The micropalaeontological biostratigraphy of the Magnus Sandstone Member of Kimmeridgian-Early Volgian age is described for the first time using data from 27 Magnus Field wells (blocks 211/12a and 211/7a). Despite extensive re-sedimentation within the Magnus Sandstone Member turbidite reservoir, a consistent sequence of nine bioevents is recognized field-wide. These include both regionally extensive bioevents and localized extinction and acme bioevents. The microfaunas are documented and key taxa, which include numerous radiolarian species, are described and figured.The bioevent scheme provides the basis for the chronostratigraphic and genetic sequence stratigraphic subdivision (sensu Galloway) of the Magnus Sandstone Member. It allows the recognition and biostratigraphic calibration of three maximum flooding surfaces (MFS) which in ascending stratigraphic order comprise: the pre-Magnus Sandstone Member top J62-basal J63 'Eudoxus' of Partington et al.

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Abstract:Over recent years changes in the application of biostratigraphy in the reservoir appraisal and development arena have greatly increased the impact and value of the discipline, giving it a central role in integrated reservoir description. These changes include placing emphasis on local field-scale bioevents to erect a reservoir framework of time slices through which reservoir heterogeneity can be modelled and the application of biosteering to maximize reservoir penetration. In addition, palaeoenvironmentally diagnostic benthonic microfacies are used to model the lateral continuity of intra-reservoir mudstones in an attempt to understand their potential as baffles/barriers to fluid flow. The evolution of this cost-effective methodology is discussed by reference to three Palaeocene turbidite reservoirs from the North Sea UK continental shelf (UKCS); the Donan, Forties and Andrew fields.

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