(PT) Dinâmica paleoambiental e mudanças climáticas do quaternário tardio registradas em ambiente lacustre da serra sul de Carajás, sudeste da Amazônia

Author(s): REIS, Luiza Santos
Summary: Several paleoecological and paleobotanists studies showed drier conditions in the Amazon during the Late Pleistocene and the Holocene (last 100,000 years), with changes in temperature and precipitation. This likely favored the contraction of the tropical forest and savanna expansion. To evaluate the influence of paleoclimate changes in the vegetation development and distribution, it was carried out an integrated study based on facies and pollen analysis of a sediment core from filled lake of the Serra Sul dos Carajás. The sedimentary profile provided ~ 47,000 years of sediment and pollen records, including environment changes occurred in the Late Pleistocene-Holocene transition. From 47,000 to 34,000 years B.P., the sedimentary deposits, predominantly muddy and organic, showed a cyclic pattern, characterized by variations in the input of allochthonous and autochthonous materials into the lake. The pollen record showed high percentages of forest formation (Miconia affinis/elata, Brosimum sp, Helicostylis sp, Casearia sp, Alchornea sp, Anacardiaceae and Burseraceae) and elements adapted to montane and cold climate conditions (Ilex, Weinmannia, Podocarpus, Alnus, Dacrydium and Myrsine). These data along with macrophytes, ferns, algae and fungi taxa, suggest wet and cold climate conditions. Later, between 34,000->20,000 B.P., it was observed a hiatus in the pollen record. Muddy deposits overlaid by a siderite layer (FeCO3) suggest relatively wet conditions interrupted by dry events from UMG, which caused diagenetic changes in sediments, likely leading to formation of siderite. From ~20,000 to 17,500 years B.P., the presence of massive mud indicates sedimentary input into the lake. The pollen record showed savannas (Poaceae, Borreria verticillata) and palm trees abundance, especially the occurrence of Mauritia sp, typical vegetation of hydromorphic environments, suggesting a shift to relatively humid conditions. The following period, between 17,500 and >5000 years B.P., was composed by high percentages of savannas and a decrease in the abundance of palm trees and forest formations. The presence of oxidized mud facies indicates the drying of lake and, consequently, the sub aerial exposure of the sedimentary deposit under drier climatic conditions, but with episodic rainfalls, during the rainy season provided to maintain the species survival mentioned above. In the last 5000 years B.P., there was the return of wet conditions. This allowed the increase of sediment input into the lake and sedimentation rates, it suggests an increase in precipitation. Furthermore, it caused the increase of the lake productivity indicated by the high percentage of algal spores. The occurrence of laminated mud facies overlapped by facies of herbaceous peat, indicates the predominant deposition of autochthonous/organic material in the sedimentary basin on the lake and the development of herbaceous vegetation in the filled lake around 2500 years B.P.
Year: 2015
Pages: 59 f.
Link: http://pergamum.itvds.org:81/vinculos//000009/00000962.pdf
Year of publication: 2015
Supervision: Dr. José Tasso Felix Guimarães
Link to PDF: Click here
Course: Master's Degree in Sustainable Use of Natural Resources in Tropical Regions