CONICET | Buscador de Institutos y Recursos Humanos

A systematic paleomagnetic study was carried outin the Vaca Muerta Formation, cropping out along the Loncoche Creek, Mendoza.The studied section is c.270 m-thickand represents a carbonate ramp system bearing ammonites that indicate UpperJurassic- Lower Cretaceous ages. The Vaca Muerta Formation is one of the mostimportant unconventional hydrocarbon reservoirs in the world and its thoroughstudy has become a relevant target in Argentina. And since it contains the J-Kboundary dated with marine fossils, Vaca Muerta Formation represents anexcellent opportunity to obtain the first Upper Jurassic- Lower Cretaceousmagnetostratigraphy of the southern hemisphere, which is in the interest of theoil industry as well. The biostratigraphy is well studied in the area, so thatpaleomagnetic sites were reliably tied, particularly by through ammonites.Almost 450 standard specimens have been processed for this study, which weresubjected to both alternating fields and thermal demagnetization. Residualmagnetizations were measured with a 2G cryogenic magnetometer. The analysis ofmagnetic components was performed using principal component analysis andremagnetization circles. The quality of isolated magnetizations is, ingeneral terms, very good. The paleomagnetic stability has been assessed bymeans of several statistical field tests that indicate its primary origin. The resultant magnetoestratigraphic scale comprises11 reverse and 10 normal polarity zones, spanning from Virgatosphinctes mendozanus to Spiticerasdamesi Zones. These polarities were successfully correlated with those of the International Geomagnetic Polarity Time Scale 2012using the corresponding ammonite zones. Consequently, it was possible todetermine more precisely ages in the section, and particularly, the position ofthe Jurassic-Cretaceous boundary.