Storm-dominated coastal dynamics in the early Ediacaran record of Argentina

Abstract

Following the development of the Piedra Amarilla Surface (PAS), where a major karstic unconformity formed during prolonged subaerial exposure, the Tandilia System underwent a profound paleoenvironmental shift in the early Ediacaran. These changes are recorded in the Colombo and Cerro Largo formations, which overlie the PAS and represent a large-scale transgressive–regressive cycle in the Sierras Bayas Group. This cycle begins with postglacialdeposits and culminates in a high-energy, storm-dominated shoreline system, marking a major reorganization of depositional environments in the basin. Sedimentological, stratigraphic, and paleocurrent analyses from eight measured sections identified twelve lithofacies, grouped into four facies associations, arranged in a coarsening-upward pattern from glacimarine deposits (FA-1) to offshore-transition deposits (FA-2), and finally to storm-wave and fair-weather-wave dominated shoreface deposits (FA-3 and FA-4, respectively). Paleocurrent data indicate a NE–SW-oriented paleoshoreline, with deeper marine areas toward the W–NW, in agreement with regional paleogeographic reconstructions. In this high-energy context, microbial mats played a key role in stabilizing substrates and preserving small-scale delicate sedimentary structures. The interpreted depositional model highlights the development of a high-energy overlaying shoreline glacimarine deposits and the dynamic interplay between storm and fair-weather wave processes in shaping early Ediacaran littoral systems.