Middle Oxfardian to Volgian sequence stratigraphy of the Greater Shearwater area

Abstract

A Middle Oxfordian to Volgian sequence stratigraphic model for the Greater Shearwater area is presented. This model builds on the genetic stratigraphic sequences of Partington et al. (19936), refining the position of key stratigraphic surfaces with an additional emphasis on sequence boundary description. Most stratigraphic surfaces are believed to be related to tectonic events superimposed on a gradual rise in relative sea-level from the Middle Oxfordian to Volgian. Biostratigraphic information drawn from throughout the UK Central Graben allied with regional log correlation and seismic data has allowed a robust sequence stratigraphic framework to be developed which is applicable to the Greater Shearwater area.

Palaeoecology of syn-rift topography: A Late Jurassic footwall island on the Josephine Ridge, Central Graben, North Sea

“…Zechstein salt halokinesis and post-Jurassic fault movements render attempts to determine exact amounts of Late Jurassic uplift extremely complex and inaccurate in this area, with previous studies implying the ridge was submerged throughout the Jurassic rift phase (Zeigler, 1990;Rattey and Hayward, 1993;Erratt et al, 1999;Jeremiah and Nicholson, 1999;Fraser et al, 2003;Sansom, 2010).…”

“…Previous models have indicated that the Josephine Ridge area was submerged during the Oxfordian and Kimmeridgian (Zeigler, 1990;Rattey and Hayward, 1993;Jeremiah and Nicholson, 1999;Fraser et al, 2003), with modelling of Upper Oxfordian submarine fan systems prograding from the Fulmar shelf and interpreted to cross-cut the Josephine Ridge (Jeremiah and Nicholson, 1999;Fraser et al, 2003). If, as we propose, the Judy Horst was subaerially exposed, forming a topographic high, then it appears unlikely that sediment would have been able to cross either arm of the Central Graben, to be deposited on the opposing side Although subaerial exposure of the Judy Horst may identify it as a source of reservoir quality sediment, the estimated size of the Judy Island at c.350 km 2 would have been insufficient to source large scale sedimentary systems with reservoir potential.…”

North Sea hydrocarbon systems: some aspects of our evolving insights into a classic hydrocarbon province

“…Howell et al (1996) offered a convincing account of the relationship between Fulmar Formation depocentres and the hinterland, with shoreface fairways forming at entry points in the relays in the graben system. This model offered a compelling fit with the recognition that the Oxfordian fairways were in turn located at the northern and southern limits of a series of en-echelon graben developing during the Oxfordian, with gradual retreat of these fairways away from the basin centres and ultimately onto the platforms in the Kimmeridgian (Erratt et al 1999;Jeremiah & Nicholson 1999). Heavy mineral analysis of the Fulmar sands indicates a progressive un-roofing of the hinterland, with sediments derived from finergrained and mixed lithologies in Triassic and Middle Jurassic sequences, indicating a less effective reservoir provenance than those feeding the South Viking Graben and Moray Firth systems.…”

“…sequences, forming local sediment traps, thereby reducing the potential for sediment bypass. & Nicholson 1999). These reservoirs are relatively thin compared with their ESB counterparts (Magnus Field well log for comparison).…”

“…They occur in fields in both deep graben settings, where the reservoirs are predominantly Oxfordian in age, and the marginal platforms, where they are largely Kimmeridgian to Volgian (e.g. Donovan et al 1993;Partington et al 1993;Wakefield et al 1993;Jeremiah & Nicholson 1999;Fraser et al 2003).…”