岩溶动力系统对典型石灰岩土肥力特征的影响

碳酸盐岩(CaCO3)—CO2(气)—水(H2O)三相组成的岩溶动力系统,通过驱动环境元素的迁移,可影响土壤的基本性质及营养元素的形态和转化。一方面土壤盐基离子(Ca、Mg、K、Na)的大量淋失,另一方面岩溶作用产生的富钙环境使土壤体系中盐基获得补充,形成偏碱的土壤环境,并因此使石灰岩土的阳离子交换量和有机质含量较高,但也降低了土壤铁、锰、磷、锌等元素的有效性,最终对土壤肥力特征及演变产生深远的影响。      

Background levels and baseline values of available heavy metals in Mediterranean greenhouse soils (Spain)

This study determines extractable levels of Cd, Cu, Pb, Zn, Ni and Co in western Almería (Spain) greenhouse surface soil horizons using EDTA solution, which is identified as the fraction available for organisms and plants. It also establishes background levels, geochemical baseline concentration and reference values (RV), and investigates the possible relationships between soil properties and elemental concentrations. The results show that the soil concentration of these extractable heavy metals was high as those reported by other authors for Spanish agricultural soils. The available RV concentrations obtained (mg kg⁻¹) were: Cd 0.17, Cu 1.6, Pb 13.8, Zn 5.0 Ni 1.7 and Co 2.9. Using the upper baseline criterion, 95% of greenhouse soils present a relatively higher content of extractable heavy metals given their Cd and Cu concentration. Significant correlations between total and EDTA-extractable metal levels were found for Zn, Pb, Cu, Cd and Ni. Soil properties also related to heavy metals content, suggesting that Cd, Cu, Pb and Zn are of similar origin and relate to anthropic activities, and implies the same interactions and/or relationships among these metals.     

观音岩水电站坝址区右岸岩体溶蚀发育机理研究

观音岩水电站位于金沙江上游,坝型初拟混凝土重力坝和心墙堆石坝组合坝.坝址区分布有侏罗系中蛇店组(J2s)地层,岩性主要为钙质铁质胶结的砾岩、石英砂岩,其中砾石成分以泥晶灰岩和生物灰岩为主.在地下水作用下砾岩钙质溶蚀形成规模较大的囊状空腔或孔洞,砂岩则表现为钙质胶结物流失溶蚀呈砂土状或砂糖状,对坝基稳定性造成了一定的影响...     

广西那坡盆地火山岩-碳酸盐岩混杂型滑塌堆积:特殊的弧前域构造指相标志及其大地构造意义

本文详细调查揭示,位于中越边境地区的那坡弧前盆地北部边缘发育17处滑塌堆积,有些表现为火山岩-碳酸盐岩块混杂型滑塌堆积,即由火山岩滑塌块体和碳酸盐岩滑塌块体无序堆积而成;有些只是具软沉积变形特征的薄层碳酸盐岩滑塌块体;还有些是砂屑灰岩滑塌块体与碳酸盐岩(或钙质)浊积岩组合以及单一的碳酸盐岩浊积岩或碳酸盐岩碎屑流。碳酸盐岩质块体流和碎屑流一般夹于大型或巨型滑塌块体间,而碳酸盐岩(或钙质)浊积岩和块状砂岩等一般发育于滑塌堆积的远端,有的覆盖于滑塌块体之上。无论是时代还是地球化学组成,滑塌堆积中的具枕状构造的火山岩块与盆地北侧富宁县架街一带的早-中三叠世弧火山岩完全一致。具软沉积变形特征的薄层碳酸盐滑塌岩块中发育有厚30cm左右的风暴沉积层,暗示这些滑塌岩块是发育于火山弧边缘的或其上的局部的碳酸盐岩台地(主要为潮坪-潟湖相)沉积。与全球不同造山带弧前盆地对比表明,这些滑塌堆积是一种发育于构造活动强烈的弧前盆地边缘的特殊的事件沉积,可作为识别弧前域大地构造相单元的普适性沉积标志,也可用以分析断定俯冲增生造山极性。本文对碳酸盐岩滑塌块体的原始层理和软沉积变形的滑塌褶皱轴面方位测量统计揭示火山弧斜坡大体向南西方向(232°~240°)倾斜,滑塌堆积远端浊积岩古水流测量与校正结果揭示沉积物搬运方向为南或南西向,这表明华南地块与北越地块之间的古特提斯分支洋盆在早三叠世期间是向北俯冲消化减的。     

Calcareous nannofossil changes linked to climate deterioration during the Paleocene-Eocene thermal maximum in Tarim Basin,NW China

The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.     

Impact of an 0.2 km3 Rock Avalanche on Lake Eibsee (Bavarian Alps,Germany) – Part I: Reconstruction of the paleolake and Effects of the Impact

Rock avalanches destroy and reshape landscapes in only a few minutes and are among the most hazardous processes on Earth. The surface morphology of rock avalanche deposits and the interaction with the underlying material are crucial for runout properties and reach. Water within the travel path is displaced, producing large impact waves and reducing friction, leading to long runouts. We hypothesize that the 0.2 km³ Holocene Eibsee rock avalanche from Mount Zugspitze in the Bavarian Alps overran and destroyed Paleolake Eibsee and left a unique sedimentological legacy of processes active during the landslide. We captured 9.5 km of electrical resistivity tomography (ERT) profiles across the rock avalanche deposits, with up to 120 m penetration depth and more than 34 000 datum points. The ERT profiles reveal up to ~50 m thick landslide debris, locally covering up to ~30 m of rock debris with entrained fine-grained sediments on top of isolated remnants of decametre-wide paleolake sediments. The ERT profiles allow us to infer processes involved in the interaction of the rock avalanche with bedrock, lake sediments, and morainal sediments, including shearing, bulging, and bulldozing. Complementary data from drilling, a gravel pit exposure, laboratory tests, and geomorphic features were used for ERT calibration. Sediments overrun by the rock avalanche show water-escape structures. Based on all of these datasets, we reconstructed both position and size of the paleolake prior to the catastrophic event. Our reconstruction of the event contributes to process an understanding of the rock avalanche and future modelling and hazard assessment. Here we show how integrated geomorphic, geophysical, and sedimentological approaches can provide detailed insights into the impact of a rock avalanche on a lake. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Biostratigraphical correlations of the calcareous nannofossil Marthasterites furcatus in the Bohemian Cretaceous Basin and Outer Flysch Carpathians,Czech Republic

The first occurrence (FO) of Marthasterites furcatus was correlated with the FOs of other nannofossils, inoceramid bivalves and foraminifers in the Bohemian Cretaceous Basin and Outer Flysch Carpathians. The correlation showed that the FO of M. furcatus was diachronous, becoming younger from east to west. In the Silesian Unit it appears in the lower Turonian in association with Eprolithus moratus (UC6b nannofossil Zone). In the Pavlovské vrchy klippes it appears in the upper middle Turonian together with Lithastrinus septenarius (UC9 Zone). In the Bohemian Cretaceous Basin, the FO of M. furcatus was observed in the lower upper Turonian just above the FO of Liliasterites angularis. The presence of M. furcatus in Turonian strata is scarce and discontinuous up to its sudden quantitative increase (represented by 5–27% in assemblages) below the FO of the inoceramid bivalve species Cremnoceramus waltersdorfensis and C. deformis erectus in the Turonian–Coniacian boundary interval. The top of the M. furcatus acme was recorded below the FO of Micula staurophora. The second quantitative rise of M. furcatus (12% in assemblage) was found in the lower lower Campanian of the Pavlovské vrchy klippes above the FO of Broinsonia parca parca in the UC14a Zone and the last occurrence of the planktonic foraminifer Whiteinella baltica. Above this second acme M. furcatus disappears. The significantly earlier appearance of M. furcatus in the Silesian Basin may be connected with a southeast-heading surface current from the North European epicontinental sea where the species appeared in the early Turonian too.     

Sedimentary facies and diagenetic features of the Early Cretaceous Fahliyan Formation in the Zagros Fold-Thrust Belt,Iran

The Early Cretaceous Fahliyan Formation (middle part of the Khami Group), is one of the important reservoir rocks in the Zagros Fold-Thrust Belt. The Zagros Fold-Thrust Belt is located on the boundary between the Arabian and Eurasian lithospheric plates and formed from collision between Eurasia and advancing Arabia during the Cenozoic. In this study area, the Fahliyan Formation with a thickness of 325 m, consists of carbonate rocks (limestone and dolomite). This formation overlies the Late Jurassic Surmeh Formation unconformably and underlies the Early Cretaceous Gadvan Formation conformably at Gadvan Anticline. The formation was investigated by a detailed petrographic analysis to clarify the depositional facies, sedimentary environments and diagenetic features in the Gadvan Anticline. Petrographic studies led to recognition of the 12 microfacies that were deposited in four facies belts: tidal flat, lagoon, and shoal in inner ramp and shallow open marine in mid-ramp environments. The absence of turbidite deposits, reefal facies, and gradual facies changes show that the Fahliyan Formation was deposited on a carbonate ramp. Calcareous algae and benthic foraminifera are abundant in the shallow marine carbonates of the Fahliyan Formation. The diagenetic settings favored productioning a variety of features which include cements from early to late marine cements, micritization, dolomitization, compaction features, dissolution fabric, and pores. The diagenetic sequence can be roughly divided into three stages: (1) eugenic stage: marine diagenetic environment, (2) mesogenic stage: burial environment, and (3) telogenic stage: meteoric diagenetic environment.     

Jacked model pile shafts in offshore calcareous soils

Abstract

This paper describes the results of laboratory tests carried out on model pile shafts in a variety of reconstituted calcareous sands and on silica sand. The factors influencing both the skin friction under static loading and the degradation of skin friction under cyclic loading have been investigated. The grading and crushability of the particles appears to have a significant influence on both, with less favourable performance being found for uniformly graded crushable particles. Relative density and overconsolidation ratio also have some influence.

Under cyclic loading, the amplitude of cyclic displacement and, more specifically, the cyclic slip displacement, influence the extent of cyclic degradation of skin friction.     

Study of dilatancy behaviors of calcareous soils in a triaxial test

Abstract

In this article, the dilatancy of calcareous soil is studied systematically based on triaxial consolidation drainage shear tests, and the difference in dilatancy between calcareous soil and siliceous soil is also investigated. It was found that: ① Calcareous soil experience obvious dilated deformation. Dilatancy tendency increases with increasing related density and decreases with increasing confining pressure. ② The volumetric strain rate initially increases from negative to positive. After it reaches a maximum, there is a small decrease in the volumetric strain rate, but it is still greater than zero, and the stress-strain curves are of softening type. ③ For the same condition, the dilatancy deformation of calcareous sand begins later than that of siliceous sand, and the volume compression before dilatancy is also larger for calcareous sand. ④ The critical state alone cannot accurately describe the entire deformation process of soil, and it is proposed that the phase transformation state be added to the standard method used to assess soil dilatation and contraction. ⑤ Based on the statistical analysis of experimental data, mathematical relationships were established between void ratio, relative density, and effective confining pressure of phase transformation state and critical state, respectively.

• Highlights

• Reports results from a well-designed experiment that includes a good amount of samples and data.

• Effects of relative density and effective confining pressure on deformation mode and mechanical properties of calcareous sand are evaluated.

• The difference in dilatancy between calcareous sand and siliceous sand was compared

• The phase-transformation state and critical state were compared with the axial strain, volumetric strain and deviatoric stress.

• Using phase-transformation void ratio and critical void ratio to describe the whole deformation process of calcareous sand is proposed.

• The mathematical expressions of phase-transformation void ratio and critical void ration were given, respectively.