CABALERI nora Graciela
congresos y reuniones científicas
Microfacies and paleoenvironments from the carbonate shelf of the southwest Laurentia border, Pozo Nuevo Formation, lower - middle Ordovician (Central Sonora, Mexico).
Congreso; 18th International Sedimentological Congress; 2010
Institución organizadora:
International Association of Sedimentologists
This work shows the results of the facies/microfacies and paleoenvironments analyses of the Pozo Nuevo Formation outcropping at the Cerro Salazar, nearby the Rancho Las Norias (Central Sonora, Mexico). The formation corresponds to the deposits of a continental carbonate shelf that developed in the southwest Laurentia extreme in the Lower - Middle Ordovician. The microfacies enables identifying different sub-environments within the carbonate shelf from minor to major depth: Beach coastal, formed by quartz sandstone and laminated quartzite with desiccation cracks; Internal shelf supratidal constituted by dolomitized wackestone and intertidal - subtidal lagoon characterized by diffuse lamination microbialites, oncoid mudstone, pelloid packstone grading to biopelloid and bioclastic packstone with foraminifera and ostracods; Frontal bars complex intertidal - subtidal composed by grainstone and packstone with crinoids and algae (Nuia) and detritic quartz and bioclastic packstone with briozoans. In the lagoon as well as in the bars environment, there are intraclastic - bioclastic packstone levels intercalated. They are interpreted as proximal stormy events. The mainly fauna components are orthid and strophomenid articulate brachiopods, trilobites, nautiloids, crinoids, archaeogastropods (Macluritids), bryozoans, calcareous algae, ostracods, foraminifera and conodonts. The facies vertical variation indicates a marked trend toward shallowing with quartz sandstone and dolomite from the top of the carbonate section. At the base, there was a deposition of fine micrite from a quiet lagoon. A crinoid bar complex in intertidal environment was developed in the middle part. Over these bars there were deposited fine laminated sediments from a restricted shallow environment and from a deeper and larger energy lagoon environment. New crinoid and briozoan bars developed toward the upper part. Stratigraphically and at the top there is an increased participation of detrital quartz with deposition of quartz sandstone from a coastal environment, recording the migration toward the basin interior of the coastline. The top of the section culminates with a significant dolomite thickness from vadose environment. The depositional shallowing model shows a gradual transition from low to high energy carbonates, with facies of quartz beach sandstones.