MORPHOLOGICAL DIFFERENTIATION OF GLOBULAR PHYTOLITHS IN MONOCOTYLEDONS: ITS APPLICATION TO FOSSIL PHYTOLITH RECORD OF PEDOSEDIMENTARY LEVELS ASSOCIATED TO “ESCORIAS Y TIERRAS COCIDAS ”, CHAPADMALAL FORMATION, BUENOS AIRES, ARGENTINA.

OSTERRIETH , MARGARITA; FERNANDEZ HONAINE, M. ; MOREL, E. ; BENVENUTO, M. L.; ERRA, GEORGINA

Encuentro; 8th International Meeting on Phytolith Research; 2011

Globular silicophytoliths have been commonly assigned to Arecaceae family; however, diverse authors have identified similar morphologies in other monocotyledons families. Due to the potentially that silicophytoliths have as indicators of plant communities of the past and the palaeoenvironments associated, it is necessary to understand the morphological differences of this characteristic morphology between monocotyledons families and if these differences can be identified in fossil record. The aims of the work were: 1) to analyze the phytolith morphologies of selected species belonging to Arecaceae, Bromeliaceae, Cannaceae and Strelitziaceae, (families that have been described as globular producers), 2) to identify and describe the morphometric characteristic that differentiate them; 3) to identify and describe the morphometric characteristic of the silicophytolits present in the pedosedimentary sequences; 4)  to analyze if such characteristics can be used to differentiate the families in fossil phytolith record. Species from the four selected families were collected and the leaves from at least two individuals were subjected to calcination technique. Phytoliths from soils and sediments were obtained after routine techniques. The plant ashes and soils and sediments phytoliths obtained were described and analyzed under optic and electronic microscope. From each plant species a minimum of 300 phytoliths were counted and 30 globular phytoliths were described according the following characteristics: form, outline, diameter, presence of spines, and form of the spines. Soils and sediments silicophytoliths were determined by observation and counting of 500 grains under optical microscope. Multivariate analyses were applied so as to analyze if differentiation between families was possible; and the results were compared with silicophytoliths present in the pedosedimentary sequences. The pedosedimentary sequences analyzed were associated to enigmatic glassy materials (escorias) and red bricklike materials (tierras cocidas) occur at a restricted stratigraphic level (the top of the Chapadmalal Formation). These materials are attributed to a mid-Pliocene impact event with a radiometric and magnetostratigraphic age of 3.3 million years ago (Ma) (sensu Schultz et al., 1998), located in Buenos Aires province, Argentina. These paleosoils presented a high percentage of globular phytoliths between 9 and 22 µm of diameter. Also, other morphologies such as elongates, rondels and bilobates were described in these samples. With the purpose to analyze the family producer of the globular phytoliths in these samples, the morphometric characteristics obtained from multivariate analyses were used for the identification. The palaeoflora inferred from phytolith analyses in these Pliocene sequences constitute an important advance toward plant palaeocommunities knowledge of Chapadmalal Formation, where no palaeobotanical evidences have been described until now.