Proveniência e análise sedimentar da porção basal do Grupo Bambuí em Arcos (MG)

The origin and evolution of Bambuí Basin has been a matter of debate, in much intensified by the recent exploratory efforts carried out by public and private companies looking for natural gas. In the southeastern portion of the basin there are rare opportunities to access the contact between the sedimentary rocks and its basement, whose characteristics are crucial\udto understanding the processes of basin installation and the early sedimentation. The analysis of drill cores allowed us to\uddescribe the lowermost Bambuí Group in Arcos (MG) region, including its basement. The sampled section displays as\udbasement an archean granodiorite (ca. 2.8 – 2.9 Ga), fractured at the time of sedimentation. The Bambuí Group basal unit is\uddm-thick, massive lodgment tillite. Grains of zircon separated from the tillite matrix were dated and show a main age peak\udat ca. 2.8 Ga, indicating provenance from the own basement. On the tillite rests an impure limestone that passes gradually\udto a muddy unit, in a retrogradational filling trend. Terrigenous fragments in the impure limestone suggests that the basement has continued to be a source of sediments in the bottom of the section. The pelitic rocks that occurs to the top has a\udlitochemical signature compatible with acidic source rocks, and shows Sm-Nd model ages of 1.7 Ga. These data suggests\udthat rocks from the Brasília Belt have acted as a source for the pelitic rocks, supporting the interpretation of a foreland set\udfor the basin