Stratigraphic transition of Bambuí and Paranoá groups in Distrito Federal

Abstract

Distrito Federal’s north area shows an expressive succession of carbonate rocks with divergent stratigraphic position and has already been included in Bambuí or Paranoá groups. In this work, the carbonates of the Paranoá Group were individualized and separated from those of the Sete Lagoas Formation, of the Bambuí Group. The Paranoá Group consists in a siliciclastic unit formed predominantly by rhythmic intercalations of siltstones and sandstones superimposed by pelito-carbonate rocks, with lenses of dolomitic limestones stromatolitic, where it is possible to observe the Conophyton metulum Kirichenko. The carbonate rocks of the Sete Lagoas Formation in the lower Bambuí Group overlies by unconformity a dolostone breccias of the Paranoá Group, and it was individualized in two stratigraphic successions. Sete Lagoas Formation’s Succession 1 comprises three distinct lithostratigraphic units: (i) the basal unit starts with a gray dolarenite overlying by a purple rhythmic succession of calcilutitos-calcarenitos with claystone, (ii) in the middle unit, pure calcarenites dominates, succeeded by (iii) the dolostones unit. An erosive surface is marked by breccia level that limits Succession 2, which begins with 1-2 meters of siltstones followed by calcarenites with clay layers growing towards the top. The north localities of Distrito Federal in the external Brasília Belt, where two perpendicular deformation phases were identified, oriented with NS and EW rough directions.