Morphological differentiation of globular phytoliths in monocotyledons: its application to fossil phytoliths record of pedosedimentary levels associated to ?escorias y tierras cocidas?, Chapadmalal formation, Buenos Aires, Argentina

OSTERRIETH MARGARITA; FERNÁNDEZ HONAINE MARIANA; MOREL EDUARDO; BENVENUTO MARÍA LAURA; ERRA GEORGINA

Colorado

Congreso; 8th International Meeting on Phytolith Research; 2011

Globular silicophytoliths have been commonly assigned ro Arecaceae family. However, d.iverse authors have identified similar morphologies in other monocoryledon families. Due to the potential that silicophytoliths have as indicators of past plant communities and their associated palaeoenviron*.ntr, it is necessary to understand the morphological differences of this characteristic morphology berween monocoryledons faiilies 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 describeá as globular producers); 2) to identify and describe the morphometric characteristic that differentiate them; 3) to identify ánd 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 p.o..rr.d through the calcination technique. Phytoliths from soils and sediments were obtained after routine iechniques. Th. pl"trt ashes and soils and sediments phytoliths obtained were described and analyzed under opti. "nd electronic microscope. From each plant species a minimum of 300 phytoliths were counted and 3-0 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 tñe differences berween families. The results were compared with silicophytoliths present in the pedosedimentary sequences. The pedosedimentary sequences analyzeáwere associated to enigmatic glassy materials (escorias) and red bricklike materials (tierras cocidas) located in discrete stratigraphiclevels (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. lVith the purpose to "rr"lyr. 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 knowiedge of Chapadmalal Formation, where no palaeobotanical evidences have been described until now. Acknowledgements: Financial support for this work has been provided by the UNMdP EXA 55ll11, the ANPCyT, PICT N´ 2010-2036, and PICT N" 1871 RsrERrr{cEs Schultz, P H, M. Zarate; ( Hames; C. Camilión and J. King., 1998. A 3.3-Ma Impact in Argentina and Possible Consequences. Science 1l Vol. 282 no. 5396, pp.206I-2063.