Tafonomia de biválvios em calcários oolíticos da formação Teresina (Bacia do Paraná, permiano médio, prudentópolis, PR)
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Data
2010-01-01
Autores
Neves, Jacqueline Peixoto [UNESP]
Rohn, Rosemarie [UNESP]
Simões, Marcello Guimarães [UNESP]
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Resumo
Herein, it is presented the first detailed taphonomic study on bivalve mollusk shells preserved in the oolitic limestones of the Teresina Formation (probably Kungurian-Roadian, Lower-Middle Permian) in the eastern margin of the Paraná basin. The selected beds are located in two quarries (informally named PRU 1 and PRU 2) in Prudentópolis municipality (Center-South Paraná State), and positioned approximately in the middle of the formation and probably in the Pinzonella illusa Zone. The PRU 1 limestone (∼30 cm thick), which is partially silicified and intercalated with predominantly pelitic rocks, is classified as a bivalve oolitic grainstone. The basal contact is erosive and the top shows symmetrical ripple marks, which are draped by shale with mud cracks. There are two fining-upwards successions characterized by dense to dispersed packing of the shells, which are usually disarticulated, randomly oriented (many nested/stacked) and mixed with some pelitic intraclasts. Microhummocky cross-stratification occurs a little below the top of the bed. The PRU2 bed is classified as ooidbivalve rudstone (∼5 cm thick), where all shells are disarticulated and fragmented, showing dense packing. The bivalves probably inhabited a muddy substrate and were mixed (as parautochtonous and allochthonous bioclasts) with ooids during high-energy storm events, including posterior shell displacement as a result of bioturbation. Thus, the calcareous beds represent amalgamated proximal tempestites with a complex taphonomic history, strong temporal/spatial mixing of bioclasts and limited paleoecological resolution. They are a typical example of shell beds generated in a huge epeiric sea, which was not necessarily connected to the ocean and where very low depositional-slope gradient, very slow subsidence and minimum sediment accommodation space caused frequent sediment reworking by storm related processes.
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Limestone, Paraná Basin, Permian, Taphonomy, Teresina Formation
Como citar
Geologia USP - Serie Cientifica, v. 10, n. 3, p. 19-36, 2010.