INVESTIGADORES
GARCIA Victoria Josefina
congresos y reuniones científicas
Título:
FIRST PALYNOLOGICAL RECORD OF THE SILURIAN/DEVONIAN BOUNDARY IN THE SAN JUAN PRECORDILLERA, ARGENTINA
Autor/es:
VICTORIA JOSEFINA GARCÍA; CLAUDIA VIVIANA RUBINSTEIN; PHILIPPE STEEMANS
Lugar:
Mendoza
Reunión:
Congreso; 4th International Palaeontological Congress. The history of life: A view from the Southern Hemisphere; 2014
Institución organizadora:
CONICET
Resumen:
The
Silurian/Devonian boundary in the Precordillera has been scarcely fossil-dated
because of the lack of accurate markers. The complexity of the Silurian and
Devonian deposits in western Gondwana is a result of the tectonic events
related to the development of a foreland basin in the active margin. Acritarch
diversity declined worldwide during late Silurian and Devonian time, probably
in response to extrinsic changes in seawater chemistry. Otherwise, terrestrial
palynomorphs are broadly used to constrain the Silurian/Devonian boundary. The
aim of this work is to present the miospore and phytoplankton assemblages
recorded in the upper part of the Los Espejos Formation and the lower part of
the Talacasto Formation in Río Jáchal section. Furthermore, this work serves
the purpose of reporting the identification of the Silurian/Devonian boundary
within the Los Espejos Formation, so far uncertainly defined in the San Juan
Precordillera, because mostly the 100 ms of the top of the Los Espejos
Formation were palynologically barren (e.g. Cerro del Fuerte and Loma de
Los Piojos sections). Ten samples were collected from the upper section of the
Los Espejos Formation and nine from the lower section of the Talacasto
Formation. The lowest studied level of the Los Espejos Formation contains Chelinospora
cf. cantabrica, which is an accessory species of the reticulata-sanpetrensis
(RS) and hemiesferica (H) biozones from Spain, pointing out a
Ludfordian-Pridoli? age. Towards the top of the unit, some Devonian badly
preserved phytoplankton and spores species have been recognized, such as cf. Latosporites
ovalis, Estiastra culcita, and cf. Thysanoprobolus polykion.
Below the top of the Los Espejos Formation, at 6.25 m from it, a single
specimen of Streelispora cf. newportensis was found, representing
the second record of this species in Gondwana. Its presence could allow the
identification of the Silurian/Devonian boundary in the Central Precordillera,
supporting the previous suggested age based on brachiopods. Also, at 4.75 m and
2.5 m below the top the Los Espejos Formation, Cymbosporites proteus and
Dictyotriletes cf. emsiensis Morphon were recorded. These species
could also support a Lochkovian age. Above the base of the Talacasto Formation,
at 8-16 m, Dictyotriletes cf. emsiensis Morphon, cf. Dibolisporites
echinatus, and cf. Zonotriletes sp. were found, which could confirm
that the Early Devonian age reaches this level. Based on palynological record,
it is possible to assign a Ludlovian/Pridoli? to Lochkovian to the studied
section. Moreover, the Silurian/Devonian boundary could be identified for the
fist time in the Argentine Precordillera.