Environmental constraints of a Middle Ordovician trace fossil association from the Lina Formation (Puna of Jujuy province, NW Argentina)

ACEÑOLAZA, G., BAYETGOLL, A., NIEVA, S. Y ARÁOZ, L.

Santa Rosa, La Pampa

Simposio; Second Latin-american Symposium on Ichnology ? SLIC 2013; 2013

The Ordovician strata of the Puna region in NW Argentina is represented by a succession of siliciclastic marine facies associated to syn-sedimentary volcanism. Three phases of basin evolution during the the Tremadocian-Darriwilian have been recognized, Platform, Volcanic and Turbidite complex. The Lina Formation is part of the Puna Turbidite Complex, and is represented by a thick sequence of slightly metamorphosed and highly deformed shales and sandstones reaching up to ca. 900 m of thickness. The unit is divided in three members, and was interpreted as deposited in depositional lobes associated to advancing or shifting channels. A Darriwilian age has been proposed for the unit on the basis of poorly preserved, graptolites that were determined as Eoglyptograptus cf. E. dentatus, Glyptograptus (?Oelandograptus sp.), Archiclimacograptus sp., Oelandograptus? sp. and Glossograptus hincksii fimbriatus. The unit displays an impoverished trace fossil association characterized by shallow tier small-sized traces including Helminthoidichnites tenuis, Lockeia? isp. and few irregularly distributed low-reliefs knobs. Trace fossils are preserved on the upper and lower surfaces of up to 10 cm thick sandstone beds present in thick packages of parallel-laminated fine-grained sandstones and shales. Microbial mat related structures are rare, and mostly represented by wrinkle?marks, while pyrite mineralization is common within the fine-grained sandstones and shales. The paucity of paleontological evidence has precluded a detailed interpretation of the biota and its relation to this complex depositional scenario. A better understanding of the relationships between the sedimentary and the fossil record will help to decipher environments and the geodynamic evolution of the region during the Ordovician