| Summary: | Some recent geological and geophysical reconnaissance studies carried out in the Alhandra Sub-basin (southern segmentof the Paraíba Basin) have revealed very interesting structural and stratigraphic behaviors that have not yet been described.Four different structural compartments with NNE-SSW trends were identifi ed, each characterized by a particularstratigraphic pile, as a result of vertical tectonic displacements, probably post-Pliocene in age: the Alto Rio MumbabaHigh (with widespread basement outcrops), the Rio Mamuaba Graben (the well-exposed Beberibe Formation with thicknessesfrom 100 m up to 300 m), the Rio Gramame High (a horst zone, with some basement outcrops, underlying the BeberibeFormation) and the Alhandra-Guruji- Conde-Caaporã monoclinal zone, east of the BR-101, limited to the west bya fault line. The stratigraphic sequence of the Paraiba basin represented by the Paraíba Group is complete only along theeastern monoclinal zone, where the Barreiras Group is also preserved. Along the Rio Mamuaba graben, occurrences of theBarreiras Group were not found as would be expected, and this seems to be an indication that more than one phase of verticalmovement occurred, the second of which had probably removed the Barreiras Group. All these observations are preliminaryand demand further geological and geophysical studies, especially at scales greater than 1/50.000.
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