Análisis sedimentológico e icnológico de testigos corona de la formación Loma Montosa, Catriel Oeste - Cuenca Neuquina

Abstract

The sedimentological and ichnological analysis of two cores from the Loma Montosa formation (Berriasiano- Early Valanginiano), corresponding to the Catriel Oeste field in the Neuquina basin, allowed the recognition of thirteen sedimentary facies comprising into three facies associations: distributary channel, delta-front and interdistributary bay deposits. The distributary channel facies association is composed of class-supported polymictic conglomerates, which have a calcareous matrix and normal gradation. Internally, they are show diffuse planar cross-stratification or massive, with multiple reactivation surfaces. These beds do not present bioturbation. The delta-front facies association shows the development of carbonaceous sand bars deposits with planar parallel lamination, planar or tangential cross- stratified beds with plant fragments, which are reworked by bioturbation representing an impoverished Skolithos ichnofacies. The interdistributary bay facies association consists of massive and laminated mudstone, nodular gypsum intergrowth, levels with microbial mats (MISS, for its acronym in English), framboidal pyrite and structures that could be assigned to desiccation cracks. This facies association shows the development of an impoverished Cruziana ichnofacies. The proposed depositional model for the Loma Montosa formation, in the Catriel Oeste field correspond to a fluvial-dominated deltaic system, represented by interdistributary channel fill, proximal delta-front and interdistributary bay deposits.