Abstract

BORDONARO, Osvaldo Luis  and  BANCHIG, Aldo Luis. Cambrian trilobite biofacies in the Alojamiento Formation, Precordillera of San Juan and Mendoza, Argentina. Ameghiniana [online]. 2007, vol.44, n.1, pp.91-107. ISSN 1851-8044.

Several Middle - Cambrian trilobite biofacies are defined from limestones of the Alojamiento Formation in the San Juan and Mendoza, Precordillera, Argentina. This study is based on the concept of dual biostratigraphy that defines biofacies as an informal biotic stratigraphic unit of environmental significance characterized by associations of higher taxa. The Alokistocaridae Biofacies is composed of 10 % polymeroids of the Alokistocaridae family representing high energy shoal - water grainstones - packstones from the cordón de Santa Clara (San Juan). The Peronopsis Biofacies is composed of ~25 % of the agnostoid Peronopsis occurring in outer platform shallow subtidal packstones - wackestones exposed in the quebrada of Aguilera in the cordón del Alojamiento (Mendoza). The Ptychagnostus Biofacies is defined by ~30 % of the agnostoid Ptychagnostus found in outer - platform deep subtidal mudstones - calcipelites cropping out in the León Creek, cordón del Alojamiento (Mendoza). Both biofacies and lithofacies show an East-West bathymetric increase from shallow inner - platform to deep outer - platform settings. The Ehmaniella, Oryctocephalus and Ptychagnostus gibbus Zones recognised within each biofacies indicate an Early Marjumian age.

Keywords : Cambrian trilobites; Alojamiento Formation; Limestones; Argentine Precordillera.