Carbonate microfacies of the San Juan Formation (Ordovician: Oepikodus evae and Oepikodus intermedius conodont zones), Niquivil, Central Precordillera, Province of San Juan (Argentina)

Abstract

This contribution presents the description and interpretation of carbonate microfacies of the San Juan Formation (Ordovician) at the Niquivil section, considering the stratigraphical interval between the Oepikodus evae and Oepikodus intermedius conodont zones. The distribution of the microfacies and the conodonts assemblages allow us to identify different sub-environments within the late Floian carbonate ramp of the Central Precordillera. Five microfacies were recognized from the base to the top: M1 Bioclastic mudstone-wackestone; M2 Bioclastic-peloidal wackestone; M3 Intra-bioclastic wackestone; M4 Intra-bioclastic packstone; M5 Peloidal grainstone. The vertical distribution of these microfacies indicates a shallowing trend of the carbonate ramp in the Niquivil section for this temporal interval, which suggests a middle ramp environment with low energy, without wave action, and that evolved towards the middle-inner ramp environment with more energy by wave action and development of tempestites.

New insights on Lower Ordovician (Floian) reefs from the Argentine Precordillera: Biostratigraphic, sedimentologic and paleogeographic implications

“…Consequently, the late Floian age (O. intermedius Zone) recorded here for the reef and shoal facies in the Niquivil section is strongly supported by the biostratigraphic proposal of Mango and Albanesi (2018a). (Albanesi and Ortega, 2002, 2017Mango and Albanesi, 2018 a, b), South China (Wang et al, 2018), Baltoscandia (Bagnoli and Stouge, 1997;Löfgren and Zhang, 2003), Newfoundland (Johnston and Barnes, 1999;Stouge, 2012), North America (Ethington and Clark, 1982; J o u r n a l P r e -p r o o f Ross et al, 1997). The shadow area shows the study precordilleran reefs age.…”

“…3). The Oepikodus intermedius Zone has already been recorded in several sections in the San Juan Formation by Sarmiento (1990), Lehnert (1993Lehnert ( , 1995, Albanesi et al (1998), Soria et al (2013Soria et al ( , 2017, Soria (2017) and Mango and Albanesi (2018b).…”

“…The top of the San Juan Formation has been dated at several localities. In the northern and south sections, conodonts rendered a Lower Ordovician age (Oepikodus intermedius Zone) for the transitional beds between the San Juan Formation and the black shale of the overlying Gualcamayo Formation (Heredia et al, 2009;Soria, 2017), whereas elsewhere in central sections, conodonts have proved a Darriwilian age for the upper limestone beds of the San Juan Formation (Lehnert, 1995;Albanesi et al, 1998;Heredia and Mestre, 2011;Mestre, 2012;2014;.…”

New early Ordovician conodont data from the San Juan Formation, Central Precordillera (Argentina): Biostratigraphic and paleogeographic significance

“…Serpagli (1974) proposed that the first occurrence of O. intermedius as the boundary between both biozones, besides recorded that the O. intermedius replacing to O. evae during the Fauna C (Serpagli, 1974, Tab.1). This conodont zone has also been recorded in several sections from the San Juan Formation by Sarmiento (1990), Lehnert (1993Lehnert ( , 1995, Albanesi et al (1998), Soria et al (2013Soria et al ( , 2017 and Soria (2017). Soria et al (2017) studied the beds that represent the O. evae and O. intermedius zones from the Niquivil section, and recording Cooperignathus aranda (Cooper) in association with O. evae, O. intermedius, B. extensus and R. andinus, among others, that represent the typical late Lower Ordovician conodont fauna from the Precordillera.…”

“…The conodont assemblage of the O. evae Zone is characterized as the Fauna B, defined by Serpagli (1974) in the San Juan River section (Central Precordillera). Later, the O. evae Zone was mentioned for several Precordilleran localities (Sarmiento, 1987;Beresi and Heredia, 1992;Albanesi, 1998;Mestre, 2008;Soria et al, 2013Soria et al, , 2017 J o u r n a l P r e -p r o o f Albanesi, 2018a), and in allochthonous blocks in the Ponón Trehué Formation (San Rafael, Mendoza) (Lehnert et al, 1998).…”