INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Middle Cambrian trilobites of La Laja Formation, Western Argentina.
BORDONARO, O.L. Y PRATT, B.R.
Congreso; 4th International Trilobite Conference.; 2008
Instituto Geologico y Minero de España
The work has revealed that the earliest Middle Cambrian is represented in the lowermost Soldano Member by Eokochaspis nodosa and other kochaspidids of the Eokochaspis nodosa Biozone and possibly other biozones of the generalized PlagiuraPoliella Zone, hitherto recognized in the Great Basin of western U.S.A. These overly a low-diversity fauna consisting of olenellids and a single antagmine ptychoparioid in the Estero Member, of latest Early Cambrian age. The succeeding Albertella Biozone may be present but this interval is badly folded and faulted and available material is as yet equivocal. The Glossopleura and Ehmaniella biozones occur in the middle and upper parts of the Soldano Member respectively. The former contains species belonging to Glossopleura and Alokistocare, while the latter contains species belonging to Ehmaniella, Altiocculus, Elrathiella, Nyella and Polypleuraspis. The Bolaspidella Biozone comprises the thickest portion of La Laja Formation, and includes the uppermost Soldano, the Rivadavia Member, the Juan Pobre Member (restricted) and the recently defined Las Torres Member. It contains species belonging to Bolaspidella, Blainia, Altiocculus, Asaphiscus, marjumiids and other genera. Several Kootenia and Olenoides species are present in the Glossopleura Zone and younger intervals, whereas agnostoids and oryctocephalids are lacking. Instead, La Laja faunas comprise a succession of inner-shelf biofacies distinct from those recognized in the Great Basin and the southern Rocky Mountains of western Canada which are predominantly outer platform in their depositional setting (Bordonaro et al., 2008).