Sequence stratigraphy of Taciba and Rio Bonito formations in Mafra/SC area, eastern Paraná Basin

Abstract

The Taciba and Rio Bonito (“lower” Triunfo Mbr) formations are divided into six depositional sequences based on cores, gamma-ray and electrical logs from shallow drillings from northern Santa Catarina State. Each sequence is formed by two systems tracts, a lower one, sandy (lowstand) and an upper one, shaly (highstand). The Taciba Formation has three sequences, S0 to S2; sequence S0 has a thick turbidite sandstone at the base (Rio Segredo Member) that pinches out towards the eastern margin and even disappears in the Mafra outcrop area. Sequence S1 varies from a thin fluvial-estuarine system to a thick turbidite sandstone of a channelized fan system; S1 upper shaly system tract is marine in well PP-11, and it is glaciallyinfluenced in well PP-10. Sequence S2 is a thick sandstone body of shallow marine origin, but restricted to one well (PP-11); its upper shaly tract is dominated by massive siltstones intercalated with thin, distal tempestites. The “lower” Triunfo Member (or “Taciba-Triunfo transition”) begins with the arrival of deltaic clastics of sequence S3 lower tract, coarsening-up from medial- to proximal delta front sandstones. Sequence S4 is quite similar to S3, both showing sandstone progradation from north to south, as opposed to the southwest-sourced transgressive diamictites. Sequence S5 consists of fluvial deposits at well PP-12, and two transgressive cycles from wells PP-11 to PP-9, each one of them composed of fluvial-estuarine to marine systems. Well PP-10 is an exception, where the lower cycle presents deglaciation to marine deposits.