A 20‐ka climate record from Central Himalayan loess deposits     

R. K. Pant  N. Basavaiah  N. Juyal  N. K. Saini  M. G. Yadava  E. Appel  A. K. Singhvi 《第四纪科学杂志》2005,20(5):485-492

The southwest monsoon that dominated Central Himalaya has preserved loessic silt deposits preserved in patches that are proximal to periglacial areas. The occurrence of such silts suggests contemporary prevalence of cold and dry northwesterly winds. Field stratigraphy, geochemistry, mineral magnetism, infrared stimulated luminescence (IRSL) and radiocarbon dating has enabled reconstruction of an event chronology during the past 20 ka. Three events of loess accretion could be identified. The first two events of loess deposition occurred betweem 20 and 9 ka and were separated by a phase of moderate weathering. Pedogenesis at the end of this event gave rise to a well‐developed soil that was bracketed around 9 to > 4 ka. This was followed by the third phase of loess accretion that occurred around 4 to > 1 ka. Episodes of loess deposition and soil formation are interpreted in terms of changes in the strength of the Indian southwest monsoon. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Zur Kenntnis der Bauxite des Parnass-Kiona-Gebirges     

György Bardossy  Erwin Mack 《Mineralium Deposita》1967,2(4):334-348

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湖泊沉积物中胶黄铁矿的鉴出及其磁学意义   总被引：6，自引：1，他引：6  

胡守云  E.Appel  V.Hoffmann  W.Schmahl  王苏民 《中国科学D辑》2002,32(3):234-238

对青藏高原东部若尔盖盆地钻孔获取的湖泊沉积物进行了详细的岩石磁学调查及矿物学鉴定, 发现大量胶黄铁矿存在, 并认定其为主要的磁载体. 该矿物颗粒细小, 粒度均匀, 可能为生物化学成因. 与大量文献报道的相反, 在长期暴露于空气后, 样品中的胶黄铁矿仍未被氧化. 这可能与钻孔内该矿物被硅质胶结物包裹有关. 研究结果初步揭示了湖泊沉积物磁学研究的复杂性, 同时也为环境磁学机理的研究提供了新的线索.  相似文献   

Where did rotational shortening occur in the Himalayas? - Inferences from palaeomagnetic remagnetisations     

E. Schill  C. CrouzetP. Gautam  V.K. SinghE. Appel 《Earth and Planetary Science Letters》2002,203(1):45-57

In metacarbonates of the Lesser (LH) and Tethyan (TH) Himalayas of Kumaon/Garhwal (N-India) characteristic remanent magnetisations carried by pyrrhotite (unblocking temperatures: 250-330°C) and magnetite (demagnetising spectra: 15-50 mT) have been identified. Negative fold tests indicate remanence acquisition after the main folding phase, which is of short-wavelength character and occurs during the early orogenese of the Himalayas. A thermal or thermochemical origin of magnetisation is likely and the age of remanence acquisition is indicated to be about 40 Ma by ⁴⁰K/³⁹Ar cooling and ⁴⁰Ar/³⁹Ar crystallisation ages. In the Kumaon LH a long-wavelength tilting is indicated by a distribution of the remanence directions along a small-circle in N-S direction. Steepening of the remanence directions in the TH related to ramping on the Main Central Thrust (MCT) was not observed, in contrast to other related studies. In the Alaknanda valley of LH a 38±8 Ma age of remanence acquisition is supported by comparison of observed inclinations to the apparent polar wander path of India. Clockwise rotation of 20.3±11.7° (LH/Alaknanda valley) and 11.3±8.5° (TH) with respect to the Indian plate is observed, indicating that there is no significant evidence for rotational shortening along the MCT since about 40 Ma. Our results suggest that most of rotational underthrusting and oroclinal bending has not been accommodated by the MCT, but by the main thrusts south of it. The latest Miocene/Pliocene age of the Main Boundary Thrust indicates that oroclinal bending is a late-orogenic process.  相似文献   

Multicomponent magnetization in western Dolpo (Tethyan Himalaya, Nepal): tectonic implications     

C. Crouzet  P. Gautam  E. Schill  E. Appel   《Tectonophysics》2003,377(1-2):179

A palaeomagnetic study has been carried out in the Tethyan Himalaya (TH; the northern margin of Greater India). Twenty-six palaeomagnetic sites have been sampled in Triassic low-grade metasediments of western Dolpo. Two remanent components have been identified. A pyrrhotite component, characterized by unblocking temperatures of 270–335 °C, yields an in situ mean direction of D=191.7°, I=−30.9° (k=29.5, α₉₅=5.7°, N=23 sites). The component fails the fold test at the 99% confidence level (k_{in situ}/k_bed=6.9) and is therefore of postfolding origin. For reason of the low metamorphic grade, this pyrrhotite magnetization is believed to be of thermo-chemical origin. Geochronological data and inclination matching indicate an acquisition age around 35 Ma. The second remanence component has higher unblocking temperatures (>400 °C and up to 500–580 °C range) and resides in magnetite. A positive fold test and comparison with expected Triassic palaeomagnetic directions suggest a primary origin.The postfolding character of the pyrrhotite component, and its interpreted age of remanence acquisition, implies that the main Himalayan folding is older than 35 Ma in the western Dolpo area. This study also suggests that the second metamorphic event (Neo-Himalayan) was more significant in the Dolpo area than the first (Eo-Himalayan) one.A clockwise rotation of 10–15° is inferred from the pyrrhotite component, which is compatible with oroclinal bending and/or rotational underthrusting models. This rotation is also supported by the magnetite component, indicating that no rotation of the Tethyan Himalaya relative to India took place before 35 Ma.  相似文献   

The effect of dissolved barium on biogeochemical processes at cold seeps   总被引：2，自引：0，他引：2  

Giovanni Aloisi  Klaus Wallmann  Alexander Derkachev  Erwin Suess 《Geochimica et cosmochimica acta》2004,68(8):1735-1748

A numerical model was applied to investigate and quantify the biogeochemical processes fueled by the expulsion of barium and methane-rich fluids in the sediments of a giant cold-seep area in the Derugin Basin (Sea of Okhotsk). Geochemical profiles of dissolved Ba²⁺, Sr²⁺, Ca²⁺, SO₄²⁻, HS⁻, DIC, I⁻ and of calcium carbonate (CaCO₃) were fitted numerically to constrain the transport processes and the kinetics of biogeochemical reactions. The model results indicate that the anaerobic oxidation of methane (AOM) is the major process proceeding at a depth-integrated rate of 4.9 μmol cm⁻² a⁻¹, followed by calcium carbonate and strontian barite precipitation/dissolution processes having a total depth-integrated rate of 2.1 μmol cm⁻² a⁻¹. At the low seepage rate prevailing at our study site (0.14 cm a⁻¹) all of the rising barium is consumed by precipitation of barite in the sedimentary column and no benthic barium flux is produced. Numerical experiments were run to investigate the response of this diagenetic environment to variations of hydrological and biogeochemical conditions. Our results show that relatively low rates of fluid flow (<∼5 cm a⁻¹) promote the dispersed precipitation of up to 26 wt% of barite and calcium carbonate throughout the uppermost few meters of the sedimentary column. Distinct and persistent events (several hundreds of years long) of more vigorous fluid flow (from 20-110 cm a⁻¹), instead, result in the formation of barite-carbonate crusts near the sediment surface. Competition between barium and methane for sulfate controls the mineralogy of these sediment precipitates such that at low dissolved methane/barium ratios (<4-11) barite precipitation dominates, while at higher methane/barium ratios sulfate availability is limited by AOM and calcium carbonate prevails. When seepage rates exceed 110 cm a⁻¹, barite precipitation occurs at the seafloor and is so rapid that barite chimneys form in the water column. In the Derugin Basin, spectacular barite constructions up to 20 m high, which cover an area of roughly 22 km² and contain in excess of 5 million tons of barite, are built through this process. In these conditions, our model calculates a flux of barium to the water column of at least 20 μmol cm⁻² a⁻¹. We estimate that a minimum of 0.44 × 10⁶ mol a⁻¹ are added to the bottom waters of the Derugin Basin by cold seep processes, likely affecting the barium cycle in the Sea of Okhotsk.  相似文献   

Towards a long-term monitoring of Central European water mite faunas (Acari: Hydrachnidia and Halacaridae) – considerations on the background of data from 1900 to 2000     

Reinhard Gerecke  Erwin O. Lehmann 《Limnologica》2005,35(1-2):45-51

The state of knowledge of the Central European water mite fauna and the research history are briefly surveyed. Several areas for which we are provided with rich data sets are of high value for the monitoring of faunistic trends on the background of local and global environmental change. The need for a database combining historical and actual faunistic information is stressed. It should facilitate the access to all data from former times, give a survey on actual activities by regular updates, and help for a better organization of future research activities. On the base of an update of the Limnofauna Europaea (K.O. Viets 1978, Gerecke in www.watermite.org) a first attempt is made to (1) recognize changes in the Central European fauna during the past 100 years; (2) emphasize species which may be endangered or have disappeared during the past 100 years. At the present state of knowledge, the degree of threat to water mite species in this area is best calculated from their preference for particular habitat types which are rare and in danger to disappear in cultivated landscapes. Our knowledge concerning neozoic water mites in the study area is discussed.  相似文献   

The lacustrine sedimentary records of coal-burning atmospheric pollution     

E. Appel  V. Hoffmann 《中国科学D辑(英文版)》2005,48(10)

With the acceleration of industrialization, coal- burning atmospheric pollution is getting more and more serious in many regions in China. However, there are only about ten odd years literature records about pollution in some large and mid-sized cities, where the atmosphere has perhaps been polluted for several decades, and therefore it is difficult to know the process and characteristic of pollution, and diffi-cult to evaluate its damage to environment. Lacustrine sediment, a natural record w…  相似文献   

Increase in Dissolved Silica of Rivers Due to a Volcanic Eruption in an Estuarine Bay (Sorsogon Bay,Philippines)     

Fernando P. Siringan  Erwin Don R. Racasa  Carlos Primo C. David  Rhodelyn C. Saban 《Estuaries and Coasts》2018,41(8):2277-2288

Mount Bulusan, the Philippines’ fourth most active volcano, erupted in February 21, 2011, sending volcanic ash and pyroclastic materials to its surrounding rivers. The waters drained into the estuary of harmful algal blooms plagued Sorsogon Bay. We aim to determine the impact of the 2011 volcanic eruption and the preceding volcanic ash emissions to the dissolved silica concentration of rivers draining the flanks of Mt. Bulusan and its possible implications to the phytoplankton assemblage of the bay. Six river water sampling periods from August 2010 to October 2012 overlapped with Mt. Bulusan’s active phase of volcanism. Our data shows that mean river silica from pre-eruption levels of ~?500 μM increased by more than 200% during and post-eruption. Highest Si concentration of 2270 μM was measured from Cadacan River in August 2011. Here, we argue that the sustained general increase of dissolved silica is due to the silica-containing materials from Mt. Bulusan’s eruption and that their concentration in river waters is also a function of watershed lithology and precipitation. Increase in dissolved silica and other nutrients caused a shift to diatom domination and, possibly, termination of Pyrodinium bahamense var. compressum blooms. Silica load increase in embayments is a natural process that controls the dominance of algae. Our study also highlights the importance of Philippine rivers to the global ocean silica budget as a function of high precipitation, tectonics in general, and volcanism in particular.  相似文献   

Mg---NH₄ exchange on humic acid: A radiotracer technique for conditional exchange constants in a seawater medium     

Marta T. Von Breymann  C. Andr  Ungerer  Erwin Suess 《Chemical Geology》1988,70(4):349-357

A radiotracer technique, employing ²⁷Mg, is used to determine the Mg released by ammonium exchange on undis-solved humic acid in a seawater medium. This new method allows for the measurement of exchangeable Mg on the solid phase surface, which eliminates the problem caused by the high-Mg background in the seawater matrix. The precision calculated from the counting statistics is better than ±2%; the reproducibility among repeated counts ranged from ±1% to ±3%. The higher sensitivity of the method allows for monitoring the Mg---NH₄ exchange at concentrations as low as 30 mM NH₄. This is a major improvement relative to the data obtained with the analytical methods used so far, which allow detection of exchangeable Mg only at NH₄ concentrations higher than 1 M. The lower experimental concentrations are more in accordance with the natural ammonium levels found in anoxic marine sediments. For the undissolved humic acid used in this experiment, the amount of exchangeable Mg in apparent equilibrium with an ammonium-free seawater matrix was found to be 96.6 ± 0.4 meq/100g. The Mg---NH₄ exchange on humic acid in seawater comes to a steady-state value in < 18 min. The conditional equilibrium constant obtained for this reaction, K_cond = 0.039 ± 0.001 M⁻¹. The technique can be expanded to other geochemical solid phases in seawater and it can be modified to study the behavior of the major cations by using ²⁴Na, ⁴²K and ⁴⁹Ca.  相似文献