Quantitative progradation dynamics and stratigraphic architecture of ancient shallow-marine clinoform sets: a new method and its application to the Upper Jurassic Sognefjord Formation,Troll Field, offshore Norway
S. Patruno, G.J. Hampson, C.A.-L. Jackson and P.S. Whipp
Journal name: Basin Research
Issue: Vol 27, No 4, August 2015 pp. 412 - 452
Info: Article, PDF ( 21.2Mb )
This article presents a new numerical inversion method to estimate progradation rates in ancient shallow- marine clinoformsets, which is then used to refine the tectono-stratigraphic and depositional model for the Upper Jurassic Sognefjord Formation reservoir in the super-giant Troll Field, offshore Norway. The Sognefjord Formation is a 10–200-m thick, coarse-grained clastic wedge, that was deposited in ca. 6 Myr by a fully marine, westward-prograding, subaqueous delta systemsourced fromthe Norwegian mainland. The formation comprises four, 10–60-mthick, westerly dipping, regressive clinoform sets, which are mapped for several tens of kilometres along strike. Near-horizontal trajectories are observed in each clinoform set, and the sets are stacked vertically. Clinoformage and progradation rates are constrained by: (i) regionally correlatable bioevents, tied to seismically mapped clinoforms and clinoformset boundaries that intersect wells, (ii) exponential age–depth interpolations between bioevent-dated surfaces and a distinctive foreset-to-bottomset facies transition within each well, and (iii) distances between wells along seismic transects that are oriented perpendicular to the clinoform strike and tied to well-based stratigraphic correlations. Our results indicate a fall in progradation rate (from 170–500 to 10–65 km Myr1) and net sediment flux (from 6–14 to ≤1 km2 Myr1) westwards towards the basin, which is synchronous with an overall rise in sediment accumulation rate (from 7–16 to 26–102 m Myr1). These variations are attributed to progradation of the subaqueous delta into progressively deeper waters, and a concomitant increase in the strength of alongshore currents that transported sediment out of the study area. Local spatial and temporal deviations fromthese overall trends are interpreted to reflect a subtle structural control on sedimentation. This method provides a tool to improve the predictive potential of sequence stratigraphic and clinoform trajectory analyses and offers a greater chronostratigraphic resolution than traditional approaches.