A silicoflagellate from the middle Albian of Austral Basin, Argentina

Abstract

Calcareous nannofossil biostratigraphic investigations of Cretaceous sediments within the southern high latitude Austral Basin, Argentina, have revealed the presence of a fragment of a silicoflagellate possibly belonging to the species Variramus aculeifera (Deflandre) McCartney, Wise, Harwood and Gersonde. Although only a fragment was identified in the samples examined from this locality, its presence is important, as it is only the second documented occurrence of an Early Cretaceous silicoflagellate. The specimen was found in a subsurface sample from the informal Palermo Aike Formation at Austral Basin. This stratigraphic level is interpreted as middle Albian on the basis of calcareous nannofossil biostratigraphy. The specimen consists of a fragmented strut with broken spines at the base, which allows the observation of the hollow skeletal structure. The strut is curved and slightly expanded at the widest part, which are characteristics diagnostic of the genus Variramus.Estudios sobre nanofósiles calcáreos en sedimentitas cretácicas de la Cuenca Austral, Argentina, revelaron la presencia de un fragmento de un silicoflagelado, posiblemente de Variramus aculeifera (Deflandre) McCartney, Wise, Harwood and Gersonde. A pesar de que se recuperó solo un fragmento, su presencia es importante porque representa el segundo registro de silicoflage-lados del Cretácico Temprano. El espécimen fue hallado en una muestra de subsuelo correspondiente a la Formación Palermo Aike, en la Cuenca Austral. Ese nivel estratigráfico fue interpretado como Albiano medio sobre la base de los nanofósiles calcáreos. El ejemplar corresponde al fragmento de una barra con espinas rotas en la base, que permitieron observar la naturaleza hueca del esqueleto silíceo. La barra es curva y presenta un leve ensanchamiento, dos características diagnósticas del género Variarmus.