Paleoecology of the Pinguela-Palmital-Malvas System, Holocene of the Pelotas Basin, RS, Brazil: an approach focused on the use of multivariate analysis for obtaining diatoms as paleoenvironmental descriptors

Abstract

This work was conducted aiming to reconstitute paleoenvironments of the lacustrine Pinguela-Palmital-Malvas System, placed on the emerged portion north of Pelotas Basin during the Holocene. This study is based on 89 subsurface samples from the PM-RS-DO1 core (4.87 m of total depth), using diatoms as descriptors. Thus, a better objectivity was obtained by defining the species indicative of sets of sampling units originated from levels of significant partitioning in grouping analyses. Between 4.600 ± 70 years BP and 3.950 ± years BP, an alternation occurred between strata constituted predominantly by mixohaline diatoms and intervals characterized by supremacy of freshwater species in a transgressive context; records of Actinocyclus normanii reflect periods of a drier climate as the volume of fresh water drained into the basin was smaller and evaporation was more intense. On the contrary, Aulacoseira cf. agassizii determined the clarification on stages of increment of the lotic influx through positive variation of intensive pluviometric regime. After 3.950 ± 70 years AP, significant sedimentological and biotic alterations, like as the establishment of facies with sandy and greater diversity and abundance of signs of periphytic species characterize the beginning of the Holocene regression process of these Coastal Plains. The maintenance of these coherent paleoenvironmental interpretations, compared with previous studies, and the discovery of original processes for the region show the efficiency of the statistical procedures here used, based on the establishment of significant groupings and the prominence of descriptor species from this partitioning.