Estudos sedimentológicos e estratigráficos dos depósitos sedimentares quaternários do Arquipélago de Anavilhanas, município de Novo Airão (Amazônia Central)

Abstract

In Anavilhanas Archipelago located in the lower course of the Rio Negro outside the m individual basis formed by rocks of Nhamundá, Alter do Chão / Novo Remanso and Quaternary sedimentary units consisting of the Upper Terraces (TFS) and the Lower River Terrace (TFI). The fluvial terraces levels TFS and TFI terraces were individualized by datings LOE that showed ages 211,394 +/- 29,300 years BP. the 69,988 +/- 8860 years BP. for TFS (Plestoceno) and ages ranging from 2558 +/- 87 a.AP. 368 +/- 145 years AP for TFI (Holocene). TFS is located on the left bank of the Rio Negro, with dimensions between 25 m to 40 and features interbedded layers of sand and mud (silt and clay), which define inclined heterolytic stratification. The coarse sediments show a predominant composition of sand, ranging from (99.99% to 75.15%) and subordinate silt (24.85%. To 0.01398%). TFI is represent by the 400 islands of the archipelago is located in the central area of the Rio Negro being made mainly of mud (silt and clay) with thin very fine sand centimeter interbedded fine with dimensions between 27 m to 41 m. In general, the mud is constituted on average by 65% silt and 30% clay and 5% sand. The C-14 dating performed on four levels of charcoal fragments representing paleosoils in the archipelago of islands showed ages of 490 years AP, AP 870 years, 1650 years BP to 2250 years BP and coincide with possible ranges of relatively drier periods and presenting possible fires in the Central Amazon Region. The preliminary result of bitemporal image analysis (Landsat-5 / TM) for a period of 18 years (between 1991 and 2009) associated with the results of grain size analyzes of the River Terrace revealed a pattern of high stability and cohesion to the Archipelago of Anavilhanas addition to characterize the pattern anabranche for this stretch of the Rio Negro