Magnetostratigraphy of the Vaca Muerta Formation (Upper Jurassic - Lower Cretaceous) at the Puerta Curaco section, Neuquén basin, Argentina

KOHAN MARTINEZ, M.; IGLESIA-LLANOS, M.P.; KIETZMANN, D.A.

Simposio; VII Simposio Argentino del Jurásico; 2019

The controversy in the equivalence between the Andean and the standard ammonite zones in the Late Jurassic-Early Cretaceous makes correlations of local and international sections based on ammonites, a relatively complex task. . Therefore, we propose the use of a different chronostratigraphic tool such as magnetostratigraphy. In this regard, we carried out paleomagnetic studies in the Vaca Muerta Formation (Tithonian - Valanginian), cropping out at Puerta Curaco, central Neuquen basin.At Puerta Curaco, we sampled c. 400 m ? thick. We distributed 61 paleomagnetic sampling sites from which we obtained 8 specimens, although only 300 were processed and analyzed for the construction of the magnetostratigraphic scale. Ages of sampling sites were tied were derived from ammonites. The characteristic remanent magnetizations were interpreted as primary, based on paleomagnetic field tests. These data allowed us to construct a magnetostratigraphic scale that was correlated to the International Geomagnetic Polarity Time Scale 2016 (GTS2016), and to calculate a paleomagnetic poles located at: Lon = 72.4ºE; Lat = 79.6ºS; A95 = 3.1; k = 34.7; N = 61. The paleopole falls with others of the same age, suggesting that the section was not affected by rotations around vertical axis or mechanical compaction.. The magnetostratigraphic scale obtained comprises 12 reverses and 12 normal polarity intervals, spanning Virgatosphinctes andesensis (Lower Tithonian) - Neocomites wichmanni Zones (Early Valanginian). The correlation with the GTS2016 indicate that the correlation is good, except in the base, where it suggests that the Virgatosphinctes andesensis and Pseudolissoceras zitteli are older than proposed by the biostratigraphic schemes. This is consistent with other magnetostratigraphic and cyclostratigraphic studies.