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 paleoseismic activity. SSDS represent depositional heterogeneities, and they may play an important role for fluid flow in porous rocks characterized as hydrocarbon or groundwater reservoirs. This paper presents the SSDS interpreted as seismites in lacustrine fine-laminated limestones of Crato Formation, Aptian post-rift sequence of Araripe Basin, NE Brazil. The seismites occur in laterally continuous layers, with an average thickness of 5 cm. The set of studied structures comprises: loopbeddings, convolute laminations, microfaults, fluid escape structures, simple and pendulous load cast, and detached pseudonodules. These structures resulted from seismic activity, earthquakes, which were generated by brittle reactivation of the Patos shear zone, which borders the Araripe Basin. This evidence points to a long history of pots-rift tectonic activity of the Borborema Province (NE, Brazil). The diversity and abundance of these structures in these post-rift deposits shows that this type of heterogenities can be formed in tectonic-sedimentary sequences otherwise considered less, or non affected, by seismic activities.