FIRST RECORD OF CALCAREOUS NANNOFOSSILS FROM CHAMBARÁ FORMATION, PUCARÁ GROUP, PERÚ: A NEW BIOSTRATIGRAPHIC TOOL FOR REGIONAL CORRELATION IN THE LATE TRIASSIC?

PÉREZ PANERA, JUAN PABLO; LYDIA CALVO MARCILESE; MARÍA JOSEFINA CUELLO; PABLO GIAMPAOLI

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleontológica Argentina

In the frame of a technical evaluation agreement between Perupetro S.A. and yPF E&P del PERU S.A.C, calcareousmicrofossils from the Pucará Group were analyzed to constrain the age and paleo-environment of deposition of the relatedunits. The samples came from Cantera Tello outcrop (Chambará Formation), East Andes, San Martín Department, northernPerú and are stored in the repository of the Biostratigraphy Laboratory of yPF TECNOLOGÍA S.A. The 42 m thick successionis composed of an alternation of ~2 to 4 m thick laminar and massive wackestones, packestones, grainstones andmudstones, in which gastropods, broken unidentified invertebrate skeletons and druses occur. Fourteen samples wereexamined for biostratigraphic analysis, all of them were barren for calcareous microfossils but 13 yielded a poorly preserved,scarce, but moderately rich calcareous nannofossil assemblages. This finding represents the second record of this groupin Late Triassic marine deposits in the Southeastern Pacific Ocean and the third outside the Tethys Realm. Assemblagesof the lower part of the Cantera Tello outcrop are characterized by nannoliths of uncertain affinity identified asPrinsiosphaera sp. In the upper part, assemblages are slightly more abundant and composed of the calcareous cystOrthophionella sp., the nannoliths Prinsiosphaera sp., Prinsiosphaera triassica and Eoconusphaera zlambachensis; and thecoccolith Crucirhabdus minutus that was recovered just in one sample. According to the Eoconusphaera zlambachensis recordin the succession, the lower part would correspond to a late Norian age and the upper part to the Rhaetian. This estimationagrees with the proposed age for the Chambará Formation in the Central Andes. Other studies conducted on the Chambaráand overlaying Aramachay and Condorsinga formations outcrops in the area, revealed similar calcareous nannofossilassemblages. These results, combined with a previous record of Late Triassic calcareous nannofossils in the Neuquén Basin,Argentina, highlights the value of this group as a promising biostratigraphic tool for regional correlation in the SouthAmerican Pacific basins.