Have the Amazonian lowlands evidenced late Pleistocene-Holocene compression?

Neotectonic reactivation has been increasingly documented in many areas of the Amazonian lowlands, but the evidence has been only for extensional structures. This work investigates a large-scale sinusoidal-shaped morphology (Ssm) in a relief dominated by Late Quaternary deposits in the north of the Solimo?es Basin. The digital elevation model (DEM) of the shuttle radar topography mission (SRTM) was used as a basis to characterize this structure and improve the knowledge of its geological context. The Ssm is a Z-shaped sinusoid with a wavelength of approximately 135 km, formed by two merged asymmetrical curves. The north curve has an amplitude of 70 km and a core topographically lower and geologically younger than the limbs, while the south curve has an amplitude of 90 km and a core with older geological units and higher relief than the limbs. A main NE-trending morphostructural lineament has horizontally displaced the rocks near the axial plane in the north curve. Several NW-trending lineaments that laterally displaced the modern and ancient valley segments are also described. Our morphological data led to hypothesize that the Ssm north and south curves record a plunged syncline and an anticline, respectively, and that the laterally displaced lineaments are strike-slip faults. Although this type of fault has already been described in the region, the propagation of folds in the Pleistocene-Holocene deposits is a new finding. Assuming this model, the SW- to WSW-plunging folds would suggest a main NW- to WNW-oriented maximum horizontal compression, activated contemporaneously or shortly after the PleistoceneHolocene deposition. This proposed orientation for the stress field is interesting because it would reveal a rotation, in this region, of the main E-W stress field recorded for South America. On the other hand, the suggested NW- to WNW-oriented compression is compatible with the models based on earthquake focal mechanisms comparing data from Brazil and the sub-Andean region. As such, the present work can bring new insights to discuss the impact of the late stage displacement of the South American plate in an intraplate region away from the passive margin, although the contribution of local stresses must be also considered.