Abstract

GRAMAL-AGUILAR, Ana et al. Cannibalization evidences of the Oriente Basin Cretaceous and Paleogene sequences the in the orogenic wedge-top of the Ecuadorian Andes. Bol. geol. [online]. 2021, vol.43, n.3, pp.15-34.  Epub Mar 29, 2022. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v43n3-2021001.

To the southeast of the Cordillera Real, on the Miriumi river section, indiscriminated metamorphosed sedimentary and igneous rocks were included in the Upano Unit, as well as the Palanda-Méndez-Cosanga fault which was considered a terrain boundary in previous research. This research aims to characterize and discriminate the Upano Unit metamorphosed sedimentary and igneous rocks from the Oriente Basin sedimentary rocks. This discrimination is supported by lithostratigraphic data, identification of sedimentary structures, the fossil record, petrographic studies, and structural data analysis. Meta-volcanic and meta-pelitic rocks crop out in the western part of the section, whilst eastward in the section, fining-upward succession of quartz-conglomerates, quartz-sandstones, mudstone and sandstone with tidal structures; mudstone and wackstone limestones, black shale with abundant traces of the ammonites and bivalves are deformed by an anticline fold. On the Upano river, limestones and fossiliferous shales are discordantly overlain by multicolored siltstones and red beds. Considering the initial description of the Upano Unit, this sequence is restricted to meta-volcanic and meta-pelitic rocks, suggesting a low metamorphic grade in the sub-green schists facies that relates to the regional geodynamic. In this research, quartz-sandstones and mudstones with tidal signatures are included in the Hollín Formation, limestones and shales with Inoceramus sp. and Harleites sp. (?) are associated with the Napo Formation; and the sequences of red beds are linked to the Tena Formation. The presence of blocks and tectonic slivers conformed by rocks of Hollín, Napo, and Tena formations in the front of the orogenic wedge-top, which are affected by a thrust belt and drag folds, suggests that the Palanda-Méndez-Cosanga fault is not a terrain boundary between metamorphic sequences of the Cordillera Real and sedimentary sequences of the Oriente Basin. On the contrary, our data agree with the cannibalization model of foreland sequences.

Keywords : Thrust belt; Cretaceous and Paleogene sequences; Wedge-top; Sub-Andean Zone.

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