Gênese de solos aluminosos na Bacia Sergipe-Alagoas, Estado de Alagoas, Nordeste do Brasil

Abstract

The geological environment of South America shows on its northeast portion different compartments, areas over crystalline basement and sedimentary basin making marginal limits to the crystalline areas. The Brazilian marginal basins results from the severance process of the mega continent West-Gondwana which took place from the superior Jurassic to Cretaceous (138-127 Ma) leading to the development of the South Atlantic rift and tectonic subsidence. These sedimentary formations are different between basins, in several aspects like stratigraphic, originating distinct saprolites and consequently soils with different characteristics. In this context, occurs the Sergipe-Alagoas Macro-Basin, located at the northeast of the country, forming a straight line along brazilian east coast. The aforementioned Macro-Basin is subdivided in Sergipe Sub-Basin and Alagoas Sub-Basin. The Alagoas Sub-Basin, located at northeast Brazil occupies the coastal portion of the state with same name, also defined as rift type basin. The genesis of aluminum soils and their chemical behavior are still not much known, especially at Northeast Brazil. The objective of this study was to detect aluminuous soils, their impact on climatic approaches through carbon storage and their relationship with factors of soil formation. Soil samples were collected form all horizons, on then macro morphological, physical, routine chemistry, mineralogical and total chemical composition analysis took place, with data were obtained mass balance. The soils showed characteristics primarily influenced by their sedimentary parent material, several textural classes, varying from sandy- loam to and clay, acid reaction, low fertility status and high associated Al content and considerable occurrence of 2:1 clay minerals with hydroxi-Al between layers, including ilite, esmectite with HIS. The increasing in exchangeable Al content suggests dissolution of non-exchangeable species coming from dissolution of HIS. The complexity of soil mineralogy suggests that the occurrence of these soils does not match with the hot weather of present climate, more humid and that the high Al contents existing on the subsurface horizons were inherit form the parent material, dominated by silty clay sediments with shale surrounding it. The greater carbon stocks were observed in accordance to the higher Al contents on subsurface horizons, so, it is proved that the Al chemistry develop relevant function mitigating atmosphere heating gases.