Palynostratigraphy of the Chapada Group and its significance in the Devonian stratigraphy of the Paranل Basin, south Brazil

The Alto Garças Sub-basin in the northern part of the Paraná Basin evolved differently from the Apucarana Sub-basin in the south. The marine environment was shallower in the Alto Garças Sub-basin, which contains proportionately more silty and arenaceous rocks. The formations and members defined in the Apucarana Sub-basin are therefore difficult to apply in the Alto Garças Sub-basin, where the Chapada Group (units 1–4) is more applicable. An integrated miospore and chitinozoan biozonation of the Chapada Group facilitates direct correlation between the Chapada Group’s units and the classical formations of the Paraná Basin as defined in the Apucarana Sub-basin. The Furnas Formation and Chapada unit 1 constitute the same lithostratigraphic unit. Beds with rhyniophytes in the uppermost part of the Furnas Formation contain palynomorphs representative of the Si phylozone within the MN spore Zone (late Lochkovian), and the rhyniophyte beds occupy the same stratigraphic interval within Chapada unit 1 (the Lochkovian of the Paraná Basin lacks chitinozoans). The lower part of Chapada unit 2 contains spores of the PoW Su spore Zone and chitinozoans of the Ramochitina magnifica and Ancyrochitina pachycerata zones, together indicating a late Pragian–early Emsian age-span. The upper part of Chapada unit 2 corresponds to the GS (AP) and Per (AD pre-Lem) spore Zones, and chitinozoans of the Ancyrochitina parisi, the informal Ancyrochitina varispinosa and Alpenachitina eisenacki chitinozoan zones, thus suggestive of a late Emsian – earliest Givetian age-span. Unit 3 is a proximal and lateral facies equivalent of the upper part of unit 2. The lower part of unit 4 includes spores typical of the early Givetian Lli (AD Lem) spore Zone and chitinozoans of the Ramochitina stiphrospinata chitinozoan Zone; the uppermost (early late Frasnian) part contains spores of the lower BMu (IV) spore Zone and chitinozoans of the Lagenochitina avelinoi chitinozoan Zone. The sandstones of unit 3 were inundated during the earliest Givetian, and the resultant flooding surface marks the base of unit 4 basin-wide. Clearly, the two sub-basins were distinct depositional centers during the Devonian.