NEW PLANTS FROM THE UPPER PALEOCENE CROSS VALLEY-WIMAN FORMATION, MARAMBIO (=SEYMOUR) ISLAND, ANTARCTIC PENINSULA

ARI IGLESIAS; ROCIO GALLARDO; SILVA EVA; SANTILLANA, S.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2025 vol. 62 p. 144 - 174

0002-7014

The Cross Valley-Wiman (CV-W) Formation is characterized by a rich flora of compressions and petrifications, preserving leaves and seeds at its uppermost section (Bahía Pingüino Allomember)which is late Paleocene (C25n, Thanetian) in age. The fossil plant record of CV-W Formationwas described by Dusén (1908) who documented at least 87 leaf taxa. Despite its SouthernHemisphere importance, a few studies have added some revisions to this macroflora. NewArgentinian field work has recognized the 26 previously known leaf fossil taxa, identified twoleaf taxa described by Dusén (1908), and established a record for 12 new taxa. In this work wehave added three new fern taxa (Hymenophyllaceae and Polypodicaeae-Dryopteridoideae), threenew members of Liliales (Potamogetonaceae, Ripogonaceae, and an indet. monocot form), fournew non-monocot angiosperm leaf morphotypes, and two new angiosperm propagules; raising to53, the number of known leaf taxa for the CV-W Formation. The new unbiased collection of 159identified examples has allowed to quantify the relative abundance of taxa and recognize thedominance of ferns (Cladophlebis and Sphenopteris) followed by Atherospermataceae,Lauraceae, Moraceae, and Winteraceae. The presence of five Nothofagus leaf species isrecognized, although at a low percentage in the flora (not dominant). The CV-W Formationexceeds the Angiosperm richness of known Patagonian Paleocene leaf floras and provides newelements for Gondwana. Based on recognized taxa and their relative abundance, the UpperPaleocene (upper Thanethian) flora developed on the continental margin of the James Ross Basinwould have developed as a temperate rainforest