Late Cretaceous-Paleogene Foreland Basin Development in the Subandean Zone and Oriente Basin of Ecuador: Provenance, Geochronological and Structural Insights

Abstract

Contractional mountain building in the Northern Andes is associated with the complex structural evolution of the fold-thrust belt, and the resulting dispersal and accommodation of clastic sediment. In this study we integrate stratigraphic, geochronologic, and provenance analyses of Upper Cretaceous–Cenozoic series of the Oriente foreland basin of eastern Ecuador, which were deposited during Andean orogenesis. This study presents over 1500 new detrital zircon U-Pb ages from Upper Cretaceous and Cenozoic stratigraphic units (Tena, Chalcana, and Arajuno formations) to provide maximum depositional ages and provenance constraints. Maximum depositional ages were obtained for the Tena (69.6 Ma), Chalcana (29.3 Ma), and Arajuno (17.1, 14.2, 12.8 Ma) formations, placing them in the Maastrichtian, early Oligocene, and early-middle Miocene, respectively. The detrital zircon U-Pb ages identify clear signatures of at least four different sediment sources: craton (1600-1300 Ma, 1250-900 Ma), Eastern Cordillera fold-thrust belt (600-450 Ma, 250-145 Ma), Western Cordillera magmatic arc (<88 Ma), and recycling of cratonic material derived from the adjacent uplifted orogen, or recycled from foredeep sediments incorporated into the deforming wedge. This study also includes a seismic structural analysis of the deformed fold-thrust front, which reveal considerable reactivation of the pre-existing fault system, helping to clarify the evolving basin geometries and paleogeographic configurations. From these data, we infer the influence of major source areas on the regional sediment distribution and dispersal patterns in the proximal foreland basin (Subandean Zone). Moreover, the provenance analyses provide general insights into the relative paleotopography in the Ecuadorian Andes and adjacent Oriente foreland basin. These findings will help diminish uncertainties regarding the timing and location of oil charge and trap development for Subandean Zone structures, and their potential along-strike analogs at the Andean fold-thrust front.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018