Quantitative estimates of temperature and precipitation changes over the last millennium from pollen and lake-level data at Lake Joux, Swiss Jura Mountains

This paper presents quantitative climate estimates for the last millennium, using a multi-proxy approach with pollen and lake-level data from Lake Joux (Swiss Jura Mountains). The climate reconstruction, based on the Modern Analogue Technique, indicates warmer and drier conditions during the Medieval Warm Period (MWP). MWP was preceded by a short-lived cold humid event around AD 1060, and followed by a rapid return around AD 1400 to cooler and wetter conditions which generally characterize the Little Ice Age (LIA). Around AD 1450 (solar Spörer minimum), the LIA attained a temperature minimum and a summer precipitation maximum. The solar Maunder minimum around AD 1690 corresponded at Joux to rather mild temperatures but maximal annual precipitation. These results generally agree with other records from neighbouring Alpine regions. However, there are differences in the timing of the LIA temperature minimum depending on the proxy and/or the method used for the reconstruction. As a working hypothesis, the hydrological signal associated with the MWP and LIA oscillations at Lake Joux may have been mainly driven by a shift around AD 1400 from positive to negative NAO modes in response to variations in solar irradiance possibly coupled with changes in the Atlantic meridional overturning circulation.     

Quantitative reconstruction of climatic variations during the Bronze and early Iron ages based on pollen and lake-level data in the NW Alps, France

Vegetation and lake-level data from the archaeological site of Tresserve, on the eastern shore of Lake Le Bourget (Savoie, France), are used to provide quantitative estimates of climatic variables over the period 4000–2300 cal BP in the northern French Pre-Alps, and to examine the possible impact of climatic changes on societies of the Bronze and early Iron Ages. The results obtained indicate that phases of higher lake level at 3500–3100 and 2750–2350 cal BP coincided with major climate reversals in the North Atlantic area. In west-central Europe, they were marked by cooler and wetter conditions. These two successive events may have affected ancient agricultural communities in west-central Europe by provoking harvest failures, more particularly due to increasing precipitation during the growing season. However, archaeological data in the region of Franche-Comté (Jura Mountains, eastern France) show a general expansion of population density from the middle Bronze Age to the early Iron Age. This suggests a relative emancipation of proto-historic societies from climatic conditions, probably in relation to the spread of new modes of social and economic organisation.     

Early Precambrian stratigraphy of central and southern Rajasthan,India

Structural, stratigraphic and petrologic studies between Amet and Sembal in the Udaipur district of southcentral Rajasthan indicate that all the rocks belonging to the Banded Gneissic Complex, the Aravalli Group and the Raialo Formation have been involved in isoclinal folding on a westerly trend, co-axial refolding, and upright folding on a north to north-northeast trend. There is neither an unconformity nor an overlap between the Aravallis and the Raialos. The conglomerates supposed to mark the erosional unconformity above the Banded Gneissic Complex near Rajnagar is a tectonic mélange of folded and torn quartz veins in mica schist within the Aravalli Group. The Aravalli—Raialo metasediments have been migmatized synkinematically with the first folding to give rise to the Banded Gneissic Complex; the gneissic complex does not have any separate stratigraphic entity. By contrast, there is an undoubted erosional unconformity between the type Aravalli rocks and the underlying Sarara granite to the south. These relations, coupled with the continuity of the Aravalli rocks of Udaipur northward to the metasedimentary rocks of the Sembal—Amet area along the strike, and a comparable structural history, point to granitic rocks of at least two generations in the Early Precambrian of central and southern Rajasthan. Preliminary radiometric dating of rocks of known stratigraphic—structural relationship seems to confirm the presence of granitic rocks of two ages in the Early Precambrian, and of a considerable interval between the deposition of the Aravalli—Raialo rocks and the Delhi rocks. The Udaipur granite, post-dating the first deformation but preceding the upright folding on the northerly trend, provides evidence for granitic activity of a third phase before the deposition of rocks of the Delhi Group.     

Reconstruction of Late-Glacial lake-level fluctuations in The Netherlands based on palaeobotanical analyses, geochemical results and pollen-density data

The Late-Glacial infills of three lake successions in The Netherlands have been analysed for their palaeobotanical content (pollen, macroremains) as well as for their physical and chemical characteristics. The macro-botanical analysis in association with the pollen analysis permitted the reconstruction of relative lake level fluctuations for each lake. There appeared to be good agreement between the three lake successions. Supporting evidence for the presence of alternating dry and wet phases was found in the geochemical results. The termination of the Bölling biozone coincides with a lowering of the lake levels that persisted throughout the Older Dryas. Water levels restore at the beginning of the Allerod biozone. Several fluctuations are recognized during the Allerod. The end of the Alleröd is characterized by a second major lowering in the lake levels, leading to an interruption in the sedimentation in cores from the fringe zone. Water depth increases at the beginning of the Younger Dryas biozone. A third major minimum in the lake levels is reached towards the end of the Younger Dryas biozone, probably explaining the recurrent hiatus at the transition to the Holocene record. Pollen concentration data in association with chronostratigraphical data provided the construction of sedimentation rate curves. Minima in these sedimentation rate curves appeared to correlate with periods of low lake level. The loss on ignition curve in association with the sedimentation rate data allowed an approximation of the organic production of the lakes involved. It revealed that the darker appearance of the Allerödin the lithologycan be ascribed mainly to a retardationin the sedimentation rate and not to a major increase in the organic production of the lakes.     

Crystallochemical studies on davidite from Bichun,Jaipur District,Rajasthan, India

Crystallochemical data on metamict davidite from albitites and albitised rocks from the Bichun area (Jaipur district, Rajasthan, India) of Banded Gneissic Complex (BGC) are provided. Davidite occurs as euhedral, subhedral to anhedral crystals in the form of disseminated grains and also as fracture filled veins. The crystals of davidite are up to 8 cm in length and 6 cm in width. The powder X-ray diffraction (XRD) pattern of the heat-treated davidite (at \(900{^{\circ }}\hbox {C}\)) reveals well-defined reflections of crystallographic planes. The calculated unit-cell parameters of the heat treated davidite are: \(\hbox {a}_{0} = \hbox {b}_{0} = 10.3556 \, \text {\AA }\) and \(\hbox {c}_{0} = 20.9067 \, \text {\AA }\), with unit-cell volume \(\hbox {(V)} = 1941.6385 \, \text {\AA }^{3}\); and \({\upalpha }={\upbeta }= 90^{\circ }\) and \({\upgamma }= 120^{\circ }\), which are in agreement with the values of davidite standard. Geochemical data reveals that the investigated davidite contains 51.5–52.6% \(\hbox {TiO}_{2}\), 14.8–15.1% \(\hbox {Fe}_{2} \hbox {O}_{3}\), 9.8–10.2% FeO, 6.97–7.12% \(\hbox {U}_{3} \hbox {O}_{8}\), 6.72–6.92% \(\hbox {RE}_{2} \hbox {O}_{3}\), 3.85–3.61% \(\hbox {K}_{2}\hbox {O}\), 0.9–1.4% \(\hbox {Al}_{2} \hbox {O}_{3}\), and 0.8–1.2% \(\hbox {SiO}_{2}\). The calculated structural formulae of the two davidite crystals are: D-1: \(\hbox {K}_{0.0044/0.004} \hbox {Ba}_{0.0044/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.053/0.053} \hbox {Mg}_{0.14/0.14} \hbox {Pb}_{0.0076/0.008} \hbox {Fe}_{2.675/2.675} \hbox {Fe}_{1.59/1.59} \hbox {Y}_{0.1175/0.118} \hbox {P}_{0.053/0.053} \hbox {Nb}_{0.008/0.008} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.033/0.033} \hbox {U}_{0.468/0.468} \hbox {Th}_{0.009/0.009} \,\,\hbox {REE}_{0.6829/0.683})_{6.05/6.05} (\hbox {Ti}_{12.15/12.15}\,\, \hbox {Fe}_{1.9022/1.903} \hbox {Si}_{0.372/0.372}\,\, \hbox {Al}_{0.517/0.517}\,\, \hbox {Cr}_{0.018/0.018} \hbox {Co}_{0.009/0.009} \hbox {Ni}_{0.027/0.027})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.319/0.319[]1.681/1.681})_{2/2}\) and D-2: \((\hbox {K}_{0.004/0.004} \hbox {Ba}_{0.005/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.05/0.05} \hbox {Mg}_{0.094/0.094} \hbox {Pb}_{0.007/0.007} \hbox {Fe}_{2.58/2.58} \hbox {Fe}_{1.71/1.71} \hbox {Y}_{0.112/0.112} \hbox {P}_{0.106/0.106} \hbox {Nb}_{0.006/0.006} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.03/0.03} \hbox {U}_{0.48/0.48} \hbox {Th}_{0.009/0.009} \hbox {REE}_{0.665/0.665})_{6.088/6.088} (\hbox {Ti}_{12.48/12.48} \hbox {Fe}_{1.87/1.87} \hbox {Si}_{0.249/0.249} \hbox {Al}_{0.334/0.334} \hbox {Cr}_{0.019/0.019} \hbox {Co}_{0.008/0.008} \hbox {Ni}_{0.04/0.04})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.098/0.098[]1.90/1.90})_{2/2}\). The calculated structural formulae are not fully stoichiometric, which could be due to metamict nature of davidite. The characteristic feature of distribution pattern of REE in davidite is unusually high concentration of LREE and HREE and substantially low content of MREE. It may be due to the occupation of REEs in two distinct crystallographic sites in davidite structure, i.e., M(1) and M(O) sites. Chondrite-normalised plot of davidite reveals a pronounced negative Eu-anomaly (\(\hbox {Eu}/\hbox {Eu}^{*} = 0.30{-}0.39\)), which suggests extremely fractionated nature of the metasomatising fluids from which davidite had crystallized. Metamict davidite-bearing U ores not only from Rajasthan, but also from other parts of India are likely to yield very high U leachability, thereby making them attractive sources of U, which otherwise are ignored by mineral engineers as uneconomic U ores.     

Geochemistry and Tungsten Metallogeny of the Balda Granite,Rajasthan, India

Balda granite occurs along the western margin of the middle Proterozoic South Delhi Fold Belt. It is a medium grained leucogranite associated with tungsten mineralisation. Wolframite mineralisation is confined to pneumatolytic quartz veins and greisenised pegmatites located mainly along shear zones within Balda granite and neighbouring metasediments. Geochemistry of Balda granite suggests that it is highly evolved, peraluminous and volatile -rich granite formed from the melt derived by partial melting of metasediments. Borates and fluorides in various complexes favoured the concentration of W in the melt, whereas sodium cations, chlorides and phosphates were the carrier of tungsten in fluid. The shear zones developed within Balda granite and neighbouring metasediments provided the channelways for fluid movement and deposition of wolframite.     

Folds in multilayered rocks of Proterozoic age,Rajasthan, India

First phase folds F₁ developed in polydeformed Ajabgarh Group rocks of Proterozoic age are studied using various geometrical methods of analysis for compatibility of homogeneous strain in both class 1–3 pairs by correlatingt′ _ga/α plots with existing curves for competent layers and matchingt _ga/α plots with the flattening curves for the incompetent layers. F¹ folds were initiated by the process of buckling but underwent [(λ₂/λ₁) = 0.2 to 0.7] for competent layers andR- values of 1.1 to 5 for incompetent layers. The varying flattening is also revealed by the geometry of folds. The apparent buckle shortening of folds which ranges between 49 and 67 per cent with a majority of the folds having shortening values between 50% and 55% (exclusive of layer parallel strain) and inverse thickness method strain up to 50%. Besides flattening, the fold geometry was also modified by the pressure solution. This is borne by the presence of dark seams rich in phyllosilicates and disseminated carbonaceous material offsetting limbs of buckled quartz veins in slates     

Evolution of the Banded Gneissic Complex of central Rajasthan,India

The Banded Gneissic Complex of central Rajasthan, the only gneissic basement in India considered to underlie an early Precambrian sedimentary suite unconformably, comprises composite gneisses formed by extensive migmatization of metasedimentary rocks of diverse composition. The migmatites and the metasedimentaries maintain a structural continuity in a plan of superposed deformations, with the migmatite front involved in the early folding but transgressing the stratigraphic boundaries. Structures in the metasedimentary palaeosomes within the gneisses match in their entirety those in the migmatite host and the metasedimentary bands outside. On a smaller scale of microsections, migmatites show para tectonic crystallization with reference to the first deformation. The Banded Gneissic Complex thus loses its unique position in the Indian Precambrians as older than the earliest decipherable sedimentary series, but is older than the Aravalli rocks of the type area, the partially migmatized metasedimentaries belonging to an earlier series.     

Primary and secondary structures in the polymetallic ores of Rajpura-Dariba,Rajasthan, India

The Precambrian Rajpura-Dariba polymetallic deposits of Rajasthan, associated with black schists, quartzite and calcsilicate rocks, exhibit several primary structures, suggesting a syn-sedimentary origin. The secondary features of the sulphides are attributed to the effects of metamorphism.     

Paleomagnetic analysis of the Marwar Supergroup,Rajasthan, India and proposed interbasinal correlations

The Marwar Supergroup refers to a 1000–2000 m thick marine and coastal sequence that covers a vast area of Rajasthan in NW–India. The Marwar Basin uncomformably overlies the ∼750–770 Ma rocks of the Malani Igneous Suite and is therefore considered Late Neoproterozoic to Early Cambrian in age. Upper Vindhyan basinal sediments (Bhander and Rewa Groups), exposed in the east and separated by the Aravalli–Delhi Fold Belt, have long been assumed to coeval with the Marwar Supergroup. Recent studies based on detrital zircon populations of the Marwar and Upper Vindhyan sequences show some similarity in the older populations, but the Vindhyan sequence shows no zircons younger than 1000 Ma whereas samples taken from the Marwar Basin show distinctly younger zircons. This observation led to speculation that the Upper Vindhyan and Marwar sequences did not develop coevally.While there are alternative explanations for why the two basins may differ in their detrital zircon populations, paleomagnetic studies may provide independent evidence for differences/similarities between the assumed coeval basins. We have collected samples in the Marwar Basin and present the paleomagnetic results. Previous paleomagnetic studies of Marwar basinal sediments were misinterpreted as being indistinguishable from the Upper Vindhyan sequence. The vast majority of our samples show directional characteristics similar to the previously published studies. We interpret these results to be a recent overprint. A small subset of hematite-bearing rocks from the Jodhpur Formation (basal Marwar) exhibit directional data (Dec = 89° Inc = −1° α95 = 9°) that are distinct from the Upper Vindhyan pole and may offer additional support for temporally distinct episodes of sedimentation in these proximal regions. A VGP based upon our directional data is reported at 1°S 344°E (dp = 5°, dm = 9°). We conclude that the Marwar Supergroup developed near the close of the Ediacaran Period and is part of a larger group of sedimentary basins that include the Huqf Supergroup (Oman), the Salt-Range (Pakistan), the Krol–Tal belt (Himalayas) and perhaps the Molo Supergroup (Madagascar).     

Biogeochemical studies at the Khetri copper deposits of Rajasthan,India

Several plants of the Khetri Copper Deposits of Rajasthan (India) accumulate very high levels of copper. The maximum concentration namely 394 ,μg/g (dry wt.) was found in the leaves of Talinum portulacifolium. Some other copper accumulators with the concentration of the metal in μg/g are: Tephrosia villosa (288), Rhus mysorensis (234) and Bouchea morubifolia (147). The respective biological absorption coefficients (copper in dried plant divided by copper in soil) for these four plants were 0.07, 1.35, 0.13 and 0.26, respectively. Leaves were found to be richer in copper than the stems. Copper levels in the leaves of Tephrosia villosa, Aerua tomentosa and Bouchea morubifolia showed a significant (linear) plant/soil relationship. Rhus mysorensis and Talinum protulacifolium showed absorption barriers at high soil copper concentrations, indicating limits to uptake in these two species.     

The problem of the Precambrian basement in Rajasthan,western India

The Banded Gneissic Complex (BGC) of Rajasthan, considered to form the basement underlying the Precambrian (Proterozoic) Aravalli metasediments, shows an erosion surface marked by a conglomerate and an angular unconformity, with gneissic foliation crossing the metasedimentary bands at only a few places. The BGC is a composite gneiss, evolved by extensive migmatization of metasedimentary rocks of diverse composition, and possibly metaigneous rocks. The contact between the BGC and the Aravalli rocks is a gently curved surface, whereas the gneissic foliation, as well as the large-scale metasedimentary enclaves within the gneissic complex, show all the intricate patterns of super-imposed folding traceable in the Aravalli rocks. This implies that the “basement” gneisses have been involved in ductile deformation with the Aravalli rocks, the migmatization being synkinematic with the first deformation in the latter. All these apparently conflicting lines of evidence can be resolved if the gneisses, as we see them now, represent not the original, but the mobilized basement, with the BGC-Aravalli boundary representing, for a large part, a migmatite front, rather than the original basement-cover interface. Only at a few places was there a chance of the original basement escaping mobilization and thus, little chance of identifying this original interface.     

Mineralogy of a scapolite-bearing rock from Rajasthan,northwest peninsular India

Electron-microprobe analyses of coexisting phases from a scapolite-garnet-epidote-calcite-plagioclase-hornblende-pyroxene (sphere-hematite-magnetite) rock of the Aravalli Group (Early Precambrian) at Karera, district Bhilwara, Rajasthan, reveal that chlorine is an important constituent of both scapolite (Me_71.3 and hornblende, making the latter a dashkesanite variety. The amphibole also contains an unusually high K₂O (3.7 wt.%), and is a chlor-potassium hastingsite. The epidote contains 41% pistacite and shows complete substitution of Al by Fe³⁺ in the Al-site and to some extent also in AIO and/or Al(OH) sites. The garnet is also rich in ferric iron and has a mol. composition Pyr₂₃Alm_8.5Gro₁₃And_54.5 Sp_1.0. The pyroxene is dominantly a hedenbergite. The phase relations and textural as well as geological criteria exclude metasomatic processes and favour equilibrium recrystallization of the scapolite-bearing assemblage; the chlorine presumably derived from an evaporite component of the Aravalli metasediments. The geothermometry based on the fractionation of Na and Ca between scapolite (EqAn 43.3) and plagioclase (An_85?90 yields metamorphic temperatures of around 700°C for the scapolite-bearing rock which are in agreement with those obtained by other mineral equilibria in the associated pelitic assemblages.     

Geochemistry and Petrogenesis of Siwana Peralkaline Granites, West of Barmer, Rajasthan, India

The bimodal Malani suite, West of Barmer, Rajasthan is characterized by discontinuous, ring shaped outcrops of Siwana peralkaline granite with minor outcrops of basalt. The peralkaline, within- plate and A-type nature of granite are evident by its chemical characteristics. The granite is characterized by high Na₂O+K₂O, Fe/Mg, Zr, Nb, Y, Zn; low Al₂O₃, CaO and Sr and is significantly low in absolute abundance of trace and REE elements compared to type area Siwana granite. The granite is correlated to the “Pan-African” event and its petrogenesis and tectonic significance are discussed.     

Mid to late holocene climate evolution of the lake telmen basin, north central mongolia, based on palynological data

Palynological and sedimentological data from Lake Telmen, in north-central Mongolia, permit qualitative reconstruction of relative changes in moisture balance throughout the mid to late Holocene. The climate of the Atlantic period (7500–4500 yr ago) was relatively arid, indicating that Lake Telmen lay beyond the region of enhanced precipitation delivered by the expanded Asian monsoon. Maximum humidity is recorded between 4500 and 1600 cal yr B.P., during the Subboreal (4500–2500 yr ago) and early Subatlantic (2500 yr–present) periods. Additional humid intervals during the Medieval Warm Epoch (1000–1300 A.D. or 950–650 ago) and the Little Ice Age (1500– 1900 A.D. or 450–50 yr B.P.) demonstrate the lack of long-term correlation between temperature and moisture availability in this region. A brief aridification centered around 1410 cal yr B.P. encompasses a decade of cold temperatures and summer frost between A.D. 536 and 545 (1414–1405 yr B.P.) inferred from records of Mongolian tree-ring widths. These data suggest that steppe vegetation of the Lake Telmen region is sensitive to centennial- and decadal-scale climatic perturbations.     

Effects of rainwater-harvesting-induced artificial recharge on the groundwater of wells in Rajasthan, India

In light of the increasing deterioration of groundwater supplies in Rajasthan, India, rainwater harvesting practices in southern Rajasthan were studied to determine the effects of artificially recharged groundwater on the supply and quality of local groundwater. A physical and geochemical investigation utilizing environmental tracers (δ¹⁸O and Cl^–), groundwater level and groundwater quality measurements, and geological surveys was conducted with two objectives: (1) to quantify the proportion of artificially recharged groundwater in wells located near rainwater harvesting structures and (2) to examine potential effects of artificial recharge on the quality of groundwater in these wells. A geochemical mixing model revealed that the proportion of artificial recharge in these wells ranged from 0 to 75%. Groundwater tracer, water table, and geological data provided evidence of complex groundwater flow and were used to explain the spatial distribution of artificial recharge. Furthermore, wells receiving artificial recharge had improved groundwater quality. Statistical analysis revealed a significant difference between the water quality in these wells and wells determined not to receive artificial recharge, for electrical conductivity and SO ₄ ^– . The findings from this study provide quantitative evidence that rainwater harvesting structures in southern Rajasthan influence the groundwater supply and quality of nearby wells by artificially recharging local groundwater.     

Measurement of soil-gas radon in some areas of northern Rajasthan,India

The health hazards of the radioactive gas radon on general public are well known. In order to understand the level and distribution of ²²²Rn concentrations in soil-gas in Sri Ganganagar district of Rajasthan, a ²²²Rn survey was carried out for the first time using RAD7, an electronic radon detector manufactured by Durridge Company (USA), at different locations covering a total area of 10,978 km ², having a population of approximately 20 lakh. The measurement of ²²²Rn concentration in soil-gas was carried out at four different depths (10, 40, 70, and 100 cm). The radon concentration in soil-gas for 10, 40, 70, and 100 cm depths ranged from 0.09–4.25, 0.15–6.30, 0.50–9.18, and 0.72–10.40 kBq m ^?3, respectively. The minimum value of radon concentration is observed in 33 GB village at 10 cm depth and maximum for Mohanpura village at 100 cm depth. As expected, our data show an increase of soil-gas radon concentration levels with depth. The present results are compared with the available radon data from other studies.     

Hydrogeomorphology of the central Luni basin,Western Rajasthan, (India)

This paper examines the interrelationships and interactions of the geomorphic features and the various hydrological parameters which control the development of water potential zones in the central Luni basin. Aerial photo-interpretation techniques were used to delineate the boundaries of geomorphological features, and facilitated the identification of twelve types of aquifers in eight geomorphological settings. The water potentials of these aquifers have been evaluated by taking into consideration nine important hydrological parameters which together govern water quality and yield. This investigation has revealed that the development of zones of ground-water potential is principally governed by the geomorphic characteristics of the terrain, which in turn is controlled by lithological variability, geological structure, drainage pattern, climatic characteristics, etc. The relevance of geomorphic characteristics has been evaluated by weight point analysis. Based on these findings, it is suggested that detailed studies of geomorphic features are of paramount significance for the rapid delineation of possible ground-water potential zones in arid and semi-arid regions.