A 450-ka long record of glaciation in Northern Mongolia based on studies at Lake Khubsugul: high-resolution reflection seismic data and grain-size variations in cored sediments

We use high-resolution reflection seismic data and detailed grain-size analysis of a drill core (KDP-01) from Lake Khubsugul (northern Mongolia) to provide an improved reconstruction of the glacial history of the area for the last 450 ka. Grain-size analysis of suspended sediment load in modern rivers draining into the lake and of moraine material from the northern part of the catchment shows that the silt fraction is transported to the central part of the lake mainly by river suspension, whereas the clay fraction is mainly transported by glacial meltwater during deglaciation. The changes in of the clay/silt ratio in Lake Khubsugul sediments correlates well with the standard global paleoclimate records: low clay/silt ratios indicate warm climates, while a high clay/silt ratio reflects glacial erosion and cold climates. Pulses of clay input into the lake occur at the final stages of glacial periods (i.e., glacial maxima and subsequent onsets of deglaciation). The periodicity in glacial clay input in Lake Khubsugul is in tune with global periods of deglaciation, but there are differences in the intensity of the deglacial events for MIS-12 and MIS-2. These differences are attributed to specific conditions in regional distribution of moisture during glaciation, glacial ice volumes, and solar insolation intensity at the onset of deglaciation. Deglaciation of the Khubsugul glaciers occurred in response to an increase in summer solar insolation above a threshold value of 490 W/m². Two types of deglaciation can be distinguished: (1) slow melting during several tens of 1,000 years during weak increases in summer insolation, and (2) short and fast melting during several thousands of years in response to strong increases in summer insolation. The maximum ice volume in the area of Lake Khubsugul during the past 450 ka occurred during the period of 373–350 ka BP (MIS 11a-10) and was caused by high levels of moisture in the region, whereas the MIS-2 and MIS-12 glacial periods were characterized by minima in ice volume, due to the strong aridity in the region.     

统计地震学的两个基本定律对应力的依赖关系

统计地震学长期使用的两个幂律关系式为:描述地震频度-震级关系的古登堡-里克特(Gutenberg-Richter)关系式[1]和描绘主震后余震随时间衰减速率特征的大森-宇津(Omori-Utsu)定律[2]。最近,地震频度-震级关系斜率(b值)与断裂模式的相关性研究确定了应力对b值的影响[3]。在此,我们以类似的方式根据主震的断裂模式对余震序列进行研究。我们发现逆冲型主震的幂律余震衰减速率起始前的延时(c值)一般比正断层型地震的短,走滑型地震的c值则处于二者之间。对断裂模式的这些类似依赖关系表明两个基本幂律都受应力状态控制。只有2%的余震有已知震源机制解。因此,c值和b值是两个独立的估算值,它们可作为推断应力场的新方法来使用,目前应力场依然难以直接测定。     

Unique desert caves as a valuable geological resource: first detailed geological heritage assessment of the Sannur Cave,Egypt

Arabian Journal of Geosciences - Surface albedo is a key parameter in earth energy budget and global climate change studies. In this aspect, variation in vegetation covers is one of the most...     

Monitoring Sea Level in the Coastal Zone with Satellite Altimetry and Tide Gauges

We examine the issue of sustained measurements of sea level in the coastal zone, first by summarizing the long-term observations from tide gauges, then showing how those are now complemented by improved satellite altimetry products in the coastal ocean. We present some of the progresses in coastal altimetry, both from dedicated reprocessing of the radar waveforms and from the development of improved corrections for the atmospheric effects. This trend towards better altimetric data at the coast comes also from technological innovations such as Ka-band altimetry and SAR altimetry, and we discuss the advantages deriving from the AltiKa Ka-band altimeter and the SIRAL altimeter on CryoSat-2 that can be operated in SAR mode. A case study along the UK coast demonstrates the good agreement between coastal altimetry and tide gauge observations, with root mean square differences as low as 4 cm at many stations, allowing the characterization of the annual cycle of sea level along the UK coasts. Finally, we examine the evolution of the sea level trend from the open to the coastal ocean along the western coast of Africa, comparing standard and coastally improved products. Different products give different sea level trend profiles, so the recommendation is that additional efforts are needed to study sea level trends in the coastal zone from past and present satellite altimeters. Further improvements are expected from more refined processing and screening of data, but in particular from the constant improvements in the geophysical corrections.     

Radiochemoecological Monitoring of the Salt Lakes of the Crimea

正1 Introduction The salt lakes of the Crimea contain the practically inexhaustible sources of salts of sodium,magnesium,bromine and other chemical elements(Ponizovskii,1965),being the potential powerful raw materials base for the     

Oxidation inhibitors occuring in bioproducers, recent sediments, ancient rocks and oils

Native antioxidants (AO) are involved in the transformation of organic matter (OM) in different stages of diagenesis. In the early stages, the geochemical significance of AO can be estimated by using AO consumption index (I). The positive I values suggest that the OM fossilization proceeded under reducing conditions which favoured the formation of oil-source rocks, while the negative I values indicate oxidizing conditions which are characterized by the formation of rocks having a low oil-generation potential. In the late stages of diagenesis, the AO content is indicative of the degree of catagenic (thermal) or biodegradation (oxidative) transformation of oils. The AO contents of Paleogenic, Mesozoic and Paleozoic oils have been found to differ approximately by one order of magnitude. A major portion of AO is concentrated in oil resins and asphaltenes. The ratio of AO to resins and asphaltenes can be used as criterion of catagenic transformation of OM.     

Sources of unique rhenium enrichment in fumaroles and sulphides at Kudryavy volcano

Rhenium (Re) is one of the least abundant elements in Earth, averaging 0.28 ppb in the primitive mantle. The unique occurrence of rheniite ReS₂ (74.5 wt% of Re) in Kudryavy volcano precipitates raises questions about recycling of Re-rich reservoirs within the Kurile-Kamchatka volcanic Island arc setting. The sources of this unique Re enrichment have been inferred from studies of Re-Os isotope systematic and trace elements in volcanic gases, sulphide precipitates and host volcanic rocks. The fumarolic gas condensates are enriched in hydrophile trace elements relative to fluid-immobile elements and exhibit high Ba/Nb (133-204), Rb/Y (16-406) and Th/Zr (0.01-0.25) ratios. They are characterised by high Re (7-210 ppb) and Os abundances (0.4-0.9 ppb), with ¹⁸⁷Os/¹⁸⁸Os ratios in a range 0.122-0.152. This Os isotopic compositional range is similar to that of the peridotite xenoliths from the metasomatised mantle wedge above the subducted Pacific plate, the radiogenic isotopic signature of which is probably due to radiogenic addition from a slab-derived fluid.Re- and Os-rich sulphide and oxide minerals precipitate from volcanic gases within fumarolic fields. Molybdenite (MoS₂), powellite (CaMoO₄) and cannizzarite (Pb₄Bi₆S₁₃) contain 1.5-1.7 wt%, 10 ppm, and 65-252 ppb of Re, respectively. Both molybdenite and rheniite contain normal Os concentrations, with total Os abundances in a range from 0.6 to 3.1 ppm for molybdenite, and 2.3-24.3 ppb for the rheniite samples. Repeated analyses of osmium isotope ratios for two rheniite samples form a best-fit line with an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.32 ± 0.15 and an age of 79 ± 11 yr, which is the youngest age ever measured in natural samples. The high Re contents in molybdenite and rheniite led to high radiogenic ¹⁸⁷Os values, even in the limited period of time, with ¹⁸⁷Os/¹⁸⁸Os ratios up to 3.3 for molybdenite and up to 4.4 for rheniite.The Os isotopic compositions of andesite-basaltic rocks from the Kudryavy volcano (¹⁸⁷Os/¹⁸⁸Os up to 0.326) are more radiogenic than those of residual peridotites and fumarolic gas condensates that are mainly constituted from magmatic vapor. Such radiogenic values can be attributed either to the addition of a radiogenic Os-rich subduction component to the depleted mantle, or to the assimilation of older dacitic caldera walls (¹⁸⁷Os/¹⁸⁸Os = 0.6) during arc magma ascent and emplacement. The latter hypothesis is supported by the correlation between ¹⁸⁷Os/¹⁸⁸Os ratio and indicators of fractionation such as MgO or Ni, and by low contents of potentially hydrophile trace elements such as Ba, Rb and Th relative to fluid-immobile elements such as Nb, Zr and Y. The high Re flux in the Kudryavy volcano (estimated at ∼46 kg/yr) can be explained by remobilisation of Re by Cl-rich water from an underplated mantle wedge and subducted organic-rich sediments of the Pacific plate.     

Tidal and residual currents over abrupt deep-sea topography based on shipboard ADCP data and tidal model solutions for three popular bathymetry grids

The response of tidal and residual currents to small-scale morphological differences over abrupt deep-sea topography (Seine Seamount) was estimated for bathymetry grids of different spatial resolution. Local barotropic tidal model solutions were obtained for three popular and publicly available bathymetry grids (Smith and Sandwell TOPO8.2, ETOPO1, and GEBCO08) to calculate residual currents from vessel-mounted acoustic Doppler current profiler (VM-ADCP) measurements. Currents from each tidal solution were interpolated to match the VM-ADCP ensemble times and locations. Root mean square (RMS) differences of tidal and residual current speeds largely follow topographic deviations and were largest for TOPO8.2-based solutions (up to 2.8 cm?s^?1) in seamount areas shallower than 1,000 m. Maximum RMS differences of currents obtained from higher resolution bathymetry did not exceed 1.7 cm?s^?1. Single depth-dependent maximum residual flow speed differences were up to 8 cm?s^?1 in all cases. Seine Seamount is located within a strong mean flow environment, and RMS residual current speed differences varied between 5 % and 20 % of observed peak velocities of the ambient flow. Residual flow estimates from shipboard ADCP data might be even more sensitive to the choice of bathymetry grids if barotropic tidal models are used to remove tides over deep oceanic topographic features where the mean flow is weak compared to the magnitude of barotropic tidal, or baroclinic currents. Realistic topography and associated flow complexity are also important factors for understanding sedimentary and ecological processes driven and maintained by flow–topography interaction.