Middle Darriwilian to Lower Sandbian conodont zones and global correlation of the Argentine Precordillera

GUILLERMO L. ALBANESI; NICOLÁS A. FELTES; FERNANDA SERRA

Mendoza

Congreso; 4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014

MIDDLE DARRIWILIAN TO LOWER SANDBIAN CONODONT ZONES AND GLOBAL CORRELATION OF THE ARGENTINE PRECORDILLERA Guillermo L. Albanesi1, Nicolás A. Feltes1 and Fernanda Serra1 The Precordillera of San Juan Province in western Argentina is characterized by over 2,200 m thick Cambro-Ordovician limestones, which were deposited cyclically in restricted to open marine platforms. The study areas of this research are located southwest of Jáchal city including the Las Aguaditas Formation at Los Blanquitos range and the Las Chacritas For-mation at La Trampa range. The sample section of the former unit involves top strata of the San Juan Formation and the overlying Las Aguaditas Formation, which is 282 m thick. The second study section includes the uppermost 10 m of the San Juan Formation, the 60 m thick Las Chacritas Formation, and the 10 m thick Las Aguaditas Formation. Both sections span the middle Darriwilian to early Sandbian time interval. A total of 10,400 identifiable conodont elements were recovered, including chronostratigraphic significant taxa such as: Lenodus variabilis, Yangtzeplacognathus crassus, Baltoniodus variabilis, Eoplacognathus pseudoplanus, E. suecicus, Dzikodus tablepointensis, Histiodella sinuosa, H. holodentata, H. kristinae, H. bellburnensis, Microzarkodina hagetiana, M. ozarkodella, Periodon ma-crodentatus, P. zgierzensis, P. aculeatus and Pygodus anserinus. On the basis of the con-odont zones identified, the index species enable confident ties between sections. The Y. crassus Zone straddles the contact between the San Juan Formation and overlying units at both study sections, i.e., Las Aguaditas and Las Chacritas formations. The E. pseudoplanus Zone, which includes the M. hagetiana and M. ozarkodella subzones, was recognized in the upper half of the lower member of the Las Aguaditas Formation and intermediate strata of the correlative Las Chacritas Formation. The E. suecicus Zone was determined only in the upper Las Chacritas Formation; whereas the upper subzone of the P. anserinus Zone was identified in the Las Aguaditas Formation at both study sections. The fossil record verifies an important hiatus with regional geotectonic significance between the lower and middle members of the Las Aguaditas Formation at Los Blanquitos, which encompasses the E. suecicus, Pygodus serra and the lower subzone of the P. anserinus zones. At La Trampa range, the hiatus suppressed the upper E. suecicus and the P. serra zones as well as the lower P. anserinus zones. The conodont records allow for establishing a biostratigraphic scheme for the middle Darriwilian and lower Sandbian in the Argentine Precordillera, with controls over numerous well-studied localities of the Central Precordillera. Global correla-tion of the analyzed interval with sections from North America, China, Thailand, Australia and Baltoscandia is consistently constrained.