Testing Experimental Concepts for Oblique Rifting with Outcrop Data from the Western U.S.A. and Subsurface Data from European Basins

Hooper, Robert¹, Ken McClay², Lech Antonowicz³, Ewa Iwanowska³, Ian Walker⁴, Tim Austin⁵ (1) CoconoPhillips, Houston, TX (2) Royal Holloway University of London, Egham, Surrey, United Kingdom (3) Geonafta, Warsaw, Poland (4) ConocoPhillips UK Ltd, Aberdeen, United Kingdom (5) ConocoPhillips Norway, Stavanger, Norway

Conceptual models from both fieldwork and scaled physical-model experiments have significantly enhanced our understanding of the geometry of rift-systems particularly when rifting is oblique to pre-existing zones of crustal weakness or when offsets occur in the rift­system. In this talk, we review recent experimental data then compare those results to out­crop examples from the western U.S.A. and subsurface data from European basins.

Obliquity can occur during a single rift-event where the location of the rift border-fault system is controlled by pre-existing basement structures that are oblique to the extension direction (e.g. on the Volcanic Tablelands near Bishop, CA, where a basement horst, oblique to the recent extension direction, has controlled the location of deformation in the overlying cover-rocks). Preexisting zones of weakness can also localize offsets within rift-systems

(e.g. at the southern-end of the Faeroe-Shetland basin-system). Obliquity can occur in amulti-rift setting where a younger-rift is oblique to an older-rift or where the direction of rift­ing changes markedly through time (e.g. as in mid-Norway). The resultant rift-architecture will combine elements from both rift events with transfer zones in the old rift-system often becoming focal points for offsets in the younger rift-system

Obliquity in a rift-system can also be introduced when marked changes in stratal facies or thickness, particularly in weak layers such as salt or shale, are oblique to subsequent deformation (e.g. on the western margin of the Polish Trough where facies variations with­in the Zechstein Fm. exert a fundamental control on the distribution of structures with the overburden).