The Upper NorthSea Group (NU) unconformably overlies the Middle North Sea Group (NM) andrecords deposition from Neogene to Present. The NU consists of post-Oligoceneshallow-marine sediments including clay, fine-to-coarsegrained sand, local gravel, peat, and brown coal seams (VanAdrichem Boogaert, and Kouwe, 1993).
The NU includes coarser sediments with more complexgeometries compared to the underlying NM (Tetyukhina et al., 2010). The targetinterval of this study comprises three formations: (1) Breda Formation, (2)Kieseloolite Formation, and (3) Oosterhout Formation. The Breda Formation consists ofMiocene to earliest Pliocene age sediments deposited in a marginal marine environment.The formation comprises foreset andbottom-set beds deposited in delta-front setting (Doppert et al., 1975). Lithologiesinclude glauconitic sand, sandy clay, andclay.
A glauconite-rich layer occurs commonly at the base, which is interpreted as aregional unconformity (Doppert et al., 1975). The KieselooliteFormation comprises Late Miocene, early Pliocene, and late Pliocene agesediments deposited in a river floodplain and coastal lowland (Van Adrichem Boogaert, and Kouwe, 1993). The formationconsists of a wide variety of fluvial and lacustrine origin lithologies. Thelower half of the formation is composed of coarse-grained clastics (sand and gravel), while the upperpart consists of clay and sand (Van AdrichemBoogaert, and Kouwe, 1993).
The lower portion of the Kieseloolite Formation merges into marinebeds of the Breda Formation, and the upper portion merges into the Oosterhout Formation.The OosterhoutFormation contains Pliocene to earliest Pleistocene sediments deposited in ashallow marine environment and in adelta-front setting. Lithologies include sand, sandy clay, and greenish clay.
The Oosterhout Formation overlies the Breda Formation and intertongues with and is overlain by thedeposits of Kieseloolite Formation, recordingprogradation (Doppert et al., 1975).