Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Controls on the Syn-rift Tectono-Stratigraphic Evolution of a Salt-Influenced Rift System: The Middle-Upper Jurassic of the Halten Terrace, Offshore Mid-Norway
(1) Department of Earth Science & Engineering, Imperial College London, London, United Kingdom.
(2) School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, United Kingdom.
(3) Department of Earth Science, University of Bergen, Bergen, Norway.
(4) Statoil Research Centre, Statoil ASA, Bergen, Norway.
(5) Statoil ASA, Harstad, Norway.
Recent research into the tectono-stratigraphic development of rift systems has mostly concentrated in regions where extension occurs within crystalline basement; however, the presence of a pre-rift evaporite detachment will profoundly influence the development of fault systems and, consequently, the syn-rift stratigraphic response. Therefore, generic tectono-stratigraphic models of syn-rift sedimentation may not be applicable to areas such as the Halten Terrace, mid Norway, where structural style and evolution during the Jurassic extension is influenced by pre-rift Triassic evaporites. These evaporite layers acted as an intra-stratal detachment surface, which greatly enhanced gravity-driven deformation in the overlying pre- and syn-rift Jurassic succession. This led to a broad zone of deformation characterised by numerous small faults.
The syn-rift sedimentary succession of the Halten Terrace is dominated by shelfal to basinal mud and siltstones of the Upper Jurassic Melke and Spekk formations, but isolated coarse-clastics do occur. The spatial and temporal distribution of the clastics is complex; they are found either fringing basement highs, as footwall-derived conglomerates, or adjacent to Jurassic fault scarps, where they are thought to be derived from local degradation of Garn Formation (Middle Jurassic) sandstones. One well-imaged footwall consists of a spectacular channelized erosion system comprised of small, linear systems up to 750 m long eroding the immediate footwall, while larger, more dendritic channel systems extend further back (up to 3 km normal to fault strike) into the footwall.
In the Halten Terrace, sediment supply and dispersal differs from classic rift models because of the broad, distributed nature of the deformation in the supra-salt cover and the absence of major footwall uplift. The detachment of the faults across the evaporite layers resulted in deepening of the basin through down-to-basin gravity driven deformation and a higher number of smaller fault blocks in the rift system. Syn-rift sediment was mainly derived from erosion of these small faults over large parts of the rift leading to localised sediment accumulation. In contrast, basement highs devoid of salt-related faulting remained sub-aerial throughout the rifting with fringing shorelines supplying large volumes sediment to the surrounding deeper basin.