Magnetostratigraphy of the Jurassic-Cretaceous Vaca Muerta Formation, Neuquén basin, Argentina

IGLESIA LLANOS, M.P.; KIETZMANN, D.A.,; PALMA, R.M,

MALARGÜE

Simposio; VI SIMPOSIO ARGENTINO DEL JURÁSICO; 2016

A systematic paleomagnetic study was carried out in the Vaca Muerta Formation, croppingout along the LoncocheCreek, Mendoza.The studied sectionis c.270 m-thick and represents a carbonateramp system bearing ammonites that indicate Upper Jurassic- Lower Cretaceous ages. The Vaca Muerta Formation is one of the most important unconventional hydrocarbon reservoirs in the world and its thoroughstudy has becomea relevant target in Argentina. And since it contains the J-K boundary datedwith marine fossils,Vaca Muerta Formationrepresents an excellent opportunity to obtain the first Upper Jurassic-Lower Cretaceous magnetostratigraphy of the southernhemisphere, which is in the interestof the oil industryas well. The biostratigraphy is well studied in the area, so that paleomagnetic sites were reliably tied,particularly by through ammonites. Almost 450 standardspecimens have been processedfor this study, which were subjectedto both alternating fieldsand thermal demagnetization. Residual magnetizations were measuredwith a 2G cryogenic magnetometer. The analysisof magnetic components was performedusing principal component analysis and remagnetization circles. The qualityof isolated magnetizations is, in general terms, very good. The paleomagnetic stability has been assessed by means of severalstatistical field tests that indicate its primary origin.The resultant magnetoestratigraphic scale comprises 11 reverse and 10 normalpolarity zones, spanningfrom Virgatosphinctes mendozanus toSpiticeras damesi Zones. These polarities were successfully correlated with those of the International Geomagnetic PolarityTime Scale 2012 using the corresponding ammonitezones. Consequently, it was possibleto determine more preciselyages in the section,and particularly, the positionof the Jurassic-Cretaceous boundary.