LOWER CRETACEOUS SEDIMENTARY SEQUENCES IN THE BASIN, NORTHEASTERN BRAZIL: A REVISION

MARIA AUGUSTA MARTINS DA SILVA

Resumo


The Araripe Basin in northeastern Brazil contain a 700 m-thick succession of JurassIc-Cretaceous strata. The 200 m-thick Lower Cretaceous is widely known for its fish-bearing concretions and gypsum deposits. Detailed field studies and core analyses provided data for revision of the Lower Cretaceous stratigraphy in the Araripe Basin. A regional disconfonnity within the Lower Cretaceous succession is described here for the flrst time. This surface divides the Aptian-Albian succession into two parts : 1. a lower sequence of black shale, laminated carbonate, algal mat carbonates, and evaporites in ascending stratigraphic order; and 2. an overlying sequence containing concretionary shale, limestone, and sandstone. These two stratigraphic divisions are herein defined as the Araripina Formation (new name) and the Santana Formation (revised), respectively. The expression of the disconformity varies across the basin. ln the southwest it is marked by caves formed in the gypsum and a karstic topography. Toward s the northeast, a 50 cm-thick layer of laminar calcareous and siliceous calcrete crust mark s th e disconformity surface.


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