Geochronology of Middle and Upper Pleistocene Loess Sections in Hungary

The application of both thermoluminescence and infrared stimulated luminescence dating to the extensively studied “classical” Hungarian loess/paleosol sequences from Basaharc, Mende, and Paks provides a reliable chronological framework and climatostratigraphic reconstruction for the last interglacial/glacial cycle. Based on this combined luminescence dating study a new chronology is proposed for the “Young Loess” in Hungary. Luminescence dating suggests that the loess below the MF2 horizon formed during the penultimate glaciation. The MF1 horizon probably formed during an interstade within oxygen isotope stage 3. For the youngest loess, overlying MF1, a very high accumulation rate was determined. Large time gaps occur above MF2 and MF1, indicating that most of the record of the last glaciation is missing in the standard sections at Basaharc, Mende, and Paks. Either large discontinuities or a very low accumulation rate occurred in all three type sections during the soil-forming periods. High-resolution studies of climatic proxies using this combined luminescence dating approach provide a reliable chronological framework for loess and loess derivatives of the last glacial cycle in Hungary, although a precise and complete chronostratigraphic reconstruction cannot be achieved from the incomplete records found at these sites.     

Rapid cooling and exhumation of eclogitic rocks from the Great Caucasus, Russia

Diffusion modelling of growth-zoned garnet is used in combination with standard geothermometric and geobarometric techniques to estimate cooling and denudation rates from the mafic eclogites of the Red Cliff area, Great Caucasus, Russia. Euhedral garnet porphyroblasts exhibit different degrees of prograde growth zoning depending on the size of the grain (100 μm to several mm in diameter). Zoning patterns are mainly expressed in terms of Fe–Mg exchange, with 100*Mg/(Mg+Fe) increasing from 18–20 to 33–37 from core to rim. Geothermobarometry yields conditions of 680±40 °C and a minimum of 1.6±0.2 GPa and of 660±40 °C and 0.8±0.2 GPa for the high-pressure and retrograde stages of equilibration, respectively. A temperature of 600±40 °C has been recorded for the late-stage metamorphic overprint in the mica schists surrounding the eclogites. Relaxation of garnet zoning profiles was modelled for three different hypothetical P–T –t trajectories, all with an initial temperature of 680 °C and a pressure change of 0.8 GPa. The first two trajectories involve decompression associated with regular cooling down to 660 °C (near isothermal) and 600 °C. The third path is a two-step trajectory comprising near-isobaric cooling down to 600 °C followed by isothermal decompression to 0.8 GPa. These P–T trajectories cover as wide a range of pressure and temperature changes endured by the rocks as possible, thus representing extreme cases for calculating cooling and exhumation rates. Calculations indicate that the zoning pattern of the smallest garnet (i.e. garnet for which the zoning is most easily eliminated during post-growth processes) along the different paths can be preserved for the following average exhumation and cooling rates: path 1, 143 mm a^?1 and 102 °C Ma^?1; path 2, 60 mm a^?1 and 171 °C Ma^?1; path 3, 11–30 mm a^?1 and 200–400 °C Ma^?1. These results are discussed in light of theoretical P–T–t paths extracted from thermal models of regions of thickened crust, and from analogue models of accretionary wedge and continental lithosphere subduction.     

Palynological Evidence for Climatic Change and Human Activity during the Holocene on Minorca (Balearic Islands)

Four pollen diagrams from Minorca (Balearic Islands) have been correlated with other previously studied sequences from Majorca and Minorca to define a Holocene landscape sequence for the region from 8000 yr B.P. to the present. The lower part of the pollen diagrams reflects a climatic phase with more rain and less-marked seasonality than today. Significant quantities ofCorylus, Buxus,and mesophilous taxa are found. In the middle part, between 5000 and 4000 yr B.P., a strong change is recorded in composition and structure of the vegetational landscape, with vegetation appearing that was adapted to Mediterranean conditions. This episode coincided with the first human colonization of the island and also with a widespread climatic change in the western Mediterranean region. The change in taxa was complex and some sclerophyllous taxa suchOleaplayed an important role in the transformation of the landscape physiognomy from the mid-Holocene until the present. Although human activities have removed much of the Mediterranean vegetation on the Balearic Islands, it seems clear that the changes have been brought about, in part, by increasing dryness.     

Ibex diggings in the Negev Desert highlands of Israel as microhabitats for annual plants. Soil salinity, location and digging depth affecting variety and density of plant species

About 400 Nubian ibex (Capra ibex nubiana) dig many hundreds of temporary night beds, approximately 80 cm × 110 cm and 15 cm deep, on slopes near the edges of the cliffs bordering the Zin valley. The beds are used according to the wind direction and the size of the ibex group, which depends on the ibex social behaviour during the year.The diggings are gradually abandoned and become important microhabitats for seed accumulation and germination, seedling development and annual plant establishment. These are influenced by soil salinity, slope direction and angle, digging depth, and the time since the diggings were abandoned. A greater variety of plant species and plant density were found in these diggings than upslope from the diggings.     

三角洲平原上网结河的发育与聚煤作用

龙潭组上段（２４＃煤顶板到１２＃煤）是盘县地区含煤最好的层段，对该区西北部本段地层的研究表明其中发育有网结河体系。河道沉积由多层叠置的鞋带状砂体组成，湿地沉积主要由菱铁质泥质岩夹薄层板状细砂岩（决口扇沉积）和煤组成。河流的发育和聚煤作用都显示幕式性，可能主要受海平面变化的控制。网结状河道被认为是海侵期对低位下切河谷充填过程中经侧向冲裂水道并相互连通形成的；稳定、连续的厚煤层发育于河道大范围废弃后的海侵晚期，其次是高水位早期。     

巴彦浩特盆地东部上石炭统羊虎沟组孢粉组合

钻井资料证实，内蒙巴彦浩特盆地东部保存有较完整的石炭系，其中上石炭统羊虎沟组厚达４５９．６ｍ。经７２块岩样分析鉴定，共发现６２属１１９种孢粉，含６个新种。可概括为上下两个孢粉组合，上组合称Ｄｅｎｓｏｓｐｏｒｉｔｅｓｂｅｌｕｌｕｓ－Ｃｒａｓｓｉｓｐｏｒａｌａｔｉｇｒａｎｉｆｅｒ－Ｌｙｃｏｓｐｏｒａｇｒａｎｕｌａｔａ（简称ＢＬＧ）组合，下组合称Ｃｒａｓｉｓｐｏｒａｌａｔｉｇｒａｎｉｆｅｒ－Ｃａｍｐｔｏｒｉｌｅｔｅｓｒｅｔｉｃｕｌｏｆｏｒｍｉｓ－Ｖｅｓｔｉｓｐｏｒａｃｏｓｔａｔａ（简称ＬＲＣ）组合。地质时限为晚石炭世中期羊虎沟组（维斯法期Ａ—Ｃ）。     

三江盆地七星河区成因地层分析

区内存在５种等时性地层界面，据此将含煤岩系划分为６个成因单元，１０个亚单元。沉积环境经历了５个演化阶段，其中扇三角洲废弃阶段为最有利的聚煤时期。聚煤的有利部位位于废弃的扇三角洲体之上。     

岩浆活动与油气成藏地质条件的关系

结合国内外众多含油气盆地中岩浆活动对油气生储盖及圈闭等条件的影响，探讨了岩浆活动与油气成藏地质条件的关系。岩浆活动伴随的高热流可以提高盆地古地温，加速烃源岩演化，亦将使与岩浆岩毗邻的烃源岩达到高成熟或过成熟；岩浆岩及其围岩蚀变带可成为良好的特殊储层；岩浆活动还可形成一些特殊类型的圈闭。另一方面，若岩浆活动时间与油气生成、运移与聚集时间不匹配，将对油气藏的形成与保存起较大的破坏作用。     

Erosion rates of alpine bedrock summit surfaces deduced from in situ Be and Al

We have measured the concentration of in situ produced cosmogenic ¹⁰Be and ²⁶Al from bare bedrock surfaces on summit flats in four western U.S. mountain ranges. The maximum mean bare-bedrock erosion rate from these alpine environments is 7.6 ± 3.9 m My⁻¹. Individual measurements vary between 2 and 19 m My⁻¹. These erosion rates are similar to previous cosmogenic radionuclide (CRN) erosion rates measured in other environments, except for those from extremely arid regions. This indicates that bare bedrock is not weathered into transportable material more rapidly in alpine environments than in other environments, even though frost weathering should be intense in these areas. Our CRN-deduced point measurements of bedrock erosion are slower than typical basin-averaged denudation rates ( 50 m My⁻¹). If our measured CRN erosion rates are accurate indicators of the rate at which summit flats are lowered by erosion, then relief in the mountain ranges examined here is probably increasing.

We develop a model of outcrop erosion to investigate the magnitude of errors associated with applying the steady-state erosion model to episodically eroding outcrops. Our simulations show that interpreting measurements with the steady-state erosion model can yield erosion rates which are either greater or less than the actual long-term mean erosion rate. While errors resulting from episodic erosion are potentially greater than both measurement and production rate errors for single samples, the mean value of many steady-state erosion rate measurements provides a much better estimate of the long-term erosion rate.     

Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau

Two Red Clay profiles near Xi’an and Xifeng were investigated in an attempt to determine magnetostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5–2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau, solar radiation, global ice volume, etc. Project supported by the National Natural Science Foundation of China and the Foundation of Xi’an Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences.