Tectonic influence and isotopic signature of pre-salt lacustrine carbonates in the Tupi field, Santos Basin

Fault networks in the Santos Basin play a key role in controlling depositional environmental conditions for sedimentation of the Barra Velha Formation. This work investigates how fault activity and reactivation affect the pre-salt carbonates and influence element distribution, integrating seismic interpretation, structural restoration and geochemical analyses for major elements (Ca, Mg, Sr, Fe, Mn) and isotopes (δ¹³C, δ¹⁸O, ⁸⁷Sr/⁸⁶Sr). Results reveal three dominant fault sets (NNW-SSE, N-S, NNE-SSW), with significant deformation in the central sector of the Iracema region indicated by section restoration. Isotopic data of δ¹³C (0.79 ‰–3.16 ‰) and δ¹⁸O (−1.22 ‰–3.86 ‰) from the studied well are consistent with other fields in the basin, which reflects that regional control overcomes local tectonic impact on deposition. However, the lacustrine depositional setting is described with episodic environmental changes as Fe and Mn present extreme outlier values and faults may influence Sr mobilization in fluid migration. The ⁸⁷Sr/⁸⁶Sr values (0.7130–0.7144) suggest a dominant felsic continental source, with minor volcanic input. These findings reinforce the role of faulting in controlling element mobility and the structural evolution of pre-salt carbonates in the Tupi field.