Deep burrows in submarine fan-channel deposits of the Cerro Toro Formation (Cretaceous), Chilean Patagonia: Implications for firmground development and colonization in the deep sea

摘要

The Glossifungites ichnofacies recognized in Cretaceous strata (Cerro Toro Formation) of the Magallanes foreland basin in southern Chile represents an important discovery in that it extends the stratigraphic utility of firmground trace-fossil suites into thick-bedded, gravity-flow deposits of submarine fan-channel environments. The trace-fossil suite consists of atypically large Diplocraterion, Skolithos, and Arenicolites, which may reach an inferred length of 7 m. The burrows penetrate muddy, matrix-supported conglomeratic deposits dewatered and consolidated as a result of burial and subsequently exhumed by erosive turbidity currents. In a stratigraphic succession dominated by coarse-grained facies >350 m thick, the burrows are abundant at one stratigraphic horizon correlatable up to 200 W. This horizon is interpreted as a stratigraphic discontinuity associated with a long-term cessation of coarse-grained, sediment-laden gravity flows into the basin. The colonized surface is the only marker horizon traceable across much of the Magallanes basin study area.