Rift Basin Characteristics Originating From Antecedent Tectonic Events — Intricacies of the Falkland Plateau

Abstract

Current literature on the evolution of the Falkland Plateau emphasizes the break-up of West Gondwana (∼130 Ma) as the controlling tectonic event. In addition, most plate models maintain the integrity of the Falkland Plateau as an extension of Patagonia throughout the creation of the South Atlantic. Our regional analysis, based on extensive seismic coverage across the two sub-basins that make up the Falkland Plateau Basin (Volunteer & Fitzroy), illustrates that this interpretation is not compatible with observable structural elements, nor is the South Atlantic opening the primary tectonic event from which the basin characteristics are derived. Rather, it is the distribution of antecedent tectonic domains that give rise to the uniqueness of each sub-basin. Understanding this structural inheritance has allowed us to more fully comprehend the Cretaceous plays that comprise the current exploration targets. Prior to the opening of the South Atlantic, the Falkland Islands were located east of South Africa. The similarities between Falkland and South African geology were described in the early 20th century by Adie (1952). He suggested that the islands underwent microplate rotation during the separation from Africa prior to reaching their current position attached to Patagonia. This interpretation has fallen out of favor, replaced with the current rigid model. However, the rigid plate model introduces difficulties in explaining how these “interior” basins formed and the differences between them. The seismic data reveal that the remnants of an orogenic belt and associated foreland basin underlie the Mesozoic rift stratigraphy. The Volunteer basin is associated with the portion of the Plateau that is underlain by an extension of the Cape Fold Belt. Extensional faulting is apparent in seismic but is controlled by reactivation of antecedent thrust faults. The Fitzroy basin was created in the portion of the Plateau that is underlain by Karoo equivalent foreland basin deposits. Both basins display characteristics of depth dependent extension, the magnitude of which varies along the margin. Such variability is well documented in other parts of the world, but here the variability may also reflect the influence of structural inheritance. The geometries of the receiving basins, the shelf to slope transitions, and the distribution of play elements also appears to be controlled by these earlier structural styles.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016