Dunlin Group Sequence Stratigraphy in the Northern North Sea: A Model for Cook Sandstone Deposition

Marjanac, Tihomir (1997) Dunlin Group Sequence Stratigraphy in the Northern North Sea: A Model for Cook Sandstone Deposition. AAPG Bulletin, 81 (2). pp. 276-292. ISSN 0149-1423

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The Dunlin Group in the northern North Sea, consisting of the Johansen, Amundsen, Burton, Cook, and Drake formations of late Sinemurian– Toarcian age, hosts important hydrocarbon reser- voirs in the Cook Formation sandstones. The Johansen Formation is associated with a relative fall of sea level and is interpreted to be a large sand- stone delta confined within a broad incised valley at the base of the group. During a later stage of rel- ative sea level rise, the finer grained Amundsen and Burton formations were deposited. The overlying Cook Formation consists of four sandstone tongues, each of which is characterized by a lower zone of sharp-based, upward-coarsening, thinly bedded shoreface sandstones and siltstones (reflecting forced regression during falling relative sea level) and an erosively based upper zone of thin tidal flat and thick deltaic/estuarine sandstones (reflecting lowstand incision, as well as initial progradation and subsequent transgressive backfill of estuaries during relative sea level rise). The Drake Formation shales were deposited during con- tinued relative sea level rise. Several types of ero- sional surfaces are recognized within the studied succession: (1) sequence boundaries occur at the base of the Johansen Formation and within the Cook Formation, and represent the bottoms of incised valleys that truncate the underlying shoreface deposits; (2) regressive surfaces of marine erosion occur at the base of Cook Form- ation units and truncate the underlying Burton and Drake shales, siltstones, and mudstones; (3) trans- gressive tidal channel (tidal ravinement) surfaces within the Cook Formation underlie the estuarine sandstones of the incised valley fills; (4) wave ravinement surfaces truncate the tops of estuarine sandstones and are overlain by thin transgressive lags that grade upward into the overlying black shales. Three-dimensional (3-D) models, based on structure-contour maps of sequence boundaries, unveil a paleotopography that controls the charac- teristics and distribution of the Dunlin Group reser- voir sandstones.

Item Type: Article
Date: 1997
Subjects: NATURAL SCIENCES > Geology
Divisions: Faculty of Science > Department of Geology
Publisher: American Association of Petroleum Geologists
Depositing User: Sonja Borak
Date Deposited: 21 Feb 2014 09:25
Last Modified: 03 Mar 2014 08:33
URI: http://digre.pmf.unizg.hr/id/eprint/445

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