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

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 mollusk assemblages, has been extensively studied taxonomically, the unit has received little attention from a sedimentologic perspective, leaving uncertainties about its depositional setting and processes. Interpretation is further complicated by its largely homogeneous, fine-grained lithology and the scarce preservation of sedimentary structures. However, the fossil content provides several clues. The mollusk-dominated fossil assemblages occur 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 to upper offshore zones of a wave-dominated but protected coastline, with low sedimentation rates and sporadic storm influence. This setting promoted pervasive bioturbation by benthic organisms. Vertical changes in faunal composition (i.e., an increasing dominance of brachiopods) and a slight fining-upward trend suggest a marine transgression during the deposition of the upper succession. The Tubul Formation fossil concentrations and their taphonomic 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 homogenous succession make its study difficult. This underscores the value of an integrated sedimentologic, ichnologic, and taphonomic approach in paleoenvironmental and paleoecologic studies. • Fossil shell concentrations from the Tubul Formation in Chile are analyzed through a taphonomy-based approach. • Five fossil concentration types reflect different sedimentary processes in shallow marine settings. • The Tubul Formation was deposited in a lower shoreface to upper offshore setting under weak to moderate storm influence.