Estratigrafía y discordancias del Cretácico Superior-Paleoceno en la region central de Tierra del Fuego.

D. R. MARTINIONI; E. B. OLIVERO; S. PALAMARCZUK

Anales SEGEMAR

Servicio Geológico Minero Argentino - Instituto de Geología y Recursos Minerales

Lugar: Buenos Aires; Año: 1999 vol. 33 p. 7 - 16

0328-2325

STRATIGRAPHY OF UNCONFORMABLE UPPER CRETACEOUS-PALEOCENE UNITS IN CENTRAL TIERRA DEL FUEGO.   -   ABSTRACT:   Marine rocks comprising three unconformably bounded units (Upper Cretaceous, Lower Paleocene and Paleocene) are first described in Sierra de Apen, The Upper Cretaceous unit has massive-faintly laminated mudstone with minor cross-stratified sandstone indicating north-northwest directed paleocurrents. Some intervals and calcareous concretions display a variety of trace fossils. Ammonites are rare and dinocysts indicate a Maastrichtian age. The unit is topped by an erosion surface, above which lays the sandier Lower Paleocene unit, with a thin basal conglomerate. Clasts are well rounded mudstone and concretions, eroded from the underlaying unit, and quartz, indurated mudstone and acidic volcanics. The dinocysts assemblage in this middle unit has an Early Paleocene age. The overlaying unit has a very coarse grained and thick polymictic orthoconglomerate resting on an apparently major unconformity that laterally eliminates all the Lower Paleocene and part of the Upper Cretaceous units within a short distance. The Upper Paleocene unit consists of fining and thinning upward lenticular conglomerates encased in thin bedded mudstone-sandstone rhythmites. Conglomerate clasts involve bluish gray sandstone and coquina, presumably derived from the underlaying Lower Paleocene unit. Clast imbrication reflects northeast directed paleoflows. Dinocysts in this unit suggest a Paleocene age. The Upper Cretaceous unit reflects deposition below wave base in the outer shelf. Both Paleogene units form part of a fan-deltaic succession. Though somewhat older, the Paleocene conglomerates correspond to part of the Chilean Ballena Formation and other rough1y age equivalent rocks of Argentinean Tierra del Fuego. The unconformities appear coeval with similar horizons in the subsurface of Austral and Malvinas basins. The Late Cretaceous N-NW directed sediment dispersal pattern probably mirrors early stages of the foreland basin development, whereas the coarser grained Paleogene represents deposition in the already defined foreland basin in front of the rising cordillera.