Advances in ammonite biostratigraphy of the marine Atacama basin (Lower Cretaceous), northern Chile, and its relationship with the Neuquén basin, Argentina

Preliminary results about the Lower Cretaceous ammonite biostratigraphy of northern Chile reveal eight fossiliferous levels: Lower–Upper Valanginian neocomitid and olcostephanid faunas in the Punta del Cobre and Abundancia Formations and Upper Hauterivian–Barremian crioceratid in the Nantoco, Totoralillo, and Pabellón Formations. The faunal affinities with the Neuquén are strong during the Valanginian and Hauterivian. In contrast, during the Barremian and Aptian, the ammonites show affinities with Austral, California, and Tethys basinal faunas. The Lower Valanginian–lower Upper Aptian series in northern Chile comprises two sedimentary cycles separated by a regressive pulse of Upper Hauterivian–Lower Barremian age. This pulse may be equivalent to the regression that ended the Early Cretaceous marine cycle in central Chile and central west Argentina, where the second marine sedimentary cycle observed in northern Chile is not represented.