We are delighted to be presenting at the AAPG Europe: Mixed/Hybrid Systems (Turbidite, MTDs and Contourites) on Continental Margins in Lisbon next week. Our Principal Reservoir Geologist, John Cater, will be presenting his works on North Sea contourites in the first session on the first day. This event is co-chaired by Javier Hernandez-Molina, of Royal Holloway University of London, and Karyna Rodriguez and Neil Hodgson, Searcher Seismic. We look forward to seeing you there!
Everything you need to know
Session: Processes & Deposits
Date & time: 21 June 2023, 12.00-12.20 (WEST)
Talk title: “Aviat, North Sea: Pleistocene Contourite or Hyperpycnite?”
Author & presenter: John Cater
Abstract
A multiproxy data set demonstrates spatially extensive glaciation of the Central Graben of the North Sea beginning in the earliest Pleistocene (Rea et al., 2018). Ice sheets repeatedly entered the North Sea, south of 60°N, in water depths of up to ~250 m from 2.53 Ma ago and subsequently grounded in the centre of the basin, in deeper water, from 1.87 Ma ago. These ice sheets were similar in spatial extent to the more widely recognised glaciers of the Middle and Late Pleistocene in NW Europe.
The Lower Pleistocene, marine-hosted sandstones that form the gas-prone Aviat reservoir are associated with this initial ice sheet. Core data suggests that they were deposited from north/northeastward directed, hyperpycnal outflows. These marine gravity-flows were generated during at least two retreats of the Early Pleistocene ice-sheet. The lower unit was extensively deformed by the advance of a grounded ice sheet, which later retreated to deposit the upper, undeformed unit. Deformation below the advancing ice sheet produced a rugose surface recognisable on regional seismic data, known as the ‘Crenulate Reflector’. Intercalated shales contain dropstones and marine foraminifera demonstrating a marine setting below storm wave-base.
The 10m-scale sandstone units are extensively cored and record deposition of well sorted, very fine to lower fine grained sand from sustained, unidirectional traction currents, resulting in spectacular climbing-rippled bed-sets. These essentially lack bioturbation, suggesting rapid sediment accumulation. The origin of these unidirectional currents is controversial. One possibility is that the flows were contour currents rather than proglacial gravity flows. Salient features seen in core and seismic will be discussed.
