Abstract
A number of small Callovian-Albian sedimentary basins occur in the NE-trending Araripe-Potiguar topographic lowlying area. These basins developed in a fairly narrow zone of Precambrian supracrustal rocks from the Middle Jurassic onwards, as a consequence of the reactivation of ancient fault lines. The basin formation and subsidence took place during five tectonic stages related with the opening of the Southern Atlantic Ocean and the split of South America from Africa. The tectonic-sedimentary sequences that fill these basins record successive evolutionary stages. 1) Proto-rift stage, with minor episodes of a) pre-rift ( Callovian -Tithonian) with basin formation and deposition of coarse to conglomeratic sandstones in alluvial fan and braided river systems; (b) tectonic quiescence with continuing subsidence, resulting in hundreds of meters of pelites accumulated mainly in lacustrine and foodplain environments (Tithonian-Berriasian). 2) Syn-rift stage: a) tectonic reactivation with erosion and deposition of sandstones in alluvial fan and braided to low-sinuosity river systems; (b) during more quiet periods, accumulation of fine-grained deposits in lacustrine, palustrine and foodplain environments took place (Berriasian-early Barremian). 3) Erosional stage that would correspond to a transitional proto-oceanic gulf phase in the southern Atlantic and a shift of rifting to the equatorial Atlantic area, causing erosion in the study area (late Barremian-early Aptian). 4) Post-rift stage: (a) related to the beginning of drift in the Atlantic Ocean. This stage is characterised by deposition in the area of shallow lacustrine fine-grained siliciclastics, limestones and gypsum under dry climate (late Aptian-early Albian); (b) two short marine transgressions affected the area and, as a consequence, shallow marine limestones were deposited (late Aptian and Albian); (c) a marine regression resulted in a return to continental conditions with deposition of coastal and lagoonal limestones, lacustrine rhythmites and fluvial sandstones (Albian-early Cenomanian?). Some of the lacustrine to fluvial dominated sequences as well as the marine deposits in these basins include highly fossiliferous units (i.e. Crato and Romualdo Fms. of the Santana Group), with very diverse, exceptionally well preserved fossil assemblages (insects, fishes and reptiles, among others), although they are mainly endemic. 5) Uplift stage: last stage of tectonic calm and slow uplift and erosion (since Cenomanian). On the basis of our proposals further sedimentological and paleontological studies have been undertaken, which confirm the existence of an alternative connection between the equatorial and southern parts of the Atlantic Ocean in Aptian-Albian times. Moreover, the last break-up stages between Brazil and Africa took place probably in the Campanian.