Late Miocene Molluscs from the Southwestern Atlantic Ocean (Argentina and Uruguay): a paleobiogeographic analysis

SERGIO MARTINEZ,; CLAUDIA DEL RÍO,; DEL RÍO, CLAUDIA JULIA

Paleogeography Paleoecology And Paleoclimatology

Lugar: Amsterdam; Año: 2002 vol. 188 p. 167 - 187

The analysis of the structure and evolutionary history of the Late Miocene marine molluscs along thesouthwestern Atlantic littoral indicates that these faunas did not give rise to the present assemblages of theArgentinean Province of the same region, the latter being characterised by a typically transitional association (in thesense of Scarabino [(1977) Com. Soc. Malac. Urug. 4, 177^285]) that developed after Miocene times once the coldMalvinas (Falkland) Current was completely operating. The Late Miocene Valdesian and Paranaian Provinces,mainly composed of paratropical warm-water faunas, are defined in this paper. The former includes assemblagesrecovered from the Puerto Madryn Formation. Its southern limit is placed at 42‡S, while in the north its boundarywith the Paranaian Province is situated approximately between 37 and 39‡S. The Paranaian Province includesassemblages belonging to the Parana¤ and Camacho Formations. It extends northwards along the Uruguayan andsouthern Brazilian littoral, but its northern boundary still remains unknown. An incipient thermal gradient isrecognised, as the temperature values for the Paranaian Province are slightly higher than those for the ValdesianProvince. Taking into account that in the Valdesian Province water temperature was in fact warm, it is concluded thatthe cold Malvinas (Falkland) Current still had a very low activity in the area during the Late Miocene. The presenceof upwelling phenomena is also suggested by the presence of widely distributed turritellid beds in the northernPatagonian region.> 2002 Elsevier Science B.V. All rights reserved.