Fossil woods from the Palaeocene of western Antarctica (Cross Valley Formation): a conifer-dominated forest with abundance of Araucariaceae

PUJANA, ROBERTO ROMÁN; MARENSSI, SERGIO A.; SANTILLANA, SERGIO N.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

A collection of more than 50 fossil woods from the Cross Valley Formation was anatomically studied. This formation crops out in Seymour/Marambio Island, western Antarctica, and it was assigned to the late Palaeocene based on palynological studies. The fossils were analyzed by SEM and acetate peels, and studied using light microscopy. Most samples are permineralized (mostly carbonates), but others are charcoaled. Due to poor preservation in many of the samples only about half of the specimens could be reliable assigned to generic or specific level. Fossil woods were assigned to the conifer families Araucariaceae (Agathoxylon), Podocarpaceae (Phyllocladoxylon and Protophyllocladoxylon) and probably Cupressaceae (Cupressinoxylon). Agathoxylon is themost common wood, an infrequent feature for the fossil wood assemblages from the Cenozoic. Results are consistent with previous works based on fossil leaves from the same formation, where Araucariaceae and Podocarpaceae leaves were described. Despite angiosperms are apparently common, based on the occurrences of fossil leaves, they are absent in the studied fossil wood collection. Taphonomical processes, angiosperm habit (herbs or small shrubs) and low abundance of angiosperms could explain this discrepancy. Apparently, these conifer-dominated forests have developed under temperate climate (based on the taxonomic composition), acceptable conditions for growing (growth rings are sometimes wide), and under marked seasonality (growth rings are well marked).