湿热的变化趋势。温度低,碳酸盐的溶解速率大;排水条件好,碳酸盐溶解释放的Ca、Mg易随风化流体排出体系。对于酸不溶物组分,淋溶实验中有:(1)K、Na、Mg、Si、P的载体矿物风化强度在干热条件下最大(至于Ca,由于方解石与白云石均是其主要的载体矿物,酸不溶物相中的Ca难以在淋出液中有效识别)。在干冷与湿热之间,K、Na、Mg等盐基离子的溶出能力大多表现为湿热>干冷,指示了温度对盐基离子释放强度的重要制约作用;而Si和P未表现出一致的变化趋势,可能源于淋溶体系微环境的差异。(2)Fe与Mn表现出弱迁移性。其中,Fe在干冷环境下淋出强度最弱,说明温度是制约含Fe矿物分解速率的重要因素。而Fe在干热与湿热之间,以及Mn在3种淋溶条件下,未呈现出一致的变化趋势。(3)Al和Ti在碳酸盐岩风化过程中表现出强烈的惰性。      

微生物对碳酸盐岩的风化作用

微生物-矿物相互作用可以促进许多表生生物地球化学反应过程,是表生地球化学研究的重要内容。通过综合岩石表面的微生物类群及其地质作用,分析碳酸盐岩微生物风化的各种现象,特别是微观尺度上的各种形态,阐述碳酸盐岩的微生物风化机制与风化产物,笔者提出微生物对碳酸盐岩风化的4种途径:(1)通过微生物在岩石表面和缝隙中生长,导致岩石表层发生生物溶蚀、生物磨蚀和生物钻孔作用,加速岩石风化进程;(2)微生物群体形成的钻孔网络可以增强岩石化学溶蚀的有效表面积并导致其表面强度减弱而促进机械侵蚀作用,微生物对周围岩石颗粒胶结结构的破坏、疏松作用也会导致岩石矿物颗粒的分解;(3)微生物的持水作用,微生物分泌的有机酸以及微生物呼吸所释放的CO2对岩表水分的酸化过程亦加速岩石矿物的分解;(4)微生物生长过程中从岩石内摄取营养元素和产生复杂的有机配体,能促进矿物元素的释放。文中提出在开展微生物对碳酸盐岩风化过程和机理研究的基础上,有必要引入微生物生物技术来综合开发本地低品位含钾磷矿产资源,加速岩溶地区山地土壤的形成与演化。     

天山北坡玛纳斯河流域晚冰期以来植被垂直带推移*

建立了反映天山北坡玛纳斯河流域典型花粉类型与气候指标（湿润指数和温暖指数）的统计函数。基于前人研究得出的玛纳斯湖沉积剖面中不同花粉的百分含量复原了晚冰期以来玛纳斯河流域古气候的变化,并基于山地植被—气候—地形关系推断了玛纳斯河流域的植被演变过程。研究结果表明：该区晚冰期以来经历了暖干—冷湿—暖干—偏冷偏湿—暖干—冷湿—暖干的气候变化过程,植被垂直带基带相应为荒漠—荒漠草原（在局部低洼地段发育有草原和低湿地草甸）—极旱荒漠—荒漠化草原—荒漠—荒漠草原（局部发育低湿地草甸和草原）—荒漠的演化过程。当气候由暖干转为冷湿时,玛纳斯河流域所有的植被界限均向下移,此时荒漠化草原面积增大,针叶林的下限可以到达今天的禾草草原,同时森林带的面积有所增加。当气候由冷湿转为暖干时,玛纳斯河流域所有的植被界限均向上移,荒漠的面积大增,禾草草原和森林的面积均有所减小。     

柴达木盆地西部第四纪气候变化和流域风化

长期以来关于构造隆升、气候变化和大陆化学风化的相互关系存在诸多争议。在气候和构造相互作用典型区域建立高精度大陆化学风化序列是解决上述科学问题的有效途径之一。位于青藏高原东北缘长期封闭的柴达木盆地,其独特的位置和连续的沉积使其成为研究构造隆升、气候变化和大陆化学风化的理想场所。本文以柴达木盆地西部千米深钻SG-1钻孔高质量的连续细粒湖相岩芯为研究对象,使用盐类矿物的硫酸根和钾离子含量、碳酸盐锰含量和硅酸盐化学蚀变指数（CIA）和Nd同位素分析,重建该区第四纪以来湖泊流域气候变化过程和硅酸盐化学风化及可能的物源变化。结果表明柴达木盆地西部第四纪以来流域物源相对稳定,流域整体呈现出气候干旱化、流域硅酸盐风化强度减弱、湖水盐度增加和湖面降低的长期一致性演化过程;上述演化进程在2.2 Ma到2.0 Ma期间短暂加强,在约1.2 Ma和约0.6~0.5 Ma出现逐步加强趋势。过去60万年,柴达木盆地西部在冰期存在的相对高湖面时期与黄土高原粒度指标反映的冬季风减弱阶段可以很好对比。北大西洋海表温度反映的高纬过程是长时间尺度（>105年）驱动柴达木盆地西部气候变化和流域硅酸盐风化强度变化的主要因素;西伯利亚高压系统和西风系统的"跷跷板关系"可能是冰期-间冰期或者更短尺度影响柴达木盆地西部气候变化的主要因素。     

亚热带岩溶森林类型和坡位对碳酸盐岩溶蚀的影响

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