Integration of sedimentological and ichnological analysis on the wave-dominated deposits of The Maastrichtian Calafate Formation, Austral-Magallanes Basin, Argentina

Abstract

An integrated study combining sedimentological and ichnological data has been conducted in the lower wave-dominated deposits of the Calafate Formation. The study aimed to assess the variation in fair-weather and storm processes, tidal flux, and the coast configuration to correctly constrain sedimentary dynamics in complex depositional systems. The wave-dominated deposits comprise foreshore to upper shoreface (FA1), middle to lower shoreface (FA2) and offshore-transition deposits (FA3) moderately affected by storms. In FA1, the most proximal strata contain Macaronichnus isp. and occur within the foreshore, while the upper shoreface shows an increased ichnodiversity associated with the occurrence of the archetypal Skolithos ichnofacies evidencing heightened energies of the upper shoreface. FA2 display a fair-weather community assigned to the proximal Cruziana ichnofacies that shows a wider range and variability of living strategies, and a storm-related community represented by opportunistic colonizers which produced burrows assigned to Ophiomorpha nodosa. The monospecific occurrence of Thalassinoides isp. at the top of FA2 in CC02P section is assigned to the Glossifungites ichnofacies, developed on a firmground and autogenic surface. The ichnoassemblage in FA3 is attributable to the transitional Skolithos-Cruziana ichnofacies, that exhibits a slightly reduced diversity of the fair-weather community and a sparse bioturbation. The distribution and the general characteristics of the ichnological assemblages are consistent with deposition in fully marine conditions. The bioturbation intensity, trace-fossil diversity, maximum penetration, and burrow size distributions indicate fully oxygenated and clear waters, normal-marine salinity conditions, abundance and accessibility of food, and continuous and moderate sedimentation. Nevertheless, the ichnological signature in FA3 is related to minor physico-chemical stress produced by strong tidal currents originated during the southward expansion of the Magallanes embayment.