Abstract
A robust biostratigraphic zonation based on microfossils supports the stratigraphic framework and correlation of the interior basins of the Lower Cretaceous of NE Brazil. This zonation has also allowed correlations with coeval sections in the Brazilian marginal basins and in the Gabon and Congo basins (central-west Africa). These records, consisting mainly of non-marine sediments, were a great challenge with regard to the correlation with the International Chronostratigraphic Chart. Therefore, local stages were used, the most recent being the Alagoas local Brazilian Stage, with which the Post-rift Sequence I of the Araripe Basin is related. Regarding lithostratigraphy, this sequence includes the Rio da Batateira (Barbalha for some authors) and Santana formations, the last one with the famous Crato, Ipubi, and Romualdo members, from the base to the top. Although currently there is a consensus on the age of the Alagoas local Brazilian Stage in the Araripe Basin, recently a new age for at least part of the Post-rift Sequence I was proposed. This new proposal, based on isotopic analysis of Re-Os, arose as a panacea to correlate the Rio da Batateira Formation and the Crato and Ipubi members with the international stages. Surprisingly, their authors, although on the one hand, they seem to underestimate biostratigraphic results, on the other they seek to support their proposal from microfossils studied by previous authors, but they do so in an inappropriate way, leading readers to misinterpret their results. Therefore, this paper presents a critical review on the age of the Alagoas local Brazilian Stage in the Araripe Basin and nearby basins, refuting a Barremian age for part of the Post-rift Sequence I. Keywords: Alagoas local Brazilian Stage, biostratigraphy, ostracods, palynomorphs, radiometric ages.
Highlights
The Post-rift Sequence I of the Araripe Basin, consisting of rocks of late Aptian/early Albian age, includes the following lithostratigraphic units, from the base to the top: Rio da Batateira (= Barbalha for some authors) and Santana formations, the later with members Crato, Ipubi and Romualdo (Ponte & Appi, 1990; Assine, 1992; Arai et al, 2001; Coimbra et al, 2002)
The Santana Formation is a world famous Fossil Lagerstätte because its rocks are among those with the greatest variety and abundance of astonishingly well-preserved Cretaceous life forms, including ostracods and palynomorphs. It is the most studied unit of the Araripe Basin, the largest NE Brazilian interior basin that originated during the break-up of the Gondwana Supercontinent (Ponte & Appi, 1990; Matos, 1992; Valença et al, 2003) (Figure 1)
It is composed of predominantly non-marine sediments deposited as a result of various geological events, most of them related to the opening of the South Atlantic Ocean that started from the South
Summary
Local stages were used, the most recent being the Alagoas local Brazilian Stage, with which the Post-rift Sequence I of the Araripe Basin is related Regarding lithostratigraphy, this sequence includes the Rio da Batateira (Barbalha for some authors) and Santana formations, the last one with the famous Crato, Ipubi, and Romualdo members, from the base to the top. Currently there is a consensus on the age of the Alagoas local Brazilian Stage in the Araripe Basin, recently a new age for at least part of the Post-rift Sequence I was proposed This new proposal, based on isotopic analysis of Re-Os, arose as a panacea to correlate the Rio da Batateira Formation and the Crato and Ipubi members with the international stages.
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