Palaeobiogeography of Early Jurassic bivalves along the southeastern Pacific margin

DAMBORENEA, S.E.

Buenos Aires, Argentina

Congreso; 13o Congreso Geológico Argentino y 3o Congreso de Exploración de Hidrocarburos; 1996

Asociación Geológica Argentina

The palaeogeographical position of South America during the Early Jurassic and the availability of outcrops make this part of Gondwana a privileged place to study the transition between Austral and Tethyan benthonic faunas. With this aim, the palaeobiogeographical distribution of bivalve species from 22o to 46o S latitude has been analyzed. In central Chile and Argentina the occurrence of typically Tethyan bivalves in the same area as high-latitude bivalve species is a consequence of a mid-latitude position of this region during the Early Jurassic without significant barriers along the East Pacific margin, the probable pantropic nature of Tethyan faunas, and a shallow sea connection with the western Tethys from middle Early Jurassic times onwards. As a result, no sharp limits between Tethyan and Austral Realms could be recognized and a wide area of mixed faunas is revealed instead. The approximate latitudinal location of the boundary area is proposed on the basis of faunal composition along the study region. There is a southward shift of the northern boundary of the Austral Realm between Hettangian and Toarcian times of about 700 to 900 km (8° to 10°).