climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems from soil water to speleothem calcite abstract understanding the relationship between stable isotope signals recorded in speleothems 13 c and 18 o and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open closed conditions with respect to co 2 the water entering the cave flows as a thin film towards the drip site co 2 degasses from this film within approx 10 s by molecular diffusion subsequently chemical and isotopic equilibrium is established on a time scale of several 10 100 s the 13 c value of the drip water is mainly determined by the isotopic composition of soil co 2 the evolution of the 18 o value of the carbonate species is determined by the long exchange time t ex between oxygen in carbonate and water of several 10 000 s even if the oxygen of the co 2 in soil water is in isotopic equilibrium with that of the water dissolution of limestone delivers oxygen with a different isotopic composition changing the 18 o value of the carbonate species consequently the 18 o value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time after the water has entered the cave the carbon and oxygen isotope composition of the drip water may be altered by co 2 exchange with the cave air exchange times ex co 2 of about 3000 s are derived thus only drip water which drips in less than 3000 s onto the stalagmite surface is suitable to imprint climatic signals into speleothem calcite deposited from it precipitation of calcite proceeds with time constants p of several 100 s different rate constants and equilibrium concentrations for the heavy and light isotopes respectively result in isotope fractionation during calcite precipitation since t ex p exchange with the oxygen in the water can be neglected and the isotopic evolution of carbon and oxygen proceed analogously for drip intervals t d p the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time the calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water for long drip intervals when calcite is deposited from a stagnant water film long drip intervals may have a significant effect on the isotopic composition of the dic in this case the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval such processes must be considered when speleothems are used as proxies of past climate variability

joint inversion of gravity and geoelectrical data for groundwater and structural investigation application to the northwestern part of sinai egypt summary the simulated annealing method was applied to jointly invert gravity and resistivity data to obtain the geometry of the density resistivity interfaces and subsurface electrical resistivity distribution the results obtained from the inversions of synthetic data indicate that the joint inversion significantly improves the solution decreasing the ambiguity of the models the method was applied to gravity and resistivity data carried out in sinai northwestern egypt the results obtained revealed the geometry of the water bearing zone with thickness ranging from 80 to 180 m and of the limestone bedrock interface dipping northwards

regularized two dimensional fourier gravity inversion method with application to the silent canyon caldera nevada a modification of the 2 d fourier gravity inversion method includes regularization and a linear density variation with depth explicit downward continuation in the fourier inversion of gravity observations from mass distributions at depth produces instability in the presence of noise and shallow mass distributions a data adaptive regularization filter tapers growth of the exponential continuation function an empirical relationship between the regularization filter parameter and a parametric model of potential field spectra results in automatic selection of the filter parameter for a given continuation depth inversion of synthetic data from a random noise contaminated basin type model produces a depth model that agrees with the synthetic structure with an rms error commensurate with the data noise a model of the silent canyon caldera buried beneath pahute mesa at the nevada test site results in a gravity field that agrees with the observations to within a 4 percent rms error the caldera gravity mode

three dimensional interpretation of gravity data from sedimentary basins using an exponential density depth function in mapping the topography of the basement of deep sedimentary basins by gravity modelling the accuracy can be improved by incorporating an exponential increase in density with depth for calculating the gravity effect of a three dimensional 3d structure with such an exponential density depth relation a frequency domain forward algorithm based on series expansion is presented the numerical evaluation of which can be performed efficiently by fast fourier transform the algorithm can be applied in a recursive procedure to give the inverse solution in terms of basement relief the inversion procedure is satisfactorily tested on a 2d synthetic example and a 3d field example of gravity data from the western margin of the pannonian basin in eastern austria where up to 2 2 km of tertiary sediments overlie an igneous or metamorphic basement the results are confirmed by basement intersections in several wells

stable inversion of gravity anomalies of sedimentary basins with nonsmooth basement reliefs and arbitrary density contrast variations we present a new stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast the subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated any vertical line must intersect the basement relief only once and the mass deficiency must be concentrated near the earth s surface subject to the observed gravity anomaly being fitted within the experimental errors in addition upper and lower bounds on the density contrast of each prism are introduced a priori one of the bounds being zero and the method assigns to each elementary prism a density contrast which is close to either bound the basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts the latter occupying the upper part

geophysical inversion using approximate equality constraints current inversion methods estimating a physical property on a grid use two kinds of constraints 1 absolute constraints requiring that the solution vector be close to a prespecified vector as for example proximity to the null vector in the ridge regression and 2 relative constraints requiring that the elements of the solution vector be close to each other as for example smoothness imposed by methods requiring that spatial derivatives of the physical property be continuous using just absolute constraints may produce a biased solution conflicting with some true geological attributes of the source on the other hand using just relative constraints may be insufficient to stabilize the inversion we present a stable inversion method incorporating absolute constraints only at points where the physical property is known as for example outcroppings and boreholes elsewhere relative constraints are introduced according to a linear relationship for the spatial distribution of the physical property the proposed method is analogous to an interpolation method applied to the physical property distribution the interpolating function must satisfy some property like continuity and pass through the data the proposed method is versatile in incorporating not only factual but also indirect information such as continuity symmetry and trends in addition it may be applied both to linear and nonlinear problems the relevant results obtained from applying the method to synthetic potential field data were 1 ability to produce reliable mappings of the basement relief of a sedimentary basin from gravity data and of an areal distribution of magnetization using only smoothness constraints and restricted surface and borehole information 2 operational simplicity because of the solution insensitivity to the damping parameter the method is also applied to the bouguer anomaly over san jacinto graben california producing results consistent with previous interpretations

2d gravity inversion of a complex interface in the presence of interfering sources we present a new semiautomatic gravity interpretation method for estimating a complex interface between two mediacontainingdensityheterogeneitiesreferredtoasinterferingsourcesthatgiverisetoacomplexandinterferinggravity field the method combines a robust fitting procedure and the constraint that the interface is very smooth near the interfering sources whose approximate horizontal coordinates aredefinedbytheuser theproposedmethoddiffersfromthe regional residual separation techniques by using no spectral contentassumptionabouttheanomalyproducedbytheinterface to be estimated i e the interface can produce a gravity response containing both low and high wavenumber features asaresult itmaybeappliedtomapthereliefofacomplex interface in a geologic setting containing either shallow ordeep seatedinterferingsources testsconductedwithsyntheticdatashowthatthemethodcanbeofutilityinestimating the basement relief of a sedimentary basin in the presence of saltlayersanddomesorinthepresenceofmaficintrusionsin the basement or in both basement and the sedimentary section the method was applied to real gravity data from two geologic settings having different kinds of interfering sources and interfaces to be interpreted 1 the interface between the upper and lower crusts over the bavali shear zone of southern india and 2 the anorthosite tonalite interface over the east bull lake gabbro anorthosite complex outcrop in ontario canada

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

interpretation of orbital scale variability in mid latitude speleothem δ18o significance of growth rate controlled kinetic fractionation effects abstract oxygen isotopes have been the most widely used climate indicator in stalagmites applied to reconstruct past changes in rainfall 18 o and cave temperature however the 18 o signal in speleothems may also be influenced by variable kinetic fractionation effects here conceived broadly as fractionation effects not arising from temperature variation the regional reproducibility of speleothem 18 o signals has been proposed as a way to distinguish the 18 o variations arising directly from changes rainfall 18 o and cave temperature from variations due to kinetic effects which may nonetheless be influenced by climate here we compare isotopic records from 5 coeval stalagmites from two proximal caves in nw spain covering the interval 140 to 70 ka which experienced the same primary variations in temperature and rainfall 18 o but exhibit a large range in growth rates and temporal trends in growth rate stalagmites growing at faster rates near 50 m yr have oxygen isotopic ratios over 1 more negative than coeval stalagmites with very slow 5 m yr growth rates because growth rate variations also occur over time within any given stalagmite the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components removal of the kinetic component of variation in each stalagmite based on the dependence of the kinetic component on growth rate is effective at distilling a common temporal evolution of among the oxygen isotopic records of the multiple stalagmites however this approach is limited by the quality of the age model for time periods characterized by very slow growth and long durations between dates the presence of crypto hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects the stacked growth rate corrected speleothem 18 o is influenced by orbital scale variation in the cave temperature and the 18 o of the ocean moisture source but also by temporally variable fractionation in the hydrological cycle the most salient trend is increased hydrological fractionation during the gi 22 period when warmer sea surface temperatures in the subtropical atlantic moisture source region may have favored greater precipitation amounts

generalized compact gravity inversion extending the compact gravity inversion technique by incorporating a priori information about the maximum compactness of the anomalous sources along several axes provides versatility thus the method may also incorporate information about limits in the axes lengths or greater concentration of mass along one or more directions the judicious combination of different constraints on the anomalous mass distribution allows the introduction of several kinds of a priori information about the arbitrary shape of the sources this method is particularly applicable to constant linear density sources such as mineralizations along faults and intruded sills dikes and laccoliths in a sedimentary basin the correct source density must be known with a maximum uncertainty of 40 percent otherwise the inversion produces thicker bodies for densities smaller than the true value and vice versa because of the limitations of the inverse gravity problem the proposed technique requires an empirical technique to analyze the sensitivity of solutions to uncertainties in the a priori information the proposed technique is based on a finite number of acceptable solutions presumably representative of the ambiguity region by using standard statistical techniques each parameter is assigned a coefficient measuring its uncertainty the known hematite and magnetite ore body shape in the vicinity of iron mountain mo was reproduced quite well using this inversion technique

understanding the gravity response variability of sedimentary basins using forward stratigraphic modelling abstract it is accepted that gravity inversions are non unique and that multiple models will fit the data equally well over sedimentary basins this implies that gravity anomalies can be equally well explained by sedimentary strata with constant densities over a highly heterogeneous basement or by highly heterogeneous sedimentary strata over a constant density basement while both scenarios minimise the difference between the predicted and observed gravity signal neither are geologically plausible in this work we explore stratigraphic modelling as a new parameterisation for gravity models by using a process based numerical simulation to generate the sedimentary basins density models we seek to focus only on geologically plausible models we then study the variability of the sedimentary strata s gravity response i e the range of possible geophysical signatures to stratigraphic parameter changes results from a study of a 2d section in the northern carnarvon basin the northwest shelf of australia emphasize that even when the stratigraphic models are trialled using a wide range of input parameters the simulated gravity response still has a limited variability when compared to model results generated using other parameterisations lastly our results provide insights into the global sensitivity of the gravity response highlighting the sedimentary and stratigraphic parameters that most affect the geophysical signal allowing for a discussion of the geologic and stratigraphic controls of the sedimentary basin s gravity response

reconstruction of geologic bodies in depth associated with a sedimentary basin using gravity and magnetic data summary we present a comprehensive review of the most comm on gravity and magnetic interpretation methods to in depth retrieval of the geometry of two types of geologic bodies associated with a sedimentary basin 1 sedimentary basement relief and 2 salt bodies in reconstructing a basement topography we identify three groups of methods the automatic the spectral and the nonspectral methods the reconstruction of salt bodies geometries from gravity data usually uses the interactive forward modeling but recently gravity inversion methods have been developed to interpret this kind of geological environment

significance of 87 sr 86 sr ratios in the merensky cyclic unit of the bushveld complex in a number of mafic layered intrusions layers with platinum group element pge mineralization coincide with breaks in cumulus mineral composition and isotopic variation trends through the layered sequence1 2 for example in the bushveld complex in south africa abrupt increases in initial 87sr 86sr ratios occur at the ug 2 and merensky pegmatoid or reef horizons both of which are exploited for pges we report here the results of a detailed sr isotope study across the merensky unit and its immediate foot and hangingwall rocks which when considered together with new ideas on processes operating in magma chambers3 5 suggest that magma mixing and post cumulus infiltration of liquids displaced from below were important during crystallization of the merensky pegmatoid

gravity interpretation of sedimentary basins with hyperbolic density contrast the variation in the density of sediments with depth in a sedimentary basin can be represented by a hyperbolic function gravity anomaly expressions for a 2d vertical prism and an asymmetric trapezium with a hyperbolic density distribution are derived in a closed form these are used in inverting the gravity anomaly of a sedimentary basin with variable density firstly the basin is viewed as a series of prisms juxtaposed with each other the initial thickness of each prism is obtained from the gravity anomaly at its centre based on the gravity anomaly of an infinite slab with a hyperbolic density contrast these thicknesses are improved based on the differences between the observed and the calculated anomalies for an improved rate of convergence of the solution these thicknesses may alternatively be refined using the well known ridge regression technique secondly the basin is approximated by an asymmetric trapezium and its anomalies are inverted for the parameters of the trapezium using the ridge regression since this approximation serves to oversimplify the floor of the basin it must be used only when the sediment basement interface has minor undulations the results of a hypothetical case and two field cases the san jacinto graben california and the godavari graben southern india are presented in both field cases the interpreted depths are comparable with the real ones proving the validity of the assumption of a hyperbolic density distribution of the sediments in the two basins considered

north iberian temperature and rainfall seasonality over the younger dryas and holocene abstract several stalagmite records have yielded important but discontinuous insights into northern iberian climate since the last glacial here we present the first continuous iberian stalagmite based reconstruction of climate since the bolling allerod interstadial from a single stalagmite sample gar 01 from la garma cave cantabria the 13 5 ka gar 01 record provides the opportunity for replication continuation and aggregation of previously published records from northern spain the gar 01 record reveals shifts in oxygen isotope ratios that are inexplicable by appealing to a single control i e exclusively temperature rainfall amount etc herein we explore the potential role of rainfall and temperature seasonality shifts on the new 18o record using a simple monte carlo approach to estimate the seasonal distribution of rainfall and the annual temperature range at 100 year timeslices across the record this model is corroborated by intervals of monthly resolved laser ablation trace element data providing glimpses into past iberian seasonality shifts the most salient features of the modelled results include extremely dry younger dryas winters 12 9 11 6 ka bp and several intervals during the mid holocene with almost no summer rainfall e g at 4 2 and 9 0 ka bp by 1 6 ka bp a near modern rainfall seasonality was established according to the modelling results seasonal rainfall and temperature distribution variability can account for 95 of the record the model presented here provides a new tool for extracting critical missing seasonality information from stalagmite 18o records intervals where the model does not converge may represent transient climate anomalies with unusual origins that warrant further investigation

determination of crustal interface topography from potential fields we present a method for determination of the topography of an interface separating two uniformly but differently magnetized media the technique is developed within the framework of discrete linear inverse theory and exploits the quasi linearity of the problem to derive a simple efficient algorithm suitable for use on large gridded data sets variation of auxiliary parameters allows a suite of acceptable models to be produced rapidly these parameters can be appraised in light of available geologic and geophysical evidence because very large matrices are involved when large amounts of data are interpreted approximate resolution measures requiring no matrix inversion provide useful information concerning averages of the constructed topography

parabolic density function in sedimentary basin modelling for modelling sedimentary basins of large thickness from their gravity anomalies the concept of parabolic density function which explains the variation of true density contrast of the sediments with depth in such basins is introduced inbott s 1960 procedure the analytical expression the gravity anomaly of a two dimensional vertical prism with parabolic density contrast needed to estimate the gravity effect of the basin in modelling procedure is derived in a closed form two profiles of gravity anomalies one across san jacinto graben california and the other across tucson basin arizona where the density of sediments is found to vary with depth are interpreted

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

modelling of sedimentary basins from gravity anomalies with variable density contrast summary the decrease of density contrast with depth in sedimentary basins could be approximated by a quadratic function the sedimentary basin is viewed as a number of outcropping vertical prisms put in juxtaposition at each observation point equations are derived for the gravity anomaly of a vertical prism for a quadratic density function the initial model is obtained by calculating the thicknesses of the prisms at each station by an infinite slab formula the differences between the observed anomalies and the anomalies of the initial model at each station are used to modify the initial model a computer program is developed for initial estimates and refinement of the model the method is applied to interpret the gravity anomaly of san jacinto graben california where sediments filling the graben have a density contrast that can be approximated to a quadratic function finally the convergence of the method is discussed

gravity inversion of basement relief constrained by the knowledge of depth at isolated points we present an interpretation method for the gravity anomaly of an arbitrary interface separating two homogeneous media it consists essentially of a downward continuation of the observed anomaly and the division of the continued anomaly by a scale factor involving the density contrast between the media the knowledge of the interface depth at isolated points is used to estimate the depth d1 of the shallowest point of the interface the density contrast between the two media and the coefficients c1 and c2 of a first order polynomial representing a linear trend to be removed from data the solutions are stabilized by introducing a damping parameter in the computation of the downward continued anomaly by the equivalent layer method different from other interface mapping methods using gravity data the proposed method 1 takes into account the presence of an undesirable linear trend in data 2 requires just intervals for both rather than the knowledge of its true value and coefficients c1 and c2

comment on stoll h et al 2015 interpretation of orbital scale variability in mid latitude speleothem δ18o significance of growth rate controlled kinetic fractionation effects quat sci rev 127 215 228