Environmental controls and facies architecture of a jurassic carbonate episode La Manga Formation), Mendoza Province, Neuquén Basin

Abstract

La Manga Formation is a vast carbonate system developed in the Neuquén Basin. The age is based in ammonite faunas, ranging from Early Callovian (Bodenbenderi-Proximum Zone) to Middle Oxfordian (Cordatum Standard Zone to Transversarium Standard Zone, and probably to the lower part of the Bifurcatus Standard Zone). A stratigraphical and sedimentological analysis, in the outcrops exposed in the south of Mendoza province, enabled the recognition of five facies associations of a carbonate ramp corresponding to (1) distal outer ramp, (2) proximal outer to distal middle ramp, (3) proximal middle ramp, (4) inner ramp deposits (shoreface, shoal, patch reef, shallow subtidal lagoon and tidal flat) and (5) paleokarstic facies. These facies correspond to homoclinal to distally steepened carbonate ramp. The facies associations are included into three third-order depositional sequences (DS-1, DS-2, DS-3) represented by transgressive and highstand systems tracts with sequence boundaries of regional character. Different controlling factors can be recognised in the deposition of this unit. The abrupt changes of facies, as well as paleokarst and epikarst discontinuity surfaces in the successions provide important evidence in terms of depositional environment and vertical evolution of the carbonate ramp. Facies patterns are variable across the outcrop area and vertically through time because of a combination of ramp morphology, siliciclastic supply, sea level changes and tectonic effects. In the southern sections, siliciclastic influx influenced the deposition of proximal middle ramp facies later overlain by scleractinian patch reefs which grew up throughout progressive stages from aggradational to progradational facies in response to climate controls and nutrient levels influence. In northern outcrops, tectonic controls affected the ramp topography and influenced the development of distal deep marine facies. Shallow subtidal and peritidal cycles indicate a combination of allocyclic and autocyclic processes controlling accommodation space and sediment accumulation.