PALEOCENE POLLEN OF CLASSOPOLLIS (PFLUG) POCOCK AND JANSONIUS FROM CENTRAL PATAGONIA, ARGENTINA

ZAMALOA, MC; VILLAR DE SEOANE, L.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

IANIGLIA Mendoza - CONICET

The distinctive genus Classopollis is traditionally regarded as conifer pollen produced by members of the extinct family Cheirolepidiaceae. Classopollis pollen grains are typically monoporate, oblate and have a circular equatorial outline. A pre-equatorial groove or rimula, with internal striations (endostriae), is a characteristic feature. The proximal pole has a triangular scar that may possess a trilete mark. A thinning of the exine with circular outline (pseudopore) is present in the distal pole. The pollen is frequently found as tetrads or dyads. Classopollis has a long geologic history. This pollen type was recorded since the Late Jurassic to the Late Cretaceous, being widespread and often dominant in the Jurassic and Cretaceous palynofloras worldwide. Remarkably, in central Patagonia Classopollis seems to have persisted at least until the earliest Paleocene, as previous and more recent studies have demonstrated. In order to test the abundance and morphological diversity of the latest members of Classopollis so far known, sediments belonging to the Salamanca Formation, in the San Jorge Basin, central Patagonia, were studied by means of light and scanning electron microscopy. The palynological samples come from Palacio de los Loros and Ormaechea sections, that were recently dated as early Danian (65.7?63.5 Ma), based on multi-disciplinary geochronologic and biostratigraphic studies. The study under LO microscopy allows gross differentiation at species level, and SEM observations produced six different pollen types. Ultrastructurally, the Patagonian Paleocene representatives of Classopollis lack the trilete scar and the sporopollenine filaments that often surround it. In both poles (proximal and distal) there is a thinning of the exine or a large and circular pore (pseudopore). All of the pollen grains are found as monads. The mentioned features are shared by the six recognised types and possibly represent an evolutionary tendency of the genus during the Paleocene. This study also demonstrates that: 1) Classopollis producers survived and were widespread until the early Paleocene in central Patagonia; 2) Danian Classopollis was abundant and diverse in the studied sections; and 3) Classopollis species richness persisted close to the time of the extinction of the genus.