Mixed carbonate-siliciclastic microfacies from Permian deposits of Western Gondwana: Evidence of gradual marine to continental transition or episodes of marine transgression?

A Permian mixohaline ostracod association of the Teresina Formation, Paraná Basin, Brazil

“…Previous studies in the Xavantes Dam outcrop reported also bivalves from the Pinzonella neotropica Biozone, vertebrate remains, sponge spicules, charophytes (Maranhão & Petri, 1996) and stromatolites (Rohn & Fairchild, 2015). Plant remains such as charophytes and the presence of microphylls of lycophytes are related to the Lycopodiopsis derbyi Phytozone, coeval to the Pinzonellinae bivalve biozones (Holz et al, 2010;Ng et al, 2019). Upper in this section (~ 40 m) lay rocks of the Rio do Rasto Formation, with beds rich in Glossopteris leaves and Leinzia similis bivalves (Rohn, 1997;Rohn & Fairchild, 2015).…”

“…In this work, two localities in the southern São Paulo State corresponding to rocks of the Teresina Formation, Passa Dois Group, are studied (Figure 1). The Passa Dois Group records mainly Middle to Upper Permian rocks (Holz et al, 2010;Ng et al, 2019), and represents a complete cycle of continentalization divided in Irati, Serra Alta, Teresina and Rio do Rasto formations (Milani et al, 1998).…”

“…These units comprise mixed carbonatesiliciclastic microfacies where part of the carbonate rocks is associated to episodic marine incursions (Ng et al, 2019). Especially in the Teresina Formation, the limestones are more abundant at the middle and upper portions of the unit, and usually present cm to dm-scale layers of bivalve and ostracod bearing limestones and microbialites.…”

“…Especially in the Teresina Formation, the limestones are more abundant at the middle and upper portions of the unit, and usually present cm to dm-scale layers of bivalve and ostracod bearing limestones and microbialites. The typically pure ones correspond to oolitic calcarenites (Ng et al, 2019) cemented by sparite, and calcilutites, which may present bivalves and ostracods with disarticulated shells (Rohn, 2001;Rohn et al, 2003). The ostracod assemblage described herein was recovered in peloidal calcisiltites from the Pau Preto Quarry and Xavantes Dam outcrops, correlated to middle to upper portion of the Teresina Formation, respectively (Mello & Sousa, 1985;Maranhão, 1995;Maranhão & Petri, 1996;Rohn & Fairchild, 2015;Bergue et al, 2020).…”

Mineralogy and Pore Structure of Marine–Continental Transitional Shale: A Case Study of the Upper Carboniferous Keluke Formation in the Eastern Qaidam Basin, China

“…Organic-rich shales and associated fine-grained transitional deposits in the Upper Carboniferous Keluke Formation in the Eastern Qaidam Basin were primarily developed in the tidal flat and lagoon facies (Zhang et al, 2016), forming frequently mixed carbonatesiliciclastic sequences (Wei et al, 2018). Currently, mixed carbonate-siliciclastic fine-grained rocks in continental and marine facies and their roles in petroleum accumulation have been widely investigated (Zecchin and Catuneanu, 2017;Abdel-Fattah et al, 2018;Zhang et al, 2018), whereas forming mechanism of high-quality reservoirs in transitional finegrained rocks is poorly understood (Ng et al, 2019;Silva et al, 2021). Previous researchers have evaluated shale gas prospects of the Carboniferous sequences in the Eastern Qaidam Basin based on outcrops and shallow well data, which reported that the Keluke Formation had good shale gas enrichment conditions (Yang et al, 2014;Liu et al, 2016).…”