The Tucano Basin (Cretaceous, Brazil) – a world-class example of an aborted rift system with anomalous depth

Abstract

The structural and stratigraphic characteristics of the central portion of the Tucano Basin, a Cretaceous continental rift basin in northeast Brazil, was investigated, using post-stack 2-D reflection seismic, gravity and well data. Methodology was steered by the principles of seismic stratigraphy, targeting at an adequate identification of stratal terminations and on the mapping of structural features, where a negative flower structure was interpreted. The identification of erosional truncations led to a stratigraphic framework of seven intra-rift unconformities, forming eight third-order rift sequences, while the literature on the Tucano basin recognizes only two depositional sequences forming the rift sedimentary infill. In order to study the abnormal depth of Central Tucano depocenter, gravity data were processed and a spectral analysis was performed, which located the depocenter at approximately 16.8 km, a rare configuration for a rift basin. Gravity models were created in order to verify the seismic interpretation and the depth found by the spectral analysis; and to provide a view of the basin in a regional scale, analysing its crustal architecture. The modelling confirmed the abnormal depth and also indicated a severe crustal thinning under Central Tucano Basin, where the Moho was interpreted around 24 km and a major crustal necking was observed. The models introduced the geometry of the lower continental crust and indicated the presence of a high-density layer (3000 kg/m3) at its base, which this work suggests to be a result of magmatic underplating. The paper closes discussing the role of tectonics and basement inheritance over the Central Tucano Basin structural framework and commenting on the mode of extension for the Recôncavo-Tucano-Jatobá rift system.