gravity inversion of 2d bedrock topography for heterogeneous sedimentary basins based on line integral and maximum difference reduction methods based on the line integral li and maximum difference reduction mdr methods an automated iterative forward modelling scheme li mdr algorithm is developed for the inversion of 2d bedrock topography from a gravity anomaly profile for heterogeneous sedimentary basins the unknown basin topography can be smooth as for intracratonic basins or discontinuous as for rift and strike slip basins in case studies using synthetic data the new algorithm can invert the sedimentary basins bedrock depth within a mean accuracy better than 5 when the gravity anomaly data have an accuracy of better than 0 5 mgal the main characteristics of the inversion algorithm include 1 the density contrast of sedimentary basins can be constant or vary horizontally and or vertically in a very broad but ap rioriknown manner 2 three inputs are required the measured gravity anomaly accuracy level and the density contrast function 3 the simplification that each gravity station has only one bedrock depth leads to an approach to perform rapid inversions using the forward modelling calculated by li the inversion process stops when the residual anomalies the observed minus the calculated falls within an error envelope whose amplitude is the input accuracy level the inversion algorithm offers in many cases the possibility of performing an agile 2d gravity inversion on basins with heterogeneous sediments both smooth and discontinuous bedrock topography with steep spatial gradients can be well recovered limitations include 1 for each station position there is only one corresponding point vertically down at the basement and 2 the largest error in inverting bedrock topography occurs at the deepest points

new standards for reducing gravity data the north american gravity database the north american gravity database as well as data bases from canada mexico and the united states are being revised to improve their coverage versatility and accuracy an important part of this effort is revising pro cedures for calculating gravity anomalies taking into ac count our enhanced computational power improved ter rain databases and datums and increased interest in more accurately defining long wavelength anomaly components users of the databases may note minor differences be tween previous and revised database values as a result of these procedures generally the differences do not impact the interpretation of local anomalies but do improve re gional anomaly studies the most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conven tionally used geoid or sea level principal facts of gravity observations and anomalies based on both revised and pre vious procedures together with germane metadata will be available on an interactive web based data system as well as from national agencies and data centers the use of the revised procedures is encouraged for gravity data reduc tion because of the widespread use of the global position ing system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with north american and national databases anomalies based on the revised standards should be preceded by the adjec tive ellipsoidal to differentiate anomalies calculated us ing heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid

the geochemistry of major and selected trace elements in a forested peat bog kalimantan se asia and its implications for past atmospheric dust deposition abstract biogeochemical processes in a forested tropical peat deposit and its record of past atmospheric dust deposition were assessed using the vertical distribution of lithophilic and plant essential elements in a dated core profile from borneo se asia peat formation started 22 120 14c yr before present bp and ca mg mass ratios of the solid peat and very low ash contents indicate a strongly ombrotrophic character throughout the deposit implying that most of the inorganic fraction has been supplied exclusively by atmospheric inputs concentration profiles of mn sr and ca suggest a very minor influence of chemical diagenesis in the underlying sediments silicon ca mg p s and k show a strong and extended zone of enrichment in the top 200 cm of the profile indicating that biological accumulation mechanisms are much more extensive than in temperate peat bogs in the lower core sections where the element distribution is dominated solely by past atmospheric deposition average al ti ratios are similar to the upper continental crust ucc whereas fe is slightly enriched and si is strongly depleted this condition favors highly weathered tropical soil dust as the main inorganic mineral source significant correlation of al fe si s ca and ti with the lithophilic elements y and zr suggests that the distribution of these elements is controlled by sources of atmospheric mineral dust the ca mg ca k and mg k ratios of the collected rainwater samples are similar to the global average of continental rainwater and suggest a continental character for the site this is supported by the similarity of the average concentration of br mg ca and s to that in temperate continental and maritime bogs in switzerland and scotland the concentration profiles of si fe al and ti show distinct peaks within the profile implying enhanced dust deposition reduced rates of peat accumulation or possibly both owing to climatic changes during the holocene enhanced dust deposition between 10 830 and 9060 14c yr bp is tentatively interpreted as a younger dryas like event with dust fluxes of 10 8 mg m2 yr the variations in al ti and fe ti profiles suggest that mineral dust sources have been changing constantly during the holocene with local sources being dominant between 7820 and 9500 14c yr bp and long range transport derived most likely from china being important during the late pleistocene and early holocene and from 7820 14c yr bp to the present

seismically imaged shallow and deep crustal structure and potential field anomalies across the eastern dharwar craton south indian shield possible geodynamical implications abstract the time bound crustal evolution and subsequent deformation of the cuddapah basin nellore schist belt and eastern ghats terrain of eastern dharwar craton which have undergone sustained geodynamic upheavals since almost 2 0 billion years remain enigmatic an attempt is made here to integrate newly available potential field data and other geophysical anomalies with deep seismic structure to examine the generative mechanism of major crustal features associated with this sector our study indicates that the initial extent of the cuddapah basin sedimentation may have been much larger extending by almost 50 60 km west of tadipatri during paleoproterozoic period which subsequently shrank due to massive erosion following thermal uplift caused by sw cuddapah mantle plume below this region crust is still quite warm with moho temperatures exceeding 500 c similarly nallamalai fold belt rocks bounded by two major faults and extremely low gravity may have occupied a large terrain in western cuddapah basin also before their abrasion no geophysical signatures of thrusting are presently seen below this region and thus it could not be an alien terrain either in contrast nellore schist belt is associated with strikingly high positive gravity possibly caused by a conspicuous horst structure and up dipping mafic crustal layers underneath that resulted due to india east antarctica collision after the cessation of prolonged subduction 1 6 0 95 ga further the crustal seismic and gravity signatures would confirm presence of a totally distinct geological terrain east of the cuddapah basin but the trace of eastern ghats belt is all together missing instead all the geophysical signatures point out to presence of a proterozoic sedimentary terrain east of nellore schist belt it is likely that the extent of prorerozoic sedimentation was much larger than thought today in addition presence of a seismically detected gondwana basin over nellore schist belt apart from some recently discovered similar subsurface gondwana occurrences in intracratonic parts would indicate that dharwar craton was rifting even during gondwana period thereby challenging the long held view of cratonic stability

multiproxy evidence of little ice age palaeoenvironmental changes in a peat bog from northern poland little ice age lia climatic deteriorations have been abundantly documented in various archives such as ice lake sediments and peat bog deposits palaeoecological analyses of peat samples have identified these climatic deteriorations using a range of techniques for example palynology plant macrofossils testate amoebae or carbon isotopic analyses the use of inorganic geochemistry and the reconstruction of dust fluxes has remained a challenge in tracing the nature of lia climatic changes although the idea of enhanced erosion conditions and storminess is commonly discussed the conditions for dust deposition in peatlands over europe during the lia are rarely favourable because the natural forest cover over europe was much more important than nowadays preventing dust deposition this intense forest canopy masks the deposition of dust in peatlands in northern poland near the baltic shore the slowin skie blota area was deforested around ad 1100 ie just before the lia and therefore constitutes a key area for the reconstruction of lia climatic change with the support of a well constrained chronology climatic fluctuations are recorded in an ombrotrophic bog using inorganic geochemistry plant macrofossils and carbon isotopic analyses the reconstruction of lia climatic changes is in good agreement with other records from poland and ne europe however a c 50 year discrepancy can be observed between various records this discrepancy is possibly due to progressive time dependent cooling gradient from north to south europe

the relationship between seismic velocity and density in the continental crust a useful constraint summary plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa although a single linear relationship is often assumed in crustal gravity calculations because of the scatter whenever rocks of known seismic velocity are converted to density using this relationship a reduction is made to the resolving power of the resulting gravity calculation if these rocks reach thicknesses of more than a few kilometres then the uncertainties become significant when compared with the size of commonly observed gravity anomalies examples are considered from the north sea mississippi and carolina trough it is concluded that the use of a seismic velocity measurement as the only indication of rock density does not provide a useful constraint when attempting to reproduce observed gravity variations an appropriate model for isostatic compensation is probably the most important factor for successful predictions of crustal structure on the basis of gravity data

modeling the tectonic development of the tucano and sergipe alagoas rift basins brazil abstract the tucano and sergipe alagoas basins of northeast brazil form part of a regional extensional basin system that was operative during the mesozoic breakup of south america and africa with both basins developing on precambrian crust the synchronous development of the rift basins suggest that they are genetically linked in space and time whereas the offshore sergipe alagoas basin is characterized by a substantial thickness of post rift sediment the tucano basin either failed to develop or at least preserve a significant thickness of post rift sediment observed primary porosities within both pre and syn rift tucano basin sediment imply that significant post rift sedimentation never occurred failure to develop significant post rift subsidence has important thermal and mechanical implications for the reaction of the lithosphere to rifting and can be explained in terms of 1 depth dependent lithospheric extension in which intracrustal detachments allow the extension of the crust to be decoupled from the thinning of the lithospheric mantle 2 small rates of extension that allow the lithosphere to cool during rifting and or 3 lithospheric rifting during which the flexural strength of the lithosphere remains high with respect to points 2 and 3 forward modeling demonstrates that finite rifting rates over a 20 25 m y period are insufficient to cool the lithosphere to the point where post rift subsidence fails to develop an interesting complication arises when the flexural strength of the lithosphere remains large during rifting it tends to suppress the vertical motions of the lithosphere such as those engendered by the cooling of the lithosphere following rifting thereby reducing significantly the amplitude of the post rift subsidence thus the lack of post rift sedimentation within a basin does not necessarily imply that extension has been limited to the crust from our kinematic modeling of the tucano basin the observed negative free air and bouguer gravity anomalies 120 mgals suggest that the flexural strength of the lithosphere has remained sufficiently large to maintain the load of the sediment we can model successfully the observed tucano basin architecture and gravity anomaly irrespective of whether we assume depth dependent or depth independent lithospheric extension primarily because the flexural strength of the lithosphere tends to buffer or suppress the amplitude of the post rift subsidence in contrast the adjacent sergipe alagoas basin is associated with low amplitude gravity anomalies which may reflect a resetting of flexural strength during rifting prior to rifting however there was no appreciable elevation difference between the tucano and sergipe alagoas regions as might be induced by a hot spot for example implying that the flexural strength of the lithosphere was similar the total thickness of the syn and post rift sediments within the sergipe alagoas basin is about the same as the thickness of rift phase sediments in the tucano basin thus the amount of crustal extension responsible for each basin was similar however since the sergipe alagoas basin contains 4 5 km of post rift sediments lithospheric mantle thinning in this region must have been significantly greater than the crustal extension to overcome the effects of flexural bufferring the need for lithospheric mantle thinning to be greater that crustal extension in the sergipe alagoas region was also a result obtained by modeling the development of the ocean continent boundary between brazil and africa from our coupled kinematic and rheological model of lithospheric extension we predict that the ocean continent boundary should form preferentially at the location of greatest crustal and lithospheric mantle thinning that is within the region of maximum depth independent lithospheric extension the ocean continent boundary formed east of the sergipe alagoas basin despite the fact that the tucano basin represents the region of greatest crustal thinning if extension had been uniform with depth beneath these basins the ocean continent boundary should have formed in the tucano basin as it did not some form of intracrustal detachment appears to have been operative to reduce lithospheric mantle thinning beneath the tucano basin while enhancing it beneath the offshore regions of the sergipe alagoas basin

inversion of gravity field inclination to map the basement relief of sedimentary basins this paper presents a method to map the basement relief of homogeneous sedimentary basins that does not require the knowledge of the basin density contrast to reach this task the proposed method relies on the invariance of the inclination of the anomalous gravity field with the density contrast caused by models constituted by two homogeneous media this invariance occurs because the density contrast appears as a constant factor in both vertical and horizontal gravity components therefore being canceled out when these components are divided during the evaluation of the field inclination for such media the field inclination is independent of the density contrast thus allowing the source geometry reconstruction even when the density contrast is unknown as the inclination is rarely measured the gravity anomaly i e the field vertical component is initially used to compute the horizontal component of the gravity field by applying a suitable linear transform the field inclination is estimated from both components and then used to invert the source geometry by fitting the inclination values under the geologic constraints attributed to the causative sources in this process the density contrast is not required nor introduced as an unknown parameter in the formulated inverse problem moreover it can be estimated later by solving a new inverse problem where the source geometry determined from the inverted inclination is fixed and the constant density contrast is determined by fitting the gravity anomaly this paper applies such ideas to map the basement relief of a sedimentary basin and to estimate its density contrast the inversion is implemented by a random search procedure that excludes extreme models and imposes constraints that the unknown interface is smooth everywhere and assumes known depth values at isolated points investigated by wells the proposed technique is tested with synthetic noisy data from homogeneous and heterogeneous basin models and is applied to invert a gravity profile from the reconcavo basin brazil the results from the real data application are compared with well data and previously published results

seismic imaging across the eastern ghats belt cuddapah basin collisional zone southern indian shield and possible geodynamic implications abstract the evolutionary nature of the area encompassing cuddapah basin nellore schist belt and the ongole domain of eastern ghats belt south india which contains paleo neoproterozoic imprints of thick sedimentation intense magmatism subduction accretion and possible collision between eastern dharwar craton and east antarctica is still being debated an attempt has been made here to decipher the deep crustal structure and tectonics of this region by reprocessing deep seismic sounding data acquired earlier through the modeling of first arrival refraction and wide angle reflection travel times the derived crustal seismic velocity structure reveals that the intracratonic proterozoic cuddapah basin containing only 4 km thick sediment is bounded by two major faults the moho reaching fault detected on its eastern boundary demarcates cuddapah basin from the nellore schist belt although a deep normal fault is mapped within the nallamalai fold belt but no thrusting signatures are apparent almost all the crustal layers beneath nellore schist belt and the ongole domain of eastern ghats belt show distinct eastward dipping trend conforming to an upthrusted feature suggesting possible presence of a collisional suture besides the areas lying east of cuddapah basin appear to be an accreted orogenic terrain beneath which lower crust has upwarped substantially the entire stretch of the studied region is underplated by unprecedently thick 20 km high velocity 7 0 7 4 km s magma layer above the moho indicating strong crust mantle thermal perturbation and massive subcrustal erosion further an expression of a deep seated mantle thermal anomaly has also been found below the parnapalle region of the sw cuddapah basin beneath which deeper crustal layers have exhumed

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

records of terrestrial sulfur deposition from the latest permian coals in sw china abstract different sulfur fractions of low sulfur average 0 11 coals from the latest permian in southwestern china were analyzed isotopically at a high vertical resolution to examine the ramifications for potential terrestrial extinction mechanisms at the permo triassic boundary s org organic sulfur accounts for 87 of the total sulfur content on average while s py pyritic sulfur is very low 13 of the total sulfur content and ca 0 01 of the whole sample weight and relatively constant throughout the profile except for some insignificant additions in clay rich layers these indicate the possible differential contribution of local diagenesis during the early stages of peat accumulation the 34 s org values have a relatively narrow range from 1 5 to 7 6 while the 34 s py values have a wider range from 0 8 to 34 1 suggesting that pyrite was possibly formed in different stages and that there was negligible bacterial contribution to the primary organic sulfur fraction thus the organic sulfur signal in the coal is largely sourced from the original plant material and records temporal variations in the isotopic composition of the sulfur input to the coal forming environment the stratigraphically lower coal b3 has 34 s org values around 4 while the stratigraphically higher coal b2 which is closer to the permian triassic boundary has clearly higher 34 s org values ranging from 5 3 to 7 6 this change is most likely due to increased marine sulfate aerosol inputs into the coal forming peatland caused by coastline retreat during late permian transgression importantly there is no evidence in these discrete intervals of coal formation to indicate a dominant role of atmospheric inputs of isotopically lighter sulfur from either h 2 s released from euxinic oceans or volcanic so 2 this militates against theories that implicate such sources of sulfur in terrestrial extinction mechanisms at the end permian

bouguer gravity anomalies and occurrence patterns of kimberlite pipes in narayanpet maddur regions andhra pradesh india the narayanpet kimberlite field that lies southwest of hyderabad the capital city of andhra pradesh india hosts a number of kimberlite pipes these pipes appear to be randomly positioned however based on regional geologic structures revealed by bouguer gravity anomalies especially in a regional gravity map their locations form a definite pattern in the narayanpet maddur region regional bouguer gravity contours exhibit some features of geologic interest 1 the eastward convex regional contours show an increase in convexity from the maddur and kotakonda area on the east to narayanpet on the west 2 convexity is maximum in the vicinity of narayanpet where a large number of kimberlite pipes occur nearly parallel to the regional contour and 3 between narayanpet and the maddur kotakonda region kimberlite pipes occur at intersections of three eastward convex concentric zones with four lineaments one trending northeast southwest and the other three nearly east west these linear trends are be

dismembered ophiolites in paleoproterozoic nappe complexes of kandra and gurramkonda south india abstract the constitution and structural architecture of ophiolites is important in the understanding of cratonic growth through subduction collision accretion history in the precambrian terrains the nellore schist belt nsb sandwiched between the eastern ghats belt egb and the eastern dharwar craton south india is known to have deformed remnants of ocean plate stratigraphy ops as at kanigiri and kandra suggesting multiple cycle of ocean opening and closure in the paleoproterozoic mesoproterozic interval the outcrop details and structural architecture of the paleoproterozoic kandra complex with geochemical character of subduction related ophiolites is described and analyzed to better constrain the accretion collision history along the southeastern margin of the indian craton imbricate thrust slices between kandra and arimanupadu host slivers of hornblende metagabbro thick massive to pillowed metabasalt sheets sheeted meta dolerite dykes and thin metapsammite and metapelite interstratified with metabasalt comparable to layer 2a of oceanic crust contractional deformation in interlayered metabasalt and quartzite around kandra is accommodated by south dipping imbricate thrust systems and n ne vergent folds the wnw trending thrust system with dominant tectonic transport toward northeast is oblique to overall n s trend of the nsb or the egb further east intercalated metabasalts deep water turbidites and thin metacherts around gurramkonda are deformed into sw vergent imbricate thrust system here occurrence of metabasalt sheets along individual thrusts suggest syntectonic emplacement of some basalts as the subducted and scraped upper oceanic crust was incorporated in the acrcetionary prism the rock sequences around kandra and gurramkonda comprising incomplete ops are tectonically stacked over granites of the eastern dharwar craton margin bivergent thrust systems around kandra possibly root into a detachment separating layers 1 2 from more rigid deeper layers cf layer 3 of oceanic crust as indicated by absence of significant volume of ultramafic rocks at the current outcrop level

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

an 8000 year record of sea level change from grain size parameters data from beach ridges in denmark the low energy beach ridge system near the town of jerup in the extreme north of denmark was sampled at 154 sites on a pattern of one per ridge intervals of 50 51 years starting about 7800 bp

characterization and quantification of inorganic constituents of tropical peats and organic rich deposits from tasek bera peninsular malaysia implications for coals abstract since the carboniferous tropical latitudes have been the site of formation of many economic coal deposits most of which have a restricted range of mineralogical composition as a result of their depositional environment climatic conditions and diagenesis mineralogical and microscopic investigations of tropical peats from tasek bera peninsular malaysia were performed in order to better understand some of these factors controlling the nature distribution and association of inorganic matter in peat forming environments distribution and nature of the inorganic fraction of peat deposits give insight into the weathering conditions and detrital input into the mire system because the inorganic composition of peat deposits is determined by plant communities height of water table and climate the results of the quantitative and qualitative analysis can be used to reconstruct palaeoclimatic conditions tasek bera is a peat accumulating basin in humid tropical malaysia with organic deposits of low to high ash yield and thus representative of many ancient peat forming environments clay minerals dominate the mineralogical composition of the peat and organic rich sediments while quartz and clays dominate the underlying siliciclastic deposits kaolinite is the most abundant clay mineral in the organic deposits with minor amounts of illite and vermiculite particle size analyses indicate that 50 of the inorganic detrital fraction is 75 of the ash constituents as a consequence the vegetational communities make an important contribution to the inorganic and overall ash composition of peats and coals the ash content of the often inundated peat consists on average of 10 opaline silica from diatoms and sponge spicules while the ash of the top deposits may have up to 50 biogenic silica hence al and si hydroxides and the opaline silica from diatoms and sponges represent a large repository of al and si which may form the basis of mineral transformation neoformation and alteration processes during coalification of the peat deposits as a result most coal deposits from paleotropical environments are anticipated to have little to no biogenic inorganic material but high amounts of secondary clays such as kaolinite detrital kaolinite resilisified kaolinite or desilisified gibbsite or illite and various amounts of detrital and authigenetic quartz

pore water indicators of rainwater dominated versus groundwater dominated peat bog profiles jura mountains switzerland the dominant inorganic anions and cations and dissolved organic carbon have been measured in the pore waters expressed from peat cores taken from two sphagnum bogs in the jura mountains of switzerland etang de la gruyere egr consists of 6 m of peat representing more than 12 000 yr of peat formation while at la tourbiere de genevez tge 1 5 m of peat have accumulated over the past 5 000 yr the pore water analyses of the core taken at egr show that the first 100 cm of the core are influenced only by atmospheric inputs the ph of the pore waters is constant 3 9 0 1 with depth relative to the average composition of rainwater in this area na is enriched throughout the pore water profile k is neither enriched nor depleted mg2 is significantly depleted in the deeper pore waters and ca2 strongly depleted throughout the profile the dominant process affecting the cations in these waters is ion exchange with the peats behaving like a simple cation exchanger with ion preference decreasing in the order ca2 mg2 h k na in contrast at tge the ph increases from ph 4 at the surface to ph 5 at 80 cm the cl and k concentrations are up to 10 times higher than rainwater values because of mixing of the bog pore water with nearby groundwaters the mg2 and ca2 concentrations increase with depth to concentrations up to 10 times higher than rainwater values mainly because of the increasing importance of mineral dissolution within the profile

u pb zircon chronology of the pangidi kondapalle layered intrusion eastern ghats belt india constraints on mesoproterozoic arc magmatism in a convergent margin setting abstract the pangidi kondapalle layered intrusion is emplaced within high grade supracrustal rocks in the southern sector of the eastern ghats granulite belt proximal to the south eastern periphery of the indian plate this layered complex consists mainly of anorthosites and gabbronorites with pyroxenite cumulates containing orthopyroxenites and chromitites in a regressive intrusive sequence here we report laser ablation icp ms data and ree geochemistry of zircons from three co spatial anorthositic bodies in this complex our results show mean 207 pb 206 pb ages of 1634 18 ma mswd 0 55 for the anorthosite from pangidi two anorthosite samples from kondapalle yield mean 207 pb 206 pb ages of 1628 36 ma mswd 0 54 and 1693 110 ma mswd 5 5 the zircons from all the anorthosite samples show high ree contents prominent hree enrichment and a conspicuous positive eu anomaly suggesting a common melt source the prominent mesoproterozoic ages revealed from our u pb dating of zircons from these layered complexes suggest subduction related magmatic underplating in a convergent margin setting associated with the amalgamation of the columbia derived fragments within the neoproterozoic supercontinent

simultaneous 3d depth to basement and density contrast estimates using gravity data and depth control at few points we have developed a gravity inversion method for simultaneouslyestimatingthe3dbasementreliefofasedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack assumingpriorknowledgeaboutthebasementdepthatafew points thesedimentarypackisapproximatedbyagridof3d vertical prisms juxtaposed in both horizontal directions of a right handed coordinate system the prisms thicknesses representthedepthstothebasementandaretheparametersto be estimated from the gravity data to estimate the parameters defining the parabolic decay of the density contrast with depthandtoproducestabledepth to basementestimates we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes we applied our method to synthetic data from a simulated complex 3d basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variationwithdepth theresultsprovidegoodestimatesofthetrue parameters of the parabolic law of density contrast decay with depth and of the basement relief inverting the gravity data from the onshore and part of the shallow offshore almadabasinonbrazil snortheasterncoastshowsgoodcorrelationwithknownstructuralfeatures

estimating free parameters in 2d inversion example of gravity inversion in a rifted basement abstract we advance a principle directed to assigning numerical values to free parameters usually present in inversion methods it may be formulated as optimum estimates of free parameters in an inversion procedure must lead in tests using synthetic data to solutions whose geometrical expression reflects the main qualitative or semiquantitative geological characteristic of the study area to this end the interpreter should i specify a typical anomalous source geometry which incorporates the most relevant geological information for the study area ii compute the corresponding gravity anomaly and iii invert the anomaly for the source geometry finding the numerical values of the free parameters that lead to a solution closest to the typical source application of the above methodology to synthetic and real data from the basement relief of a rift basin has asserted its efficacy

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

deep pass an aeromagnetic data filter to enhance deep features in marginal basins abstractan aeromagnetic data filter was tested as a tool in enhancing the magnetic responses of deep sources associated with marginal basins our approach consists in amplifying the responses of magnetic sources which extend through the continental slope and continental rise this amplification compensates for the magnetic response attenuation over the continental slope as a result of 1 the seaward increase of the distance between the source and the magnetometer and 2 the seaward decrease in the volume of sources within the continental crust to amplify the source response we multiply the total field anomaly at a given location by the exponential of the bathymetric depth at the same point tests on synthetic and real data showed that the filter was able to recover the locations of linear magnetic responses not clearly seen in the total field anomaly map when compared with the analytic signal amplitude and the total horizontal derivative filters the proposed filter proved to be complementary in enha

mesoproterozoic ophiolitic melange from the se periphery of the indian plate u pb zircon ages and tectonic implications abstract the kanigiri melange within the proterozoic nellore khammam schist belt in southern peninsular india includes ophiolitic fragments that represent the remnants of an oceanic plate the ophiolitic units were accreted along a ne trending suture that juxtaposes the proterozoic eastern ghats granulite belt eggb against the archean nellore schist belt of the dharwar craton the ophiolite components in the kanigiri melange include plagiogranites and gabbros which show mutually intrusive relations indicating their coeval nature we report laser ablation icp ms age data and ree geochemistry of zircons from the gabbro and granite the zircons from both gabbro and granite show high ree contents prominent hree enrichment and a conspicuous negative eu anomaly suggesting a common melt source zircon ree abundances and normalized patterns show little intersample and intrasample variations u pb dating of the zircons reveals prominent mesoproterozoic ages for the plagiogranite with the ca 1 33 ga age of the kanigiri ophiolitic melange offering important clues for arc continent collision during the final stages of amalgamation of the columbia derived fragments within the neoproterozoic supercontinent assembly

origin of beach ridges and swales abstract sandy beach ridges occur in four main categories 1 swash built 2 settling lag 3 eolian 4 storm surge ridges in the first two classes are geometrically regular only a few tens of centimeters above adjacent swales and commonly in ridge sets and systems tens to hundreds of ridges each individual sets of 5 25 ridges tend to stand 0 5 m to 2 m above or below adjacent sets ridges in the third and fourth classes do not have these characteristics do not occur in sets and are generally not suitable for detailed historical studies no one of these ridges is the same as the storm built berm which is almost never preserved swash built sandy beach ridges have diagnostic 1 map spacing 2 accretion rate 3 periodicity 4 crossbedding and 5 granulometry the last two indicate fair weather waves on a sandy beach in contrast with settlinglag ridges postma style which have the same external geometry but which were deposited without important wave work and in contrast with storm built berms generally seen on eroding coasts but rarely or never in beach ridge plains the grain size kurtosis of beach sand is an excellent index to near shore wave energy density changes in kurtosis at ridge set boundaries mark changes in long term wave energy density hence in sea level the latter can be deduced also from set height differences and from spacing differences periodicity is typically 30 60 years map spacing 25 50 m and accretion rate fairly close to 1 m yr a few ridge sets with intervals of 3 7 10 12 or 18 19 years have smaller spacings this is not what can be done if each ridge is built by one storm if each ridge had been built by one storm wide beach ridge plains like one in denmark dating from about 11 700 yr b p would have been formed in the last 30 50 years at accretion rates of hundreds of meters per year instead each swash type sandy beach ridge was made by a sea level rise and fall couplet amplitude 5 30 cm the swale marks the lower position this mechanism reflects the fact that the transverse profile from beach to sea is gently concave upward with maximum curvature close to shore this is a shape which is out of adjustment with the shoaling wave system shortly after a small sea level change settling lag ridges were built without waves hence the ridge and swale sequence in this case cannot be attributed to waves either fair weather or storm these ridges show the same historical pattern as do swash built ridges this fact suggests that both were controlled by the same mechanism sea level change

thin tephra layers in peat revealed by x radiography x radiography has been found to provide a rapid economical non destructive method of locating very thin fine grained tephra of icelandic origin in scottish peats tephra layers form time parallel marker horizons or isochrones that are of great archaeological significance because they cover large areas offer precise chronological control for associated material and occur at times of significant cultural and environmental changes not all of the discrete deposits of recent volcanic fallout in scotland are sufficiently dense to show clearly on x radiographs but those which do provide particularly clear easily located marker horizons with many applications in palaeoenvironmental studies the tephra layer in caithness produced by fallout from a c 4000 by eruption of hekla provides a particularly good example of the use of x radiography to locate volcanic ash the method also reveals other structures of archaeological and palaeoenvironmental significance butler 1992 journal of archaeological science 19 151 161

the structure and origin of prydz bay and macrobertson shelf east antarctica abstract a marine geophysical survey in early 1982 conducted by the australian bureau of mineral resources indicated that much of prydz bay is underlain by a sedimentary basin severe seismic multiples preclude an accurate estimate of total sediment thickness but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km the trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall nne trend roughly orthogonal to the continental margin in the south of prydz bay two series of seismic sequences are evident separated by a mildly erosional unconformity the lower series ranges from poorly to well stratified has minor folding and faulting and probably derives from continental and perhaps shallow marine pre breakup sediments the upper series is generally well stratified and prograded near the shelf edge it probably represents shallow marine post breakup sediments the seabed is distinctly unconformable with the underlying sediments implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the amery ice shelf and that present sedimentation rates are very low possible thin moraines or tillites in the northeast part of the prydz bay are also attributed to these glacial advances the continental slope and rise sedimentary section ranges from at least 3 km thick off prydz bay to thin off the macrobertson shelf to the west reflecting the more prolific sediment source in prydz bay the deep water section includes several seismic sequences the most distinctive being interpreted as sheet volcanics and turbidite fans the deepest visible unconformity is locally strongly faulted and may separate the pre breakup and post breakup sediments indo antarctic breakup has been tentatively dated as early neocomian 130 ma and the e w orientation of the resultant antarctic coast invites interpretation of the lambert glacier prydz bay structure as a possible failed rift arm of a triple junction direct information on the age and nature of the sediments under prydz bay is lacking but permian continental sediments cropping out at beaver lake to the south may correspond to the lower pre breakup series this interpretation gains some support from analogies with fault bounded intracratonic basins in india which contain permian to triassic continental strata and which may have been juxtaposed prior to breakup the upper series probably consists of upper cretaceous and cainozoic sands and shales with moraines or tillites at the top of the section

the last termination in the south indian ocean a unique terrestrial record from kerguelen islands 49 s situated within the southern hemisphere westerly belt the awareness of the significance of the southern ocean in the earth s climate system has become increasingly obvious the deglacial atmospheric co2 rise during warming periods in antarctica has been attributed to co2 ventilation from the deep ocean caused by enhanced upwelling around the antarctic divergence it has been hypothesized that more intense southern hemisphere westerly winds aligned with the antarctic circumpolar current due to a southward shift of the wind belt from its last glacial maximum equator ward position are the main drivers reconstructions of past changes in atmospheric circulation in the southern hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results for obvious reasons most terrestrial records originate from southern south america and new zealand here we present a terrestrial record from the indian sector of the southern ocean from kerguelen islands located at 49 s a peat record is investigated using a multi proxy approach pollen and plant macrofossils magnetic susceptibility xrf analyses biogenic silica content rock eval6 analysis and humification degree peat accumulation starts at about 16 000 cal yr bp with relatively warm and dry conditions the most prominent change in our proxy data occurs at 13 600 cal yr bp when peat ponds were established on the peat surface resulting in lacustrine type deposits as a result of very high humidity and with proxies implying very windy conditions within chronological uncertainties this onset coincides with the onset of the so called oceanic cold reversal based on the deuterium excess data in the epica dome c ice core record kerguelen islands are located in the moisture source area of dome c and a change in atmospheric circulation at that time could explain both records around 12 900 cal yr bp at the end of the antarctic cold reversal pond lake sediments give way to more peaty deposits with proxies suggesting slightly drier less windy and probably warmer conditions kerguelen islands became less influenced by the southern hemisphere westerly winds and these conditions were amplified during the early holocene climate optimum as found in antarctic ice core records

holocene vegetation climate and history of a raised bog complex northern new zealand based on palynology plant macrofossils and tephrochronology a holocene history of vegetation climate and ombrogenous mire development is presented from pollen and plant macrofossil analyses of sediments at kopouatai bog a large raised restiad bog in northern new zealand tephra layers of established ages supplemented by numerous radiocarbon dates provide a secure chronology the earliest peats overlying last glacial sediments and dated at c 11700 radiocarbon years bp with extensive accumulation after c 10360 bp are dominated by pollen of warm temperate podocarp angiosperm forest indicating a moist mild early holocene climate the bog began as a series of small soligenous mires within lowland podocarp dominated swamp forest but was mostly oligotrophic by c 8500 bp peat accumulation rates have varied spatially and temporally averaging 0 9 mm yr 1 in central and southern areas the deposition of deltaic muds in the northern part of the bog accompanied a marine transgression c 6500 5000 bp while elsewhere an associated groundwater table rise result

on new standards for reducing gravity data the north american gravity database the paper new standards for reducing gravity data the north american gravity database which summarizes revisions to the north american gravity database is testimony to the importance of gravity data reduction although the methods described by the authors establish the north american gravity database geophysicists all over the world will take these methods as models to establish such databases for their respective regions or countries as a result it is important for the geophysical community to consider the benefits and drawbacks of these methods

behaviour of sulphur during diagenesis of a maritime ombrotrophic peat from yell shetland islands uk abstract surface water pore water vegetation and peat cores were sampled from a waterlogged ombrotrophic peat bog on the shetland isles uk and analysed for different s forms and their isotopic composition in an attempt to elucidate the biogeochemical processes affecting s during peat diagenesis surface waters show that inputs of s to the peat have a maritime dominated isotopic composition close to 20 cdt uptake of s by vegetation introduces a 10 shift in 34s from these input values below the vegetation layer and down to 18 cm depth bacterial so 4 2 reduction is the major control on s species distribution and isotopic composition within the solid peat and pore waters in this part of the peat preferential reduction of 32so4 in pore water during metabolism produces isotopically light sulphide which is incorporated into the solid phase in both inorganic and organic forms while pore water so 4 2 becomes enriched in 34s from 18 to 28 cm organic s content falls relative to c and residual organic s becomes 34s enriched indicative of mineralization of organic s a process which releases isotopically light s to the pore waters still deeper in the core 28 to 50 cm bacterial reduction of pore water so 4 2 now enriched in 34s results in addition of isotopically heavy s to the solid phase limited pore water data suggest that below 50 cm mineralization reactions again release s from the organic fraction of the peat

early proterozoic melt generation processes beneath the intra cratonic cuddapah basin southern india early proterozoic tholeiitic lavas and sills were emplaced during the initial phase of extension of the intra cratonic cuddapah basin southern india ar 40 ar 39 laser fusion determinations on phlogopite mica from the tadpatri fm mafic ultramafic sill complex constrain the age of the initial phase of extension and volcanism in the basin at 1 9 ga despite their early proterozoic age the igneous rocks are unmetamorphosed undeformed and remarkably fresh they exhibit a wide range in mgo contents 4 28 wt and have undergone varying degrees of accumulation or crystal fractionation variable la nb ratios 1 2 3 7 and epsilon nd values 1 to 10 suggest that some but not all of the mafic rocks have been affected by crustal contamination this appears to have taken place in magma chambers at similar to9 kbar i e the base of the continental crust forward modelling of major and trace elements fe and nd and inverse modelling of rare earth elements suggest that the primary cuddapah melts were generated by similar to10 15 partial melting of a lherzolite mantle source this corresponds to a mantle potential temperature of similar to1500degreesc the thickness of the mechanical boundary layer predicted by the geochemical modelling is 70 km with a minimum initial lithospheric thickness of 120 kin this corresponds to a stretching factor of 1 6 1 8 richter s 1988 secular cooling model for the earth predicts that at 1 9 ga the ambient mantle had a potential temperature of similar to1500degreesc i e similar to200degreesc hotter than phanerozoic mantle if the cooling model is correct then proterozoic lithospheric stretching and mantle melting beneath the intra cratonic cuddapah basin could have been caused by passive rather than active rifting

a peat bog record of natural pre anthropogenic enrichments of trace elements in atmospheric aerosols since 12 370 14 c yr bp and their variation with holocene climate change abstract a peat bog in the jura mountains switzerland provides a continuous record of peat accumulation since 12 370 14 c yr bp periods of enhanced soil dust deposition 10 590 14 c yr bp 8230 14 c yr bp and after 5320 14 c yr bp are characterized by strongly elevated ti sc and zr sc ratios which imply an increase in the abundance both relative and absolute of heavy minerals such as ilmenite and zircon with respect to trace elements such as cu zn as cd sb and au the m sc ratios are at their lowest and often approach crustal values during periods of enhanced soil dust deposition the lowest rates of atmospheric deposition of soil dust date from 8030 to 5320 14 c yr bp corresponding to the holocene climate optimum but here many trace elements exhibit their greatest natural enrichments the average enrichment factor calculated using sc as the reference element and normalizing to crustal abundance was zn 4 1 1 4 sb 4 8 1 4 cu 8 8 3 3 as 14 9 3 2 au 53 9 25 1 and cd 357 4 53 8 these enrichments cannot be explained by chemical diagenesis within the deeper sections of the peat profile during or subsequent to peat formation but rather reflect the chemical composition of airborne material supplied to the surface layers of the bog at the time of deposition the enrichments of trace metals in ancient peats relative to crustal abundance most likely reflects the natural enrichment of these elements in the fine fraction of soils during rock weathering periods of enhanced soil dust deposition such as the younger dryas cold climate phase 10 590 14 c yr bp are characterized by reduced vegetation cover greater exposed soil surface and higher wind strengths these conditions promote the transport of locally derived soil materials of greater particle size lower concentration of trace metals and m sc ratios approaching crustal values during the holocene climate optimum vegetation cover was extensive and with lower wind strengths and a reduction in erodible soil materials long range transport of soil dust became relatively more important to the soil dust inventory of the bog soil dust particles in this size class are characterized by strong enrichments of a wide range of trace elements at the end of the holocene optimum dust fluxes increased once again due mainly to soil erosion resulting from the combined effects of human activities tillage and the climatic deterioration at the beginning of the neoglaciation period this promoted the supply of local more coarse soil particles with m sc ratios approaching those of crustal rocks while biological cycling and volcanic emissions probably also contributed to the atmospheric supply of many of these elements in the pre anthropogenic past these contributions appear to be less important than the chemical weathering physical fractionation and atmospheric transport of soil dust particles

gravity inversion of 2d basement relief using entropic regularization we have developed a gravity interpretation method for estimating the discontinuous basement relief of a sedimentary basin the density contrast between the basement and the sediments is assumed to be known and it could be either constant or vary monotonically with depth the interpretation model consists of a set of vertical juxtaposed prisms whose thicknesses are the parameters to be estimated we used the entropic regularization that combines the minimization of the first order entropy measure with the maximization of the zeroth order entropy measure of the solution vector we validated the method by applying it to synthetic data produced by a simulated basin bordered by high angle step faults we obtained a good definition of the relief particularly of the discontinuities we also applied the method to a profile across the buyuk menderes valley in west turkey and obtained a solution exhibiting a gravity fault with large slip on the northern border of the valley when applied to the interpretation of a discontinuous basement relief the method has a better performance than the global smoothness method it is comparable to the weighted smoothness method but it does not require the a priori knowledge about the maximum basin depth

proterozoic orogens in southern peninsular india contiguities and complexities abstract the precambrian terranes of southern peninsular india have been central to discussions on the history of formation and breakup of supercontinents of particular interest are the proterozoic high grade metamorphic orogens at the southern and eastern margins of the indian shield skirting the 3 4 ga dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics but also carry imprints of the tectonic framework related to the assembly of the major neoproterozoic supercontinents rodinia and gondwana these proterozoic orogens are described as southern granulite terrane sgt in the southern tip and the eastern ghats mobile belt egmb in the eastern domains of the peninsula the contiguity of these orogens is broken for a distance of 400 km and disappears in the bay of bengal these orogens expose windows of middle to lower crust with well preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems some of which represent collisional sutures the sgt and egmb carry several important features such as fold thrust tectonics regional granulite facies metamorphism of up to ultrahigh temperature conditions in some cases multiple p t paths development of lithospheric shear zones emplacement of ophiolites presence of alkaline and anorthositic complexes development of crustal scale flower structures transpressional strains and reactivation tectonics a heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified both egmb and sgt share a common transpressional deformation history during the latest neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics our synthesis of the spatial distribution geometry kinematics and the transpressional strain of the shear zone systems provides insights into the tectono metamorphic history of the proterozoic orogens of southern india and their contiguity and complexities recent understanding of subduction accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in earth history although the major and common structural architecture was built during the final assembly of the gondwana supercontinent

late holocene sea level changes from grain size data evidence from the gulf of mexico grain size kurtosis of sand in the beach ridge plain of st vincent island florida is numerically reasonably uniform within any one ridge set but changes at important set boundaries where these changes are found there are also differences in air photo and field appearance and in measured ridge set heights sets with low kurtosis 3 0 stand topographically high and sets with higher values 3 6 stand low study of wave energy levels and beach sand grain size kurtosis along modem gulf of mexico beaches shows that kurtosis is an inverse function of surf zone energy density storms and storminess for the study area can be evaluated in the framework of the selective transport model of may 1973 the actual data sequence is greatly different from what is required by the model and therefore storms and storminess cannot be invoked to explain the history of the area instead the data sequence matches results predicted by the model for small sea level changes storms and tectonism do not have appropri

crustal structure of the west bengal basin india from deep seismic sounding investigations summary basement and sub basement crustal configuration of parts of the west bengal basin has been delineated from inverse and forward modelling of refraction and wide angle reflection data obtained along two east west profiles a beliatorburdwan bangaon profile 1 about 180 km long and b gopali tamluk port canning profile 2 about 140 km long the study has revealed the existence of four groups of prominent refractors velocities 1 7 2 1 km s 2 7 3 2 km s 3 74 2 km s and 4 6 5 3 km s overlying the crystalline basement with a velocity of 5 8 6 2 km s rajmahal traps velocity 4 6 5 3 km s averaging 4 8 km s l occur beneath the base of the tertiary sediments in the middle parts of the profiles the presence of sub trappean gondwanas is also indicated from the wide angle reflection modelling supported by deep well lithological information in general depth to the basement is found to increase from west to east with a maximum depth of around 10 to 11 km at the extreme eastern parts of the profiles a basement upwarp with a sharp flexure west of bishnupur on profile 2 in combination with the fault west of shantipur on profile 1 possibly brings into focus the regionally extending nne ssw hinge zone a low velocity layer lvl of about 2 to 3 km thickness velocity 5 6 5 8 km s has been inferred in the upper crust in this area in general the thickness of the upper including the sedimentary column and the middle 6 4 6 6 km s velocity parts of the crust is found to be larger thickness varying between 22 and 27 km than the lower crustal column interval velocity 6 8 7 0 km s l with a thickness of 5 to 10 km the moho lies at varying depths of 36 to 26 km along profile 1 with a prominent domal feature of about 40 km width between satgachia and west of shantipur in the middle part of profile 2 the moho occurs at depths of 32 to 34 km with a mild flexure east of tamluk configuration of the moho indicates that the crust is more akin to continental in nature in the western and middle parts of the basin whereas significantly thinned continental crust is indicated in the eastern and southeastern parts

a pollen based pseudobiomisation approach to anthropogenic land cover change the degree of anthropogenic modification of land cover through the mid to late holocene is of significant interest for archaeologists climate modellers and conservation ecologists amongst others spatially extensive pollen data provide an appropriate resource for the reconstruction of land cover change however traditional simple methods e g the ap nap ratio do not provide the degree of detail required for these user groups a range of more sophisticated methods have been developed e g mechanistic model based methods but they require a high degree of understanding of the pollen vegetation relationship which is resource and time consuming this paper proposes a method of intermediate complexity by which major land cover changes can be assessed for individual sites and regions a pseudobiomisation approach is used in which pollen taxa are assigned to different land cover classes lcc and the sum of adjusted pollen proportions for each class used to determine an lcc affinity score for individu

late quaternary volcanic ash in the peatlands of central alberta three distinct volcanic ash layers were identified in peat deposits through visual microscopic and chemical means these layers were related to known volcanic events through the 14c dating of 34 peat samples the upper layer was probably bridge river ash deposited about 2350 years bp the middle layer was possibly st helens y tephra deposited around 3400 years bp the lower ash was related to mazama tephra deposited about 6600 years bp ash enriched layers were formed in the accumulating peat as aerial deposition of tephra occurred often for several hundred years before and after the presumed main eruption as shown by 14c dates and peat accumulation rates this implies periodic eruptions by the volcanoes not all of which produced distinct ash layers in areas distant from the source redeposition from wind eroded beds of mazama ash during the dry postglacial climatic maximum is a possibility

petrological and geochemical characterization of proterozoic ophiolitic melange nellore khammam schist belt se india abstract the ophiolitic melange occurs close to a major fault within the metavolcanics of kanigiri area in the western margin of the khammam nellore schist belt andhra pradesh india the unique feature of kanigiri melange is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust the ophiolitic melange is composed mainly of blocks of variably deformed and metamorphosed pillow basalts serpentinized ultramafic rocks meta gabbros cherts and pelagic sediments in a pervasive scaly argillite matrix the melange has a tectonic contact with a granite intrusion and numerous thrust faults cut across the melange exposures primary magmatic features such as drainage cavities in pillow basalts magmatic layering in gabbros and clinopyroxene cumulates in ultramafic rocks are well preserved in low strain domains mafic components enclosed in the melange are characterized by low pressure secondary mineral assemblages retrograded from amphibolite down to greenschist facies as commonly observed in subducted and exhumed orogens all amphiboles in the studied fragments are calcic and cluster in the range from winchite actinolite to hornblende amphibole compositions are characterized by al 2 o 3 2 4 13 8 feo 5 13 k 2 o 0 04 0 7 and x mg 0 67 0 77 the metabasalt and wherlite samples exhibit light rare earth element lree enriched patterns and negative high field strength element hfse zr and ti consistent with a suprasubduction zone geodynamic setting a notable feature of both metabasalt and wherlite samples is their pronounced negative ce anomaly and a positive eu anomaly as observed in a number of modern island arc suites as the petrological features and the geochemical characteristics of the remnant fragments we analyzed in this study are reminiscent of their phanerozoic ophiolite counterparts we suggest that these rocks were derived from a proterozoic oceanic plate belonging to a suprasubduction ophiolite assemblage subduction zone geochemical signatures and ophiolite like crustal lithologies in the study region are consistent with the accretion of juvenile oceanic fragments to the pre existing continental blocks through a forearc continent collision

seismic imaging of the proterozoic cuddapah basin south india and regional geodynamics abstract cuddapah basin has been believed to be one of the largest intra cratonic proterozoic sedimentary basins of india situated in the eastern part of the dharwar craton of the south indian shield which is magmatically infested and contain thick column of sediments its overall sedimentary thickness as well as the nature of crustal evolution has remained enigmatic based on deep seismic sounding and other geological studies in the past it was perceived that this basin may contain as much as 10 12 km thick sediments the results of our present analysis derived up to a depth of 12 km reveals five layered upper crust associated with velocities i 4 50 km s ii 5 20 5 30 km s iii 5 50 5 80 km s iv 5 85 6 00 km s and v 6 40 km s out of which second and third layers correspond to upper and lower cuddapah sediments the results suggest the presence of only 4 0 km thick sediments in the deepest part of the basin below the nallamalai fold belt which has its implications in the developmental history of the basin a thermal driving force was invoked by earlier workers to account for estimated 10 12 km thick sediments however the present estimate of only 4 km basement depth in the cuddapah basin shows that the role of the thermal driving force may be marginal particularly in the deeper eastern cuddapah as isostatic subsidence due to sedimentary accumulation alone is enough to explain the basin depth further a basement sag of about 10 km would have logically needed lateral extension of the order of several hundreds of kilometers however as our present estimate of the sediment thickness gets reduced from earlier 10 km to only 4 km the size of the basin 44 500 km 2 would be in conformity with isostatic subsidence due to sedimentary accumulation hypothesis the structural features derived from present analysis like maximum depth observed near the thrust suture on the basin margin from where it decreases away from it its association of shallow marine sediments the arcuate shape of the basin along with its areal dimension resembles foreland basin between continent continent collisions

emplacement and deformation of the vinukonda meta granite eastern ghats india implications for the geological evolution of peninsular india and for rodinia reconstructions abstract the u pb and rb sr systematics of zircon populations from two samples and biotite white mica pairs from four samples constrain the time of emplacement and deformation of the vinukonda meta granite eastern ghats india sm nd and lu hf systematics of whole rock samples provide information on the magma source and its evolution the granitic magma intruded into granitic gneisses of the vinjamuru domain krishna province andhra pradesh india which were already deformed and metamorphosed at epidote amphibolite facies peak conditions consistent sm nd and lu hf whole rock model ages suggest an isotopically homogeneous crustal source and a multi stage evolution of the granitic magma u pb analyses of prismatic zircon multi grain fractions define two discordias with identical upper intercepts at 1588 4 7 1 and 1589 7 5 7 ma interpreted to date magma emplacement rb sr ages of strongly annitic biotite xmg 0 07 0 20 and phengitic white mica 3 13 3 23 si pfu show a complex age pattern due to low temperatures during deformation the rb sr system only partly re equilibrated in biotite synkinematically grown phengitic white mica evidence a low grade metamorphic overprint at 501 474 ma the deformation was associated with w nw directed nappe stacking which caused the actual geological configuration of southern andhra pradesh with the arcuate nallamalai fold belt as most prominent feature regional considerations lead to the proposition that thrusting in the krishna province is the expression of intracratonic deformation in response to the amalgamation of the eastern ghats rayner province terrane with subcontinental india in early palaeozoic time

structure of alluvial valleys from 3 d gravity inversion the low andarax valley almeria spain test case this paper presents a gravimetric study based on 382 gravimetric stations in an area about 32 km2 of a nearly flat basin the low andarax valley this alluvial basin close to its river mouth is located in the extreme south of the province of almeria and coincides with one of the existing depressions in the betic cordillera the paper presents new methodological work to adapt a published inversion approach growth method to the case of an alluvial valley sedimentary stratification with density increase downward the adjusted 3d density model reveals several features in the topography of the discontinuity layers between the calcareous basement 2 700 kg m3 and two sedimentary layers 2 400 and 2 250 kg m3 we interpret several low density alignments as corresponding to se faults striking about n140 145 e some detected basement elevations such as the one previously known by boreholes in viator village are apparently connected with the fault pattern the outcomes of this work are 1 new gravimetric data 2 new methodological options and 3 the resulting structural conclusions

new beach ridge type severely limited fetch very shallow water abstract the southern end of laguna madre texas north of the rio grande mouth is marked by very shallow water wide tidal flats lunettes islands made of beach ridges and lesser features the number and variety of islands in the lagoon is remarkable the lunettes clay dunes are made primarily of quartz sand and coarse silt they are commonly 15 35 feet 5 10 meters high irregular is shape and steep sided they were deposited from wide transport and did not migrate those that are islands in the lagoon predate present position of sea level islands made of beach ridges were built from the lagoon side photo analysis field work and granulometry all show that this sand was not moved into these ridges by gulf of mexico waves trenches in 12 beach ridges showed horizontal bedding but neither low angle nor steep cross bedding hence quite unlike swash built beach ridges the ridges were built by wind tide lag effects not from the swash therefore these beach ridges are a new type in addition to swash built eolian and storm surge ridges growth of the ridges appears to be over

imprints of a proterozoic tectonothermal anomaly below the 1 1 ga kimberlitic province of southwest cuddapah basin dharwar craton southern india summary a detailed 2 d modelling of the seismic structure and other geological and geophysical signatures across the cuddapah basin of the southern indian shield suggests upwarping of highvelocity and high density layers which are observed close to the surface below the southwestern part of the basin this anomalous feature is constrained by i a strong gravity high anomaly of about 55 mgal ii a 100 km wide high conductivity anomaly resistivity 100 m extending from surface to a minimum depth of 50 km in the mantle lithosphere and iii large scale massive intrusive activity these features are interpreted to be an expression of a thermal anomaly which may have acted like a plume during the proterozoic and could well correspond to a 1 1 ga kimberlitic activity below this region the thin granitic gneissic crust is underlain by well differentiated high velocity layers possibly due to underplating and densification of much of the crust by extruded magma

gravity inversion of basement relief and estimation of density contrast variation with depth we present a method to estimate the basement relief as well as the density contrast at the surface and the hyperbolic decaying factor of the density contrast with depth assuming that the gravity anomaly and the depth to the basement at a few points are known in both cases the interpretation model is a set of vertical rectangular 2d prisms whose thicknesses are parameters to be estimated and that represent the depth to the interface separating sediments and basement the solutions to both problems are stable because of the incorporation of additional prior information about the smoothness of the estimated relief and the depth to the basement at a few locations presumably provided by boreholes the method was tested with synthetic gravity anomalies produced by simulated sedimentary basins with smooth relief providing not only well resolved estimated relief but also good estimates for the density contrasts at the surface and for the decaying factors of the density contrast with depth the method was ap

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

gravity anomalies of 2 5 d multiple prismatic structures with variable density a marquardt inversion we present an inversion technique based on the marquardt algorithm to estimate the depth of a 2 5 d sedimentary basin in addition to the regional gravity anomaly that is associated with the residual gravity anomaly wherein the density contrast varies parabolically with depth forward modeling is carried out through a derived analytical gravity expression of a 2 5 d vertical prism inversion of a theoretical gravity anomaly with and without a regional gravity anomaly illustrates the procedure that it is found to be insensitive to the regional gravity effect furthermore the algorithm is exemplified with the gravity anomalies of the derived density depth model of the godavari subbasin india with a parabolic density profile resulting in a more consistent geological model rather than a constant density profile the main advantage of this method is that it works well even when the profile of interpretation does not bisect the strike length of the sedimentary basin

determination of the crustal and thermal structure of the erzurum horasan pasinler basins eastern turkiye using gravity and magnetic data the erzurum horasan pasinler basin which surrounds miocene rocks is oriented approximately e w and is located in eastern anatolia turkiye east anatolia where ophiolitic and young volcanic rocks are widespread is situated in the alpine himalayan fold thrust fault belt the nw se trending north anatolian transform fault zone and the ne sw trending east anatolian transform fault zone formed by the compressional regime of east anatolia control the main tectonics of the study region while the moho and conrad depths of the study region are 43 0 and 20 9 km respectively the average sedimentary thickness has been determined to be 5 2 km by using the power spectrum method on the other hand it is found that the depth of the moho in the region varies from 41 0 to 44 5 km and the depth of the conrad discontinuity varies between 22 and 26 km as computed using empirical equations the basement of the sedimentary layer is calculated to be 6 km by using inversion results applied to the residual gravity data the curie point depth and average heat flow value in this region are calculated as 18 0 km and 89 1 m wm 2 respectively geotherm calculations reveal that the moho temperature is 1 028 0 c based on the crustal model the high heat flow values obtained are attributed to tectonic activities and melting of the lithospheric mantle caused by upwelling of the asthenosphere

six millennia of atmospheric dust deposition in southern south america isla navarino chile to characterize dust deposition in southern south america for the holocene a 542 cm long core from a peat bog in southern chile oreste bog isla navarino was studied peat formation started 11 160 14c yr before present bp the titanium ti concentration in bulk peat combined with dry bulk density and peat accumulation rate were used to calculate the mineral accumulation rate mar in the oreste bog the distribution of calcium ca manganese mn and titanium ti showed that mineral accumulation for the last c 6000 yr was predominantly atmospheric with a record of effectively constant deposition 0 43 0 12 g m2 per yr similarly ti and zirconium zr concentrations in the acid insoluble ash aia were also effectively constant and agreed well with the mar for the last six millennia except at c 4200 cal yr bp where zr was enriched relative to ti here scanning electron microscope sem micrographs showed that the aia was dominated by volcanic particles 20 40 m with the mt burney

the cuddapah salient a tectonic model for the cuddapah basin india based on landsat image interpretation abstract analysis of geologic geophysical data and lineaments derived from landsat image interpretation has revealed a pattern of tectonic inheritance of archean structural elements by the folded and thrusted eastern margin of the middle late proterozoic cuddapah basin in india a structural pattern set by deep crustal faults in the archean and intracratonic basin fabric is apparent in both sedimentary and tectonic trends in the basin the lineaments represent broad zones of en echelon and parallel alignments that appear to have nucleated on deep crustal faults which were reactivated as structural uplifts lateral and frontal ramps and transverse tear faults the major zones recognized are the northeast trending veldruti guntur lateral ramp to the north and the northwest trending cuddapah nellore transverse tear fault to the south east west directed compression during the eastern ghats latest proterozoic orogeny was apparently confined within these converging lineament zones that effectively buttressed the west verging thrust fronts block uplift along the ne trending veldruti guntur lateral ramp acted as a boundary to east to west thrust translation the northeastern ends of folds and thrusts were pinned down with relative displacement being clockwise and greater increasing to the southwest the lack of a lateral ramp or basement buttress to the south resulted in the development of the left lateral cuddapah nellore transverse tear fault steep imbricate thrust ramps in the foreland resisted further movement westward the resulting convex to the west arcuate nallamalai and vellikonda thrust fronts broadly paralleled by the east coast gravity high anomaly kaila and bhatia 1981 is herein named the cuddapah salient

geologically constraining india in columbia the age isotopic provenance and geochemistry of the protoliths of the ongole domain southern eastern ghats india abstract the ongole domain in the southern eastern ghats belt of india formed during the final stages of columbia amalgamation at ca 1600 ma yet very little is known about the protolith ages tectonic evolution or geographic affinity of the region we present new detrital and igneous u pb hf zircon data and in situ monazite data to further understand the tectonic evolution of this columbia forming orogen detrital zircon patterns from the metasedimentary rocks are dominated by major populations of palaeoproterozoic grains ca 2460 2320 2260 2200 2100 2080 2010 1980 1920 1850 and 1750 ma and minor archaean grains ca 2850 2740 2600 and 2550 ma combined u pb ages and lu hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent dharwar craton instead they were likely derived from east antarctica possibly the same source as parts of proterozoic australia magmatism occurred episodically between 1 64 and 1 57 ga in the ongole domain forming felsic orthopyroxene bearing granitoids isotopically the granitoids are evolved producing ehf values between 2 and 12 the magmatism is interpreted to have been derived from the reworking of archaean crust with only a minor juvenile input metamorphism between 1 68 and 1 60 ga resulted in the partial to complete resetting of detrital zircon grains as well as the growth of new metamorphic zircon at 1 67 and 1 63 ga in situ monazite geochronology indicates metamorphism occurred between 1 68 and 1 59 ga the ongole domain is interpreted to represent part of an exotic terrane which was transferred to proto india in the late palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south west baltica and south eastern laurentia given the isotopic geological and geochemical similarities the proposed exotic terrane is interpreted to be an extension of the napier complex antarctica and may also have been connected to proterozoic australia north australian craton and gawler craton

concept of effective density key to gravity depth determinations for sedimentary basins the gravity anomaly observed over a layered sedimentary basin is close to that calculated over a basin with the same configuration and depth but filled by homogeneous sediments with density equal to the effective weighted average density of the real layered basin therefore it is possible to calculate the effective density contrast of a basin from the residual gravity anomaly over it if the depth of the basin is known at least at one point assuming a mathematical function for density depth dependence an expression for the gravity depth dependence using the infinite slab bouguer formula can be developed this expression makes it possible to calculate the depth of a basin or an isopach map from gravity data an exponential function and a new hyperbolic density depth function and their gravity depth functions are analyzed and implemented for determining the depths of basins from gravity data for the san jacinto graben california and the tucson basin southern arizona the hyperbolic functions are m

total variation regularization for depth to basement estimate part 1 mathematical details and applications we have developed an inversion approach that estimates the basement relief of a fault bounded sedimentary basin the sedimentary pack is approximated by a grid of 3d or 2d vertical prisms juxtaposed in the horizontal directions of a right handed coordinate system the prisms thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data to obtain depth to basement estimates we introduce the total variation tv regularization as a stabilizing function this approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution we have deduced a compact matrix form of the gradient vector and the hessian matrix of the approximation to the tv function that allows a regularized gauss newton minimization approach because the hessian matrix of the approximation to the tv function is ill conditioned we have modified this hessian matrix to improve its condition and to accelerate the convergence of the gauss newton algorithm tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small slip step faults tests on field data from the almada basin brazil and from the san jacinto graben california u s a confirm the potential of the method in detecting and locating in depth normal faults in the basement relief of a sedimentary basin

three dimensional gravity or magnetic constrained depth inversion with lateral and vertical variation of contrast depth mapping inversion of gravity or magnetic fields generally assumes that anomalies originate from a main density or magnetization contrast interface this particular inversion takes into account inhomogeneous density or magnetization distributions reflecting sediment compaction and basement heterogeneities above the interface the density can be approximated by an exponential function and below it an intrabasement contrast map can be used the inversion also integrates local depth constraints from wells or seismic data as well as general constraints set on the geometry and the contrast of the interface after field transformations spectral analysis and con straints help to define a starting model characterized mainly by the interface mean depth and the mean parameter contrast between the two media the depth adjustment is completed iteratively under constraints using a space domain formulation derived from the bouguer slab approximation the interface model effect is computed in the wavenumber domain a model data example shows the accuracy of the inversion and illustrates the role of the constraints in a field example of a basin area where constraints can be derived from numerous well data successive inversions of gravity data result in an isodepth map of the basement the compatibility of the map with local depth constraints from wells is obtained by taking into account density heterogeneities related to known lithologic variations in the basement

preservation of environmental sulfur isotope records in maritime peats a test of baseline pre anthropogenic signal and diagenetic effects in a mid pleistocene peat abstract different sulfur fractions in a mid pleistocene peat from fugla ness shetland isles uk were separated and analysed isotopically in order to establish whether an unequivocal pre anthropogenic baseline sulfur isotopic signal is preserved or whether syn depositional or subsequent diagenetic effects obscure any such information such a test is vital if peats are to be used as historical archives for the extent and timing of anthropogenic sulfur deposition by recording changing sulfur isotopic composition as anthropogenic sulfur emissions increased sulfidic sulfur isotopic compositions in the peat are highly variable 34 s from 10 4 to 58 6 largely reflecting post depositional diagenetic effects organic sulfur isotopic compositions however are much less variable 34 s from 3 3 to 15 4 the fugla ness peat would have been subject to a maritime dominated sulfate input and its organic sulfur isotopic compositions generally parallel those of modern peat bog flora in pristine maritime settings peat samples from clay peat interbeds show a bias to more 34 s depleted isotopic compositions as a result of diagenetic addition of sulfur to the organic pool this only has a significant effect in a small fraction of samples analyzed to a large extent the organic sulfur isotopic composition shows no evidence of significant diagenetic alteration

a new gravity inversion method for multiple subhorizontal discontinuity interfaces and shallow basins 1 we present a method for 3 d gravity inversion designed to obtain density contrast models described by subhorizontal layers limited by irregular discontinuity interfaces and models constituted by shallow basins with light infill it is based on a previously published inversion method that provides in a nearly automatic approach the 3 d geometry of isolated anomalous bodies the basic adjustment constraints are model fitness fitting the anomaly data and model smoothness minimizing the total anomalous mass for models corresponding to subhorizontal layers we consider an additional minimization condition the proximity to prescribed horizontal interfaces this condition is arranged by including an additional weighting inverse proportional to the distance to the interface in the covariance matrix for model parameters the approach works according a growth process that increases step by step the volume of the adjusted anomalous bodies some advantages of the method are simultaneous adjustment of a linear regional gravity trend possibility of including simultaneously positive and negative anomalous structures in the model and unified inversion approach for isolated bodies basins and subhorizontal interface structures we include several simulation examples and an application case layered model for the volcanic island of tenerife

atmospheric deposition and mass balance of major and trace elements in two oceanic peat bog profiles northern scotland and the shetland islands a mass balance was performed on the major si al fe na k mg ca and some trace elements rb sr cl br s in peat cores from two oceanic blanket bogs in northern scotland loch laxford ll is 15 km east of the open ocean in the extreme northwest of the scottish mainland fleck s loch fl is on the small 15 km2 island of foula 50 km west of the mainland of shetland the supply of these elements to the peats can be explained in terms of two main atmospheric sources mineral aerosols from weathering of crustal rocks and sea salt spray the average al sc and fe sc ratios of the peats at both sites are comparable to the corresponding ratios in soil derived aerosols suggesting that crustal inputs account for essentially all of the al and fe in the profiles the si sc ratios of the peats from ll again correspond with the value for soil derived aerosols but at fl there is an excess of si in the uppermost part of the profile mainly because of quartz from sources immediately around the bog in contrast to al fe si the concentrations of na mg ca and sr in the peats exceed the corresponding ratios in soil derived aerosols by 5 to 30 times reflecting the importance of marine aerosols for these elements the conservative behaviour of cl allows the concentration of this species in the pore waters to be used as a quantitative indicator of the relative importance of sea salt inputs to the two bogs in contrast the concentrations of other important pore water species so42 br na k mg2 and ca2 do not simply reflect their concentrations in rainwater because of biological transformations s br k ion exchange na k mg ca and possibly mineral dissolution na mg ca the average pore water cl concentrations at fl 97 0 15 2 mg 1 show that marine inputs are 4 times greater than at ll 24 0 2 6 mg 1 the concentrations of other major and trace elements in the rainwater supplied to the bogs were calculated using the known abundances of the elements in seawater and normalizing to the pore water cl concentrations at the two sites these estimated rainwater compositions were then combined with rainfall data to calculate the annual inputs to the bogs the peat core inventory of major and trace elements corrected for crustal contributions was compared with these inputs to determine the percentage of each element retained in the peat profiles these findings indicate that 91 5 to 99 9 of the major elements cl na mg k ca and trace elements br sr rb supplied to the bogs by rainwater are not retained by the peat thus none of these elements in the solid phase peat can be used as a quantitative measure of sea salt inputs to the bogs

multi stage deformation in the nallamalai fold belt cuddapah basin south india implications for mesoproterozoic tectonism along southeastern margin of india abstract the common occurrence of small scale refolded folds deformed lineations and overprinting of foliation in the northern nallamalai fold belt nfb within the intracratonic cuddapah basin south india suggest three phases of deformation d 1 d 2 and d 3 during the late paleoproterozoic to neoproterozoic d 1 structures are represented by tight to isoclinal folds a slaty cleavage and local development of mylonites d 2 structures include ne trending tight to open folds f 2 with variable plunge indicating control of large domal structures and a steep crenulation cleavage developed in phyllites and other schistose rocks the above structures are overprinted by e w trending d 3 folds and cleavage which affect mesoproterozoic rocks of the srisailam formation uppermost nallamalai group in the e w trending vami konda range and metasediments of the palnad area thought to be equivalent of the neoproterozoic kurnool group taking into account the ages of intrusive vellaturu granite 1575 ma which is post d 2 deformation in the nfb and the chelima lamproite 1400 ma which intrudes the folded nallamalai rocks we suggest that the earlier episodes of multiple deformation in the nfb represent either late paleoproterozoic or early mesoproterozoic nw se compression in this part of the east gondwana the e w fold thrust structures affecting the srisailam quartzite and adjacent metasediments in the palnad area represent late mesoproterozoic and or neoproterozoic event the granite gneisses and schists of the nellore schist belt bordering the nfb are affected by both early and later events and thrust over rocks of the nallamalai group we propose that early deformation in the nfb lying southwest of the eastern ghats and roughly parallel to the present southeastern coast of india was unrelated to and occurred prior to the main deformation in the eastern ghats which is generally correlated with the 1000 ma old grenville event alternatively in view of the complex protracted evolution of the eastern ghats and published geochronological data supporting pre grenvillian tectonism particularly in the western charnockite zone of the eastern ghats d 1 and d 2 deformation in the nfb may be linked to this older 1600 1400 ma tectonic disturbance in the eastern ghats

sources and sinks of sea salt in a newfoundland blanket bog over an oceanic peatland the concentration of na in fog averaged 38 1 mgl 1 compared with 1 8 mgl 1 in rain resulting in a significant flux of mineral elements to the surface between 16 may and 20 june 1990 the average mass flux of na to the bog surface by fog rain and dry deposition was 21 9 10 4 and 7 0 mg m 2 d 1 there was little long term storage of na within the peatland system where na losses measured in stream runoff averaged 34 8 mg m2 d 1 and deep groundwater losses 4 mg m 2 d 1 calcium and mg were preferentially retained in the organic soil whereas k was relatively mobile potassium tended to become concentrated in the unsaturated zone stream runoff had a consistently higher ph than groundwater corresponding to higher ca and mg concentrations which may have been from mineral sources in the headwater ponds otherwise the stream water chemistry was closely related to groundwater in the upper layers of the peat deposit

geochemistry mineralogy and geochemical mass balance on major elements in two peat bog profiles jura mountains switzerland abstract the mineralogical and chemical composition of peats from two sphagnum bogs in the franches montagnes region jura mountains switzerland were compared the peats in the top 102 cm at etang de la gruere egr represent 2110 years of peat formation compared with 1730 years for the first 84 cm at tourbiere de genevez tge scandium was used as a conservative tracer to distinguish between the primary sources of major elements to the bogs atmospheric deposition of soil derived aerosols egr and tge physical incorporation of elements along with mineral matter from the underlying sediments tge and adsorption or complexation by the peat following diffusion from groundwater tge these results support previous findings which showed that the egr core 102 cm is exclusively ombrogenic compared with tge where the peats below approx 30 cm become predominantly minerogenic the modern rates of sc accumulation past 100 years are similar in the two cores 39 g m 2 a 1 at egr versus 52 g m 2 a 1 at tge however comparison with deeper sections of the egr core reveals that the present day rates of atmospheric sc deposition are nearly 3 times greater than the long term average rate reflecting the higher concentrations of soil derived atmospheric aerosols today the rates of sc accumulation in the tge core are slightly higher than at egr this reflects the incorporation of mineral matter from the underlying sediments in the deeper minerogenic peats at tge the long term rates of fe and ca accumulation are 5 and 7 times higher respectively than in the egr core these fluxes greatly exceed the difference in sc flux and cannot be explained by the differences in amount of mineral matter in the peats these enrichments require an independent explanation and are most likely the result of adsorption and or complexation of cationic ca and fe species diffusing from deeper layers in the profile the mineralogical composition of the ash is mainly quartz 60 90 with feldspar 5 15 and muscovite 5 15 although various other minerals 5 10 are commonly present biogenic si represents another important fraction of ash and is abundant 30 70 at discrete depths the vertical profiles showed no significant changes in mineralogy with depth assuming a constant composition of source materials the lack of progressive mineralogical change suggests that the fine grained silicates supplied by soil dust have not been measurably weathered during the past two millennia a number of peaks in fe sc are found in both cores above peaks in ash content and density these appear to correspond with temporal fluctuations in wet dry conditions accumulation of fe oxides during dry periods and leaching during wetter conditions

seismically derived gondwana and proterozoic sediments east of cuddapah basin south indian shield and its possible geotectonic implications the study area situated east of the intracratonic proterozoic cuddapah basin that covers nellore schist belt ongole domain of the eastern ghats belt and adjacent east coast terrain forms a geodynamically important segment of the dharwar craton this region came into focus due to proposition that during paleoproterozoic to mesoproterozoic era it underwent persistent oceanic subduction continent continent collision and multi stage accretional growth in view of this we have reprocessed in detail the deep seismic sounding data over this region and integrated the obtained results with other geophysical studies to decipher the deep subsurface crustal structure underneath the derived shallow seismic section across this region showed the presence of a thin layer 250 m of gondwana sediments with a distinct velocity of 4 20 km s and a lateral dimension of about 40 km around vinjamuru region of the nellore schist belt another important finding has been the depiction of 5 3 and 5 5 km s velocity sediments comparable to upper and lower cuddapah sediments between nellore schist belt and the east coast indicating the possible presence of an additional proterozoic sedimentary terrain named here as east coast sedimentary basin overlying the concealed archean crystalline basement the presence of this sedimentary terrain which is separated from the cuddapah basin by an exhumed horst like feature situated below nellore schist belt would indicate proterozoic sedimentation in a much larger area during columbia and rodinia supercontinental assembly periods than hitherto known importantly no seismic trace of the eastern ghats belt has been found between nellore schist belt and the east coast it appears that during the gondwana period entire eastern segment of the east dharwar craton has been persistently rifting uplifting and eroding together with other gondwana grabens in india thereby leaving behind only a thin veneer of gondwana sediments at many places in view of the presence of number of gondwana occurrences all along the east coast it is felt that the rifting during the gondwana period may have been a prelude to india antarctica breakup with final separation between the two taking place much later during early cretaceous

icelandic volcanic ash and the mid holocene scots pine pinus sylvestris pollen decline in northern scotland a volcanic ash layer in peat from northern scotland has been identified and coincides exactly with an abrupt decline in pinus sylvestris l scots pine pollen frequencies this provides an isochrone time equivalent marker horizon with which to investigate the timing of the holocene pine decline furthermore two possible causes of the southward shift of the range of pinus in scotland c 4000 bp are suggested a direct effect of acid pollution by chemicals produced by the eruption of hekla h 4 or a volcanically induced climatic perturbation these possibilities have wider implications for the influence of volcanism on postglacial environmental change

gravity data as a tool for detecting faults in depth enhancement of subtle almada s basement faults brazil we demonstrate the potential of gravity data to detect and to locate in depth subtle normal faults in the basement relief of a sedimentary basin this demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere we inverted the gravity data from the onshore almada basin in northeastern brazil and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging the inversion methoddelineatedwellboththediscontinuitieswithsmallor largeslipsandasequenceofstepfaults usingsyntheticdata weperformedasystematicsearchofnormalfaultslipsversus fault displacement depths to map the fault detectable region inthisspace thismappinghelpstoassesstheabilityofgravityinversiontodetectnormalfaults mappingshowsthatnormalfaultswithsmall0 5 km mediumabout1 km and large about 2 km vertical slips can be detected if the maximummidpointdepthsofthefaultplanesaresmallerthan1 8 3 8 and6 8 km respectively

fast nonlinear gravity inversion in spherical coordinates with application to the south american moho estimating the relief of the moho from gravity data is a computationally intensive non linear inverse problem what is more the modeling must take the earths curvature into account when the study area is of regional scale or greater we present a regularized non linear gravity inversion method that has a low computational footprint and employs a spherical earth approximation to achieve this we combine the highly efficient botts method with smoothness regularization and a discretization of the anomalous moho into tesseroids spherical prisms the computational efficiency of our method is attained by harnessing the fact that all matrices involved are sparse the inversion results are controlled by three hyper parameters the regularization parameter the anomalous moho density contrast and the reference moho depth we estimate the regularization parameter using the method of hold out cross validation additionally we estimate the density contrast and the reference depth using knowledge of the moho depth at certain points we apply the proposed method to estimate the moho depth for the south american continent using satellite gravity data and seismological data the final moho model is in accordance with previous gravity derived models and seismological data the misfit to the gravity and seismological data is worse in the andes and best in oceanic areas central brazil and patagonia and along the atlantic coast similarly to previous results the model suggests a thinner crust of 30 35 km under the andean foreland basins discrepancies with the seismological data are greatest in the guyana shield the central solimoes and amazonas basins the parana basin and the borborema province these differences suggest the existence of crustal or mantle density anomalies that were unaccounted for during gravity data processing

seismic signature of sub trappean gondwana basin in central india abstract the digitized and trace normalized record sections of original analog deep seismic sounding dss data collected along the multai pulgaon profile have been re interpreted to find basement and intra basement structure in the area between the satpura basin and the pranhita godavari gondwana graben in central india it is found that the data are best satisfied by a model with a low velocity zone in between the deccan traps and the basement the study delineates a basement fault that could be associated with the known gavaligarh salbardi lineament low velocity sediments vp 3 7 km s delineated from the present study could be gondwana sediments which have been reported in surrounding areas this finding indicates the possible extension of gondwana formations of the pranhita godavari graben to the satputra basin through the wardha valley

deep seismic sounding in the godavari graben and godavari coastal basin india abstract deep seismic sounding investigations along two profiles one along and the other across the godavari graben delineate the northeastern extension of the bapatla ridge which separates the godavari graben from the godavari coastal basin the godavari graben is filled with a maximum of 2 8 km thick lower gondwana upper permian to lower triassic sediments it is inferred on the basis of p wave velocities that the upper precambrian pakhal formation does not continue south of paloncha the upper gondwana upper jurassic to lower cretaceous rocks with marine incursions appear to continue towards the southeast for about 15 km from the exposures below the rajahmundry sandstone mio pliocene two dimensional velocity modelling of the upper crust indicates a major interface at 3 5 km depth in the upper crust where the velocity increases from 5 4 5 5 km s 1 to 6 2 6 4 km s 1 this interface shows a dpmal upwarp across the godavari graben which may be an indication of ne sw crustal extension in this region the deeper part of the crust consists of a large number of almost horizontal small reflector segments two dimensional crustal velocity modelling for some correlatable wide angle reflections yielded a three layered structure below 10 km depth with the moho at about 41 to 43 km

understanding conspicuous gravity low over the koyna warna seismogenic region maharashtra india and earthquake nucleation a paradigm shift the continued seismicity in koyna warna region of the western part of maharastra india and its relationship with subsurface structures concealed below thick volcanic sequences are studied in detail using gravity field along with newly available deep scientific drilling results this seismically active zone is marked by a large conspicuous negative gravity anomaly the causes of which are yet to be fully understood recent findings from the boreholes drilled in the koyna gupta et al in int j earth sci 104 1511 1522 2015 and killari seismic zones both of which penetrated the thick deccan volcanic cover and the underlying archean crystalline basement have motivated us to revisit the bouguer gravity field over this region using a newly developed finite element method of regional residual separation our study reveals the presence of two thick low density low velocity crustal zones below the koyna warna region the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the moho both of these zones appear to contain mantle metasomatised and fractionated magmatic material respectively interestingly the hypocenters of all m 5 koyna earthquakes occur within the upper low velocity low density zone we also suggest high order crustal exhumation below this region which led to the removal of the entire sedimentary and granitic upper crustal column this process has brought denser mid crustal lithological facies close to the surface quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing a paleo rift may have existed beneath this region below which moho temperatures 600 c and mantle heat flow 31 mw m2 are still high

increased atmospheric dust deposition during the neoglacial in a boreal peat bog from north eastern canada abstract dust deposition in north eastern canada was estimated from the geochemical signature of a boreal peat bog from the james bay lowlands the rare earth elements and other lithogenic elements as well as nd isotopes were measured by q icp ms icp oes and mc icp ms respectively along a 4 20 m peat core covering the last 7000 years a principal component analysis performed on the geochemical dataset shows that rees display the same chemical behavior as other lithogenic elements such as al and ti which suggests that they are immobile in the peat column and can be used as tracers of dust deposition after 4000 cal yr bp peaks in dust deposition associated with greater variability in testate amoebae assemblages and plant macrofossil composition as well as a change in nd values are observed between 7000 and 4100 cal yr bp the nd values varied from 36 to 29 while they gradually increased from 4100 cal yr bp until 1500 cal yr bp suggesting proportionally less dust from local source s is deposited in favor of more regional source s from 1500 cal yr bp nd values remained relatively stable around 15 and 12 most of the dust peaks correspond to documented cold and dry periods likely linked to intrusion of arctic air masses a migration of the polar front might explain the more frequent intrusion of arctic air masses in the region and the greater variability in the lg2 record over the last 4000 years

holocene dynamics of the southern westerly winds over the indian ocean inferred from a peat dust deposition record abstract the southern westerly winds sww play a major role in climate variability in southern hemisphere mid and high latitudes regulating rainfall ocean circulation and the southern ocean carbon sink despite their importance little is known about millennial scale changes in the sww and how they have influenced the climate system in the past and interacted with the earth s surface elements such as dust nutrients and carbon here we present a dust record from a 6 6 kyr old peat core in amsterdam island ams situated at the northern edge of the sww 37 s in the southern indian ocean mineral dust flux was used to track atmospheric dust production long distance transport and subsequent deposition dust provenance was determined from rare earth element ree and nd isotopic signatures end in the peat core compared with a reference dataset of southern hemisphere dust sources using a multi proxy mixing model the end and ree ratios show a relatively uniform mixture of ca 40 local 15 southern african and 45 southern south american dust sources since 6 6 cal kyr bp however from 1910 ad onwards there is a doubling in the contribution from southern africa 32 two mineral dust flux minima occur at 6 2 4 9 cal kyr bp and 3 9 2 7 cal kyr bp interpreted as periods with equatorward shifted and or strengthened sww at the northern edge of the wind belt conversely periods of higher dust flux at 6 6 6 2 cal kyr bp 4 9 3 9 cal kyr bp and 1 4 cal kyr bp onwards are interpreted as poleward shifted and or weakened sww these interpretations are based on the findings that higher lower wind speeds lead to enhanced less removal of distal dust on the way to ams by wet deposition and turbulence published holocene sww records at the northern edge of the wind belt 33 41 s covering south america southern africa and australia show much variability over the last 6 6 kyr we suggest this reflects complex regional climate variability in the different sh longitudinal sectors indicating that sww are not zonally homogeneous at the northern edge of the wind belt the recent shift in dust provenance is not accompanied by enhanced total dust deposition at ams we therefore suggest that human impact e g land use changes and drier climate conditions in southern africa have led to enhanced dust mobilization

a finite element method for computation of the regional gravity anomaly a regional gravity anomaly based on element shape functions used in finite element analysis is developed the regional gravity is approximated by a weighted sum of discrete gravity values at eight stations coinciding with the eight nodes of a second order or at twelve stations coinciding with the twelve nodes of a third order isoparametric element superimposing the map space the computations are carried out on a reference space with the shape functions acting as weighting factors and subsequently translated to the real map space in this technique no observed gravity data lying inside the survey area enter into the regional computation tests on the gravity field in harris county texas a well known hydrocarbon prospect during the 1940s and the klamath mountains and the cascade range in california confirmed the efficacy of this method

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

recreating atmospheric sulphur deposition histories from peat stratigraphy diagenetic conditions required for signal preservation and reconstruction of past sulphur deposition in the derbyshire peak district uk three modern pristine and one previously polluted ombrotrophic peat were sampled and analysed to investigate whether the isotopic composition of atmospheric sulphur inputs could be preserved in the organic fraction of ombrotrophic peats without undue alteration through syn depositional or diagenetic effects peat type reflecting the environment of deposition and diagenesis was shown to be critical in determining whether an environmental archive of sulphur deposition could be preserved within the profile of the pristine peats sampled hummock peat from shetland proved to be the most suitable exhibiting a near constant 34s characteristic of the growing vegetation in the organic fraction of peat in the upper 30 cm of the profile however only short to medium term changes 600 years in input are likely to be preserved due to the masking effect produced by incorporation of sulphide derived from bacterial sulphate reduction bsr into the organic fraction at depth the organic fraction of peat sampled from waterlogged pools at forsinard ne scotland was masked by sulphide incorporation throughout the profile while peat from abisko n sweden was exposed to annual freeze thaw cycles which appear to have produced significant decomposition of the organically bound sulphur and loss of the original depositional isotopic signal three peat types were sampled from the southern pennines an area with a gross history of sulphur pollution during the industrial revolution high hummock peat low hummock peat and waterlogged peat from a pool complex in drier high and low hummock peat types diagenesis and decomposition were not found to be significant processes in the upper portions of the peat hence alterations in the isotopic composition of the organic sulphur fraction in the profile reflect that of the depositional environment in the hummock peats organically bound sulphur becomes isotopically lighter at around 1400 ad which may reflect alterations in local sulphur inputs at this time due to the small scale smelting of lead in the area isotopic compositions become progressively lighter still towards the peat surface layers which correlate well with the excesses of sulphur deposition largely from coal burning during the industrial revolution

geochemical stability of fine grained silicic holocene tephra in iceland and scotland this paper tests two assumptions fundamental to the use of fine grained silicic tephras from iceland for creating chronological frameworks in northwest europe it is shown firstly that glass shards can retain their overall chemical integrity on at least a four millennial time scale in contrasting depositional environments in iceland and scotland and secondly that an acid digestion process the most practical method for extracting tephra from peat does not significantly bias the results of major element analysis by electron microprobe the implication is that there is great potential and an appropriate method for developing both the resolution and the spatial coverage of chronologies based on silicic icelandic tephras in northwest europe

deep crustal electrical signatures of eastern dharwar craton india abstract wide band magnetotelluric mt investigations were carried out along a profile from kavali in the east to anantapur towards west across the eastern ghat granulite terrain eggt eastern dhanvar craton edc and a proterozoic cuddapah basin this 300 km long profile was covered with 20 stations at an interval of 12 18 km the mt data is subjected to robust processing decomposition and static shift correction before deriving a 2 d model the model shows a resistive crust 10 000 30 000 ohm m to a depth of 8 10 km towards west of the cuddapah basin the mid crust is less resistive about 500 ohm m and the lower crust with a slight increase in resistivity about 1 500 ohm m in the depth range of 20 22 km the resistivity picture to the east of the cuddapah basin also showed a different deep crustal structure the resistivity of upper crust is about 5 000 ohm m and about 200 ohm m for mid and lower crust the sediment resistivity of cuddapah basin is of the order of 15 20 ohm m mt model has shown good correlation with results from other geophysical studies like deep seismic sounding dss gravity and magnetics the results indicate that the lower crustal layers are of intermediate type showing hydrous composition in eastern dhanvar craton

gravity analysis of salt structures an example from the el kef ouargha region northern tunisia triassic outcrops in the atlassic zone of northern tunisia may be modelled in two ways salt bodies piercing through cretaceous terrains or triassic salt flows stratified within an albian series both models find support from gravity data and are debatable to evaluate the mass distribution changes with depth the bouguer anomaly of the el kef ouargha region was successively decomposed into regional and residual components to construct multiple pseudo depth slices and apparent density maps analyses of gravity lows clearly show a vertical continuity of less dense materials below the triassic salt outcrops these features can be explained by salt diapirism during mesozoic and cenozoic further gravity data tend to indicate less dense materials below aptian outcropping in jebel aite oued bou adila thus suggesting triassic materials occurring at depth in addition dense entities were recognized under mio pliocene and quaternary deposits which are thought to correspond to cretaceous paleoshoals currently collapsed by non outcropping faults our findings lend support to a diapir model intruding overburden rather than the salt glacier model stratified in the albian series proposed by some authors as the genetic structural model for triassic material bearing series in the north of tunisia

14 kyr of atmospheric mineral dust deposition in north eastern china a record of palaeoclimatic and palaeoenvironmental changes in the chinese dust source regions a multi proxy record of holocene and late pleistocene aeolian mineral dust is reconstructed using a combination of geochemical trace elements mineralogical and grain size analyses on cores from