Model for a Passive to Active Continental Margin Transition: Implications for Hydrocarbon Exploration

Abstract

This paper proposes a model for the transition of a passive, Atlantic-type continental margin to an active one with reverse polarity, prior to its ultimate collision with an island arc or continent. Significant morphological and stratigraphic patterns which are believed to characterize this transition include: (1) reactivation as reverse faults of preexisting listric, normal faults (not Gulf Coast-type growth faults, but those affecting basement as well) that were established during the margin's most recent period of extension; (2) landward migration with time of this fault rejuvenation; (3) development of deeper water-shallower water-deeper water or deeper water-unconformity-deeper water stratal assemblages on the margin; (4) regional flexure of the continental margin, a in to that known for the outer rise area of oceanic plates, landward of the subduction zone; and (5) landward migration of major unconformities coeval with continental margin flexure. This model creates implications for hydrocarbon exploration because: (1) it predicts the presence or absence of unconformities and thus potential stratigraphic traps among units of a particular basin; (2) provides spatial and temporal constraints for secondary-porosity development in potential reservoirs; (3) allows more accurate interpretations to be made of thermal or burial-history diagrams constructed for the purpose of determining relative thermal maturities of potential source units; and (4) helps distinguish between basement reactivation and decollement or Gulf Coast-type growth faulting. The orogenic phase of the margin's development, however, may later overprint or conceal these morphological and stratigraphic patterns to the extent that they might be unrecognizable. Because they have implications from both academic and economic perspectives, the role of these patterns in the margin's evolution should not be overlooked.