Concentraciones fosilíferas autóctonas y para-autóctonas en la Formación Acoite (Ordovícico Temprano), Cordillera Oriental, Provincia de Jujuy. Consideraciones tafonómicas y paleoecológicas

WAISFELD, B.G.

Mendoza

Congreso; XII Congreso Geológico Argentino y II Congreso de Exploración de Hidrocarburos; 1993

Autochtonous and parautochtonous trilobite-dominated fossil concentrations from the Acoite Formation in the western flank of Cordillera Oriental are analysed from taphonomi and paleoecologic standpoint. They occur in the inner shelf and shoreface enviroments. The taphonomic study involved the effect of the biostratinomic processes (fragmentation, reorientation, selection and disarticulation) upon the exoeskeletons of trilobites. Two types of fossil concentrations are distinguished on the basis of their preservational styles: type I are slightly reworked concentrations composed of predominantly disarticulated sclerites formed under low to moderate rates of sedimentation during backgrounds sedimentations periods; the skeletal elements remained unburied on the substrate where physical agents yield their taphonomic configuration; type II concentrations are formed under conditions of sudden burial in the in the distal parts of the shelf in view of the high abundance of articulated trilobites.The trilobite assemblages in type II concentrations display high values of diversity and richness, although the suspension-feeding forms are reduced. This pattern of trilobite diversification and suspension feeders reduction is probably due to the physical disequilibrium caused by epiodes of sudden burial in the distal parts of the shelf that eanable soft bottom-adapted trilobites to proliferate.