IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
artículos
Título:
Microfacies, biota y paleoambientes sedimentarios del Ordovícico
Autor/es:
BERESI, MATILDE; CABALERI, NORA G.; BUITRÓN, BLANCA, E.; RODRIGUEZ, M. CECILIA; HEREDIA, SUSANA; TORTELO, M. FRANCO
Revista:
REVISTA MEXICANA DE CIENCIAS GEOLóGICAS
Editorial:
CENTRO GEOCIENCIAS UNAM
Referencias:
Lugar: México; Año: 2012 vol. 29 p. 330 - 330
ISSN:
1026-8774
Resumen:
This work shows the results of facies/microfacies and paleoenvironmental analysis of the Pozo Nuevo  Formation outcropping at the Cerro Salazar, nearby the Rancho Las Norias (Central Sonora, Mexico).  The Pozo Nuevo Formation represents Early-Middle Ordovician deposits of a continental carbonate  shelf that developed in the southwestern tip of Laurentia. The conodonts and trilobites described from the  unit indicate a late Floian-early Dapingian age. The microfacies analysis enables identifying different  sub-environments within the carbonate shelf from minor to major depth: a coastal beach, represented by quartz sandstone and laminated quartzite with desiccation cracks; an inner shelf which includes a supratidal setting constituted by dolomitized wackestone and an intertidal-subtidal lagoon characterized by diffusely laminated microbialites, oncoid mudstone, pelloid packstone grading to biopelloid and bioclastic packstone containing foraminifera and ostracods; and a subtidal  setting composed of grainstone and packstone with crinoids and algae (Nuia) and  detritic quartz and bioclastic packstone with bryozoans. In the lagoon as well as in the subtidal platform, there are intercalated intraclastic - bioclastic packstone levels, which are interpreted as proximal stormy events. The vertical variation of facies indicates a marked trend toward shallowing. At the base of the section fine micritic sediments deposited in a quiet, low energy lagoon, whereas a deeper subtidal environment with diverse faunas was developed in the middle part. On the other hand, at the top of the succession there is an increased participation of detrital quartz with deposition of coastal quartz sandstone culminating with thick dolomite levels of a vadose environment.