Soft-sediment deformation structures in Aptian lacustrine laminites: Evidence of post-rift paleoseismicity in the Araripe basin, NE Brazil

Abstract

Soft-sediment deformation structures (SSDS) represent synsedimentary structures that can be formed under different tectonic regimes and are considered of great importance for studies associated with the paleoseismic activity. SSDS represent depositional heterogeneities and play an important role in fluid flow, thus influencing hydrocarbon or groundwater reservoirs. This paper describes the SSDS in Aptian lacustrine finely laminated limestones of Crato Formation, the post-rift sequence of Araripe Basin, NE Brazil. SSDS occur in laterally continuous beds, with an average thickness of 5 cm. The set of studied structures comprises loop beddings, convolute laminations, micro faults, fluid escape structures, simple and pendulous load cast, and detached pseudonodules. We interpreted that these structures resulted from seismic activity associated with brittle reactivation of the Patos shear zone, a major structure that borders the Araripe Basin. This interpretation points to a long history of post-rift tectonic activity of the Borborema Province (NE, Brazil). The diversity and abundance of these structures in these post-rift deposits show that this type of heterogeneities can be formed in tectonic-sedimentary sequences otherwise considered less, or non-affected, by seismic activities.