Stratigraphy, Sedimentology, Geochemistry and Diagenesis of the Aptian-Albian Lacustrine Systems of the Araripe Basin, NE Brazil

By

 Virgínio Henrique Neumann¹, Llu’s Cabrera², Angeles Borrego³, Lœcia Maria Mafra Valença¹

(1) Federal University of Pernambuco, Recife-PE, Brazil (2) University of Barcelona, Barcelona, Spain (3) CSIC, Oviedo, Spain

 This work is the synthesis of the modelization of the Aptian-Albian lacustrine deposits of the Araripe basin, NE Brazil, their control factors and influence. The sedimentary post rift fill of the Araripe basin is represented by the Santana Group, that include the Rio da Batateira, Crato, Ipubi, Romualdo and Arajara Formations. The Aptian-Albian terrigenous and carbonate sedimentary record initiated with a transgressive pulse over the fluvial units of the Rio da Batateira Formation and closed with the development of discontinuity surface, upon which were deposited the evaporites of the Ipubi Formation. The lacustrine successions are grouped as transgressive-regressive sequences of different hierarchy orders which have had a marked expansive tendency. The Crato Formation is the focus of this work and is defined as a group of interfingering terrigenous and carbonate bodies, being the carbonate bodies that was detailed in this work. Six mainly lacustrine carbonate episodes of sedimentation were recognized and their geometry are related to the detrital facies of deltaic-fluvial system. The six carbonate units are composed by two lithofacies: clay-carbonate rhythmites and laminated limestone, both characterized by syndepositional deformations (loop bedding and microslumps). The paleobiological record of the laminated limestone includes well preserved fish, insect and plant fossils. Trace and rare earth elements analyses indicate that the source area do not vary substantially and the d13C and d18O covariance points to a hydrologically closed system. The origin of the organic matter is mainly terrestrial, but there are some contributions of planktonic elements.