C-isotope Composition of Carbonates from Indravati Basin, India: Implications for Regional Stratigraphic Correlation     

Anil Maheshwari  A.N. Sial  Rajeeva Guhey  V.P. Ferreira 《Gondwana Research》2005,8(4):603-610

The Indravati Basin represents an unmetamorphosed and unfossiliferous sequence and shows a broad similarity in lithological association with other Purana Basins of Central India. The carbonates belonging to Indravati Basin have on average, moderately positive δ13 C values (up to +4.5). Numerous successions reported from other parts of world, show similar δ13 C values and contain evidence to suggest that the latest Mesoproterozoic to early Neoproterozoic period may represent an isotopically recognizable interval globally. The elevated δ13 C values of Indravati Basin are also correlatable with other Purana Basins in India including Upper Vindhyan Supergroup.  相似文献   

Identifying sources of groundwater recharge in the Merguellil basin (Tunisia) using isotopic methods: implication of dam reservoir water accounting   总被引：1，自引：0，他引：1  

Lassaad Dassi  Kamel Zouari  Serigne Faye 《Environmental Geology》2005,49(1):114-123

Thirty-two groundwater samples collected from the Merguellil Wadi basin (central Tunisia) complemented by the Haouareb dam reservoir water samples have been isotopically analysed in order to investigate the implication of the reservoir water to recharging the aquifer, and also to infer the sources, relative ages and mixing processes in the aquifer system. Plots of the stable isotopes data against the local meteoric lines of Tunis-Carthage and Sfax indicate a strong implication of the dam water noticeable up to a distance of 6–7 km. A contribution as much as 80% of the pumped water has been evidenced using isotopic mass balance. In addition, poorly distinguished water clusters in the stable isotope plots, but clearly identified in the diagrams δ¹⁸O versus ³H and ³H versus ¹⁴C, indicate various water types related to sources and timing of recharge. The isotopic signatures of the dam accounting water, the “old” and “native” recharged waters, have been evidenced in relation to their geographical distribution and also to their radiogenic isotopes (³H and ¹⁴C) contents. In the south-western part of the aquifer, mixing process occurs between the dam reservoir water and both the “old” and “native” water components.  相似文献   

Seasonal records of climatic change in annually laminated tufas: short review and future prospects   总被引：3，自引：0，他引：3  

J. E. Andrews  A. T. Brasier 《第四纪科学杂志》2005,20(5):411-421

Many Recent and fossil freshwater tufa stromatolites contain millimetre‐scale, alternating laminae of dense micrite and more porous or sparry crystalline calcites. These alternating laminae have been interpreted to represent seasonally controlled differences in the biotic activity of microbes, and/or seasonally controlled changes in the rate of calcification. Either way, couplets of these microbially mediated alternating calcified laminae are generally agreed to represent annual seasonality. Combined stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg, Sr, Ba) geochemistry from Recent tufa stromatolites show that seasonal climatic information is available from these calcites. Variability in δ¹⁸O (and in one case Mg concentration) has been shown to be controlled primarily by stream temperature change, usually driven by solar insolation. In arid climates, seasonal evaporation can also cause δ¹⁸O enrichment by at least 1‰. Variability in δ¹³C results potentially from: (1) seasonal change in plant uptake of ¹²C‐enriched CO₂; (2) seasonal change in degassing of ¹²C‐enriched CO₂ in the aquifer system; and (3) precipitation of calcite along the aquifer or river flow path, a process that increases δ¹³C of dissolved inorganic carbon (DIC) in the remaining water. Mechanisms 2 and 3 are linked because calcite precipitates in aquifers where degassing occurs, e.g. air pockets. The latter mechanism for δ¹³C enrichment has also been shown to cause sympathetic variation between trace element/Ca ratios and δ¹³C because trace elements with partition coefficients much greater than 1 (e.g. Sr, Ba) remain preferentially in solution. Since degassing in air pockets will be enhanced during decreased recharge when water saturation of the aquifer is lowest, sympathetic variation in trace element/Ca ratios and δ¹³C is a possible index of recharge and therefore precipitation intensity. High‐resolution geochemical data from well‐dated tufa stromatolites have great potential for Quaternary palaeoclimate reconstructions, possibly allowing recovery of annual seasonal climatic information including water temperature variation and change in rainfall intensity. However, careful consideration of diagenetic effects, particularly aggrading neomorphism, needs to be the next step. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America     

Bruce J. MacFadden 《Quaternary Research》2005,64(2):113-124

The toxodont megaherbivores Toxodon and Mixotoxodon were endemic to South and Central America during the late Quaternary. Isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat. Tooth enamel carbon isotope data from six regions of South and Central America indicate significant differences in toxodont diet and local vegetation during the late Quaternary. Toxodonts ranged ecologically from C₃ forest browsers in the Amazon (mean δ¹³C = −13.4‰), to mixed C₃ grazers and/or browsers living either in C₃ grasslands, or mixed C₃ forested and grassland habitats in Honduras (mean δ¹³C = −9.3‰), Buenos Aires province, Argentina (δ¹³C = −8.7‰), and Bahia, Brazil (mean δ¹³C = −8.6‰), to predominantly C₄ grazers in northern Argentina (δ¹³C = −4.4‰), to specialized C₄ grazers in the Chaco of Bolivia (δ¹³C = −0.1‰). Although these toxodonts had very high-crowned teeth classically interpreted for grazing, the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation. In the ancient Amazon region, carbon isotope data for the toxodonts indicate a C₃-based tropical rainforest habitat with no evidence for grasslands as would be predicted from the Neotropical forest refugia hypothesis.  相似文献   

Systematic Variation of Sr-, Nd- and Pb-Isotopes with Time in Lavas of Mauritius, Reunion Hotspot     

NOHDA  SUSUMU; KANEOKA  ICHIRO; HANYU  TAKESHI; XU  SHENG; UTO  KOZO 《Journal of Petrology》2005,46(3):505-522

We report Sr-, Nd- and Pb-isotopic compositions for the lavasof Mauritius, the second youngest volcanic island in the Réunionhotspot. The lavas of the Older Series (7·8–5·5Ma) have identical isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0·70411to 0·70422,¹⁴³Nd/¹⁴⁴Nd = 0·512865 to 0·512854,and ²⁰⁶Pb/²⁰⁴Pb = 19·016 to 19·041) to those ofRéunion, where the center of volcanic activity is currentlylocated. The lavas of the Intermediate Series (3·5–1·9Ma) and Younger Series (0·70–0·17 Ma) areshifted to lower Sr-isotopic compositions (0·70364–0·70394,with ¹⁴³Nd/¹⁴⁴Nd = 0·512813 to 0·512948 and ²⁰⁶Pb/²⁰⁴Pb= 18·794 to 18·984). The Intermediate Series lavashave similar trace-element characteristics (e.g. Zr–Nb,Ba–Y) to those of Rodrigues, in both cases requiring theinvolvement of an enriched mantle-like component in the mantlesource. During the volcanic history of Mauritius, the magmaslost the principal isotopic characteristics of the Réunionhotspot with time, and became gradually imprinted with the isotopicsignature of a shallower mantle source that produced the CentralIndian Ridge basalts. KEY WORDS: hotspot; isotopes; Mauritius; Réunion; trace element  相似文献   

Environmental significance of C/C and O/O ratios of modern land-snail shells from the southern great plains of North America     

Meena Balakrishnan  James L. Theler  Don G. Wyckoff 《Quaternary Research》2005,63(1):15-30

¹³C/¹²C and ¹⁸O/¹⁶O ratios of aragonite shells of modern land snails from the southern Great Plains of North America were measured for samples from twelve localities in a narrow east-west corridor that extended from the Flint Hills in North Central Oklahoma to the foothills of the Sangre de Cristo Mountains in Northern New Mexico, USA. Across the study area, shell δ¹⁸O values (PDB scale) ranged from −4.1‰ to 1.2‰, while δ¹³C values ranged from −13.2‰ to 0.0‰. δ¹⁸O values of the shell aragonite were predicted with a published, steady state, evaporative flux balance model. The predicted values differed (with one exception) by less than 1‰ from locality averages of measured δ¹⁸O values. This similarity suggests that relative humidity at the time of snail activity is an important control on the δ¹⁸O values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells. Correlated δ¹³C values of coexisting Vallonia and Gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern Great Plains plant ecology. Although there is considerable scatter, multispecies, transect average δ¹³C values of the modern aragonite shells are related to variations in the type of photosynthesis (i.e., C₃, C₄) in the local plant communities. The results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals, species, etc., and thus better represent the “neighborhood” scale temporal and/or spatial environmental variations of interest in studies of modern and ancient systems.  相似文献   

Mixing of event and pre‐event water in a shallow Entisol in sloping farmland based on isotopic and hydrometric measurements,SW China          下载免费PDF全文

Pei Zhao  Xiangyu Tang  Peng Zhao  Wei Zhang  Jialiang Tang 《水文研究》2016,30(19):3478-3493

Water percolation and flow processes in subsurface geologic media play an important role in determining the water source for plants and the transport of contaminants or nutrients, which is essential for water resource management and the development of measures for pollution mitigation. During June 2013, the dynamics of the rainwater, soil water, subsurface flows and groundwater in a shallow Entisol on sloping farmland were monitored using a hydrometric and isotopic approach. The results showed that effective mixing of rainwater and soil water occurred in hours. The rebound phenomenon of δD profiles in soils showed that most isotope‐depleted rainwater largely bypassed the soil matrix when the water saturation in the soil was high. Preferential‐flow, which was the dominant water movement pattern in the vadose zone, occurred through the whole soil profile, and infrequent piston‐flow was mainly found at 20–40 cm in depth. The interflow in the soil layer, composed of 75.2% rainwater, was only generated when the soil profile had been saturated. Underflow in the fractured mudrock was the dominant flow type in this hillslope, and outflow was dominated by base flow (groundwater flow) with a mean contribution of 76.7%. The generation mechanism of underflow was groundwater ridging, which was superimposed upon preferential‐flow composed mainly of rainwater. The quick mixing process of rainwater and soil water and the rapid movement of the mixture through preferential channels in the study soil, which shows a typical bimodal pore size distribution, can explain the prompt release of pre‐event water in subsurface flow. Water sources of subsurface flows at peak discharge could be affected by the antecedent soil water content, rain characteristics and antecedent groundwater levels. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A preliminary estimate of how stream water age is influenced by changing runoff sources in the Nagqu river water shed,Qinghai-Tibet Plateau     

Yuheng Yang  Baisha Weng  Denghua Yan  Xiaoyan Gong  Yanyu Dai  Yongzhen Niu 《水文研究》2021,35(10):e14380

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Nine thousand years of upper montane soil/vegetation dynamics from the summit of Caratuva Peak,Southern Brazil     

《Journal of South American Earth Sciences》2014

Biodiversity loss, climate change, and increased freshwater consumption are some of the main environmental problems on Earth. Mountain ecosystems can reduce these threats by providing several positive influences, such as the maintenance of biodiversity, water regulation, and carbon storage, amongst others. The knowledge of the history of these environments and their response to climate change is very important for management, conservation, and environmental monitoring programs. The genesis of the soil organic matter of the current upper montane vegetation remains unclear and seems to be quite variable depending on location. Some upper montane sites in the very extensive coastal Sea Mountain Range present considerable organic matter from the late Pleistocene and other from only the Holocene. Our study was carried out on three soil profiles (two cores in grassland and one in forest) on the Caratuva Peak of the Serra do Ibitiraquire (a sub-range of Sea Mountain Range – Serra do Mar) in Southern Brazil. The δ¹³C isotopic analyses of organic matter in soil horizons were conducted to detect whether C₃ or C₄ plants dominated the past communities. Complementarily, we performed a pollen analysis and ¹⁴C dating of the humin fraction to obtain the age of the studied horizons. Except for a short and probably drier period (between 6000 and 4500 cal yr BP), C₃ plants, including ombrophilous grasses and trees, have dominated the highlands of the Caratuva Peak (Pico Caratuva), as well as the other uppermost summits of the Serra do Ibitiraquire, since around 9000 cal yr BP. The Caratuva region represents a landscape of high altitude grasslands (campos de altitude altomontanos or campos altomontanos) and upper montane rain/cloud forests with soils that most likely contain some organic matter from the late Pleistocene, as has been reported in Southern and Southeastern Brazil for other sites. However, our results indicate that the studied deposits (near the summit) are from the early to late Holocene, when somewhat wetter and warmer conditions (since around 9000 cal yr BP) enabled a stronger colonization of the ridge of Pico Caratuva by mainly C₃ plants, especially grassland species. However, at the same time, even near the summit, the soil core from the forest site already presented the current physiognomy (or a shrubby/elfin or successional forest), indicating that the colonization of the neighboring uppermost saddles and valleys were probably populated mainly by upper montane forest species.  相似文献   

Taxonomy,location of origin and health status of proboscideans from Western Canada investigated using stable isotope analysis          下载免费PDF全文

Jessica Z. Metcalfe  Fred J. Longstaffe  Christopher N. Jass  Grant D. Zazula  Grant Keddie 《第四纪科学杂志》2016,31(2):126-142

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