Glacial events in Carboniferous sequences from Paganzo and Río Blanco Basins (Northwest Argentina): Palynology and depositional setting

PEREZ LOINAZE, V.S.; LIMARINO, C.O.; CÉSARI, S.N.

GEOLOGICA ACTA

UNIV BARCELONA

Lugar: Barcelona; Año: 2009

1695-6133

<!-- /* 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 age and depositional setting of two glacial events recognized in the western basins of Argentina are discussed in this paper. The older one corresponds to diamictites identified in the upper member of the Cortaderas Formation (Visean, Río Blanco Basin). The glacial sequence consists of shales, dropstone-bearing shales massive matrix-rich diamictites, massive clast-rich diamictites, and stratified diamictites, all of them interpreted as deposited in distal glaciomarine settings. Palynological remains recovered from shales interstratified with diamictites were referred to the late Visean Reticulatisporites magnidictyus-Verrucosisporites quasigobbettii Biozone. Younger glacial deposits were studied at the base of the Guandacol Formation (Paganzo Basin) where are made up by clast-poor massive diamictites, clast-rich massive diamictites, stratified diamictites, thinly-bedded dropstone-bearing diamictites, rhythmites, dropstone-bearing shales, and barren of dropstone shales. The whole sequence is interpreted as deposited in low-relief proximal glaciomarine environments (morainal banks). The abundant palynological assemblages found in the glacial interval were included in the subzone A of the Raistrickia densa–Convolutispora muriornata Biozone which is considered Serpukhovian in age. Palynological remains found in the Cortaderas Formation suggest that the beginning of the Glacial 2 event in Gondwana (according to Isbell´s chronological proposal for glacial and interglacial stages) should be considered late Visean while the end, according to the assemblages recovered from the Guandacol Formation, was not younger than Serpukhovian. Moreover, sedimentological and stratigraphic data suggest the existence of a short interglacial period between the Cortaderas and Guandacol glacial events.