Gravimetric Surveys Research Articles

Refinement of Mean Dynamic Topography Over Island Areas Using Airborne Gravimetry and Satellite Altimetry Data in the Northwestern South China Sea

AbstractThe determination of high‐quality mean dynamic topography (MDT) over island areas faces multiple challenges, due to the error in a global geopotential model (GGM) as well as the contaminated waveforms of satellite altimetry data and scarcity of surveyed gravimetric observations. We study the potential to enhance regional quasi‐geoid/MDT over island areas by using recently released satellite altimetric gravity data and airborne gravimetric observations. Numerical experiments over the Paracel Islands in the northwestern South China Sea show that the combination of airborne gravity data enhances the local gravity field, and reduces the errors in the associated quasi‐geoid, in comparison to the result directly derived from a GGM. The results demonstrate that the direct application of a GGM may cause significant oscillations in MDT determination over island areas, by a magnitude exceeding 6 cm. The incorporation of altimetric gravity data slightly reduces these errors; however, the bubble‐like errors are prominent, suggesting that altimetry data alone may be insufficient for high‐accuracy MDT recovery. In contrast, combining airborne gravity data dramatically reduces these oscillations, by a magnitude of several centimeters, indicating that airborne gravimetric surveys may be necessary for MDT determination with centimeter‐level accuracy over coastal/island areas. Further comparison with independent ocean data shows that the geostrophic velocities computed by merging a high‐degree GGM and local airborne gravity data can reconstruct real surface ocean circulation; and the GOCE‐based (Gravity Field and Steady‐State Ocean Circulation Explorer) GGMs may be preferable as the reference models in MDT determination.

Generalizing the results of fracture zones study in the Upper Kama potassium salt deposit with the help of gravity study

Introduction. The history of the Upper Kama potassium salt deposit (VKMKS) exploration and operation should be divided into two periods. The first period lasted from 1929, the start of exploitation, until 1986, when the water-protective barrier collapsed and the largest VKMKS mine, the 3rd Berezniki mine, was flooded. The second period began in 1986 and continues to the present day. The first period is characterized by a low level of technogenic load on the geological environment, significantly less than its long-term strength. After 60 years of VKMKS large-scale exploitation, the technogenic load on the geologic environment has increased significantly. As a result, its equilibrium state was upset, giving rise to destruction, accompanied by various dynamic events: caves-in, surface collapses, rockbursts, and tectonic rockbursts. VKMKS structural-tectonic profile study revealed that active faults, nodal structures, and fracture zones have a decisive effect on the geologic environment equilibrium state. Research methodology. When structural and tectonic elements are formed in the supra-salt, salt, and subsalt strata of the deposit, the geologic environment density characteristic changes naturally leading to the development of local density inhomogeneities within. It is possible to locate these inhomogeneities and establish their relationship with structural and tectonic elements of the geological environment, particularly, fractured zones, only by studying the gravity field of the deposit. For this purpose, an areawide, detailed, and high-precision gravimetric survey was performed at a scale of 1:25,000, the results of which were used to identify and study the fracture zones. Research results. Based on the results of gravity field anomalies interpretation on the territory of VKMKS, the horizontal position and size of about 200 local negative linear anomalies of the near northsouth, north-east, and north-west orientations were determined, the sources of which were confidently identified with the fracture zones. Conclusions. The experience of studying the structural and tectonic structure of VKMKS has shown that currently for the deposit’s physical and geological conditions, the detailed, high-precision aerial gravity study is the most effective geophysical method for fracture zones mapping

Development of monitoring gravimetric survey method for studying karst processes

Within the framework of solving the fundamental issue of ensuring the safety of mining camps, mines, and vital functioning of the population, a methodology and a software algorithmic apparatus have been developed for processing and interpreting monitoring gravimetric observations which are aimed at identifying karst areas in the massif. A complex of prospective geophysical works aimed at detecting areas with intensive development of karst processes has been tested. The authors of the project carried out experimental methodological geophysical works including high-precision gravimetric observations on the territory of the Verkhnekamskoye potash deposit. These works were carried out to test various options for the field work methodology on specific geological objects. In a broader sence, the results of the work are an example of a wide approbation of an advanced research methodology aimed at predicting the destructive consequences of karst-suffusion process

Parallel residual projection: a new paradigm for solving linear inverse problems

A grand challenge to solve a large-scale linear inverse problem (LIP) is to retain computational efficiency and accuracy regardless of the growth of the problem size. Despite the plenitude of methods available for solving LIPs, various challenges have emerged in recent times due to the sheer volume of data, inadequate computational resources to handle an oversized problem, security and privacy concerns, and the interest in the associated incremental or decremental problems. Removing these barriers requires a holistic upgrade of the existing methods to be computationally efficient, tractable, and equipped with scalable features. We, therefore, develop the parallel residual projection (PRP), a parallel computational framework involving the decomposition of a large-scale LIP into sub-problems of low complexity and the fusion of the sub-problem solutions to form the solution to the original LIP. We analyze the convergence properties of the PRP and accentuate its benefits through its application to complex problems of network inference and gravimetric survey. We show that any existing algorithm for solving an LIP can be integrated into the PRP framework and used to solve the sub-problems while handling the prevailing challenges.

Deep structure and geodynamic conditions of granitoid magmatism in the Eastern Russia

We investigated the deep structure of the lithosphere and the geodynamic conditions of granitoid magmatism in the Eastern Russia within the borders of the Far Eastern Federal District. The relevance of the work is determined by the need to establish the geotectonic and geodynamic conditions of the granitoids petrogenesis and ore genesis in the Russian sector of the Pacific Ore Belt. The purpose of the article is to study the deep structure of the lithosphere and determine the geodynamic conditions of granitoid magmatism in the East of Russia. The author's data on the magmatism of ore regions, regional granitoids correlations, archive and published State Geological Map data, survey mapping, deep seismic sounding of the earth's crust, gravimetric survey, geothermal exploration, and other geophysical data obtained along geotraverses. The magma-controlling concentric geostructures of the region are distinguished and their deep structure is studied. The connection of plume magmatism with deep structures is traced. The chain of concentric geostructures of Eastern Russia controls the trans-regional zone of leucocratization of the earth's crust with a width of more than 1000 km, which includes the Far Eastern zone of Li-F granites. Magmacontrolling concentric geostructures are concentrated in three granitoid provinces: Novosibirsk-Chukotka, Yano-Kolyma, and Sikhote-Alin. The driving force of geodynamic processes and granitoid magmatism was mantle heat fluxes in the reduced zones of the lithospheric slab. The distribution of slab windows along the Pacific mobile belt's strike determines the location of concentric geostructures and the magnitude of granitoid magmatism in the regional provinces. Mantle diapirs are the cores of granitoid ore-magmatic systems. The location of the most important ore regions of the Eastern Russia in concentric geostructures surrounded by annuli of negative gravity anomalies is the most important regional metallogenic pattern reflecting the correlation between ore content and deep structure of the earth's crust.

Морфология Горихинского гранитного массива с помощью методов математической статистики

The Gorikhinsky granite massif is located in the marginal part of the Khentei highlands (Mongolian-Transbaikalian folded system, Central Mongolia). The massif is composed of coarse-grained weak-porphyry leucocratic granites, granite porphyry, and pegmatites. In the rocks of the massif, rock crystal deposits have been discovered. In certain pegmatite bodies, in addition to smoky quartz and morion crystals, the study has found the presence of fluorite, topaz, biotite, tourmaline, beryl, garnet, and allanite. The accessory minerals are cyrtolite, xenotime, zircon, sphene, rutile, apatite, cassiterite, etc. Thus, the study of the geological structure of the above object is of interest not only from a scientific but also from a practical point of view. The research data have become the basis for setting areal gravimetric work to determine the features of the massif’s geological structure. The work has been performed by the standard procedure using Scintrex Autograv CG-5 gravimeters. The height of the observation points has been determined by Trimble 5700 GPS devices. The RMS accuracy of the gravitational anomalies calculation as well as the density of the observation network meet the technical requirements for 1:100000 scale gravimetric surveys. Using the results of the gravity survey, a map of gravity anomalies in Bouguer has been compiled. Based on the interpretation of the map, with the use of the methods of mathematical statistics, quantitative characteristics of the shape and size of the body have been defined and a three-dimensional model of the massif has been built. For the purpose of the transformation and inversion of the gravitational field, the variance and regression methods of mathematical analysis have been used. The maximum thickness of the granites is 3.5 km; the area of the earth's surface projection is twice that of the granite outcrop. The obtained estimates are confirmed by the results of solving the inverse problem of gravimetry using the method of model selection. The article concludes that the use of the regression and variance analysis methods of mathematical statistics in the studies of the morphology of the intrusive bodies has proved most effective. The information on the shape and size of the massif will be used in concluding on the prospects of the massif’s metallogenic trend.

Crustal structure of the Ulaanbaatar region, Mongolia according to gravimetric data

E stablish ing relationship s between the regional seismicity and the depth geometry and composition s of large -size density inhomogeneities of the upper crust is one of the ways to determine the p arameters of mean long-term seismicity . The origin of geological bodies and mechanism s of penetration of intrusive bodies in to the upper crust are detectable from the shape s and size s of such bodies. K nowledge o n the shape s and size s of large intrusive bodies is important for prospecting and exploration of mineral resources. Based on t he medium - scale areal gravimetric survey data, a regional map of Bouguer gravity anomalies was constructed for the Ulaanbaatar region , Central Mongolia. I nterpret ed gravimetric data from the sol utions of the inverse problem of gravimetry based on the body - shape selection were used to develop the 3D models showing the largest crustal density inhomogeneities of the study area – the Tolskaya ( Ula a n ba at a r) basin , Nalaiha depression and Bogdoulin granite massif. It is confirmed that the basement of these depression s has a block structure. The basement of the Tolskaya basin includes two depressions , the western and eastern ones . In the western depression, t he sediment thickness is 150 m . It amounts to 400 m i n the eastern depression at the intersection of the Selbin and Tolsk aya deep fault systems. The i nformation on the shape s and thicknesses of the sediment bodies is used in the seismic studies aimed at obtaining a more precise assessment of seismic hazard of the Ul a an ba at a r city and the region . In the Nalai ha depression, the sediments are 8 00 m thick . The morphology of the basement and the thickness of sediments in this depression can be used to update the mining prospects of the Nalaiha coal deposit. The maximum thickness of granitoids in the Bogdoulin massif is 9.0 km . T he area of its projection to the ground surface is twice as big as the area of the outcrops . Our research results can be useful for assessing the metallogenic specialization of granitoids, which indicators in relation to some minerals are related to the specific features o f the Bogdoulinsky massif . Such indicators have been discovered by the geological, geophysical and geochemical methods . Our study shows that t he geophysical methods (in particular, gravimetr y ) can considerably expand the knowledge of the morphology of geological objects at depth and facilitate reaching a new level in structural analysis, wh ich is critical for develop ing new ideas to clarify the geological history and tectonic conditions of the formation of the Mongolia-Siberian region.

Geophysical methods for mapping Quaternary sediment thickness: Application to the Saint-Lary basin (French Pyrenees)

This study aims at mapping the sediment infill thickness in the Saint-Lary basin (Aure valley, French Pyrenees). For this purpose, we combine passive seismic and gravity surveys. The resonance frequencies of the sediment body are retrieved from seismic ambient measurements, while the gravimetric survey shows negative residual anomaly of about −3 mGal in the basin. Both methods reveal unexpected but consistent bedrock shape. The southern Saint-Lary basin appears deeper than its northern part, with maximal infill thickness of about 300 m and 150 m, respectively. Valley cross sections show regular and smooth “U”-shape in the southern Saint-Lary basin, in contrast to an irregular and asymmetric pattern in the northern basin. This basin shape may be related to Quaternary fluvio-glacial carving processes especially controlled by a regional fault (the Soulan fault), variations in bedrock hardness, and preferential ice flow paths.

SRTM2gravity: An Ultrahigh Resolution Global Model of Gravimetric Terrain Corrections

AbstractWe present a new global model of spherical gravimetric terrain corrections that take into account the gravitational attraction of Earth's global topographic masses at 3″ (~90 m) spatial resolution. The conversion of Shuttle Radar Topography Mission‐based digital elevation data to implied gravity effects relies on the global evaluation of Newton's law of gravitation, which represents a computational challenge for 3″ global topography data. We tackled this task by combining spatial and spectral gravity forward modeling techniques at the 0.2‐mGal accuracy level and used advanced computational resources in parallel to complete the 1 million CPU‐hour‐long computation within ~2 months. Key outcome is a 3″ map of topographic gravity effects reflecting the total gravitational attraction of Earth's global topography at ~28 billion computation points. The data, freely available for use in science, teaching, and industry, are immediately applicable as new in situ terrain correction to reduce gravimetric surveys around the globe.

Tribological investigation of epoxy/seed particle composite obtained from residues of processing Jatropha Curcas L. fruits

Natural particles e.g. in a form of wooden powder but also of fruits residues serve for decreasing costs and for an optimization of some mechanical characteristics in the area of composite materials. For this reason, in this study, a first mechanical characterisation (Hardness) and a tribological characterisation of an epoxy matrix filled with secondary commodities coming from the pressing process of Jatropha Curcas L. seeds was carried out. Three different materials have been used as reinforcement of the composite material: Whole seeds (SC), Seed shells (S) and Seed kernels (SKC). A ball-on-flat tribometer with reciprocating motion was employed with frequencies of 5 Hz and 10 Hz. The tribo test was carried out by using an 8 mm diameter steel ball of AISI 420C (X46Cr13) sliding on a flat specimen of the investigated composite materials without presence of lubricant (dry conditions). The flat specimens of the composite material were made with three different reinforcement concentration (10%, 15% and 20%) materials for any part of the JL seeds used (SC, S and SKC). With the purpose to assess the wear mass loss in the tribo-test a gravimetric analysis was accomplished. An electron microscope was used for the evaluation of particle topography in the worn area of the specimen, after tribo-tests, and in interfacial interaction in this area. 3D topography analysis was carried by using a Confocal Microscope in order to obtained qualitative information on the wear process. From a comparison of the tribological response to the various types of reinforcement, it has emerged that the lower coefficients of friction and wear rate are realized with a reinforcement constituted by the core of the seed (SKC). The gravimetric survey conducted revealed a greater resistance to wear in the composites made with the seed core (SKC). In fact, the lowest value, of the wear mass loss, of the whole series of experiments was obtained in the case of specimens with 20% of reinforcement seed core (SKC) and with 10 Hz of reciprocating motion of the ball on the specimen. This value was of 0.07 mg.

Characteristics of the gravity field of predictive oil-gas areas in the DDD region according to satellite model EGM08 and gravity measurements at the beginning of the XX century

Gravimetric information is the basis for mineral exploration. The foundations of resource research in Ukraine were started by a large-scale gravimetric survey performed by the Poltava Gravimetric Observatory (PGO) in 1926—1934. Modern geological exploration uses information from Earth remote sensing, obtained with the help of special equipment installed on space vehicles. Satellite data on the distribution of gravitational anomalies (D g ) are displayed in the model of the gravitational field of the Earth EGM08, created for the practical use on the data of the special missions CHAMP and GRACE. The features of the structure of the gravitational field for perspective oil and gas areas located in the Dnieper-Donetsk depression (DDD) are considered, based on the model EGM08 and gravity measurements performed in the first half of the XX century. This al-lows: 1) to test the geological information of the model EGM08; 2) to assess the nature of the age-old changes in gravity in areas that have a specific and similar geological structure by comparing these data sets. For most sites it is typical: 1) the complex structure of the field of gravity, the presence of local “potential wells” with fluctuations in gravity anomalies of 10―30 mGl, characteristic of fault zones; 2) mainly negative values of anomalies by area (D g < 0), which is typical for the rocks with reduced density and increased porosity. These results confirm the correct nature of the model EGM08. The secular changes of the gravity dD g for the corresponding points were estimated as the anomaly difference according to the EGM08 model data and the classical measurements previously reduced to the WGS84 system. For most points, there are: 1) a multidirectional change in dD g ; 2) for about 20 % of points the values |dD g | ³ 5 mGl, which does not exclude the influence of local technogenic or geophysical factors. A statistically significant increase in the age-old change in gravity on + 3.3 mGl was found for the northwestern section of site No. 2 (Lokhvitsa segment of DDD), where the density of groundbased measurement points is high.

The study of geothermal resources of Avacha volcanoes group and its flanks

The article is based on the results of the geologic-geophysical researches carried out during different years around the Avacha volcanoes group and its flanks. More attention was paid to the results of electric exploration by the method of magnetotelluric sounding and gravimeter survey of 1:50 000 scale. Works results in the context of heat and power territory potential utilization were given. The complex of geophysical methods to study morphology of the peripheral chamber under Avacha volcano and search of potentially possible zones of chamber interaction with meteoric waters was recommended.

Surface and Subsurface Investigations for the Detection and Mapping of Underground Karst Cavities in MChentel Area, Cheria Basin, Northeast of Algeria

Abstract A combined approach using the surface geophysical method (microgravimetric survey) and sub-surface investigations (speleology) was undertaken at an experimental karst site located in the MChentel area near Cheria town (Northeast of Algeria). The gravimetric survey, carried out by a gravimeter GNU-KC 444 during March-April 2016, allowed the procurement of 614 gravimetric measurements distributed on the whole of the zone of study. The gravimetric data shows a reduction in the values of the Bouguer anomaly between two collapses. This trend probably implies an effect of karstification that would explain the reduction in the values of the Bouguer anomaly while moving towards the centre of the zone of study. The results provided in this work of underground exploration by the team of speleologists from Polytechnic Nice-Sophia in 2013 and 2014 are particularly well illustrated by the topography of the cavities upstream and the real photographs, the micromorphology and the microstructures of the walls of the cavities explored. The joint application of the microgravimetry and speleology make it possible to evaluate the advantages and effectiveness of the microgravimetry for the detection of underground cavities. This improves knowledge of the karstic system structure of Eocene carbonates in the studied area.

ОПРЕДЕЛЕНИЕ ДОПУСТИМОЙ ПОГРЕШНОСТИ ВЫСОТ ГРАВИМЕТРИЧЕСКИХ ПУНКТОВ В УСЛОВИЯХ НЕОДНОРОДНОГО ГРАВИТАЦИОННОГО ПОЛЯ

The paper presents the rationale for using the vertical gradient of normal gravity to determine the allowable error in determining the heights of gravimetric points in the territory of the Novosi-birsk region. The results of the accuracy of the high-altitude binding of gravimetric points, taking into account the heterogeneity of the gravitational field in the study area. Recommendations are given to improve the accuracy of calculating the allowable errors of the high-altitude support of gravimetric surveys in the plain and in areas with a large elevation difference or a high anomaly of the gravitational field.

Regional gravimetric survey of central Slovenia

This paper presents the regional gravimetric survey of the central part of the Republic of Slovenia. The need for a new gravimetric survey, the survey plan and the actual field measurements are presented. Data processing, control calculations, data adjustment in the form of a gravimetric network and accuracy estimations of the results obtained during the regional gravimetric survey are described. Furthermore, the impact the new gravimetric data had on the quasigeoid model determined in 2016 and consequentially on determining normal height by GNSS levelling was analysed. The analysis were based on the comparison of the normal heights determined by GNSS levelling and the control points obtained from the 2010 and 2016 quasigeoid models. The results show that the new gravimetric data improved the newly calculated quasigeoid model or height reference surface of Slovenia and consequently made the determination of the normal heights by GNSS levelling more precise. The comparison of old and new height reference surfaces shows there are differences in investigated area from −6.9 cm to +9.0 cm and mean difference is 1.5 cm.

Development of Innovative Methodological Support for Marine Gravimetric Surveys

The authors discuss their main achievements in developing innovative methodological support for marine gravimetric surveys. They have actively participated in the development of gravimeters and created several generations of gravimetric equipment in cooperation with other organizations. The main characteristics and results of laboratory and marine tests of the mobile Chekan-AM and Shelf gravimetric systems are briefly considered. These systems have operated successfully in harsh Arctic conditions, including the first high-precision marine gravimetric survey in the region of the North Pole. The authors describe the methodological support, results from modern models of Earth’s gravitational field, and integration of data from various gravimetric instruments in the interests of marine gravimetry. The increase in accuracy and resolution of Earth gravitational field models has led to their use beyond solving only fundamental problems. In most areas of the World Ocean, the model field can be used as a reference field when performing a direct marine gravimetric survey. Innovative developments have increased the reliability and accuracy of marine surveys primarily due to the control and correction of systematic errors arising in marine measurements. They make it possible with no loss of measurement reliability to produce surveys at marine test ranges with an error of 0.5 mGal or less, expand the planning capabilities of the survey network, increase the reliability of long-term route surveys, reduce the time of reference measurements, and perform marine gravimetric surveys with only one onboard marine gravimeter and no need for shore-based reference points. An innovative method of accounting for the ocean tide with loading models of the ocean gravitational effect was developed based on the ATLANTIDA3.1_2014 program. Experiments have shown that random errors can thus be reduced by more than 20%. The results of the research have been used to develop ready-made innovative and promising methods for measuring the parameters of Earth’s gravitational field on the surface water area of the World Ocean.

Unique basite-metabasite structures of the Pobuzhsky ore mining region, their geological significance and ore-bearing prospects (by geophysical and geological data)

The structure and prospects for ore content of three basite-metabasite massifs of the Pobuzhsky ore mining district — Bandurovsky, Troyan and Tarasovsky are considered using the example of the Tarasovska structure of the Middle Bug River of the Ukrainian Shield (USh). The assumption suggested by geologists back in 1990 about the geological and metallogenic uniqueness of these massifs is confirmed by the analysis of both regional geophysical surveys and materials of detailed geophysical works performed within the Tarasovska structure (basite-metabasite massif) in 2017 in connection with the geological-search works. It is shown that all three massifs are located within the epicentral regions of the largest gravity anomalies of the USh — Golovanevska and Bandurovska (68 and 49 mGal, respectively) — and they correspond to local maxima D g a with intensity up to 3—7 mGal against these anomalies. The most ancient enderbite-gneisses of the Yatransky and Khoshchevato-Zavalievsky blocks hosted the considered basite-metabasite massifs. The shape of the arrays is oval-concentric, that is why most geologists viewed them as brachisynclinal folds. According to the data of magnetometric and gravimetric surveys at a scale of 1 : 10,000 and small drilling volumes, the Tarasovska structure 3 ´ 5,5 km in size represents itself as a massif of apo-gabbroids — bipyroxene and amphibole-pyroxene crystal shales (in some places of norites and gabbros) of a clear oval shape surrounded by arcuate bands of skarnoids, garnet-bearing aluminous gneisses and calciphyres, bipyroxene and hypersthene crystal shales, among which for the first time manganese-containing gondites were encountered in the USh. Despite the presence of sedimentary cover overlapping the Tarasovska structure (Sarmatian and Quarterian deposits) of about 25—40 m thick, the massifs of apo-gabroids are distinguished on the background of the surrounding diurnal relief by distinct uplands with amplitude from several up to 10 m that supports the strength of these formations even on the background of enclosing granitoids. Geophysical, structural, petrological and geochemical data support the intrusive nature of the apogabbroids and the contact-metasomatic origin of their banding, rather than the brachisynclinal fold of metamorphosed sedimentary-volcanogenic rocks. The absence or very in-significant content of graphite gneisses in the framing structures of the Tarasovsky massif distinguishes these bands of gneisses, crystal shales and calciphyres from the sections of the Kosharo-Aleksandrovska and Khoshchevato-Zavalievsky suite of the Bug series with specific wide distribution of gneisses of graphite and biotite-graphite composition. The contact-metasomatic nature of the gneiss-crystal-shale-calciferous formations of the Tarasovo structure, as well as the possible metasomatic nature of the graphite and some other gneisses of the Middle Bug River, according to some researchers, raises the issue of the necessity of discussing and in-depth analysis of stratigraphic schemes of the Early Precambrian of the USh. The further direction of geological prospecting within the Tarasovska structure for apatite and titanium ores is discussed, and the most promising areas for the drilling of wells are also considered.

Tectonic evolution of the Paranoá basin: New evidence from gravimetric and stratigraphic data

Field gravimetric and stratigraphic surveys were conducted with the aim to constraint the mechanisms responsible for the initiation of the Stenian-Tonian Paranoá basin, central Brazil, a subject not yet studied in detail. The Paranoá Group crops out in the external zone of the Brasília Belt, a Neoproterozoic orogen in the western margin of the São Francisco Craton. Detailed geological mapping confirmed the existence of a regional scale fault that controlled sedimentation of the Paranoá Group during the deposition of its basal formations, revealing important details about basin initiation and early evolution. Gravimetric modeling indicates the existence of paleorift structures beneath the Paranoá sequence in the study area. Results from both stratigraphic and gravimetric surveys show strong evidence of mechanical subsidence by faulting during basin initiation. Unsorted, angular, clasts cut by quartz veins and brecciated boulders present in the basal conglomerate, support this hypothesis. Basin initiation faults coincide with deeper paleorift faults and are thus interpreted as reactivations of the older Statherian Araí Rift. The reactivations favored an initial regime of mechanical subsidence, dominated by the development of epirogenic arches subsiding at different rates. Apart from faulting activity, the post-basal sequence presents no evidence of rift environment in the strict sense. Besides, the great lateral continuity and relatively constant thickness of facies, indicate that an initial mechanic subsidence rapidly gave way to flexural subsidence during subsequent stages of basin evolution. The Paranoá Group do not present reliable characteristics that would allow its strict classification as a passive margin. Its main stratigraphic characteristics, tectonic location and basement architecture, indicate that the Paranoá Group was deposited in a cratonic margin basin, and may have been either connected to a passive margin basin at times of sea level rise, or evolved to a passive margin later in time.

3D Geological modelling and gravity inversion of a structurally complex carbonate area: application for karstified massif localization

AbstractThis paper proposes a new methodology to improve the location of potential karstified areas by gravity inversion of a 3D geological model. A geological 3D model is built from surface observations, 2D seismic reflection profiles and well data. The reliability of this geological 3D model obtained from integration, interpretation and interpolation of such data is first tested against the structural consistency of the model. Its theoretical gravimetric response is compared to gravity field during the forward problem in order to evaluate the validity/robustness of the geological model. The coherency between the gravity field and the gravimetric response is tested. The litho‐inversion modelling quantifies the distribution of rock density in a probabilistic way, taking into account the geology and physical properties of rocks, while respecting the geological structures represented in the 3D model. The result of the inversion process provides a density distribution within carbonate formations that can be discussed in term of karstification distribution. Thus, lower densities correlate with areas that are strongly karstified. Conversely, higher than mean densities are found in carbonate formations mostly located under marly and impervious formations, preserving carbonate from karstification and paleokarstification.

Modern Geodetic Measurement Techniques in Gravimetric Studies on the Example of Gypsum Karst in the Siesławice Region

In the region of Siesławice (near Busko-Zdrój, Poland) there are unique phenomena of gypsum karst. Atmospheric factors caused numerous gypsum outcrops, canals and underground voids. The article presents the possibility of using non-invasive gravimetric surveys supplemented with geodetic measurements to illustrate karst changes occurring around the void. The use of modern geodetic measurement techniques including terrestrial and airborne laser scanning enables to generate a digital terrain model and a three-dimensional model of voids. Gravimetric field studies allowed to map the anomalies of the gravitational field of the near-surface zone. Geodetic measurement results have made it possible to accurately determine the terrain correction that supplemented the gravimetric anomaly information. Geophysical interpretation indicate the presence of weathered rocks in the near surface zone and fractures and loosened zones located surround the karst cave.