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An Alternative Geodynamic Model for the Oriente-Northern Marañon Foreland Basin Petroleum System

Barragan, Roberto1; Baby, Patrice; Nino, Christian; and Rivadeneira, Marco
1[email protected]

The prolific Oriente-Northern Marañon Basin (~ 45 BBO estimated Oil in place) is part of the asymmetric foredeep portion of the present day sub-Andean foreland system. This supercharge basin is associated with the same petroleum system, the Cretaceous marine shales/limestones of the Napo-Chonta Fm. However, this source rock is either immature along the entire Oriente Basin (Ro ~ 0.3-0.6) or of poor TOC content (<1%) along the Marañon Basin. The accepted geological model associates the origin of this Cretaceous petroleum system to a hypothetical kitchen located west along the present-day Ecuadorian Interandean zone, named "Quito Kitchen", already exhumed/eroded or metamorphosed by Andean orogeny. However, this hypothesis is speculative and implies very efficient preservation and long remigration process.

A regional scale geodynamic framework combined with an extensive geochemical database, allows us to define an alternative model that can explain the origin of this rich Cretaceous petroleum system. The same proposes two major kitchens that generate oil during a distinctive stage of the Cretaceous-Cenozoic basin evolution: The first kitchen, it corresponds to a major depocenter along the south western portion of the basin, the present-day Santiago Basin, developed since upper Cretaceous time (-90 Ma) as a direct response of to the late Cretaceous syn-depositional uplift of the northern Ecuadorian sub Andean zone. The generation and expulsion of hydrocarbons took place since late Paleocene-Eocene times, associated with the deposition of the early Tertiary section that records the most important subsidence event. NNE long distance migration from this paleo-basinal area was facilitated by the continuity of the late Cretaceous/early Tertiary tectonic fabric associated to the major transpressive driven inversion of NNE-SSW Triassic–Jurassic grabens which extend to the north in the Oriente Basin. The second kitchen, it corresponds to the present day deepest portion of the foreland Basin. It was formed as a direct response of the Santiago Basin tectonic uplift and exhumation since late Miocene times (~10 Ma). New geochemical analysis confirms this kitchen as the responsible for the generation and expulsion of hydrocarbons since late Miocene, related to the deposition of the Mio-Pliocene section. The present day foreland geometry facilitated the migration of the new oils towards the east to the current forebulge position of the basin (Iquitos arch).

 

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013