BIOSTRATIGRAPHICAL AND PALEOBIOGEOGRAPHICAL SIGNIFICANCE OF LYTOCERATID AMMONOIDS FROM THE SANTONIAN MAASTRICHTIAN OF THE JAMES ROSS BASIN, ANTARCTICA

RAFFI, MARÍA EUGENIA; MILANESE, FLORENCIA N.; OLIVERO, EDUARDO B.

Punta Arenas

Congreso; IX Congreso Latinoamericano de Ciencia Antartica; 2017

Instituto Antártico Chileno

Although paleontological studies of Antarctic ammonites have been published since the early 1900s, the James Ross Basin (Fig. 1) lytoceratid fauna was scarcely known, supporting previous assumptions that lytoceratids, particularly the gaudryceratids, were rare in the Upper Cretaceous of southern latitudes. In addition, the lytoceratids, particularly the Gaudryceratidae, are considered of low biostratigraphic importance based on the assumption that they are a compact group of Cretaceous ammonoids with relatively stable morphology and long-ranging stratigraphic distribution. Belaying these previous assumptions, we havefound that gaudryceratids ammonites are abundant in the Santonian-Campanian of the James Ross Basin, with more than 2000 specimens collected from the classical localities of the basin, and this gaudryceratid fauna is very diverse, including five genera and 16 species. Thus, the main objectives of this presentation is to briefly discuss the biostratigraphical and paleobiogeogeographical significance of this fauna.The biostratigraphical zonation of the Santonian-Maastrichtian of the Marambio Group was mainly based on kossmaticeratid ammonoids at the generic level (Olivero and Medina, 2000;Olivero, 2012). Nonetheless, the study of more than 2000 Upper Cretaceous lytoceratid specimens have resulted in the recognition of five successive stratigraphic intervals (Fig. 2;3) characterized by: 1) Gaudryceras cf. G. strictum, Santonian; 2) Gaudryceras santamartense Raffi and Olivero 2016, Santonian?early Campanian, 3) Gaudrycerasbrandyense Raffi and Olivero 2016, Tetragonites cf. T. glabrus variety I and Anagaudryceras sp. juvenil, late early Campanian??basal mid Campanian; 4) Gaudryceras cf. G. mite, Gaudryceras rabotense Raffi and Olivero 2016, Gaudryceras sp. nov. Anagaudryceras sp.nov. A y B, Zelandites sp. and Tetragonites cf. T. glabrus variety II; and 5) Anagaudrycerassp nov. C., Anagaudryceras sp. nov. D and Saghalinites sp. nov., late Campanian?Maastrichtian. The paleobiogeographical analysis indicates a dominant cosmopolitan Santonian-early Campanian distribution and an endemic mid Campanian-Maastrichtian distribution. In this context, while Gaudryceras cf. G. strictum, G. santamartense and Gaudryceras cf. G. mite have strong affinities with cosmopolitan or Indopacific ? Norpacific species; Gaudryceras brandyense, Gaudryceras rabotense, Gaudryceras sp. nov. and the newAntarctic species of Anagaudryceras are clearly different from other species of their genus and appear to be mainly restricted to Antarctica, with the exception of Gaudryceras rabotense and Anagaudryceras sp. nov. A also recorded in the Campanian of the Austral-Magallanes Basin. Moreover, the species of the subfamily Tetragonitinae, Tetragonites and Saghalinites, present a worldwide distribution in the Santonian-Maastrichtian. However,while the Campanian Tetragonites species have some affinity with the Indo-Pacific speciesTetragonites glabrus, the Antarctic species of Saghalinites differs clearly from other species of the genus and appears to be mainly restricted to the late Campanian-late Maastrichtian of Antarctica