Synchronizing the astronomical time scales in the Valanginian?Hauterivian from the Neuquén Basin (Argentina) and the Tethyan area

MARTINEZ, M.; OMARINI, J.; AGUIRRE-URRETA, M.B.; TUNIK, M.; LESCANO, M.

Congreso; 10th International Symposium on the Cretaceous; 2017

Importantdiscrepancies between the numerical ages stated by the Geological Time Scale 2016and radio-astrochronological works have been reported in the last years(AGUIRREURRETA et al., 2015; MARTINEZ et al., 2015; OGG et al., 2016). Largeuncertainties notably exist for the Valanginian-Hauterivian stages for whichthe recently provided timescales are still debated. Here, we present anastronomical calibration for the Agrio Formation (Neuquén Basin, Argentina) tobetter constraint the durations of the Valanginian and the Hauterivianstages.The formation is divided into a lower and an upper member (called Pilmatué and Aguade la Mula members, respectively) composed of marl-limestone alternationsdeposited in a semi-pelagic to outer ramp environment and related to an orbitalforcing. A rapidly (<0.5 myr) deposited member of continental sandstone,separates these two members. A total of 2130 bulk-rock samples have beencollected each 25 cm and their mass-corrected magnetic susceptibility has beenmeasured to detect lithological cycles. In the lower part of the PilmatuéMember (Lower Agrio), the record of the 405-kyr eccentricity cycle is obviousbut its amplitude promptly decreases at younger intervals. However, the orbitalcycles of precession, obliquity and 100-kyr eccentricity are recorded, allowingthe duration of the Pilmatué Member to be assessed at 4.70 myr. Anchoring thisduration to the CA-ID-TIMS age of 130.39 ± 0.16 Ma provided in the PilmatuéMember, the age of this member ranges from 133.76 to 129.07 ± 0.16 Ma. The ageof the top of the Lower Agrio slightly overlaps the age of the base of theUpper Agrio (129.09 ± 0.16 Ma). Such an overlap falls in the range of theuncertainties in the CA-ID-TIMS ages. First correlations to the Tethyan areasuggest that the early Hauterivian has a duration of 2.1 myr, falling in therange of uncertainty mentioned by MARTINEZ et al. (2015) (2.5 ± 0.4 myr), butbeing much longer than the duration of 1.21 myr proposed in the geological timescale 2016 (OGG et al., 2016), suggesting the duration of the Hauterivian stagehas to be increased by, at least, 0.9 myr for the next compilation.