印度河文明兴衰和地理环境变迁

历史学界证实,约发端于公元前3000年的印度河文明,历经千年辉煌后,突然衰落了。此文着重探讨了与这一兴衰过程相伴的地理环境变迁问题。初步结论是:印度河流域的热带森林,孕育了古代农业,并成为阶级社会诞生、发展的自然基础。青铜利刃、文明之火,砍尽、烧光了一片又一片原始森林,终于引发了良性生态平衡的崩解,导致难以逆转的沙漠化过程,使一个兴旺的古代社会衰落到死亡的边缘。雅利安人的入侵和其后的漫漫风沙,彻底埋葬了印度河古代文明。     

1997年7—9月的全球地震动态

１９９７年第三季度,全球地震活动又恢复到中等偏低水平。克马德克群岛地区发生７．０级地震。美洲地震带于７月份发生３次７级左右地震,活动强度与大洋岛弧带相近。太平洋西北边缘带地震活动偏低。亚欧带西段的意大利发生６级强震。澳大利亚西部和非洲的坦噶尼喀湖发生６级左右地震。     

辽东太子河流域石炭系下部红层腕足动物群研究

早石炭世晚期至晚石炭世早期,太子河流域发育了一套红层沉积,泥岩中含有丰富的腕足动物化石,共计２１属３９种。系统分析了腕足动物群性质;结合围岩和地球化学特征等,识别出ＬｉｎｏｐｒｏｄｕｃｔｕｓＯｖａｔｉａ群落,它生活在与广海相连的浅水海湾低潮线附近地带;对同期腕足动物群进行了比较和讨论,提出当时研究区属于天山—辽吉腕足动物生物地理分区的观点。     

A 14,300-year-long record of fire-vegetation-climate linkages at Battle Ground Lake, southwestern Washington

High-resolution macroscopic charcoal analysis was used to reconstruct a 14,300-year-long fire history record from the lower Columbia River Valley in southwestern Washington, which was compared to a previous vegetation reconstruction for the site. In the late-glacial period (ca. 14,300-13,100 cal yr BP), Pinus/Picea-dominated parkland supported little to no fire activity. From the late-glacial to the early Holocene (ca. 13,100-10,800 cal yr BP), Pseudotsuga/Abies-dominated forest featured more frequent fire episodes that burned mostly woody vegetation. In the early to middle Holocene (ca. 10,800-5200 cal yr BP), Quercus-dominated savanna was associated with frequent fire episodes of low-to-moderate severity, with an increased herbaceous (i.e., grass) charcoal content. From the middle to late Holocene (ca. 5200 cal yr BP to present), forest dominated by Pseudotsuga, Thuja-type, and Tsuga heterophylla supported less frequent, but mostly large or high-severity fire episodes. Fire episodes were least frequent, but were largest or most severe, after ca. 2500 cal yr BP. The fire history at Battle Ground Lake was apparently driven by climate, directly through the length and severity of the fire season, and indirectly through climate-driven vegetation shifts, which affected available fuel biomass.     

Radioactivity in sediments and gross alpha–beta activities in surface water of Fırtına River, Turkey

The concentrations and distribution of natural and artificial radionuclides in sediment and water samples collected from Fırtına River in the Eastern Black Sea region of Turkey were investigated with an aim of evaluating the environmental radioactivity and radiation hazard. Natural gross α and gross β activities were determined for 21 different water samples, and the activity concentrations were obtained for ²²⁶Ra, ²¹⁴Pb, ²¹⁴Bi, ²²⁸Ac, ²⁰⁸Tl, ⁴⁰K and ¹³⁷Cs in 20 different sediment samples. The obtained results showed that natural gross α and gross β activity concentrations in water samples range from 12.4 ± 3.4 to 66.2 ± 9.2 mBq l⁻¹ and from 27.9 ± 3.3 to 133.3 ± 4.1 mBq l⁻¹, respectively. The mean activity concentrations were 32.6 ± 3.8 mBq l⁻¹ for gross α and 69.9 ± 4.4 mBq l⁻¹ for gross β. Generally, the gross β activities were higher than the corresponding gross α activities. The average concentrations of ²³⁸U and ²³²Th daughter products vary from 11 to 167 Bq kg⁻¹ and from 16 to 107 Bq kg⁻¹, respectively. The concentrations of ⁴⁰K and ¹³⁷Cs vary from 51 to 1,605 Bq kg⁻¹ and from 0.8 to 42 Bq kg⁻¹, respectively. Sediment characterization was also investigated using grain size, thin section and XRD analysis.     

Groundwater arsenic contamination in Manipur,one of the seven North-Eastern Hill states of India: a future danger

Manipur State, with a population of 2.29 million, is one of the seven North-Eastern Hill states in India, and is severely affected by groundwater arsenic contamination. Manipur has nine districts out of which four are in Manipur Valley where 59% of the people live on 10% of the land. These four districts are all arsenic contaminated. We analysed water samples from 628 tubewells for arsenic out of an expected total 2,014 tubewells in the Manipur Valley. Analyzed samples, 63.3%, contained >10 μg/l of arsenic, 23.2% between 10 and 50 μg/l, and 40% >50 μg/l. The percentages of contaminated wells above 10 and 50 μg/l are higher than in other arsenic affected states and countries of the Ganga–Meghna–Brahmaputra (GMB) Plain. Unlike on the GMB plains, in Manipur there is no systematic relation between arsenic concentration and the depth of tubewells. The source of arsenic in GMB Plain is sediments derived from the Himalaya and surrounding mountains. North-Eastern Hill states were formed at late phase of Himalaya orogeny, and so it will be found in the future that groundwater arsenic contamination in the valleys of other North-Eastern Hill states. Arsenic contaminated aquifers in Manipur Valley are mainly located within the Newer Alluvium. In Manipur, the high rainfall and abundant surface water resources can be exploited to avoid repeating the mass arsenic poisoning that has occurred on the GMB plains.     

The relationship between saline groundwater within the Arava Rift Valley in Israel and the present and ancient base levels as detected by deep geoelectromagnetic soundings

The time domain electromagnetic (TDEM) geophysical method was employed to detect saline groundwater bodies within and in the close margins of the Arava Rift Valley. The Arava Valley aquifers are known to occupy fresh to saline groundwater. The lateral subsurface inflow to the Arava from west and east is characterized by fresh to brackish waters. The results of the present study indicate that salination of groundwater is controlled by both present day and ancient base levels, namely by the Dead Sea in the north and by the Gulf of Elat in the south. The configuration obtained by the TDEM survey exhibits interfaces and palaeo-interfaces between fresh to brackish waters and underlying seawater or diluted seawater intruded inland from both base levels as well as brines intruded from the northern base level. The central Arava structural and hydrological divide seems to escape seawater or brine encroachment at least to the considerable depth of the TDEM measurements.     

Corroded cobbles in Southern Death Valley: Their relationship to honeycomb weathering and lake shorelines

In southern Death Valley, pits similar in morphology to honeycomb weathering (herein referred to as corrosion pits) occur on the surfaces of cobbles that are associated with wave-produced benches. The pitted cobbles include a variety of igneous, metamorphic, and siliciclastic rocks; corrosion pits are rare to absent in limestones or dolomites. Pit morphology is controlled by cobble lithology. In massive rocks the pits are arcuate, elongate, and gently tapering; corrosion of laminated or foliated rocks has produced irregular, more jagged pits. The presence of desert varnish has strongly inhibited the corrosion process. The corroded cobbles are inferred to reflect both chemical and physical weathering of rocks along Pleistocene lacustrine strandlines. Corrosion took place through salt-weathering and/or heat-moisture expansion processes and through chemical dissolution of selected minerals as a result of splash-zone wetting and drying. The ancient lake waters may have had high pH and high total dissolved solids contents. The recognition of corroded cobbles may be important in the reconstruction of the position of ancient shorelines for certain types of alkaline lakes and in the reconstruction of their ancient chemistries.     

Dynamic process-response model of river channel development

Feedback mechanisms, which operate upstream through drawdown and backwater effects and downstream through sediment discharge are responsible for channel evolution. By combining these mechanisms with channel processes it euables a dynamic process-response model to be developed to simulate the initial evolution of straight gravel-bed channels. When erosion commences on a land surface, sediment entrained in the headwater reach by hydraulic action is selectively transported, deposited and reworked. This produces a damped oscillation between degradation and aggradation as the channel and valley respond to spatial and temporal variations in sediment calibre and hydraulic conditions. The initial cut and fill phases are responsible for valley incision and floodplain development while secondary and subsequent activity can produce river terraces. Eventually sediment entrainment in the headwaters declines as slopes are reduced. Subsequent channel evolution is relatively insignificant because it is dependent on local weathering activity producing material that can be transported on declining slopes. Therefore landforms produced during the initial phase of development, when local weathering was non-limiting, dominate the landscape.     

Paleomagnetism of ordovician lamprophyres from Taylor Valley,Victoria Land,Antarctica

Paleomagnetic study of specimens from four lamprophyric dykes on the Kukri Hills, Taylor Valley (77.64°S, 163.35°E) has yielded a primary mean direction of magnetization ofD=222.6 andI=+0.6 with ₉₅=10.9° after AF cleaning. The magnetization of five other dykes and of the amphibolitic basement was either unstable or not fully reliable.The corresponding pole position lies at 9.3°S and 26.7°E and confirms the previous results from Lower Ordovician rocks from distant areas of East Antarctica.A Lower Ordovician mean pole position recalculated from valid data lies at 17°S, 21°E.