SEDIMENTARY MODEL FOR THE ORIENTE BASIN OF ECUADOR DURING THE CRETACEOUS.
1996
During the Cretaceous, the Andean margin of Peru and Ecuador comprised arc and forearc zones, a subsident western trough, an axial threshold, and a shallow marine to continental eastern basin, often named the Oriente basin. Therefore, the latter represented the easternmost marine area of the active margin. The mainly marine Albian-Maastrichtian succession of the Oriente Basin of Ecuador (Napo Gp, fig.) is marked by four conspicuous facies (Jaillard et al. 1995). The first one consists of massive transgressive, often glauconitic sandstones with erosional base. The second one is made of thin-bedded bioclastic limestones with erosional base, deposited in an open marine shallow shelf environment. The third one is constituted by unbioturbated laminated black shales deposited in a marine, very low-energy, disoxic to anoxic environment. The fourth facies is represented by massive laminated and unbioturbated limestones deposited on a very low energy, disoxic marine shelf. Other facies include open marine marls, marine sand sheets and prograding sandstones. Such a facies succession express the alternation of open marine environments with moderate energy, and restricted low-energy depositional periods. This alternation can be explained through the dynamics of the marine Cretaceous sedimentation of the Oriente basin, controlled by palaeogeographic and climatic features, and by the creation rate of accomodation space. CHARACTERISTICS OF THE ORIENTE BASIN OF ECUADOR
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