Lower Jurassic calcareous nannofossils from the Neuquén Basin, Argentina: New insight for the opening of the Hispanic Corridor

CHAUMEIL RODRÍGUEZ, MICAELA; MATTIOLI, EMAUELA; PÉREZ PANERA, JUAN PABLO

Santos

Congreso; INA Meeting 17; 2019

The existence of a marine connection between the Tethys and Panthalassa Oceans has been a topic of debate since long time. Ziegler (1971) first proposed the existence of a seaway - the Hispanic Corridor- in the Early Jurassic, but the precise timing of its definitive opening is still unknown. Although consensus set the Early Pliensbachian as the age of this event, most studies were conducted on macrofossils or nectonic organisms, relegating other data like microfossils (Bown, 1992; Boomer & Ballent, 1996; Arias, 2007; Angelozzi & Pérez Panera, 2016; Martínez & Olivera, 2016) and isotopes (van de Schootbrugge et al., 2005; Dera at al., 2014). As for the nannofossils, the classical region studied in detail to interpret paleogeographical changes in Lower Jurassic is the Western Tethys (Europe and North Africa), and sporadically coccolith record has been documented from the Southern hemisphere (Pacific Realm). We present a detailed report on calcareous nannofossils from this last region. The Matuasto I section (Los Molles Formation, Neuquén Basin), dated to Early Pliensbachian (~190Ma) between the FO of Similiscutum and the FO of Biscutum grande, yields an assemblage with abundant typical tethyan taxa like Mitrolithus lenticularis and Schizosphaerella punctulata. The occurrence of these species is sporadic in the Northern Tethys, but they are common in its Southern part (Bown, 1987) and in the Proto-Atlantic region (Portugal and Morocco). The most parsimonious explanation is the presence of an effective connection between the Tethys and Panthalassa Oceans at that time, because nannoplankton need a well-established active current system to migrate. Thus, calcareous nannofossils can be a powerful tool to improve the reconstructions of the connection between the Tethys and Panthalassa Oceans through the Jurassic.