Chronostratigraphy and environment of Furnas Formation by trace fossil analysis: Calibrating the lower Paleozoic Gondwana realm in the Paraná Basin (Brazil)

Abstract

Ichnology is an important tool for facies and sequence stratigraphic analysis, typically yielding greater resolution than that provided by body fossils. Less commonly, ichnofossils also can be applied to ichnostratigraphy, a variant of biostratigraphy that aids in determining stratigraphic age of sedimentary sequences. Previous publications on the Furnas Formation (Paraná Group, early Paleozoic of the Paraná Basin), have yielded different interpretations of age, depositional environment, and sequence stratigraphic framework. Deposition in fluvial environments has been proposed in many papers, although a tide-influenced marine context has been inferred since the presence of Cruziana and Rusophycus was reported during the 1990s. Sequence stratigraphic interpretations also differ, mainly regarding the presence or absence of a sequence boundary between the middle and upper units of the Furnas Formation. The absence of body fossils in all but the topmost part of the upper unit, which contains Lochkovian (Lower Devonian) palynomorphs and primitive plants, has precluded age determination for the Furnas Formation in general. Here, we demonstrate the utility of both ichnofacies and ichnostratigraphic analysis to elucidate such questions. The studied sections are located in the cities of Tibagi, Palmeira and Ponta Grossa (Guartelá, Sítio Canei and São Jorge sections, respectively). Seventeen ichnotaxa are recognized, doubling the number of previously known ichnotaxa: Cruziana acacensis elongata and Rusophycus acacensis n. ichnosp. (in the lower and middle units); Arthrophycus alleghaniensis, A. brongniartii, Rhizocorallium commune, Didymaulyponomos rowei and Heimdallia chatwini (middle unit only); Arenicolites, Cylindrichnus and Diplocraterion (lower and upper units); Lockeia siliquaria and Psammichnites implexus (middle and upper units); Rosselia socialis (upper unit); and Palaeophycus tubularis, Didymaulichnus lyelli, Skolithos, and Thalassinoides (all units). Assemblages of these ichnofossils are assigned to Skolithos and proximal Cruziana ichnofacies. Ichnologic data, combined with associated physical sedimentary facies associations, indicate predominantly tide-influenced marine depositional environments. The presence of ichnotaxa of stratigraphic value (Arthrophycus alleghaniensis, A. brongniartii and Cruziana acacensis elongata) in lower and middle units indicates an Early Silurian age. This, in turn, indicates that a significant unconformity exists between the middle and upper units of Furnas Formation. Although the precise magnitude of this stratigraphic gap is difficult to establish, this break likely is linked to the Late Silurian global regression.

The oldest Devonian circumpolar ray-finned fish?

“…Host matrix comprises bioturbated yellowish siltstone with parallel lamination and lenticulation. It contains a lingulid brachiopod indicative of a marine setting (electronic supplementary material S1), narrow burrows oriented parallel to bedding with rare interconnecting vertical tubes (see Thalassinoides [23]), and multiple undulating horizontal burrows (see Phycosiphon [24]).…”

“…Candidate deposits in Ponta Grossa are exclusively Palaeozoic and lie within the Apucarana sub-basin of the Paraná Basin (figure 1 a , b ). The upper Silurian–Lower Devonian (Pridoli–Lochkovian) Furnas Formation is the oldest and comprises sandstones, shales and mudstones representing a fluvial or coastal setting [24,26]. This disagrees with the associated matrix and seems unlikely on biostratigraphic grounds.…”

Paleoenvironments of a regressive Devonian section from Paraná Basin (Mato Grosso do Sul state) by integration of ichnologic, taphonomic and sedimentologic analyses

“…At least in the south part of the basin, the Paraná Supersequence spans in age from Lower Silurian (Sedorko et al 2017) to Middle Devonian (Grahn et al 2013) in outcrops, with Upper Devonian ages preserved only in subsurface (Bergamaschi 1999, Grahn et al 2013, Sedorko et al 2018c). Grahn et al (2013) used microfossil zonation to correlate the ages of the lithostratigraphic units from southern basin (referred by them as Apucarana sub-basin) and northern (Alto Garças sub-basin).…”

“…The Chapada Group unit 1 contains the basal marginal-marine and shallow marine sandy deposit and is mostly correlated with Furnas Formation from southern part of the basin (Grahn et al 2013). The lower and middle units of Furnas Formation were deposited during Lower Silurian, based on its trace fossils with ichnostratigraphic value (Sedorko et al 2017).…”

Ichnological Research of Silurian–Devonian Strata and the Zoophycos Distribution in the Paraná Basin

“…The early records of trace fossils for the Silurian-Devonian strata of Paraná State were made by Oliveira (1912), Clarke (1913), and Lange (1942), with references to the presence of "tubes of worms" for the Furnas and Ponta Grossa formations. However, ichnologic studies in that units were more frequent in the literature between the 1980s and 1990s (Ciguel & Aceñolaza, 1986;1989;Campanha, 1985;Fernandes & Melo, 1985;Assine, 1996;Fernandes, 1996), although recent studies are available in the literature (Netto, Tognoli, Assine & Nara, 2014;Sedorko et al, 2017, Sedorko, Bosetti & Netto, 2018aSedorko, Netto & Savrda 2018b;Sedorko, Netto & Horodyski, 2018c, 2019Sedorko et al, 2021).…”