INVESTIGADORES
KROHLING Daniela Mariel Ines
congresos y reuniones científicas
Título:
Phytolithic composition of the Tezanos Pinto Formation (Late Pleistocene loess) at the Southwest of the Entre Ríos province, Argentina
Autor/es:
ERRA, GEORGINA; ZUCOL, ALEJANDRO; KRÖHLING, DANIELA
Lugar:
Mar del Plata
Reunión:
Congreso; 7th IMPR 4th SMPR- 7th International Meeting of Phytolits Research and 4to. Encuentro de Investig. Fitolíticas del Cono Sur; 2008
Institución organizadora:
Universidad de Mar del Plata
Resumen:
The Tezanos Pinto
Formation (Last Glacial Maximum in age) appears as a continuous mantle in the Southwest
of Entre Ríos province (14.000 km²; North Pampa) forming the Crespo Loessic
Hills Geomorphological Unit. This unit forms the northeastern border of the
Peripherical Loessic Belt of the Pampean Aeolian System, defined by Iriondo and
Kröhling in 1996. The Quaternary stratigraphic sequence of the study area
comprises two defined cycles of aeolian deposition. The Tezanos Pinto Fm
corresponds to the most recent cycle, accumulated during the Oxygen Isotopic Stage
2 (OIS 2), in a range spanning from 36,000 to 8,500 years BP. The aeolian
facies of the unit formed by primary loess is dominant in the area, with an
areal thickness ranging between 2 - 5 meters. It corresponds to a friable and
permeable brown (7.5 YR 5/4) massive deposit, with prevalence of silt (63-4 μm;
60,7-80,3%), with subordinate clay and scarce very fine sand, that forms
vertical cliffs. In order to investigate its phytolith composition,
representative profiles from the Southwestern Entre Ríos province, were relevated
by continuous sampling (equidistant points 10 cm) following a NW-SE
transect. Samples were processed according to the methodology of Zucol and
Osterrieth (2002) . The
studied profiles of the Tezanos Pinto Fm showed high abundance of phytolith,
with dominance of prismatic, globular and truncated cone morphotypes. The
flattened prismatic morphotypes, with side edges smooth (the most frequent
type), scalloped, serrated or wavy, mainly with graminoid affinities, were
associated with others of probable cyperoid affinities. Other phytoliths with
graminoid affinities, such truncated cones, mainly of arundinoid or more rarely
pooid type were also present. Less frequent forms included phytoliths
originated by prickles or trichomes, symmetrical or asymmetrical fan-shaped,
saddle forms of chloridoid affinity, polyhedral and bilobate or dumbbell-shaped
with panicoid affinity. The assemblage also includes abundant sponge spicules,
primarily smooth macroscleres from freshwater sponges, as well as stomatocysts
from Chrysostomataceae, and in lower proportions, different types of diatoms. No compositional changes were observed along the sampled
sequence. The paleocommunity would have been formed by gramineans
(primarily arundinoid types, arid warm climates, and pooid, and to lesser
extent chloridoid and panicoid) with associated palm trees and sedges. The
presence of freshwater sponge spicules with scarce degree of alteration, joined
with the occurrence of diatoms, indicate the existence of water bodies. The low
percentage of cyperacean phytolits and chrysostomatacean cysts indicates
scarcity of lentic water bodies. This scenario agrees with geological
interpretations that indicate arid conditions for the first cycle (3616 ka), and semiarid characteristics for the second
cycle (14-8.5 ka) of depositation of this formation in Santa Fe province.