Upper Cretaceous Limnocytheridae (Ostracoda Crustacea) From Argentina.

CARIGNANO, A; CUSMINSKY G. C.

Roma

Simposio; 17th International Symposium on Ostracoda; 2013

Universidad de Roma tre

In the Upper Cretaceous of Argentina, although dominated by cypridoids,the limnocytherids are a common component of the ostracods associations.Severalspecies were described from the Allen and Loncoche formations (late Campanian-early Maastrichtian, Neuquén Basin), recovered from sediments deposited underfresh to brackish water conditions. Wolburgiopsis sp.differs from W. neocretacea(Bertels) in its left valve that overlaps the right one in the posterior border, reticulated surface of broad muri and the smooth margins of the carapace. Both taxa presents spread sieve pores over the surface and are the most common limnocytherids in the associations. A related genus, Looneyellopsis K RÖMMELBEIN & WEBER, 1971 previously described from the Lower Cretaceous of Brazil and Argentina (MUSACCHIO, 1970), is represented in the uppermost Cretaceous of the Neuquén Basin by Looneyellopsis sp. This species presents the carapace surface strongly ornamented by tubercles, slender ribs and deep pits over the tubercles, resembling a honey- comb. Another component of the associations is Paralimnocythere Carbonnel, with two species characterized by a squarish posterior border, dorsal margin sloping backwards, and an alar expansionthat modifies the carapace in dorsal view. Finally, the Timiraseviinae are represented by Vecticypris sp. 1, distinguishable by a swollen carapace with pitted surface (CARIGNANO & VARELA, 2011) and Vecticypris sp. 2, whose surface is covered by an irregular reticulum that becomes parallel to the margins of each valve. In summary, during Campanian-Maastrichtian times the Limnocytherinaeare represented by a group of small ostracods and become an important component of the assemblages, with the Timiriaseviinae remaining as a minorpart. Probably, these taxa were better adapted to the changes in the environmental conditions, since several parts of Argentina were covered by a very shallow sea, with a flat coast and surrounded by lagoons with freshwater input. On the other side, the limnocytherids described here show more affinitieswith those of the Adamantina Formation(BaurúGroup, Brazil), considered by DIAS-BRITO et al. (2001) as Turonian-Santonian, rather than with theoverlying Marília Formation (Maastrichtian). More studies in pre-Campaniansediments of the Neuquén Basin should be done to resolve this matter.