Remarks on the cenomanian-santonian stratigraphic interval in some brazilian marginal basins andimplications for the tectonic and sedimentation history of the continental margin

Abstract

lnitíal results of a research project now underway on the stratigraphy of the Cenomanian-San­tonían interval in the Santos, Campos, Esplrito Santo, Sergipe, and Potiguar basins are presented. Three rou­ghly synchronous events are distinguished in the section: 1) - the Late Cenomanian/Early Turonian maximum transgression; 2) - a Late Turonian/Early Coniacian (88-89.5 m.y.B.P.) erosive unconformity (subaerial and submarine); and 3) - basic magmatism beginning 90 m.y.B.P. The Late Turonian/Early Coniacian uncon­formity marks the beginning of an intraplate tectonic event that prompted marked changes in the floors, bar­der topography, and depositional history of these marginal basins. General reorganization of the geometry or a change in the speed of displacement of the South American plate, probably coeval with magnetic anomaly 34, may be the causes behind these deformations. A well-dated regional unconformity like the Late Turonian/ Early Coníacian serves as an excellent reference element in unifying the still uncertain ages and origins of va•rious geological phenomena involving the South American plate.