Neotectonic influence on a delta landscape genesis downstream the Amazon River – North Brazil

Many researchers have inferred that the genesis and formation of fluvial features at the mouth of the Amazon River (North Brazil) are related only to the sea level changes occurred in the Quaternary. In addition, there are still few works that take into account the possible influence of Neotectonics on the formation of these features, such as in the Breves-Boiuçu delta, located close to the Marajó Island, at the mouth of the Amazon River. This delta formed during the marine regression occurred around 5000 years BP, which caused silting of important rivers within the current delta feature. However, possible relations between the delta genesis and tectonic structures that have been reactivated since Miocene, as the Gurupá Arch, are still under debate. In this sense, the objective of this work is to evaluate the possible neotectonic influences on the formation of the Breves-Boiuçu delta. In order to achieve this objective, semi-automatic detection of structural lineaments was performed. Following the classical paradigm of Donald Wise, we have considered that the trend of the principal lineament domain corresponds to the main horizontal crustal stress (Shmax). Such lineaments were identified on pre-processed Shuttle Radar Topography Mission (SRTM) data, by means of the software SID3. These information were cumulated in databases and statistically analyzed by Daisy 3 software (https://host.uniroma3.it/progetti/fralab/Downloads/Daisy_Program/). In addition, drainage anomalies were mapped, considering that they are indicative of tectonic control on the river network. Finally, the possible size variation of the delta in the last 30 years was analyzed, evaluating its progradation rate through satellite images (Landsat 7 and Sentinel2). The results of the analysis of the lineament domains for the regional and local scale point to two possible tectonic models, in which it is possible to recognize the subsidiary fractures and shear fractures associated to a main regional strike-slip (R-Riedel shears, T-tension fractures, Y and X –shear fractures). According to the first model, dextral shear corridor E-W trending characterizes the investigated area with Shmax NW-SE oriented. Normal faults, joints, and T fractures follow this last orientation, whereas the structures E-W and N-S mapped correspond to, respectively, Y (dextral) and X (sinistral) faults. In the second model, a dextral shear zone NE-SW orientated exists, and E-W structures correspond to T fractures, whereas the N-S structures are dextral P faults. Regarding the drainage network analysis, several tectonic indicators were identified, such as: rectilinear drainages, elbows, and paleo-channels. Further studies are necessary to understand which tectonic model better characterizes the region, as well as the influence of neotectonic activity on the evolution of the deltaic landscape.