UPPERMOST CRETACEOUS SEDIMENTATION, TECTONICS AND PALEOGEOGRAPHY OF THE EASTERN SLOPE OF THE PERUVIAN ANDES

RENE MAROCCO
Orstom, Dpt. Toa Ur 111,213 Rue Lafayette, 75480 Paris Cedex 10, France.

In Peru the first Andean tectonic event began in the Uppermost Cretaceous continued on until the Upper Eocene. It consisted of compressive tectonics and lasted for approximatlvely 45 my. This tectonic phase initiated important geodynamic changes that progressively shaped the actual morpho-tectonlc features of Peru. These principal changes were:

1. Under the effect of the compressive tectonics, the western part of present Peru (Coast and Western Cordillera) was uplifted to form a Tectonic Belt that overthrusted the eastern fore-land. The thickening of the Peruvian continental crust began during the Uppermost Cretaceous to Upper Eocene tectonic phase.

2 The uplift of the western part of Peru displaced the ocean shoreline westwards. From this period, the Peruvian Andean region was moved away from the influence out of the Pacific Ocean.

3 Formation of a continental magmatic arc centred on the actual Western Cordillera.

4 In the present High Plateaus zone, between Eastern and Western Cordilleras, on theeastern front of the Tectonic Belt, highly subsident continental intermontane basins (Red Beds) became established which were controlled by the compressive tectonics. In these foreland red bed basins, the coarsening upward clastic sedimentation indicates that the Tectonic Belt and its related uplift was growing to the NE.

5 A marine transgression, coming from the north (probably from the Caribbean zone) penetrated in the easternmost region of the new Andean
palegeographic arrangement and reached, the actual Pew Bolivia Altiplano, to the south.

The paleogeographic arrangement initiated during the Uppermost Cretaceous evolved during Cenozoic times. The deformation reached progressively eastwards to produce the present state of the Peruvian Andes in which the Eastern Cordillera over-thrusts the Cenozoic continental basins of the Subandean Zone.

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