PALYNOLOGY FROM THE CENOMANIAN PUESTO EL MORO FORMATION (SANTA CRUZ PROVINCE, ARGENTINA)

SANTAMARINA, P.; PEREZ LOINAZE, V.S.; LIZZOLI, S.; VARELA, A.N.

Otro; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2023

Angiosperms originated during the Early Cretaceous in low latitudes and spread towards the poles through Late Cretaceous. This event reconfigured the continental biomes, altering the abundance of previous dominant groups and causing extinctions and the origin of new clades. Despite of all the work done on paleobotany in Argentina, there are still gaps in our understanding on how the origin and rise to dominance of angiosperms altered the continental biomes. Here we present the palynological content of the Puesto El Moro Formation (Cenomanian, Santa Cruz Province). The unit is composed by dark colored siltstone and claystone which turn reddish to the top of the unit, interbedding with fine to medium-grained sandstones. Three different informal sections were described for the unit, based on their depositional environments, these are: a shallowing-upward estuary (lower section), followed by a braided type fluvial system (middle section), and completed with a distributary fluvial system (upper section). Paleosol development were recognized in the three sections. The Puesto El Moro Formation was stratigraphically correlated with the Cenomanian Mata Amarilla Formation, which outcrops 50 kilometers to the south-east of the study area. Fifteen levels were surveyed taken from the first two informal sections, were both continental and marine elements were recovered. The samples were collected in the Estancia Kachaike (49°04’32’’S - 2°06’06’’W). Palynological counts were possible on 11 of the surveyed levels. This data was used for calculations on richness and evenness. A total of 138 continental species were identified, comprising 23 bryophytes and lycophytes, 66 ferns, 34 gymnosperms, and 15 angiosperms. Also, seven species of fresh water algae were recognized. Gymnosperms dominate the assemblages (average= 76%), with Classopollis, Cyclusphaera, and Podocarpidites as the most representative taxa. Ferns are the second most abundant group (average= 22%), with Cyathidites, Gleicheniidites, and Cicatricosisporites as the most represented taxa. Angiosperms, bryophytes and lycophytes represent 2% of the assemblages in average. Foraminisporis and Densoisporites are the most abundant bryophytes taxa, and Clavatipollenites is the most represented angiosperm taxa. The richness values obtained for the Puesto El Moro Formation display a general increasing trend across the section, with three peaks in richness observed. Regrettably, the lack of internal stratigraphic control in the Puesto El Moro Formation prevents us to make more detailed correlations with the Mata Amarilla Formation.