New Insight into Supradetachment Basin Formation and Fill from Basin-margin Growth Strata, Hornelen Basin, Norway
Aschoff, Jennifer L.
Improved understanding of supradetachment basins provides a valuable lens to view resource potential in subbasins that were traditionally lumped into passive margins, but are best interpreted as supradetachment basins. Supradetachment basins form an important subset of extensional basins that develop in high-strain regions of the crust. These basins form in the hangingwall of low-angle normal faults that sole into a sub-horizontal detachment at depth. Incremental displacement on the headwall fault followed by down-dip translation and rotation of syntectonic sediments along the detachment helps account for the anomalously thick (up to 10's of km's) basin-fill in these basins. Displacement on the main headwall fault is typically normal, but the marginal faults are typically oblique-slip. Some of these detachment faults are responsible for exhuming deep, middle to lower crustal rocks, as is the case in metamorphic core complexes in North America. Classic examples are found in highly extended regions such as the Apennines, the Aegean, North American Basin-Range, western Norway (Hornelen, Hasteinen , and Kvamshesten basins), as well as the California Ridge Basin, NW Mexico Laguna Salada and Crete. Supradetachement basins have been studied since the 1970's, yet there are numerous aspects of their generation that are poorly understood. Much of our understanding of these basins derives from forward modeling, structural restoration and stratigraphic analysis of basin-fills that tend to be generalized due their overwhelming thickness. However, additional insights are offered by analyzing the complex growth-strata assemblages that are developed along the basin margins, where the "skewed" (sensu Steel 1978) alluvial fan-bodies and systematic growth strata geometries record vertical and lateral components of basin-margin development. Spectacular large- and small-scale growth strata are preserved in several locations along the margin of the Hornelen basin, Norway. Growth-strata are particularly important in the Hornelen basin because the north and south boundaries of the basin have been overprinted by younger faults, leaving growth strata as the best record of basin-margin kinematics. This study first reviews current models for supradetachment basins, and presents new data from growth strata developed on the northern margin of the Hornelen basin that record a complex history of vertical and lateral motion along the northern boundary fault.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013