Print this pageSediment Supply Control of Reservoir Distribution and Volume in Paleogene Sequences of the North Sea Basin
GALLOWAY, WILLIAM E.
The early Paleogene Cenozoic sedimentary record of the North Sea Basin illustrates the logical progression of depositional systems and stratigraphic architectures created by episodic, tectonically-forced sediment supply into a narrow, deep trough. Seven genetic sequences (Maureen, Andrew, Balmoral, Forties, Domoch, Beauly-Balder, Frigg) record a late Paleocene-early Eocene episode of sand-rich sediment supply of 4 m.y. duration. This long-term episode consists of two shorter pulses separated by a 2 m.y. phase of moderate supply.
Implications of sediment supply as the primary control on North Sea depositional history are four-fold. (1) Each of the seven sequences displays a distinctive paleogeographic array of depositional systems and stratigraphic architecture. Intervening periods of rapid change in sediment supply regime (amount, textural composition, and/or transport axes) destabilized the sediment dispersal systems, resulting in reorganization of depositional systems tracts and creating new patterns of reservoir distribution and stacking. (2) Regrading of depositional profiles in the face of changing supply regime created stratigraphic surfaces, which now form sequence boundaries that reflect submarine sediment starvation with concomitant erosion and/or bypass throughout the hydrocarbon-productive basin center. (3) Calculated volume distributions of individual sandy turbidite and gravity-mass transport complexes, which contain the 8 billion bbls and 23 tcf of recoverable Paleogene reserves, are directly related to the episodic sediment supply history and long-term depositional reduction of intrabasinal relief. (4) Slope and base-of-slope reservoir systems evolved from allochthonous, sand-rich delta and shelf-aprons and fans (Andrew, Forties) to heterolithic, debris-flow-dominated, autochthonous aprons and tongues as sediment supply waned (Beauly-Balder, lower Frigg).