Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

130 PATA Days 2024 other hand, structures like load cast, ball-and-pillow structures, pseudonodules, and flame structures have been interpreted with magnitudes between 5.5 to 8 (Rudersdorf et al., 2017). Deformed lamination structures have been associated with seismic events with magnitudes of at least 5.5 (Rodrı́guez-Pascua et al., 2000). Finally, the high-angle brittle normal micro- faults may have been caused by seismic movements of magnitude equal to or greater than 6. The analysis of the tectono-sedimentary regime of the Upper Cretaceous Amazon Basin indicates significant tectonic activity coinciding with the deposition of the Tena Formation. This formation, originating during the Maastrichtian in a continental depositional environment, is contemporaneous with the basin inversion period induced by the uplift of the Andes Mountains (Gaibor et al., 2017). It is concluded that seismic events occurring in the Upper Cretaceous likely triggered liquefaction and fluidization processes, leading to the formation of the observed SSDS. These seismic events are estimated to have had a magnitude exceeding 5.0, meeting the threshold required to induce liquefaction processes. C O N C L U S I O N In conclusion, at least four stratigraphic units composed of mudstone, claystone, and fine-grained sandstone display extensive structures of soft sediment deformation. These structures exhibit ductile features including loop bedding, pseudonodules, ball-and-pillow, deformed lamination, load cast, and flame structures. The estimated magnitudes associated with the paleoseismic events that led to the formation of the SSDS in the study area likely exceeded Mw 5. Furthermore, analysis of the tectono- sedimentary context suggests that the inversion of the Amazon Basin during the Upper Cretaceous, within the context of the uplift of the Andes, was the most probable source of seismic activity triggering the SSDS. Acknowledgements: I want to thank the Research Project CTC-006-2020 and the OLLIN Project, because within them this research was possible. I also give thanks to INQUA/TERPRO, the OLLIN Network, and the Universidad Regional Amazónica Ikiam for the scholarships I received to conduct this study and participate in international events. Their assistance has been essential in carrying out this work. • Triggering mechanics The research delves into the formation of SSDS and explores various potential triggers, encompassing storm waves, bioturbation, tsunamis, glacial activity, rapid sedimentation, and seismic events. The identified deformationstructuresinclayeyandmuddysedimentary deposits suggest the occurrence of liquefaction and fluidization processes (Menzies et al., 2016). The prospect of glacial activity inducing liquefaction and/or fluidization in the Tena Formation is dismissed, as the prevalent climate in the Upper Cretaceous in the Amazon Basin was arid to semi-arid (Alencar et al., 2021). Bioturbation is also ruled out due to the lack of evidence for invertebrate burrows or vertebrate traces. Moreover, the dominance of continental deposits in the Tena Formation (Gaibor et al., 2017), coupled with the abundance of very fine-grained sediments in low-energy conditions, implies a lagoon, swamp, or floodplain environment, thereby eliminating the possibility of liquefaction and/or fluidization triggered by storm waves and/or tsunamis. The absence of coarse deposits, blocks, and debris flow- associated sediments further negates the presence of steep slopes, excluding gravitational detachment and landslides as plausible mechanisms.The research inclines toward seismic activity as the probable triggering mechanism for SSDS. Supporting evidence includes similarities between observed structures and those generated in laboratory seismic simulations, along with morphological characteristics consistent with seismicity-induced deformations observed globally. The stratigraphic column highlights specific layers with deformation structures, underscoring the instantaneous nature of the triggering mechanism. • Estimating magnitudes Attributing the deformation structures to a seismic origin, we will proceed to interpret the possible magnitude of the events causing the structures in the Tena Formation based on the research by Rodríguez-Pascua et al. (2000). The formation of deformation structures like loop bedding reflects weak and repetitive seismic shaking affecting the layers during their lithification process. These structures have been associated with magnitudes below 5 (Calvo et al., 1998). On the