Testing
Experimental Concepts for Oblique Rifting with Outcrop Data from the
Hooper, Robert J.1, Ken McClay2,
Lech Antonowicz3, Ewa Iwanowska3, Ian Walker4,
Tim Austin5 (1) ConocoPhillips, Houston, TX (2) Royal Holloway
University of London, Egham, 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
rift-system. In this talk, we review recent experimental data then compare
those results to outcrop examples from the western
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 a multi-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).
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California