Carbon isotope and magnetostratigraphy of the Cretaceous (Barremian – Aptian) Pabellón Formation, Chañarcillo Basin, Chile

Abstract

New oxygen and carbon isotopic analyses of fine–fraction samples from the Pabellón Formation (Chañarcillo Basin, Chile), together with magnetostratigraphic data, are presented. The carbon isotope curve shows a distinctive pattern including a negative isotope excursion preceding a positive event. Within the Lower Aptian this chemostratigraphic event is widely used for correlation of marine and continental stratigraphic sections and confirms the global nature of the episode. The carbon isotope profile improves the stratigraphic correlation of the formation and, together with published ammonite data, the lower part of the succession is interpreted as early Aptian in age, whilst the upper part of the succession is of late Aptian age. The oxygen isotope data are consistent with a diagenetic and metamorphic overprint of the sediments. The palaeomagnetic data are consistent with the rocks having suffered a substantial clockwise rotation during a younger tectonic event, consistent with other units in the wider area and these data do not therefore help further constrain the age of deposition.