Stratigraphy of the late Cretaceous–Paleogene deposits of the cordillera occidental of central ecuador: geodynamic implications

Abstract

Two accreted oceanic terranes are classically recognized in the Cordillera Occidental of central Ecuador: the Macuchi island arc to the west and the Pallatanga oceanic terrane to the east. Detailed stratigraphic studies of the sedimentary cover of the Pallatanga terrane show that it actually comprises two terranes. During the late Campanian-early Maastrichtian, the eastern terrane received partially continent-derived turbidites, which demonstrates that it was accreted to the Andean margin before mid-Campanian times (i.e. 85–80 Ma ago). Meanwhile, the western terrane received fine-grained, pelagic, siliceous black cherts, which indicates that it belonged to the oceanic realm during mid-Campanian–Maastrichtian times. Both series are unconformably overlain by a thick, coarsening upward, siliciclastic series of Paleocene age; thus, the western terrane accreted to the eastern one during the late Maastrichtian (≈69–65 Ma). The thick Paleocene clastic series records the uplift of the Eastern Cordillera, which was triggered by the latter accretion and enhanced by the Late Paleocene accretion (≈58 Ma) of the Piñón oceanic terrane of southern coastal Ecuador.