Trazas fósiles, paleoambiente y paleogeografía del Silúrico Inferior del Cordón de Lila, Región de Antofagasta, norte de Chile

Acta geológica lilloana 21 (2): 2009

Abstract

Thee trace fossils here studied belong to beds located at the top of the basal section of the Llandoverian (Lower Silurian) Quebrada Ancha Formation in the Cordón de Lila, Antofagasta Region, northern Chile. The measured succession is 275 m thick and is formed by very fine to coarse-grained quartzarenite s with abundant planar and trough cross bedding. At the top of the studied succession beds with moderate to intense bioturbation are exposed in which trace fossils were identified: Arthrophycus linearis, Skolithos linearis, Arthrophycus alleghaniensis, Planolites beverleyensis, Palaeophycus tubularis, Zoophycos circinnatus, Monocraterion tentaculatum and Polykladichnus aragonensis. A. alleghaniensis and A. linearis are frequent in Silurian strata of different parts of South America and other gondwanan and laurentian localities. The stratigraphical and sedimentological analysis of the succession show that it was deposited in a shoreface environme nt, with paleocurrents directed towards the northwest. Specially Arthrophycus has been reported before as a form characteristic of siliciclastic facies of shallow waters in a high en ergy environment, strong tidal currents and sporadic storms. The succession is the first outcro p of Silurian reported in Chile. It formed part of a Chilean-Bolivian basin intermedious between the Arequipa Terrane and the "Central argentinian Ridge" and is a new fact for the interpretation of the evolution of the southwestern border of Gondwana during the Early Silurian (Llandoverian).