Integrated sedimentological and palynological analysis from Early Cretaceous estuarine deposits in the southern-central Neuquén Basin, Argentina

Abstract

The Mulichinco Formation represents one of the main gas producer unit in the Neuquén Basin and particularly, an improvement in its reservoir qualities are mostly indicated in subsurface for its upper section. Because the economic importance of this interval, sedimentological and palynological analysis were made on deposits from outcrops of the upper section of the unit, located at the southern-central Neuquén Basin. The studied section includes four main facies association which represent accumulations in a wave-dominated estuary, non-previously described for the Mulichinco Formation in the study area. In addition, sixty-six new palynomorphs species were identified which were new for the unit, including fifty-six spore species, twenty-five pollen grain taxa, and two algae. Ferns and conifers species were identified as dominant taxa. Moreover, mega and palynofloristic assemblages provide information about drainage conditions of the inhabited environment, suggesting spatial variations when comparing upland subaerial well-drained plains with lowland subaqueous poorly-drained areas and, at the same time, climatic variations are considered, inferring temperate to warm and wet palaeoclimatic conditions. The integration of sedimentological and palynological interpretations provides a more complete picture of the Valanginian estuarine system and ecosystem that developed towards the southern-central area of the Neuquén Basin. Furthermore, the studied palynological assemblages are consistent with a Late Valanginian age, and can be referred to the Zone 2 and to the Cyclusphaera psilata-Classopollis Association suggested for the Neuquén Basin.