Abstract
A sedimentological, paleontological and paleoenvironmental study of the Andapaico Formation is presented (southern sector of the Paganzo Basin, San Juan). This unit overlies with an angular unconformity the Punta Negra Formation, and has a thickness of 430 m of siliciclastic sediments, that include deposits formed predominantly in nearshore environments. Lower shoreface (facies association I), anastomosed rivers and floodplain (II), high sinuosity rivers (III), beach (IV), eolian system (V), barrier island (VI) and lagoon (VII) deposits were identified. Facies association I (lower part of the unit) and VII (upper part) and their associated palynoflora assign them to the early Cisuralian (I) and late Cisuralian-early Guadalupian (VII, Lueckisporites-Weylandites Biozone). From the facies I association a fossil plant assemblage was obtained that allows it to be referred to the Ferugliocladus Superzone of the early Permian of the Tepuel-Genoa Basin, which reinforces the hypothesis of this age for the lower part of the Andapaico Formation.
Highlights
A sedimentological, paleontological and paleoenvironmental study of the Andapaico Formation is presented. This unit overlies with an angular unconformity the Punta Negra Formation, and has a thickness of 430 m of siliciclastic sediments, that include deposits formed predominantly in nearshore environments
Facies association I and VII and their associated palynoflora assign them to the early Cisuralian (I) and late Cisuralian-early Guadalupian (VII, Lueckisporites-Weylandites Biozone)
From the facies I association a fossil plant assemblage was obtained that allows it to be referred to the Ferugliocladus Superzone of the early Permian of the Tepuel-Genoa Basin, which reinforces the hypothesis of this age for the lower part of the Andapaico Formation
Summary
En el margen occidental del Gondwana, las cuencas neopaleozoicas fueron modificadas por diferentes avances y retrocesos del mar (Limarino y Spalletti, 2006), tal como se reconoce en particular en la Cuenca Paganzo (Azcuy y Morelli, 1970), limitada al oeste por la Protoprecordillera (Salfity y Gorustovich, 1983; González Bonorino, 1991), la cual presentaría sectores de comunicación por donde el mar comunicaba desde el oeste con la Cuenca Calingasta-Barreal (Baldis y Chebli, 1969). La Cuenca Paganzo, una cuenca de retroarco según Limarino y Spalletti (2006), con una superficie aproximada de unos 140.000 km, presenta en el sur de la provincia de San Juan (Precordillera Central) sucesiones continuas que abarcan del Pennsylvaniano al Pérmico. Casi continuos entre el sur de Jáchal y el norte de la provincia de Mendoza (Limarino et al, 1996; Ramos y Vujovich, 2000), tienen forma de fajas alargadas en sentido norte-sur, que recibieron diferentes nombres formacionales (Guandacol-Tupe-Patquía; Río Francia-Patquía; La Deheza-Ojo de Agua y Andapaico) según el área donde fueron caracterizadas (Harrington, 1971; Furque, 1963; Cuerda y Furque, 1981, 1983; Bossi y Andreis, 1985). Coca y Bercowski (1994) caracterizaron desde el punto de vista paleoambiental la Formación Andapaico, como integrada de base a techo, por sedimentitas de origen lacustre, ríos entrelazados y eólicas. A partir del hallazgo de nuevos restos megaflorísticos y del primer registro de material palinológico se discute su ubicación cronológica
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