Depositional processes of submarine channel-fill carbonate (Late Precambrian, Salamanca, Spain)

Abstract

In the SW of the province of Salamanca (Spain) there are extensive outcrops of late Precambrian rocks commonly termed the «Complejo Esquisto Grauwackico (CEG)». These rocks contain, in their upper part, several discontinuous siliciclastic-carbonate bodies. Carbonate sediments overlie an erosive surface which cuts 10 m into underlying siliciclastic deposits. Nine sequences are observed in these carbonates. Each sequence is composed of two facies: calcareous breccias at the base and thin-bedded carbonates towards the top. The breccias are generally clast-supported, with flat and angular clasts. The thin-bedded carbonates are mainly composed of sandstone-limestone couplets that are either parallel and current-ripple cross-laminated, or structureless. In the thin-bedded carbonates there are also pebbly-sandy limestone layers with inverse grading, and a few layers with large-scale cross-lamination. These carbonate sequences are interpreted as submarine channel fill deposited by viscous debris flows, density modified grain flows and high-density sandy turbidity currents. Sporadic tractional processes and low-density turbidity currents, fluidization and load processes also occur.