Cyclostratigraphy of an upper Valanginian - lower Hauterivian mixed siliciclastic-carbonate ramp succession (Pilmatue Member of the Agrio Formation), Loma La Torre section, northern Neuquen Basin, Argentina

摘要

Detailed sedimentological and stratigraphical studies were performed in the Pilmatue Member of the Agrio Formation at Loma La Torre area, to recognize orbital signals in the Valanginian-Hauterivian of the Neuquen Basin. Facies analysis allowed us to recognize 4 facies associations, interpreted as a mixed siliciclastic-carbonate ramp setting. A sequence stratigraphic analysis was performed allowing to recognize two composite sequences and five high-frequency sequences. This eurybathic/eustatic trend was subtracted from time series constructed by lithological rhythms (limestone/marlstone couplets) to stabilize its variance. Cyclostratigraphic analysis shows that the rhythmic late Valanginian - early Hauterivian succession presents a cyclical stratigraphic pattern composed by elementary cycles (lime-stone/marlstone couplets), bundles (4-5 elementary cycles) and superbundles (4-5 bundles) suggesting a climatic Milankovitch control. The found periodicities correspond to the precession cycle (similar to 20 ky), which is modulated by the eccentricity cycle (similar to 90 and similar to 400 ky). Some statically low-significant periodicities of similar to 42 ky and similar to 33 ky can be assigned to the obliquity signal. That periodicities fit well with the so-called precession-eccentricity syndrome (PES) characteristic of mid and low latitudes, where obliquity is erratically identified. Our results indicate that the early Hauterivian has a minimum duration of similar to 3 myr, considerably longer than the durations proposed in the GTS. (C) 2019 Elsevier Ltd. All rights reserved.