Taphonomic analysis of storm-influenced shallow-marine deposits in the Tubul Formation (Pliocene-Pleistocene), Chile

Abstract

The Upper Pliocene – Lower Pleistocene Tubul Formation of south-central Chile contains one of the richest pre-Holocene marine faunas of the southeastern Pacific margin. While its fossil content, particularly the molluskassemblages, has been extensively studied taxonomically, the unit has received little attention from a sedimentologicperspective, leaving uncertainties about its depositional setting and processes. Interpretation isfurther complicated by its largely homogeneous, fine-grained lithology and the scarce preservation of sedimentarystructures. However, the fossil content provides several clues. The mollusk-dominated fossil assemblagesoccur predominantly as fossil concentrations, enabling the use of a taphonomic approach for their study.Integrating taphonomic, sedimentologic, and ichnologic evidence reveals deposition in the lower shoreface toupper offshore zones of a wave-dominated but protected coastline, with low sedimentation rates and sporadicstorm influence. This setting promoted pervasive bioturbation by benthic organisms. Vertical changes in faunalcomposition (i.e., an increasing dominance of brachiopods) and a slight fining-upward trend suggest a marinetransgression during the deposition of the upper succession. The Tubul Formation fossil concentrations and theirtaphonomic analysis prove to be a useful tool in the study of storm-influenced shallow-marine deposits,particularly as a case in which the lack of other well-preserved sedimentary structures and a relatively homogenoussuccession make its study difficult. This underscores the value of an integrated sedimentologic, ichnologic,and taphonomic approach in paleoenvironmental and paleoecologic studies.