EXCEPTIONAL PRESERVATION OF PLANTS IN CALCAREOUS CONCRETIONS FROM SANTA MARTA FORMATION (LATE CRETACEOUS), JAMES ROSS ISLAND, ANTARCTIC PENINSULA

SILVA EVA; ARI IGLESIAS; BRIAN ATKINSON; SELENA SMITH; EDUARDO OLIVERO

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2025 vol. 62 p. 130 - 143

0002-7014

The nowadays polar desert of the Antarctic continent preserves a diverse Late Cretaceous terrestrial biota in the James Ross Basin. Within the upper section of the Santa Marta Formation (Santonian–middle Campanian; Chron C33n, ~80 Ma), the Sitio Feliz locality preserves abundant permineralizedplant remains in calcareous marine concretions. In this work, we provide the first taphonomicconsideration of this concretionary material and illustrate the exceptional preservation of vegetative andreproductive plant organs in order to emphasize the quality of preservation of the new fossils that willpermit full anatomical descriptions. Based on the presence of massive bioclast sediment,microframboids and framboids of pyrite, and fine microcrystalline calcite cement without dissolutionor recrystallization evidence, we conclude that a rapid burial event and very early calcareousprecipitation prevented bacterial decomposition in plant tissues and subsequent pyritization, as well aspossible later bioturbation and compaction of the sediments. These conditions permitted the exceptionalpreservation of plant organs like the presence of delicate vascular and mesophyll cells, and variousreproductive structures such as fruits and seeds with carpels and seed coats. Although concretionarylevels within the Santa Marta Formation are common, the type of concretion described herein demonstrates a distinctive preservation, unlike others concretions described on the unit. The exceptional fossilization offers a rare opportunity to reconstruct the Antarctic continental floras in a much more complete approach than other types of paleobotanical remains.