重庆芙蓉洞崩塌作用及其环境效应

利用洞穴调查和各类次生化学沉积物同位素测年技术等方法,对芙蓉洞内崩塌物进行研究。结果表明芙蓉洞内崩塌物规模巨大,为多期次崩塌作用的产物,分别形成于大于35万年、35～20万年间、10～2.6万年间、2.5万年后及旅游开放后的1995、2000、2003、2008年,既有洞顶围岩的规模性崩塌,也有洞顶石钟乳的崩落和洞底石笋、石柱的倒塌,分别起因于地壳抬升背景下洞内水流下切使原先浮力消失引起洞顶围岩地应力失衡、洞顶石钟乳不断联合使重量超过联合体-洞顶围岩接触面的临界结合力和洞底石笋、石柱受崩落的钟乳石砸中或强地震引发。崩塌作用引起了洞腔的规模性扩大、钟乳石景观和旅游设施的破坏、被迫改变游览线路等环境效应。针对芙蓉洞崩塌特点,提出了洞穴旅游开发的一些建议。     

基于统计-动力反演的近千年印度夏季风驱动机制探讨

过去1000年的气候变化是最近数十年人类活动影响加强情况下全球气候变化的自然背景, 其变化规律和驱动机制的研究对预测未来气候变化有着重要意义。非线性统计-动力反演方法结合了统计模型和动力模型的优点, 能充分利用观测数据反演系统各因子之间的相互关系。本文尝试应用非线性统计-动力反演方法建立印度夏季风的动力方程, 为研究印度夏季风的驱动机制提供量化参考。经研究发现:近千年印度夏季风系统是复杂非线性动力系统; 工业革命前印度夏季风变化的主要驱动力是北大西洋海表温, 其次是温室气体(N2O和CO2)浓度与阿拉伯海海表温、ENSO及太阳辐照度等的相互作用; 在工业革命后期, 温室气体(CH4、N2O和CO2)浓度及其与北大西洋海表温、太阳辐照度、ENSO及北极温度等的相互作用成为印度夏季风的主要驱动力; 单因子甲烷和N2O是印度夏季风的驱动力, 而它们的非线性相互作用(两个因子的交叉项)却是稳定作用力。总体来说, 工业革命前, 北大西洋海表温度是印度夏季风的主要驱动因子; 工业革命后, 温室气体则成为主要的驱动因子。     

Origin of the sedimentary deposits of the Naracoorte Caves, South Australia

The origin of the sediments located in the Naracoorte Caves (South Australia) was investigated via the analysis of strontium isotope ratios (⁸⁷Sr/⁸⁶Sr), elemental geochemistry, and mineralogy. Sedimentary deposits located in Robertson, Wet, Blanche and several other chambers in Victoria Cave are all variable mixes of fine sand and coarse silts, which display similar and consistent strontium isotope ratios (0.717–0.725). This suggests that over the 400 ka time frame that these deposits span there has been minimal variation in the source of the clastic sediments. Increased strontium concentrations for these cave sediments correspond with increasing silt content, yet there is no correlation between ⁸⁷Sr/⁸⁶Sr ratios and silt content. This implies that the silt-sized component of the sediments is the main contributor of strontium to the cave sediments. Comparisons of ⁸⁷Sr/⁸⁶Sr with regional surficial deposits show a significant correlation between the cave sediments (avg: 0.7228; n = 27), the fine silt lunettes of the Bool Lagoon area (avg: 0.7224; n = 4), the sandy A horizons of the Coonawarra Red Brown Earths (RBEs; avg: 0.726; n = 5), and Holocene age podsolic sand deposits (0.723). These data suggest that there has been substantial flux from this group of deposits to the caves, as would be expected considering prevailing winds. This relationship is further supported by a strong correlation between many trace elements, including Ti, Zr, Ce, and Y; however, variations in clay mineralogy suggest that the fine silt-dominated lunettes and Padthaway RBEs were not significant contributors to the cave deposits. Hence, the detritus entering the caves was more than likely from areas proximal to the cave entrance and was dominated by medium grain-sized materials. Major regional deposits, including the coarser-grained, calcite-rich Bridgewater Formation sands, basalts from the lower SE, Padthaway Horst granites, Gambier limestone, and metamorphics from the Adelaide geosyncline show minimal correlation in ⁸⁷Sr/⁸⁶Sr ratios, elemental geochemistry, and mineralogy with the cave sediments, and are discounted as significant sources. In comparison, ⁸⁷Sr/⁸⁶Sr ratios for the Coorong silty sands (0.717–0.724), Lower Murray sands (0.727–0.730), and the medium size silt component of the Murray–Darling River system (0.71–0.72), compare favourably with the cave sediments. This relationship is further supported by similarities in elemental chemistry and mineralogy. Thus, much of the strontium-rich silt that is now located in the Naracoorte Cave sediments likely originated from the Murray–Darling basin. Over time, this material has been transported to the SE of South Australia, where it mixed with the medium sand component of the regressive dune ridge sequence, locally derived organic matter, limestone fragments, and fossil material to produce the unique deposits that we see evident in many of the chambers of the Naracoorte Cave system today.     

The role of inherited Pb in controlling the quality of speleothem U-Pb ages

Over two decades of technical and application-based advances to the speleothem U-Pb chronometer have cemented this terrestrial archive at the forefront of landscape reconstruction, palaeoclimatology, and palaeoanthropology. The ability to access speleothem palaeoclimate records beyond the 650 ka limit of the U-Th system has opened many avenues to such ‘deep-time’ considerations. Yet still this chronometer remains a challenging analytical exercise, more-so as the technique becomes routinely applied to carbonates with less-than-ideal U/Pb ratios. In this contribution, we review the vadose speleothem U-Pb system, as revealed by 68 previously published isochrons produced from 474 solution-mode analyses across three separate geographical regions. We develop a new statistical parameter of ‘average distance’ to quantify the dispersion or ‘spread’ along the previously published isochrons and compare this with available U and Pb elemental concentrations. Our findings highlight the importance of regional geology and karst morphology in controlling the speleothem's overall U/Pb ratio. Furthermore, we show that variability in the amount of inherited Pb across the sampling layer (average variability of 63% relative to sample average) – not uranium (23% variability) or by extension radiogenic Pb – is a main factor controlling the resulting isochron's quality. This is demonstrated using Z-score distributions of the U and Pb concentrations and isochron average distance values. By making this distinction we hope to initiate further research into Pb-specific transportation vectors through the karst, in addition to physical/chemical processes that fractionate inherited Pb at the speleothem precipitation site. We go on to extend the use of Tera-Wasserburg common Pb anchors to the ‘classical’ U-Pb isochrons as an example of the utility gained by considering the role of inherited Pb within speleothems. Finally we argue that an improved theoretical understanding of inherited Pb distributions within speleothems would greatly benefit solution mode sampling strategies, especially for poor-to-moderate U/Pb speleothems.     

Magnetostratigraphy of Plio–Pleistocene fossiliferous cave sediments in the Bubing Basin,southern China

Our understanding of the chronological sequence of Pleistocene land mammal faunas (including hominids) preserved in caves and fissures in the karstic terrain of subtropical southern China has been greatly impeded by the discontinuous nature of the strata yielding the fossils. A contributory issue is the lack of suitable elements for numerical dating, especially for the Early Pleistocene cave sediments. Here we present new magnetostratigraphic dating results for five cave sedimentary sequences in the Bubing Basin, Guangxi Zhuang Autonomous Region, which contain the typical Pleistocene Gigantopithecus fauna and Ailuropoda–Stegodon fauna of southern China. The five karstic caves are situated at elevations ranging from 252 m to 191 m above sea level. The integrated dating results reveal that the five cave sedimentary sequences span an age range from the late Gauss normal Chron to the early Brunhes normal Chron. The faunas are assigned to >2.6 Ma (Mohui–houshan Cave), 1.95–1.78 Ma (Mohui Cave), 0.99–0.78 Ma (Baolai Cave) and ∼0.7 Ma (Upper Wuyun and Ganxian Caves). Furthermore, by combining our new magnetostratigraphy work with previously published magnetostratigraphic, U–series and electron spin resonance dating results, a chronological sequence of the Plio–Pleistocene mammalian faunas from cave sites in southern China has been established. The chronological sequence contributes to an improved understanding of the evolutionary processes of Plio–Pleistocene land mammals, as well as of early humans in subtropical southern China.     

临汾台洞体形变典型干扰与地震异常图像识别

文章分析了临汾台水平摆、垂直摆两套洞体形变观测仪记录曲线的正常变化形态,讨论了人为和自然因素引起干扰的图像特征,以及山西带南部3次中等地震前典型异常图像特征,分析结果为今后观测数据处理、异常识别及异常跟踪分析判定提供参考。     

Influences of agricultural practices on water quality of Tumbling Creek cave stream in Taney County,Missouri

Influences of agricultural practices on water quality of the Tumbling Creek cave stream are of particular interest because of the karst nature of the area and the recent implementation of a Better Management Practice (BMP). Water quality parameters, measured bi-weekly during one year, consisted of pH, turbidity, water temperature, specific conductivity, total dissolved solids, alkalinity, and chloride. Heavy metals, nutrient and bacteria levels were also monitored during the study. Effects of land use were most obvious in turbidity, nitrate, chloride, and bacteria levels. Sites within the recharge area that pose a major threat to its water quality were identified. Results provide a baseline for these water quality parameters and their seasonal variability that can be used in future studies to address the effects of water quality and stream sediment contamination on the caves ecosystem and to determine the effectiveness of the BMP implemented in this karst area.     

Chemistry of waters from selected caves in Slovakia—a reconnaissance study

The chemical composition of water samples was studied from different caves in Slovakia. The water samples were collected from caves of two karst regions: (1) the Demänovský Cave System (DCS), situated in the Low Tatra Mountains (Northern Slovakia), which is mainly formed of limestone and dolomites; and (2) the Slovakian Karst to the Southeast is formed of limestone. A considerable difference between water from the two regions was shown. The waters from the DCS, that were controlled by vadose water percolating through different types of host rocks, contained more Mg ions than those from the Slovakian Karst caves whereas, the concentration of SO₄ was controlled by the dissolution of displacive gypsum and/or oxidation of pyrite. The distribution of NO₃ in the studied samples was random, hence nitrates probably derived from few pollution sources. The total mineralization of the water was covariant with calcite and aragonite saturation indices. In general, both parameters are higher in the Slovakian Karst caves than in the DCS. It is controlled probably by differences in climatic conditions, soil and plant covers between these two regions. The main goal of this article is to characterize the major-ion water chemistry within the studied caves as well as some microelements. The results have confirmed the dominant role of the bedrock petrography in forming the general chemistry of cave waters.     

文山普者黑机场地下溶洞裂隙稳定性分析

对工程场区溶洞、溶隙的埋深、充填物及其性能、顶板厚度与洞跨、荷载作用形式及大小等因素进行综合分析，判断溶洞、溶隙的稳定性及其对工程建设运营的影响，提出相应的处治方案。