Sediment gravity flow deposits of an Ordovician deep-sea fan system (western Precordillera, Argentina)—Discussion

Abstract

Abstract Ordovician siliciclastic sequences of Portezuelo del Tontal Formation (PTF) in the western Precordillera, Argentina, are interpreted to be deep-sea deposits which formed on a passive continental margin. Several facies and layer divisions have been identified and interpreted as high- and low-density turbidites, debrites, and contourites-hemipelagites. Outer and inner (upper-middle) submarine fan subenvironments have been recognized. Outer-fan associations consist of lobe and lobe-fringe sequences. Inner-fan associations are defined by coarse-grained and channelized deposits. The vertical arrangement of facies associations is interpreted in terms of progradational and retrogradational processes. Some sharp progradational and retrogradational transitions were controlled by allocyclic factors, such as sea-level changes and tectonics of the source areas. The submarine fan model for the PTF is an intermediate type between the pelite-rich and the sand-rich fans. It was formed in a narrow and elongate deep-sea basin controlled by the contemporaneous evolution of an oceanic rift in the direction of progradation.