Holocene palaeoenvironmental and palaeoclimatic reconstruction of a native ecosystem on the coastal plain of southern Brazil through multi-proxy analysis

Abstract

The Butiazal de Tapes (30°31′39.86″S, 51°21′31.02″W) region is located in southern Brazil on the western shore of the Patos Lagoon and presents a remnant of a native palm grove ecosystem known as butiazal. It is characterized as savanna dominated by palm trees from the Butia genus, and spreads throughout southern Brazil, Uruguay and Argentina. Species from this genus are threatened by monoculture and livestock farming. In this region there are outcrops of Pleistocene coastal deposits which were exposed to the Holocene climate and to the influence of coastal dynamics. It is therefore an excellent location for palaeoclimatic and palaeoenvironmental reconstruction of the past 11,000 years. For such a reconstruction, and better understanding as to how this unique ecosystem was formed, tools such as bioindicators (phytoliths and palynomorphs), X-ray diffractometry analysis, total organic matter content determination, particle size analysis and carbon-14 AMS dating were used. Indications of the presence of Butia in the region from at least 11,125 to 10,751 yr cal BP were identified, along with the importance of the climate during its formation and expansion. Although the climate changes in the analysed interval were not expressive, it was possible to divide the profile into 4 zones according to plant cover and observe the influence of sea-level shifts during the Holocene on the evolution of the palaeoenvironment in the region, besides the evident human influence on vegetation evolution.