Arboreal paleocomunities reconstruction by means of phytolithic analysis in sediments from the Upper Paleocene (Las Flores Formation), Chubut, Argentina.

ZUCOL, A. F., M. BREA, M. S. RAIGEMBORN Y S. MATHEOS.

Tafí del valle, Tucumán

Otro; The 3rd EIF (Latinoamerican Phytolithic Meeting),; 2005

Instituto de Arqueología y Museo. Facultad de Ciencias Naturales e IML, UNT

In the San Jorge Gulf basin, during the Upper Paleocene, an important fluvial cycle is developed whose sediments have been called the Rio Chico group conformed by three formations: Peñas Coloradas, Las Flores and Koluél Kaike. The sedimentary samples studied come from the Barranca Colhué Huapi profile, Gran Barranca from the lake Colhué Huapi ((45° 43’ 26’’ SL and 68° 37’ 14’’ WL), Sarmiento (Chubut). In the present contribution, phytholith morphotypes are shown found in the Las Flores Formation. The phytholith assemblage is characterized by the abundance of phytholith morphotypes allocated to conduction elements dissociated wood dicotyledons. These present two characteristic anatomic types: the first (A) is characterized for presenting thin and long vessel elements with thin walls, with scalariform perforation plates with 6-8 and 12-16 bars, intervessel pits scalariform and intervessel pits transitional and opposed, at the end of the vessel elements is oblique and absence of helical thickenings (relative frequency: 80%). The second (B) is integrated by short and medium vessels, with simple perforation plates, small intravessel pits, opposite and alternate, disjunctive and at the end of the vessel elements is oblique (relative frequency: 20%). From the evolutionary point of view, the anatomic characters type A is indisputably primitive features of the secondary xylem evolution. From the adaptative point of view, this phytholith assemblage shows a predominance of elements with scalariform perforation plates. Studies made over the ecological aspects of the anatomic characters of the wood in different types of vegetation and geographic areas suggest that these types of element conduction proportions are found in current communities developed in tropical to subtropical mountains zones. On their part, the paleoxylologic records as well as the climatic inferences obtained by means of the sedimentological characteristics of these deposits support the existence of these climatic conditions for the Upper Paleocene in this region.   This work was subsidized in its totality with funds from the PICT 07-08671.<0}