Palaeoenvironmental changes of the Late Miocene Puerto Madryn Formation (Península Valdés, Argentina) detected using sedimentological, palaeontological and ichnological approaches

AYLÉN ALLENDE MOSQUERA; JOSÉ IGNACIO CUITIÑO; SERGIO CELIS; PEREZ, DAMIÁN EDUARDO; MARCELA A. ESPINOSA

Congreso; Palaeontological Virtual Congress; 2023

The aim of this study is to reconstruct the palaeoenvironmental evolution of the lower part of the Late Miocene Puerto Madryn Formation at Punta Buenos Aires (NE Patagonia, Argentina) by integrating sedimentology, fossil diatoms, macroinvertebrates, and ichnology. The 45m-thick sedimentary section was divided into eight intervals separated by different types of stratigraphic surfaces. Marine fossils are abundant and diverse in shoreface to offshore deposits, while two intervals are barren of fossils, and are interpreted as prodelta and estuarine deposits. Different groups of bivalves dominated by pectinids and oysters, together with bryozoans, brachiopods, and gastropods are documented in sand-prone deposits, along with an ichnological association dominated by Helicodromites, Ophiomorpha, Taenidium, Teichichnus, and Thalassinoides, indicating moderate-energy shoreface environments. In contrast, mudstone deposits characterized by Panopea in life position and abundant Chondrites, suggest lower-energy, offshore environments. At the top of the section, reworked shell fragments, together with Thalassinoides and Skolithos in cross-bedded sandstones, suggest tidal channel deposits. Diatom assemblages are dominated by Paralia sulcata, with the exception of one sample dominated by the marine genus Pseudopodosira. P. sulcata indicates accumulation in coastal marine environments, whereas Pseudopodosira might be reflecting a deeper (offshore) environment. All data indicate that the studied deposits accumulated in a wide range of palaeoenvironments, suggesting the occurrence of several relative sea-level variations. It is still unclear why the diatom composition remains unchanged along so different palaeoenvironments as well as what factors provoked the intercalation of fossil-barren prodelta deposits within a fossil rich and diverse succession.