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

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

Lyon

Congreso; 10ème Congrès des Doctorants de l'Observatoire des Sciences de l'Univers; 2021

A marine connection between the Tethys and Paleo-Pacific (Panthalassa) Oceans likely existed since the Early Jurassic, but the nature of such connection has been long debated. The earliest mention of the existence of a seaway in the Early Jurassic - the so-called “Hispanic Corridor” - appeared in the early 70’s, but the precise moment of its opening is still discussed. The age of this event was set in the early Pliensbachian (190.8-182.7 My), however a sea-floor crust indicating oceanic opening is dated to Bathonian-Callovian (168.3-163.5 My). Most studies were conducted on nektonic or nekto-benthonic organisms -such as ammonites, marine reptiles, bivalves, brachiopods, fishes- which were able to actively migrate. The use of microfossils, which comprise remains of planktic organisms such as calcareous nannoplankton, providing information about established oceanic currents, is much limited yet. Neodymium isotopes were used to assess oceanic circulation in the Early Jurassic, but the limited set of data prevents interpretations on the existence of an oceanic connection.The classical region studied for Early Jurassic calcareous nannofossils is the Western Tethys (Western Europe and North Africa), letting the coccolith record from the southern hemisphere (Pacific Realm) far behind. Herein, a detailed report on calcareous nannofossils from the Neuquén Basin (Argentina) is presented. The Matuasto I section of Los Molles Formation, dated to as Pliensbachian based on nannofossil zones (NJT4a to NJT4c) was compared to contemporaneous records from Western Europe. The section yields an assemblage with abundant typical Tethyan taxa, like Biscutum grande Bown, 1987, Mitrolithus lenticularis Bown, 1987 and Schizosphaerella punctulata Deflandre & Dangeard, 1938. These species occur sporadically in the early Pliensbachian of the Northern Tethys, but they are common in its Southern part and in the Proto-Atlantic region (Portugal and Morocco). The most parsimonious explanation for these similarities is the presence of an effective connection between the Tethys and Paleo-Pacific Oceans since the early Pliensbachian, because nannoplankton need a well-established active current system to migrate. Hence, calcareous nannofossils prove to be a powerful tool to enhance paleobiogeographic and palaeoceanographic reconstructions.