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; FERNÁNDEZ HONAINE, MARIANA; MOREL, EDUARDO; BENVENUTO, MARIA LAURA; ERRA, GEORGINA

Colorado

Encuentro; 8th International meeting on phytolith research; 2011

PaleoResearch Institute (PRI), Golden, Colorado

Globular silicophytoliths have been commonly assigned ro Arecaceae family. However, diverse authors have identified similar morphologies in other monocotyledon families. Due to the potential that silicophytoliths have as indicators of past plant communities and their associated palaeoenvironments, it is necessary to understand the morphological differences of this characteristic morphology berween monocotyledons families in the fossil record. The objectives of the study were: l) 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; and, 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 processed through the calcination technique. Phytoliths from soils and sediments were obtained after routine techniques. The final ashes and soils and sediments phytoliths obtained were described and analyzed under optical 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 to analyze as much as possible the differences between families. 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) located in discrete stratigraphic levels (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 Ma (sensu Schultz et al., 1998), in the Buenos Aires Province, Argentina- The studied paleosols presented a high percentage of globular phytoliths between 9 and 22 pm in 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.