Fossil flora (woods and stems) suggest a warm climate at the southern of Chile during the Upper Cretaceous

MARTINEZ, LEANDRO CARLOS ALCIDES; LEPPE, MARCELO; HINOJOSA, LUIS FELIPE; MANSILLA, HÉCTOR; DUTRA, TÂNIA; MANRÍQUEZ, LESLIE

Paraná

Simposio; XVII Simposio Argentino de Palebotánica y Palinologìa; 2018

Asociación Latinoamericana de Palebotánica y Palinologìa

Fossil plants (large trunks, stems, some branches and twigs) were collected from Maastrichtian (68,9 Mya) upper Dorotea Formation (Magallanes Basin) 16 km to the north of Cerro Guido locality, Magallanes Region, southern Chile. These fossils have a length between 0.2 m and 2.2 m. To study permineralized fossils, petrographic slides in three sections (cross, radial and tangential) were made, and analyzed under light microscopy. The woods and stems fossils were classified as Ginkgoxylon Saporta, Agathoxylon Hartig, Podocarpoxylon Gothan, Palmoxylon Schenk and an indeterminate angiosperm. In order to obtain palaeoecological data, the growth rings of gymnosperms were analyzed. The mean sensibility index was employed to obtain palaeoecological data, with values between 0.25 and 0.40, indicating that some trees were sensitive to local climate conditions. All these data suggest that some trees grew under several fluctuations of environmental conditions. Furthermore, to determine the deciduousness on the forests, 4 parameters were calculated: skew of the cumulative sum deviation from the mean (CSDM) curves, percentage of latewood, percentage of cell diminution in ring increments and ring markedness index (RMI). Some taxa show CSDM curves which are dominantly left-skewed which indicates deciduous habit. In addition, new record of Palmoxylon extends a southernmost distribution of the genus. The data obtained from fossil woods suggest warm and humid conditions to this southern locality of South America during Upper Cretaceous.