Tectonic and Eustatic Controls on Facies Distribution in the Middle to Upper Jurassic, Viking Graben, Norwegian North Sea

Abstract

The Middle of Upper Jurassic in the Viking Graben area was deposited during an overall transgression. From the lower Toarcian to the base of the cretaceous, there are seven 2nd-order (3-5 m.y.) transgressive-regressive (T/R) facies cycles that are related to regional tectonic events. These cycles dominate facies distribution, appear synchronous, and can be correlated throughout the study area. Local tectonics and sediment supply can modify these cycles. Local tectonics, sediment supply, and position in the T/R facies cycles control development of 3rd-order (0.5-3 m.y.) cycles. Where sediment supply is low, 3rd-order sequences are poorly developed. During a 2nd-order regression, shelfal areas and local highs are often eroded. Third-order sequences have well developed lowstands system-Y tracts (LST) and poorly developed transgressive systems tracts (TST). During 2nd-order transgressions, 3rd-order sequences have enhanced TST, starved HST, and poorly developed LST. Thick, stacked, shoreface sandstones may develop in the TST on terraces or on gently dipping slopes if sediment supply is high. The base of these sequences often shows an abrupt basinward shift in facies followed by backstepping facies. turbidites develop during 3rd-order lowstands when there is a steeply dipping slope and high sediment supply, but their distribution is more limited.