Sedimentary palaeoenvironments and provenance of the Miocene Vinchina Formation, north-western La Rioja Province
The Vinchina Formation is a thick (5,100 m) red-bed sequence of sandstone, mudstone, intra- and extraformational conglomerate and scarce tuff. This unit was deposited in an Andean foreland basin, formed during the Miocene between the Sierras Pampeanas to the east and the Precordillera to the west. S...
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| Autores principales: | , , , , , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_00044822_v56_n4_p443_Tripaldi |
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| Sumario: | The Vinchina Formation is a thick (5,100 m) red-bed sequence of sandstone, mudstone, intra- and extraformational conglomerate and scarce tuff. This unit was deposited in an Andean foreland basin, formed during the Miocene between the Sierras Pampeanas to the east and the Precordillera to the west. Seven facies associations have been recognised in this unit. Associations I, II and III correspond to the Lower Member while IV, V, VI and VII are found in the Upper Member of the Vinchina Formation. The oldest interval (association I) is composed of cross-bedded sandstone, mudstone and scarce intraformational conglomerate deposited in an anastomosing fluvial system with dominant sandy flood plains. These rocks are covered by a thin interval of fine and very fine cross-bedded sandstone (association II) sedimented in an intermontane aeolian environment. Association III is comprised of sandstone, mudstone and intra- and extraformational conglomerate, probably deposited in an anastomosing network of channels with dominantly muddy floodplains and well-developed upward-coarsening crevasse splay sequences. The base of the Upper Member is marked by a low-angle erosive surface covered by coarse conglomerate and sandstone deposited by braided rivers (association IV). These rocks pass upward to thick sequence of sandstone and mudstone belonging to association V and amalgamated sandstone corresponding to association VI. It is very probable that both facies associations were deposited by rivers, with a meandering pattern of channels in association V and a braided network in association VI, At the top of the sequence there is a thin intercalation of lacustrine sediments included in association VII. Detrital modes suggest derivation from a mixed area and a dissected volcanic arc. Chemical data are consistent with petrographic analysis and clearly point out to an active continental margin characterized by felsic to intermediate volcanic source rocks. |
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