SEQÜÊNCIAS DEPOSICIONAIS DA FORMAÇÃO TACIBA (GRUPO ITARARÉ, NEOCARBONÍFERO A EOPERMIANO) NA REGIÃO DE MAFRA (SC), BACIA DO PARANÁ

Abstract

The Taciba Formation constitutes the third major finingupward cycle of Itararé Group, and encompasses three members: Rio Segredo sandstone, Chapéu do Sol diamictite, and Rio do Sul rhythmite, siltstone and shale). In Mafra area, eastern margin of Paraná Basin, the Rio Segredo sandstone do not occur, and the Chapéu do Sol diamictite abruptly overlies the Lontras Shale (top unit of the underlying Campo Mourão Formation). The study of four cored wells and complementary nearby outcrops, allowed to identify two depositional sequences for Taciba Formation. In the Vila Ruthes well (VR-1) and outcrop section, the lower, Taciba-I sequence (TC-I) consists of a 65m-thick interval of diamictite with intercalations of massive argillaceous sandstone (slurry), siltitstone and thin rhythmite; these lithologies display slumping, contorted beds, sandstone dykes, and also a large, in situ turbidite block with dropstone. In its upper part the diamictite is stratified and contains abundant dropstones; it passes laterally in well PP-10 (westwards) to a coarsening-upwards succession of varvic shale, siltstone and slumped thin rhythmite. In the absence of a lowstand tract (Rio Segredo Member), all the above lithofacies can be assigned to transgressive and highstand systems tract. A sandstone interval displaying different facies and thicknesses occur at the base of sequence TC-II, possibly as a lowstand systems tract. In RB-3 well there are 52m of channelized turbidites (A3 Sandstone) overlying thin-bedded rhythmites with dropstones of a glaciolacustrine or marine setting; in the outcrop section which complements the SL-2 well, it occurs 40m of sigmoidal sandstones of fluvio-deltaic origin (A2 Sandstone). The PP-10 well recovered 4.5m of fluvial-estuarine sandstone (A4 Sandstone), and in Vila Ruthes outcrop section (complementary of well VR-1) the A1 Sandstone is composed of a deglaciation system with dropstone-bearing varvites overlain by delta front sandstone. The outcrop section which complements RB-3 well is composed of a deglaciation interval with 10m-thick stratified diamictite, overlain by thin stratified conglomerate and sandstone, bioturbated fossiliferous sandstone and shale, representing the transgressive systems tract. Finally the PP-10 well sampled the upper part of sequence TC-II: two coarsening-upward successions of varved shale, siltstone and rhythmite, with slump structures and few dropstones, forming the highstand systems tract of the sequence.