The Guará and Botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the Rio Grande do Sul State (Southernmost Brazil). The Guará Formation (Upper Jurassic) displays a well-defined facies shift along its outcrop belt. On its northern portion it is characterised by coarse-grained to conglomeratic sandstones with trough and planar cross-bedding, as well as low-angle lamination, which are interpreted to represent braided river deposits. Southwards these fluvial facies thin out and interfinger with fine- to medium-grained sandstones with large-scale cross-stratification and horizontal lamination, interpreted as eolian dune and eolian sand sheets deposits, respectively. The Botucatu Formation is characterised by large-scale cross-strata formed by successive climbing of eolian dunes, without interdune and/or fluvial accumulation (dry eolian system). The contact between the Guará and the Botucatu formations is delineated by a basin-wide deflation surface (supersurface). The abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change, from semi-arid (Upper Jurassic) to hyper-arid (Lower Cretaceous) conditions. A rearrangement of the Paraná Basin depocenters is contemporaneous to this climate change, which seems to have changed from a more restrict accumulation area in the Guará Formation to a wider sedimentary context in the Botucatu Formation. 相似文献
Ion-microprobe U–Pb zircon dating of lower-crust metasedimentary granulite are reported on samples from two localities in Europe in order to determine (a) how this environment recorded the Variscan and eo-Alpine events, and (b) whether the transition between the two orogenic cycles was continuous or separated by a gap. The samples come from enclaves hosted by Miocene volcanoes at Bournac in the French Massif Central, and from the granulitic metasedimentary basement of the Alpine Santa Lucia nappe in Corsica, on the South European paleomargin of the Ligurian branch of the Tethys Sea. The zircon ages from Bournac range between 630 and 430 Ma and between 380 and 150 Ma with a major frequency peak at 285 Ma; the zircons older than 430 Ma are interpreted as detrital, whereas those younger than 380 Ma are considered to have formed by metamorphic processes after burial in the lower crust. Zircon ages from Santa Lucia range from to 356 to 157 Ma, with exception of one inherited Archean grain, and are interpreted like the younger Bournac zircons as having been formed by metamorphic processes.
In a granulite metamorphic environment, as opposed to an anatectic environment, new zircon growth can occur in the solid state. Once Zr has been incorporated into zircon, however, it is difficult to remobilize without dissolution; thus Zr available for new zircon growth must result from the breakdown of Zr-bearing minerals during prograde and/or retrograde events. In this light, the U–Pb zircon-age probability curves are interpreted as markers for major tectonometamorphic events, as suggested by the close correspondence between peaks in the curve and geological events recorded in the upper-crust, such as magma emplacement and basin subsidence.
Evidence of a tectonometamorphic gap between the Variscan and Alpine orogeneses is provided by the Santa Lucia zircon-age probability curve, which reveals a probable interlude during the Variscan–Alpine transition between 240 and 210 Ma. Here, the peak at 240 Ma is interpreted as the very beginning of crustal extension and the low at 210 Ma as a period of quiescence prior to the formation of an active margin and oceanization. 相似文献
Substantial damage to water supply systems, including water delivery pipelines, water treatment plants, reservoirs, and water
storage tanks, was reported after the 1999 Chi–Chi Taiwan Earthquake. This paper first summarizes the damage survey and then
presents the results of seismic fragility analysis for underground pipelines. Construction blueprints of the water delivery
pipelines and repair work orders of 11 townships and cities in the disastrous area were digitized into a Geographical Information
System (GIS) for analysis and assessment. With the aid of the GIS system, we found that PVC pipes made up 86% of water delivery
pipelines while steel, cast iron, ductile iron, PE and others took the rest. Therefore, this paper focuses on the fragility
analysis of PVC pipes. Three different methods were applied to derive the fragility relations between the PVC water pipes
having nominal diameters (approximately inner diameters) greater than or equal to 65 mm and earthquake intensity parameters
such as peak ground acceleration and peak ground velocity. The results were then examined with those of other countries. The
discrepancy between our results and the empirical equation used by HAZUS, an earthquake loss estimation software developed
by the Federal Emergency Management Agency was not significant. 相似文献
The alluvial aquifer is the primary source of groundwater along the eastern Dead Sea shoreline, Jordan. Over the last 20 years, salinity has risen in some existing wells and several new wells have encountered brackish water in areas thought to contain fresh water. A good linear correlation exists between the water resistivity and the chloride concentration of groundwater and shows that the salinity is the most important factor controlling resistivity. Two-dimensional electrical tomography (ET) integrated with geoelectrical soundings were employed to delineate different water-bearing formations and the configuration of the interface between them. The present hydrological system and the related brines and interfaces are controlled by the Dead Sea base level, presently at 410 m b.s.l. Resistivity measurements show a dominant trend of decreasing resistivity (thus increasing salinity) with depth and westward towards the Dead Sea. Accordingly, three zones with different resistivity values were detected, corresponding to three different water-bearing formations: (1) strata saturated with fresh to slightly brackish groundwater; (2) a transition zone of brine mixed with fresh to brackish groundwater; (3) a water-bearing formation containing Dead Sea brine. In addition, a low resistivity unit containing brine was detected above the 1955 Dead Sea base level, which was interpreted as having remained unflushed by infiltrating rain. 相似文献
Composition and distribution of benthic foraminifers, being coupled with isotopic-geochemical data on Upper Pleistocene and Holocene sediments from the southern Bering Sea (Core GC-11; 53°31′ N, 178°51′E, water depth 3060 m), demonstrate variations in bottom water properties during the last 54 kyr. Their abundance increased to some extent during short periods corresponding to warm Dansgaard-Oeshger interstadials 14, 12, 8, and 2 of marine isotopic stages (MIS) 3 and 2. The first and second deglaciation phases separated by the Younger Dryas cooling episode are marked by significant abundance peaks of benthic foraminifers (an order magnitude higher than in the glacial period), although their share in community of benthic and planktonic foraminifers taken together decreases. Species typical of stable high-productivity areas gain the dominant position. A significant proportion of agglutinated species in the Holocene sediments is indicative of Ca ions deficiency that accelerates dissolution of carbonate tests up to their disappearance approximately 2.5–3 ka ago. 相似文献
Hydrochemical investigations in the Kalambaina Formation have been initiated to determine potability and suitability of the shallow groundwater for domestic and agricultural uses. This limestone formation is an extensive aquifer supplying water to livestock and domestic wells in its outcrop areas. The aquifer is recharged by rainfall and discharges mainly into the Sokoto–Rima River system and lakes at Kware, Gwadabawa and Kalmalo in Nigeria. Because recharge to the aquifer is mainly from rainfall, the quality of the groundwater is controlled essentially by chemical processes in the vadose zone and locally by human activities. Water samples were taken at 11 sites comprising boreholes, dug wells and a spring and were chemically analysed for their major ion components. Hydrochemical results show water of fairly good quality. It is, however, hard and generally of moderate dissolved solids content. Concentration of the total dissolved solids is between 130 and 2,340 mg/l. Concentrations of ions vary widely but a high concentration of K+ is found in places. NO3− is on the higher side of the World Health Organization (WHO) permissible limits, indicating pollution in such areas. Groundwater chemistry is predominantly of two facies, namely the calcium–magnesium–bicarbonate and calcium–magnesium–sulphate–chloride facies. These facies probably evolved primarily as a result of dissolution of calcium and magnesium carbonates as well as some human/land-use activities. 相似文献
Based on the cost-benefit data (1980-2002) of farm products and China Agriculture Yearbooks, this paper studies the regional disparity in the changes of the agricultural land use in China during the period 1980-2002 from three aspects such as the degree of intensity, the sown area and the abandoned farmland. The results show that: (1) The degree of intensity of land use in the westena region during 1980-2000 has a strong uptrend, but in the eastern and central regions the degree of intensity descends obviously and has shown a continuous downtrend since 1997. (2) The total sown area shrinks notably in the eastern region, while it enlarges constantly in the western region. (3) The sown area in the eastern, central and western regions has gone through a similar cyclic process: down (1980-1985)-up (1985-1991)-down (1991-1994)-up (1994-1999)-down (1999-2002). However, there are obvious differences in amplitude variation and tendency among them. The sown area has shrunk in the eastern region and expanded in the central and western regions especially before 1999. (4) The most cases of abandoned farmland are reported in the central region, the second in the eastern region and the least in the western region. The abandonment phenomena chiefly occurred during 1992-1995 in the eastern region, and during 1998-2002 in the central region. 相似文献