Oxygen and carbon isotopes in Jordanian phosphorites and associated fossils

Stable isotopes have proven to be efficient tools for paleoenvironmental analysis and interpretation of paleotemperature. Oxygen and carbon isotopes were analyzed in carbonate flourapatite (francolite), oyster shells, tests of foraminifera and ostracods from the Phosphorite Unit throughout Jordan.Isotopic analysis showed δ¹⁸O to be enriched in authigenic francolite in Upper Cretaceous in NW Jordan, indicating lower temperatures, a deeper depositional environment and lower salinity than Central Jordan. In Central Jordan, the local basin of Hafira shows enrichment of δ¹⁸O indicating a deeper depositional environment than shallower highs in Mutarammil and Wadi El-Hasa. The δ¹³C shows that the depositional environment was oxic to suboxic and may have reached the suboxic to anoxic interface in the deeper environment in NW Jordan.δ¹⁸O values in tests of foraminifera and ostracods are similar to δ¹⁸O values of authigenic phosphate, which is enriched in NW Jordan, indicating lower temperature, lower salinity and a deeper environment than Central Jordan. In Central Jordan, δ¹³C shows more depletion in the Sultani section due to land derived organic carbon (food web supply) carried by terrestrial water draining to the sea.The δ¹⁸O in oyster shells show an upward enrichment in the Wadi El-Hasa section, which indicate an increase of intense upwelling, enrichment of nutrients, development of productivity and growth of oyster buildups. Meanwhile, Hafira shows enrichment of δ¹⁸O and lower temperature, in agreement with foraminifera and ostracods. The two samples of oysters from SE Jordan, although affected by diagenesis, show heavier oxygen to the north, indicating a deeper water environment and lower salinity in the same basin.     

Aspects of the structural evolution of the Lusitanian Basin in Portugal and the shelf and slope area offshore Portugal

The study provides a regional seismic interpretation and mapping of the Mesozoic and Cenozoic succession of the Lusitanian Basin and the shelf and slope area off Portugal. The seismic study is compared with previous studies of the Lusitanian Basin. From the Late Triassic to the Cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence. The Triassic rifting was concentrated in the central part of the Lusitanian Basin and in the southernmost part of the study area, both as symmetrical grabens and half-grabens. The evolution of half-grabens was particularly prominent in the south. The Triassic fault-controlled subsidence ceased during the latest Late Triassic and was succeeded by regional subsidence during the early Early Jurassic (Hettangian) when deposition of evaporites took place. A second rift phase was initiated in the Early Jurassic, most likely during the Sinemurian–Pliensbachian. This resulted in minor salt movements along the most prominent faults. The second phase was concentrated to the area south of the Nazare Fault Zone and resulted here in the accumulation of a thick Sinemurian–Callovian succession. Following a major hiatus, probably as a result of the opening of the Central Atlantic, resumed deposition occurred during the Late Jurassic. Evidence for Late Jurassic fault-controlled subsidence is widespread over the whole basin. The pattern of Late Jurassic subsidence appears to change across the Nazare Fault Zone. North of the Nazare Fault, fault-controlled subsidence occurred mainly along NNW–SSE-trending faults and to the south of this fault zone a NNE–SSW fault pattern seems to dominate. The Oxfordian rift phase is testified in onlapping of the Oxfordian succession on salt pillows which formed in association with fault activity. The fourth and final rift phase was in the latest Late Jurassic or earliest Early Cretaceous. The Jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones. However, only salt pillow development can be demonstrated. The extensional tectonics ceased during the Early Cretaceous. During most of the Cretaceous, regional subsidence occurred, resulting in the deposition of a uniform Lower and Upper Cretaceous succession. Marked inversion of former normal faults, particularly along NE–SW-trending faults, and development of salt diapirs occurred during the Middle Miocene, probably followed by tectonic pulses during the Late Miocene to present. The inversion was most prominent in the central and southern parts of the study area. In between these two areas affected by structural inversion, fault-controlled subsidence resulted in the formation of the Cenozoic Lower Tagus Basin. Northwest of the Nazare Fault Zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed. The Miocene compressional stress was mainly oriented NW–SE shifting to more N–S in the southern part.     

Weathering processes in the Indus River Basin: implications from riverine carbon, sulfur, oxygen, and strontium isotopes

This study deals with the major ions and isotope systematics for C, O, S, and Sr in the Indus River Basin (IRB). Major ion chemistry of the Indus, and most of its headwater tributaries, follow the order Ca²⁺>Mg²⁺>(Na⁺+K⁺) and HCO₃⁻>(SO₄²⁻+Cl⁻)>Si. In the lowland tributaries and in some of the Punjab rivers, however, (Na⁺+K⁺) and (SO₄²⁻+Cl⁻) predominate. Cyclic salts, important locally for Na⁺ in dilute headwater tributaries, constitute about 5% of the annual solutes transported by the Indus. Weathering of two lithologies, sedimentary carbonates and crystalline rocks, controls the dissolved inorganic carbon (DIC) concentrations and its carbon isotope systematics throughout the Indus, but turbulent flow and lower temperatures in the headwaters, and storage in reservoirs in the middle and lower Indus promote some equlibration with atmospheric carbon dioxide. Combined evidence from sulfur and oxygen isotopic composition of sulfates refutes the proposition that dissolution of these minerals plays a significant role in the IRB hydrochemistry and suggests that any dissolved sulfates were derived by oxidation of sulfide minerals.

In the upper Indus, silicate weathering contributes as much as 75% (or even higher in some tributaries) of the total Na⁺ and K⁺, declining to less than 40% as the Indus exits the orogen. In contrast, about two-thirds of Ca²⁺ and Mg²⁺ in the upper Indus (over 70% in some tributaries) and three-fourth in the lower Indus, are derived from sedimentary carbonates. The ⁸⁷Sr/⁸⁶Sr ratios tend to rise with increasing proportions of silicate derived cations in the headwater tributaries and in the upper and middle Indus, but are out of phase or reversed in the lower Indus. Finally, close to the river mouth, the discharge weighted average contribution of silicate derived Ca²⁺+Mg²⁺ and silicate derived Na⁺+K⁺ are, respectively, about one-fourth and two-thirds of their total concentrations.     

Sodium and strontium in mollusc shells: preservation,palaeosalinity and palaeotemperature of the Middle Pleistocene of eastern England

This paper revisits the utility of sodium (Na) content in aragonite and calcite mollusc shells as an indicator of palaeosalinity. The data come mainly from a related suite of Middle Pleistocene marine and freshwater fossils that have been subject to broadly similar diagenetic histories. Environmental salinity is re-affirmed as the primary factor in determining the sodium content of modern and ancient mollusc shells: values <2000 ppm Na are generally indicative of non-marine environments while values >2000 Na ppm are typically from marine shells. There is a positive relationship between Na (salinity) and Sr which is a helpful discriminator of palaeosalinity in the fossil data set. The Na and Sr data give confidence that the fossil shells have not suffered pervasive diagenetic alteration and that the marine fossils lived in fully marine conditions. Oxygen isotope values in the best-preserved, fully marine fossil shells, suggest Middle Pleistocene ‘eastern England’ seawater temperatures were broadly similar to those of the modern North Sea.     

Constraining diamond metasomatic growth using C- and N-stable isotopes: examples from Namibia

The present paper provides C- and N-stable isotope characteristics, N-contents and N-aggregation states for alluvial diamonds of known paragenesis from placers along the Namibian coast. The sample set includes diamonds with typical peridotitic and eclogitic inclusions and the recently reported “undetermined” suite of Leost et al. [Contrib. Mineral. Petrol. 145 (2003) 15] which resulted from infiltration of high temperature, carbonate-rich melts. δ¹³C-values range from −20.3‰ to −0.5‰ (n=48) for peridotitic diamonds and from −38.5‰ to −1.6‰ (n=45) for eclogitic diamonds. Diamonds belonging to the “undetermined” suite span a narrower range in δ¹³C from −8.5‰ to −2.7‰ (n=13). When compared with previous studies, diamonds from Namibia are characterised by unusually low proportions of N-free (i.e. Type II) peridotitic and eclogitic diamonds (3% and 2%, respectively) and an unprecedented high proportion of N-rich diamonds (15% and 73%, respectively, have N-contents >600 ppm). δ¹⁵N-values for diamonds of the peridotitic, eclogitic and “undetermined” suites range from −10‰ to +13‰ without correlations with either N-content or δ¹³C. The similarity in N-isotopic composition and the N-rich character of diamonds belonging to the eclogitic, peridotitic and “undetermined” suites is striking and suggests a close genetic relationship. We propose that a large part of the diamonds mined in Namibia formed during metasomatic events of similar style that introduced carbon and nitrogen into a range of different host lithologies.     

Palaeoclimate of the Late Jurassic of Portugal: comparison with the Western United States

Investigation of the palaeoclimatic conditions associated with Upper Jurassic strata in Portugal and comparison with published palaeoclimate reconstructions of the Upper Jurassic Morrison Formation in western North America provide important insights into the conditions that allowed two of the richest terrestrial faunas of this period to flourish. Geochemical analyses and observations of palaeosol morphology in the informally named Upper Jurassic Lourinhã formation of western Portugal indicate warm and wet palaeoclimatic conditions with strongly seasonal precipitation patterns. Palaeosol profiles are dominated by carbonate accumulations and abundant shrink‐swell (vertic) features that are both indicative of seasonal variation in moisture availability. The δ¹⁸O_SMOW and δD_SMOW values of phyllosilicates sampled from palaeosol profiles range from +22·4‰ to +22·7‰ and ?53·0‰ to ?37·3‰, respectively. These isotope values correspond to temperatures of formation between 32°C and 39°C ± 3°, with an average of 36°C, which suggest surface temperatures between 27°C and 34°C (average 31°C). On average, these surface temperature estimates are 1°C higher than the highest summer temperatures modelled for Late Jurassic Iberia using general circulation models. Elemental analysis of matrix material from palaeosol B‐horizons provides proxy (chemical index of alteration minus potassium) estimates of mean annual precipitation ranging from 766 to 1394 mm/year, with an average of approximately 1100 mm/year. Palaeoclimatic conditions during deposition of the Lourinhã formation are broadly similar to those inferred for the Morrison Formation, except somewhat wetter. Seasonal variation in moisture availability does not seem to have negatively impacted the ability of these environments to support rich and relatively abundant faunas. The similar climate between these two Late Jurassic terrestrial ecosystems is probably one of the factors which explains the similarity of their vertebrate faunas.     

Identifying low-temperature hydrothermal karst and palaeowaters using stable isotopes: a case study from an alpine cave,Entrische Kirche,Austria

The area south of the prominent east–west trending Salzach Valley at the northern rim of the Central Alps of Austria has long been known to host anomalously warm springs emerging from a highly deformed calcite marble (Klammkalk). This unit also hosts cavities whose shapes suggest a hydrothermal karst origin and which are lined by calcite spar. We report here petrographic and isotopic evidence suggesting that dissolution by ascending low-temperature thermal waters also played an important role in the origin of a large cave in this region, Entrische Kirche. A paleo cave wall, preserved behind a thick flowstone in the interior of this cave, revealed a brownish bleaching zone which contrasts to the medium grey colour of the unaltered marble beneath. Across this zone the C and O isotope values gradually decrease by 3 and 11‰, respectively. These compositions are very different from those of the speleothem above but are similar to phreatic calcite spar from hydrothermal karst cavities in other outcrops in the area, where the absence of two-phase fluid inclusions suggests a low-temperature (less than ca. 50°C) hydrothermal origin. U/Th dating of the flowstone capping the alteration zone yielded a minimum age of the thermal water invasion in Entrische Kirche of ca. 240 kyr. There is no evidence in Entrische Kirche that these palaeowaters reached the point of calcite precipitation, but it is physically conceivable that higher and as yet unexplored parts of this deep (ca. 900 m) cave contain cavities lined by phreatic cave spar.     

Carbon and oxygen isotopes: a tool for Jurassic and early Cretaceous pelagic correlation (southern Spain)

The isotopic evolution of δ¹³C and δ¹⁸O is reported for the Jurassic and early Cretaceous in two pelagic sections of the External Zones in the Betic Cordilleras (SE Spain). Stable isotope curves from pelagic trough and swell sections display similar patterns. Variations in δ¹⁸O and δ¹³C values from strata at equivalent age probably reflect both early diagenetic cementation and later temperature‐related burial diagenesis. Comparison of global isotope curves with those presented in this work allows the differentiation of global from local events. Thus, the anoxic event during the early Toarcian (falciferum Zone) is characterized by elevated δ¹³C and depressed δ¹⁸O values. The isotopic record also allows the detection of the middle Oxfordian transgression. There are other peaks for the late Toarcian, early Bajocian, Callovian and early Berriasian that can also be used as tools for correlation purposes. Copyright © 2002 John Wiley & Sons, Ltd.     

Diagenesis, palaeoclimate and tectono-sedimentary influences on clay mineralogy and stable isotopes from Upper Cretaceous marine successions of the Basque-Cantabrian Basin (N Spain)

Clay mineralogy and whole-rock stable isotopes (δ¹⁸O and δ¹³C) of Upper Cretaceous marly sediments on the Basque-Cantabrian Basin have been integrated to determine the main effects of diagenesis, palaeoclimate and tectono-sedimentary factors in sections belonging to deep- (Barrika) and platform-marine (Isla de Castro, Villamartín and Olazagutía) settings.The mean values for the clay assemblages and δ¹⁸O exhibit notable differences among the sections, partially explainable by the influence of diagenesis. The Barrika sediments, with more diagenetically advanced illite-smectite (I-S) mixed-layer (R1, 70% illite), authigenic chlorite, and low δ¹⁸O (−4.05‰ PDB), experienced higher diagenetic grade than Isla de Castro and Olazagutía, which have R0 I-S (20% illite) and heavier δ¹⁸O. Villamartín was also affected by higher diagenesis than Isla de Castro and Olazagutía, given the occurrence of R1 I-S (60% illite) and low δ¹⁸O (−4.11‰ PDB). However, the absence of other clays in Villamartín (e.g. authigenic chlorite) is indicative of less diagenetic grade than Barrika. These results show the useful integration of clay mineralogy and stable isotopes to detect different diagenetic grades in distinct marine successions of the same basin.Despite being influenced by diagenesis, the clay mineralogy partially preserves its inherited signature. This allows detection of major contents of I-S and mica, and minor kaolinite, interpreted as indicative of warm palaeoclimatic conditions. High kaolinite content in Villamartín and absence of kaolinite in Isla de Castro, though, are considered to be a product of neither diagenesis nor palaeoclimatic influences. Instead, tectono-sedimentary causes, related to unsuitable conditions for clay formation and transport from the local source areas, contributed to original clay differences. The inferred effects of diagenesis, palaeoclimate and tectono-sedimentary factors make this work important to show the potentially great variety of controls on the clay mineralogy of marine sections, which are often uncritically treated in studies concerning the Late Cretaceous.     

Fe-Cu-Zn同位素在矿床学和找矿勘查中的应用

金属稳定同位素已经广泛应用于矿床学研究以及找矿勘查。金属来源及其成矿过程是金属矿床研究以及找矿勘查中重点关注的基本核心问题。金属稳定同位素这项新技术进一步提高了我们对地壳中金属来源、迁移和富集的认识。这项新技术的优点是我们可以直接从矿石矿物本身获取信息。在本文中,我们重点关注矿石、水、岩石、土壤、植物等测量出的Fe-Cu-Zn同位素分馏,聚焦于Fe-Cu-Zn同位素从最深部岩浆系统开始一直向上延伸到浅部表生系统的过程中Fe-Cu-Zn同位素如何应用于矿床学研究以及找矿勘查,试图展示这些相对较新的技术可以提供的潜在应用范围。经过系统研究和总结,我们认为金属稳定同位素数据可以从三方面加以利用。首先,地表的植物、水、风化的岩石以及土壤中产生的较大的同位素分馏可以作为地下矿产勘查的指示标志;第二,矿区范围内金属稳定同位素往往具有系统的空间变化规律,可以指示成矿热液空间演化模式和矿体延伸方向;第三,金属元素作为成矿元素,其同位素可以直接有效地约束矿石的形成过程、成因以及源区特征。     

Sulphur and carbon isotopic composition of power supply coals in the Pannonian Basin, Hungary

The present work is an attempt to establish the stable isotope database for Mesozoic to Tertiary coals from the Pannonian Basin, Hungary. Maceral composition, proximate analysis, sulphur form, sulphur isotopes (organic and pyritic), and carbon isotopes were determined. This database supports the assessment of the environmental risks associated with energy generation, the characterization of the formation and the distribution of sulphur in the coals used.The maceral composition, the sulphur composition, the C, S isotopic signatures, and some of the geological evidences published earlier show that the majority of these coals were deposited in freshwater and brackish water environments, despite the relatively high average sulphur content. However, the Upper Cretaceous, Eocene, and Lower Miocene formations also contain coal seams of marine origin, as indicated by their maceral composition and sulphur and carbon chemistry.The majority of the sulphur in these coals occurs in the organic form. All studied sulphur phases are relatively rich in ³⁴S isotopes (δ³⁴S_organic = + 12.74‰, δ³⁴S_pyrite = + 10.06‰, on average). This indicates that marine bacterial sulphate reduction played a minor role in their formation, in the sense that isotopic fractionation was limited. It seems that the interstitial spaces of the peat closed rapidly during early diagenesis due to a regime of high depositional rate, leading to a relative enrichment of the heavy sulphur isotopes.     

Constraining flow paths of saline groundwater at basin margins using hydrochemistry and environmental isotopes: Lake Cooper,Murray Basin,Australia

Solutes in saline groundwater (total dissolved solids up to 37 000 mg/L) in the Lake Cooper region in the southern margin of the Riverine Province of the Murray Basin are derived by evapotranspiration of rainfall with minor silicate, carbonate and halite dissolution. The distribution of hydraulic heads, salinity, percentage modern carbon (pmc) contents, and Cl/Br ratios imply that the groundwater system is complex with vertical flow superimposed on lateral flow away from the basin margins. Similarities in major ion composition, stable (O, H, and C) isotope, and ⁸⁷Sr/⁸⁶Sr ratios between groundwater from the shallower Shepparton Formation and the deeper Calivil – Renmark aquifer also imply that these aquifers are hydraulically interconnected. Groundwater in the deeper Calivil – Renmark aquifer in the Lake Cooper region has residence times of up to 25 000 years, implying that pre-land-clearing recharge rates were <1 mm/y. As in other regions of the Murray Basin, the low recharge rates account for the occurrence of high-salinity groundwater. Shallow (<20 m) groundwater yields exclusively modern ¹⁴C ages and shows a greater influence of evaporation over transpiration. Both these observations reflect the rise of the regional water-table following land clearing over the last 200 years and a subsequent increase in recharge to 10 – 20 mm/y. The rise of the regional water-table also has increased vertical and horizontal hydraulic gradients that may ultimately lead to the export of salt from the Lake Cooper embayment into the adjacent fresher groundwater resources.     

Small-scaled environmental changes: indications from stable isotopes of gastropods (Early Miocene, Korneuburg Basin, Austria)

The Korneuburg Basin, with mainly upper Lower Miocene (Karpatian) sediment filling, is divided by the Mollmannsdorf–Obergänserndorf Swell into two sub-basins characterised by different environmental settings. Paleoecological data indicate a marine northern part and a mainly estuarine southern part. Nevertheless, short-termed marine ingressions from the north allowed marine faunas (ostracods, molluscs, and echinoids) to temporarily settle the southern part of the basin. The carbon and oxygen isotopic composition of gastropod shells from these different environmental settings were investigated. Highest δ¹⁸O and δ¹³C values are found in Turritella shells from the northern part of the basin, and in Turritella shells from layers interpreted as a marine ingression in the south. Generally, components of the mudflat fauna (Tympanotonos cinctus, Granulolabium bicinctum, Terebralia bidendata, and Ocenebra crassilabiata) have slightly lower isotope values. Considerable freshwater influx in the southern part is documented by abundant freshwater genera such as Melanopsis, which show low carbon and oxygen isotope values. Data of identical taxa, especially Turritella and Granulolabium, reflect a trend from higher isotope values at the marine northern part to slightly lower values in the mainly estuarine southern part of the basin. Differences in δ¹⁸O between the marine and the estuarine assemblages are interpreted to be caused by changes in salinity and isotopic composition of ambient water rather than by temperature. Paleotemperature estimates derived from oxygen isotope data are in good agreement with existing paleoclimatic proxies for the Korneuburg Basin. Hence, an annual range of the sea-surface temperature from 13 to 26°C can be predicted within that protected basin.     

Quantification of karst aquifer discharge components during storm events through end-member mixing analysis using natural chemistry and stable isotopes as tracers

Karst aquifer components that contribute to the discharge of a water supply well in the Classical Karst (Kras) region (Italy/Slovenia) were quantitatively estimated during storm events. Results show that water released from storage within the epikarst may comprise as much as two-thirds of conduit flow in a karst aquifer following rainfall. Principal components analysis (PCA) and end-member mixing analysis (EMMA) were performed using major ion chemistry and the stable isotopes of water (δ¹⁸O, δ²H) and of dissolved inorganic carbon (δ¹³C_DIC) to estimate mixing proportions among three sources: (1) allogenic river recharge, (2) autogenic recharge, and (3) an anthropogenic component stored within the epikarst. The sinking river most influences the chemical composition of the water-supply well under low-flow conditions; however, this proportion changes rapidly during recharge events. Autogenic recharge water, released from shallow storage in the epikarst, displaces the river water and is observed at the well within hours after the onset of precipitation. The autogenic recharge end member is the second largest component of the well chemistry, and its contribution increases with higher flow. An anthropogenic component derived from epikarstic storage also impacts the well under conditions of elevated hydraulic head, accounting for the majority of the chemical response at the well during the wettest conditions.     

Earliest mordellid-like beetles from the Jurassic of Kazakhstan and China (Coleoptera: Tenebrionoidea)

Within this study the subfamily Praemordellinae is reviewed and the holotype of Praemordella martynovi Scegoleva-Barovskaja, 1929 is re-described. The genera Cretanaspis Huang and Yang, 1999, Mirimordella Liu et al., 2007, Bellimordella Liu et al., 2008 and Wuhua Wang and Zhang, 2011 is attributed to Praemordellinae. One new species, Wuhua peregrina sp. nov., is erected based on two well-preserved specimens from the Middle Jurassic Daohugou Biota (Inner Mongolia, China). The morphological characters of Praemordellinae are given and a key to genera of Praemordellinae is presented. Praemordellinae is closely related to extant Mordellidae in having humpbacked body, strongly deflexed head, filiform antennae and pectinate tarsal claws, but it is differing in that the pygidium absent and hind femora not well developed. It is also similar to Ripiphoridae in having a convex body and simple tarsi, but differs Ripiphoridae in having filiform antennae. Praemordellinae is probably a stem group including the ancestor of Mordellidae and Ripiphoridae. Also, within this paper, the fossil record of Mordellidae is summarized.     

Characterisation of recharge processes and groundwater flow mechanisms in weathered-fractured granites of Hyderabad (India) using isotopes

In order to address the problem of realistic assessment of groundwater potential and its sustainability, it is vital to study the recharge processes and mechanism of groundwater flow in fractured hard rocks, where inhomogeneties and discontinuities have a dominant role to play. Wide variations in chloride, δ¹⁸O and ¹⁴C concentrations of the studied groundwaters observed in space and time could only reflect the heterogeneous hydrogeological setting in the fractured granites of Hyderabad (India). This paper, based on the observed isotopic and environmental chloride variations of the groundwater system, puts forth two broad types of groundwaters involving various recharge processes and flow mechanisms in the studied granitic hard rock aquifers. Relatively high ¹⁴C ages (1300 to ～6000 yr B.P.), δ¹⁸O content (?3.2 to ?1.5‰) and chloride concentration (<100 mg/l) are the signatures that identified one broad set of groundwaters resulting from recharge through weathered zone and subsequent movement through extensive sheet joints. The second set of groundwaters possessed an age range Modern to ～1000 yr B.P., chloride in the range 100 to ～350 mg/l and δ¹⁸O from ?3.2 to +1.7‰. The δ¹⁸O enrichment and chloride concentration, further helped in the segregation of the second set of groundwaters into three sub-sets characterized by different recharge processes and sources. Based on these processes and mechanisms, a conceptual hydrogeologic model has evolved suggesting that the fracture network is connected either to a distant recharge source or to a surface reservoir (evaporating water bodies) apart from overlying weathered zone, explaining various resultant groundwaters having varying ¹⁴C ages, chloride and δ¹⁸O concentrations. The surface reservoir contribution to groundwater is evaluated to be significant (40 to 70%) in one subset of groundwaters. The conceptual hydrogeologic model, thus evolved, can aid in understanding the mechanism of groundwater flow as well as migration of contaminants to deep groundwater in other fractured granitic areas.     

Using hydrogen,oxygen, and tritium isotopes to identify the hydrological factors contributing to landslides in a mountainous area,central Taiwan

Over a 1-year period, 343 samples, including precipitation, creek, pond, and groundwater, were collected from June 2003 to May 2004. Analyses were performed for stable oxygen and hydrogen isotope compositions. Selected samples were also analyzed for tritium. The goal was to identify possible hydrologic factors contributing to a severe landslide in the Li-Shan area, central Taiwan. The isotope characteristics indicate that groundwater from Fu-Shou-Shan farm located up-slope from the landslide area is a major source for slope groundwater, in addition to precipitation. The groundwater is mainly recharged by pond water at Fu-Shou-Shan farm. According to the calculation of a two-end member equation with δ ¹⁸O, the contribution of farm groundwater to slope groundwater is significantly higher than that of precipitation, up to a factor of five. The estimated drainage efficiency of the existing system is only 23%. Draining off the slope groundwater in the up-slope region to decrease farm groundwater flow into the slope area is a feasible strategy to effectively reduce the risk of landslide.     

Lithofacies associations and stable isotopes of palustrine and calcrete carbonates: examples from an Indian Maastrichtian regolith

Detailed information on semi‐arid, palustrine carbonate–calcrete lithofacies associations in a sheetwash‐dominated regolith setting is sparse. This is addressed by studying the Lower Limestone of the Lameta Beds, a well‐exposed Maastrichtian regolith in central India. The general vertical lithofacies assemblage for this unit comprises: (a) basal calcareous siltstones and marls with charophytes, ostracods and gastropods; (b) buff micritic limestones associated in their upper parts with calcretized fissure‐fill sandstones; (c) sheetwash as fissure‐fill diamictites and thin pebbly sheets, locally developed over a few metres; and (d) sandy, nodular, brecciated and pisolitic calcretes at the top. The sequence is ‘regressive’, with upsection filling of topographic lows by increased sheetwash. Lateral lithofacies change is marked, but there are no permanent open‐water lake deposits. In topographic lows close to the water table, marshy palustrine or groundwater calcretes formed, whereas on better drained highs, brecciation and calcretization occurred. Prolonged exposure is implied, suggesting that shrinkage was the main cause of brecciation. Evidence for rhizobrecciation and other biological calcrete fabrics is sparse, contrasting with the emphasis on root‐related brecciation in many studies of palustrine lithofacies. Stable isotope (δ¹⁸O and δ¹³C) values are consistent with the palustrine limestones being fed from meteoric‐derived groundwater with a strong input of soil‐zone carbon. There is overlap of both δ¹⁸O and δ¹³C values from the various palustrine and calcrete fabrics co‐occurring at outcrop. This suggests that, in groundwater‐supported wetlands, conversion from palustrine carbonate to calcrete need not show isotopic expression, as the groundwater source and input of soil‐zone carbon are essentially unchanged. Cretaceous–Tertiary δ¹⁸O and δ¹³C values from palustrine lithofacies and associated calcretes appear to be strongly influenced by the inherited values from lakes and wetlands. Hydrologically closed lakes and marine‐influenced water bodies tend to result in low negative palustrine δ¹⁸O and δ¹³C values. During brecciation and calcretization, the degree of isotopic inheritance depends on whether or not alteration occurs in waters that are different from those of the original water body or wetland. Marked biological activity (e.g. rhizobrecciation or root mat development) during calcretization may lower δ¹³C values where C₃ plants are abundant but, in shrinkage‐dominated systems, δ¹³C values will be largely inherited from the palustrine limestones.     

新疆包古图斑岩铜矿床成矿流体及成矿物质来源——来自硫、氢和氧同位素证据

包古图大型斑岩铜矿位于准噶尔盆地西缘。铜矿化主要呈浸染状、细脉浸染状分布于似斑状(石英)闪长岩、闪长玢岩、隐爆角砾岩和少量花岗闪长岩中。依据矿脉的穿插关系和矿物组合,成矿过程经历了黑云母-钾长石-钠长石阶段、石英-硫化物阶段和石英碳酸盐阶段。矿脉中石英的δDSMOW值介于-107‰～-86‰,δ18OSMOW值变化于11.3‰～16.2‰,δ18OH2O值为4.4‰～9.3‰,表明成矿流体来源为深源的岩浆水。硫化物的δ34S值介于-5.1‰～0.7‰,平均为-1.8‰,表明硫来源于深部岩浆或地幔。结合Ⅱ、Ⅲ和Ⅴ号含矿岩体锆石LA-ICP-MSU-Pb年龄及辉钼矿Re-Os年龄,推断包古图铜矿床成矿作用发生在晚石炭世,与中酸性斑岩体的侵入有密切成因关系。     

四川盆地东部地区寒武系洗象池群碳酸盐岩碳、氧同位素特征及其意义*

四川盆地东部地区寒武系洗象池群碳酸盐岩的碳、氧同位素组成受后期成岩作用影响较小,基本保留了原始海洋的同位素组成,笔者根据采集的111个碳、氧同位素数据,研究、讨论了盆地东部地区中上寒武统碳酸盐岩碳、氧同位素组成、演化及地质意义。研究表明,δ¹³C值变化介于-3.36‰~2.65‰之间,均值为-1.027‰,绝大多数的样品都分布在-2‰~2‰的区间,δ¹⁸O值分布于-11.1‰~-6.01‰之间,均值为-7.991‰,在-10‰~-6‰的范围内波动。通过对碳、氧同位素数据分析研究,认为四川盆地东部地区洗象池群主要发育在盐度较高、温暖—炎热的近岸海相沉积环境;洗象池群沉积早期和中期经历了短暂而快速的海侵后进入缓慢的海退,在晚期缓慢海侵后的快速海退,碳同位素组成反映的海平面变化趋势与沉积相演化一致。洗象池群沉积中期显著的碳同位素正向漂移,标志着较高的生产力和有机碳埋藏率,具有重要的石油地质学意义。