IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
New palynological record of the Ordovician/Silurian boundary in the Argentine Cordillera Oriental, Central Andean Basin.
Autor/es:
RUBINSTEIN, C. V., DE LA PUENTE, G. S., DELABROYE, A. & ASTINI, R. A.
Lugar:
Bonn, Alemania
Reunión:
Congreso; 12th International Palynological Congress - 8th International Organisation of Palaeobotany Conference; 2008
Institución organizadora:
Steinmann Institute, Division of Paleontology, University of Bonn
Resumen:
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The characterization of the Ordovician/Silurian
transition represents a challenge for palynologists because of relevant changes
in marine microplankton related to a major climatic event recorded by the
Hirmantian glaciation that exerted a strong influence on sea level and a
profound effect on life, creating extensive hiatuses and fossil rework. Ordovician/Silurian
successions from the Central
Andean Basin
contain marine palynomorphs as acritarchs and chitinozoans, and subordinated
terrestrial components as cryptospores and probable fresh-water algae as Proteolobus. In the Caspalá section, surveyed
within the Cordillera Oriental, NW Argentina,
five productive levels come from the base of a glacial horizon. Important soft-sediment
deformation would indicate strong reworking of previous sedimentary record.
Samples coming from layered diamictites show mixed faunal assemblages. Chitinozoans
are poorly preserved, hence the specific determination is difficult to carry
out. These include typical elements of the Darriwilian, Sandbian, and Katian Global
Stages as Belonechitina cf. micracantha
and B. cf. robusta. Acritarchs from the same levels are relatively diverse,
with scarce Late Ordovician (Katian) diagnostic species and high participation
of Early and Mid Ordovician taxa. Acritarch assemblage contains Neoveryhachium sp. A in Molyneux, 1988, Orthosphaeridium
cf. rectangulare, Stellechinatum cf. brachyscolum, Tylotopalla sp., Vilosacapsula setosapellicula. Arkonia
sp., Ferromia pellita and Stelliferidium striatulum are among the
reworked species. Hirnantian index-palynomorph taxa have not been found in the
studied levels. The overlying Lipeón Formation, regarded as Silurian, represents
the transgression afterglacial waining. The lower productive level of this unit yielded
chitinozoans such as Linochitina
penequadrata and Cingulochitina
dreyensis and a diverse acritarch assemblage containing Dactylofusa
marahensis, Domasia amphora, D. trispinosa. Duvernysphaera
aranaides, Tunisphaeridium tentaculiferum and Tylotopalla
caelamenicutis among others. The upper level records a distinct chitinozoan
assemblage composed by Angochitina cf.
hansonica, A. longicollis, Lambdachitina
bipedata and L. cf. synaphacantha. Both groups would indicate
an age no older than Telychian. First palynological work in this new section
allows bracketing glaciation to Hirnantian-earliest Silurian. However, given
the fluvial facies association related to the glacial record in this region, it
is possible that it was emergent during some time previous to being onlapped by
the Silurian Series.