INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Silurian chitinozoans and organic-walled phytoplankton from northwestern Argentina, Western Gondwana
DE LA PUENTE, G. SUSANA; RUBINSTEIN, CLAUDIA V.; ASTINI, RICARDO A.
Congreso; 46th Annual Meeting AASP - The Palynological Society San Francisco, U.S.A. October 20-24, 2013; 2013
AASP-TSP, Dino10, CAP, NAMS, CIMP
Chitinozoans and organic-walled phytoplankton from different outcrops of the Silurian Lipeón Formation along the Capillas River in the Sierras Subandinas, Argentina, on the western Gondwana margin are studied. The Capillas River crosses the anticline of the Zapla Range, which exposes the most complete Ordovician-Silurian sections of the eastern part of the Central Andean Basin, considered to have one of best exposures of the Paleozoic of South America. The Lipeón Formation has been traditionally assigned to the Silurien according to its stratigraphic characters and paleontological content. The basal part of this unit has been assigned to the Aeronian-Telychian according to graptolites and phytoplankton studies in the Los Colorados area of the Cordillera Oriental in the middle part of the Central Andean Basin. New chitinozoan-based studies carried out in the area of the Capillas River indicate that the deposition of the lower part of the Lipeón Formation could start in the Rhuddanian in the eastern part of the Central Andean Basin (de la Puente et al., 2012).The Lipeón Formation initiates its deposition with a flooding surface which is characterized by several basin-wide oolitic ironstones that record high-frequency sea-level fluctuations. This condensed section (~5 m thick) contains Rhuddanian-Aeronian chitinozoan assemblages (de la Puente et al., 2012). The rest of the unit in the area is composed of pervasively bioturbated silty-sandy shales (~340 m thick). The chitinozoan assemblages from the Lipeón Formation are moderately preserved and diverse. In this study, the following chitinozoan associations, overlying the Rhuddanian-Aeronian condensed section of the unit, in a ~100 m thick outcrop, have been observed: (A) Eisenackitina sp. cf. dolioliformis, Desmochitina densa, Desmochitina sp., Margachitina margaritana (2 m above the condensed section); (B) E. bejui, E. causiata, E. anulifera, Cingulochitina crassa, Bursachitina wilhelmi (20 m over the condensed section); (C) Pogonochitina inornata spinifera, Angochitina sp. (32 m over the condensed section); (D) Cingulochitina sp. cf. Ci. serrata, Angochitina sp. cf. longicollis, C. proboscifera, M. margaritana, Pogonochitina spp. (40 m over the condensed section); (E) Angochitina longicollis, Cyathochitina sp., Calpichitina sp., Pogonochitina spp., Ancyrochitina sp. (60 m over the condensed section); (F) Desmochitina sp. (67 m over the condensed section); (G) Anthochitina sp. (80 m over the condensed section). These chitinozoan associations indicate a Telychian-early Sheinwoodian age.The organic-walled phytoplankton are very poorly preserved and mainly contain Duvernaysphaera aranaides, Onondagaella asymmetrica, Eupoikilofusa cf. striatifera, Nanocyclopea sp., Tylotopalla caelamenicutis, Tylotopalla cf. digitifera, Diexallophasis remota group and Quadrisporites cf. horridus. The assemblages indicate an Aeronian-Telychian age and can be compared to the Llandoverian part of the La Chilca Formation in the Argentine Precordillera. The integrated chitinozoans and organic-walled phytoplankton from the Lipeón Formation in different sections along the Capillas River allow constricting its age to be from the Rhuddanian to the upper Telychian-Sheinwoodian in the southeastern end of the Central Andean Basin on the western Gondwana margin.