An analysis of magnetic susceptibility and natural gamma radioactivity is presented as indirect proxies of the characteristics of sandstones and limestones of the Sabinas basin. These rocks are located in the sedimentary sequence ranging from the Upper Jurassic to the Cretaceous. The magnetic susceptibility indicates changes in the magnetic composition of these rocks and suggests changes in their weathering degree. Ranges of values of magnetic susceptibility in sandstones and limestones allow classifying them into different groups, suggesting variability regarding conditions of origin and evolution. High values of magnetic susceptibility in limestones can be linked to sedimentation in anoxic or reducing environment, as well as with its siliciclastic content. The natural gamma radioactivity expressed in the contents of Th and relationships U / K and Th / U also suggest the degree of weathering of these rocks, mainly in the sandstones. These relations also highlight others characteristics in the sandstones related the probable provenance of sediments, its distance, degree of weathering and transport dynamics. Using the values of U / K ratio in the sandstones, it is possible to suggest the probable quartz-feldspar relationships. These ratio values classified rocks as arkose or quartzarenite, indicating the maturity of the sandstones. According to the U / K ratio values, most of these rocks which show little maturity are called arkose. Using the values of the Th / U ratio, it is possible to suggest the textures of quartzarenites, classifying them as rocks with fabric that is clast-supported or matrix-supported.

Se obtuvo un modelo tridimensional de la corteza mediante un proceso de inversión de datos gravimétricos para la región oriental de Cuba. Los datos y el modelo cubren un área rectangular de 64 600 km 2 . El modelo inicial fue constreñido con la geología de superficie, la información sísmica y de perforación. Se aplicó un algoritmo de inversión que utiliza los datos de gravedad para estimar las topografías 3D a partir de las unidades geológicas principales. El modelo nos proporciona información cuantitativa sobre las profundidades y espesores de las formaciones geológicas más importantes. En el mismo se observan las secuencias alóctonas de diferente composición y origen sobre el

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This study combined geophysical, geologic, and topographic information to investigate the Mayarí-Baracoa ophiolitic belt in eastern Cuba. A recently developed interpretation technique for 3D inversion of magnetic data was employed to determine the geometry at depth of ophiolitic and other rocks. Based on measured susceptibilities, lithologies were divided into four groups. The geophysical data allowed 3D imaging of ophiolites ͑serpentinized peridotites and gabbros͒, as well as sedimentary and volcanic rocks. The study verified that both the Pinares de Mayari Plateau and the Sagua de Tánamo Basin have been strongly influenced by tectonic activity. The modeling showed evidence of more east-west structural deformation of the ophiolite belt than had been previously reported. The depth of the depocenter of the Sagua de Tánamo basin and its rate of subsidence were determined. We identified some areas with potential for economic deposits of chromium, cobalt, and nickel, as well as precious metals; these were related to the thickness of the peridotite layer. The modeling also corroborated the presence of previously mapped faults and revealed other previously unrecognized faults.

We present a three-dimensional multi-formation inversion model for the gravity anomaly over Chicxulub Crater, constrained with available marine seismic data and land boreholes. We used eight formations or rock units as initial model, corresponding to: sea water, Paleogene sediments, suevitic and bunte breccias, melt, Cretaceous carbonates and upper and lower crust. The model response fits 91.5% of the gravity data. Bottom topography and thickness plots for every formation are shown, as well as vertical cross-sections for the 3-D model. The resulting 3-D model shows slightly circular features at crater bottom topography, which are more prominent at the base of the breccias unit. These features are interpreted as normal faults oriented towards the crater center, revealing a circular graben-like structure, whose gravity response correlates with the rings observed in the horizontal gravity gradient. At the center of the model is the central uplift of upper and lower crust, with the top covered by an irregular melt layer. Top of the upper crust shows two protuberances that can be correlated with the two positive peaks of the gravity anomaly. Top of Cretaceous seems to influence most of the response to the gravity anomaly, associated with a high density contrast.