|Premise||The formation is included in the Schieland Group. It was defined by NAM and RGD in 1980 and amended by Herngreen & Wong (1989) and by Van Adrichem Boogaert & Kouwe (1993). NAM & RGD (1980) considered their Puzzle Hole Formation to be a silty- sandy tongue within the Kimmeridge Clay Formation, and part of the Scruff Group. Because of its predominantly terrestrial- paralic character, Herngreen & Wong (1989) attributed the Puzzle Hole Formation to the Central Graben Group. In Van Adrichem Boogaert & Kouwe (1993) it is transferred in the new Schieland Group, into which the Central Graben Group has been amended as a subgroup. The top of the type section has been shifted in order to transfer the atypical, marine interval 2175- 2149 m to the Kimmeridge Clay Formation. This is supported by log patterns and palynology. The Puzzle Hole Formation can be differentiated from other formations in the Central Graben Subgroup by its large number of intercalated coal seams. The other formations contain at most only a few coal seams.|
|Derivatio nominis||Named after the Puzzle Hole Bank in the Dutch northern offshore region.|
|Type section||Location map||See figure (pdf)|
|Depth||2175 to 2397 m|
|Length||222 m along hole|
|Definition||The formation consists of light brownish-grey carbonaceous claystones with intercalations of siltstones and thin sandstones. Coal seams are frequent (10 to 20 seams per 100 m interval) and give the formation the typical seismic response. The sandstones, in particular to the south, show a fining-upward character. The Puzzle Hole Formation displays a typical serrate pattern on both gamma-ray and sonic logs as a result of the rapid alternation of thin sandstones, siltstones, clay- stones and coal seams.|
|Upper Boundary||In most wells the Puzzle Hole Formation is overlain uncon- formably by sediments of the Rijnland Group or younger groups as a result of Sub-Hercynian/Laramide inversion erosion. In the type section (Van Adrichem Boogaert & Kouwe, 1993, Annex G-4), however, the marine claystones of the Kimmeridge Clay Formation conformably overlie the Puzzle Hole Formation. The Puzzle Hole Formation occupies an intermediate position between the Friese Front Formation to the south and the Upper Graben Formation and Kimmeridge Clay Formation to the north. The transition to the Friese Front Formation is a fault-associated boundary through the F15-F17 blocks.|
|Lower Boundary||The formation conformably overlies the Middle Graben Formation. This boundary gradually becomes younger from south to north, so the uppermost parts of the Middle Graben Formation in F08/F11, and the upper Friese Front Member in the southern Dutch Rifgronden, are time equivalent to the lower beds of the Puzzle Hole Formation in F14. The upper Middle Graben Formation is characterised by a very low sand/clay-stone ratio and an absence of coal beds.|
|Distribution||The Puzzle Hole is deposited in the central part of the Dutch Central Graben, the southern parts of blocks F05 and F06 and blocks F08, F09, F11, F12 and F14 (see pdf).|
|Age||Sequence 1 sensu Abbink et al. (2006): Middle Oxfordian to Early Kimmeridgian. In occasional marine incursions characteristic dinoflagellate associations comprise Dichadogonyaulax chondrum (LOD: E. Kimmeridgian, cymodoce Ammonite Zone), Gonyaulacysta jurassica (abundant; LCOD: E. Kimmeridgian, cymodoce Ammonite Zone), Hystrichosphaerina orbifera, Occisucysta monoheuriska and Systematophora. Among the sporomorphs Trilites minutus, Precicatricosisporites complex (LOD: early Late Kimmeridgian, mutabilis Ammonite Zone), Retitriletes undulates (LOD: early Late Kimmeridgian, mutabilis Ammonite Zone) and Striatella reticulata occur. Eripleura eleanorae and Galliaecytheridea punctata are important ostracods.Galliaecytheridea punctata are important ostracods.|
|Depositional Setting||Lower delta plain; lagoonal tidal flats, estuary and tidal channels, bay head deltas and mouthbars.|
|References||See References Upper Jurassic/ Lower Cretaceous|
D.K. Munsterman, R.M.C.H. Verreussel, H.F. Mijnlieff, N. Witmans, S. Kerstholt-Boegehold & O.A, Abbink (2012), Revision and update of the Callovian-Ryazanian Stratigraphic Nomenclature in the northern Dutch Offshore, i.e. Central Graben Subgroup and Scruff Group. Netherlands Journal of Geosciences-Geologie en Mijnbouw, 91 (4):555-590.
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