Late Cretaceous palynomorphs from the Golfo San Jorge Basin, Argentina

摘要

A lithofacial and palynological study was carried out on the Can?ad?on Seco Formation in the La Frieda Oeste x-1 well (Golfo San Jorge Basin). According to sedimentological characteristics of the core four main litofacies lithofacies are defined: 1. Cross-bedded sandstones, 2. Interlaminated fine-grained sandstones and mudstones, 3. Shales, and 4. Muddy tuff. The cross-bedded sandstones correspond to channel deposits, which are interpreted as lateral bars (point bars) or attached bars. The interchannel area is dominated by interlaminated fine-grained sandstones and mudstones, together with shales. The former represents sedimentation occurred in proximal floodplain areas, while shales correspond to deposition in distal floodplains, where thin and scarce muddy tuff intercalations indicate ash fall events. The palynological assemblage here analyzed was recovered from the green shales corresponding to distal floodplains areas, probably surrounding temporary water bodies. The floristic assemblage contains abundant fern spores as a dominant group, followed by angiosperm and gymnosperm pollen grains. Bryophyte and lycophyte spores, along with fungal remains, are also present in lower proportions. Based on the taxonomic content of the palynoflora, a Turonian?Coniacian age is suggested for this assemblage. Additionally, some taxa present in the assemblage allow inferring temperate to warm and humid conditions. This new record represents a period of time little known for the evolution of angiosperms in the southern region of Gondwana.