Structural controls on the stratigraphic architecture of net‐transgressive shallow‐marine strata in a salt‐influenced rift basin: Middle‐to‐Upper Jurassic Egersund Basin, Norwegian North Sea

Abstract

In this study, we integrate 3D seismic reflection, wireline log, biostratigraphic and core data from the Egersund Basin, Norwegian North Sea to determine the impact of syn-depositional salt movement and associated growth faulting on the sedimentology and stratigraphic architecture of the Middle-to-Upper Jurassic, net-transgressive, syn-rift succession. Borehole data indicate that Middle-toUpper Jurassic strata consist of low-energy, wave-dominated offshore and shoreface deposits and coal-bearing coastal-plain deposits. These deposits are arranged in four parasequences that are aggradationally to retrogradationally stacked to form a net-transgressive succession that is up to 150-m thick, at least 20 km in depositional strike (SW-NE) extent, and >70 km in depositional dip (NW-SE) extent. In this rift-margin location, changes in thickness but not facies are noted across active salt structures. Abrupt facies changes, from shoreface sandstones to offshore mudstones, only occur across large displacement, basement-involved normal faults. Comparisons to other tectonically active salt-influenced basins suggest that facies changes across syn-depositional salt structures are observed only where expansion indices are >2. Subsidence between salt walls resulted in local preservation of coastal-plain deposits that cap shoreface parasequences, which were locally removed by transgressive erosion in adjacent areas of lower subsidence. The depositional dip that characterizes the Egersund Basin is unusual and likely resulted from its marginal location within the evolving North Sea rift and an extra-basinal sediment supply from the Norwegian mainland.

Architecture and controls of thick, intensely bioturbated, storm-influenced shallow-marine successions: An example from the Jurassic Neuquén Basin (Argentina)

“…As in the Ula Formation example, total bioturbation in the offshore transition zone of the Fulmar Formation was interpreted as the result of low magnitude and/or low frequency of storm events (Howell et al, 1996). Collectively, these Upper Jurassic units of the Central Graben developed in a rifting tectonic stage and show long-term (several million years) aggradational to retrogradational stacking patterns (Howell et al, 1996;Mannie et al, 2014;2016) (Fig 11).…”

Architecture and controls of thick, intensely bioturbated, storm-influenced shallow-marine successions: an example from the Jurassic Neuquén Basin (Argentina)

“…As in the Ula Formation, intense bioturbation in the offshore transition zone of the Fulmar Formation was interpreted as the result of low magnitude and/or low frequency of storm events (Howell and Flint, 1996). Collectively, these Upper Jurassic units of the Central Graben developed in a rifting regime and show long-term (several million years) aggradational to retrogradational stacking patterns (Howell and Flint, 1996;Mannie et al, 2014Mannie et al, , 2016 (Fig. 11).…”

Organic content and maturation effects on elastic properties of source rock shales in the Central North Sea

“…Uplift and erosion in multiple phases, as recent as Neogene, have had laterally varying effects across the region (Hansen et al, 2017). Additionally, Triassic and Early Jurassic sediments are absent in certain areas due to Early Jurassic uplift of the Mid North Sea Dome causing erosion and nondeposition (Ziegler, 1992;Mannie et al, 2014).…”