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:
<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> 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.
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