Chapter 5. Sequence stratigraphy scheme for the uppermost Middle Jurassic – lowermost Cretaceous of the North Sea area

Abstract This chapter describes uppermost Middle Jurassic to lowermost Cretaceous second order stratigraphic sequences J40, J50, J60 and J70, and their component third order sequences, J42–J46, J52–J56, J62–J66 and J71–J76. The latest Callovian to Berriasian was an interval of significant tectonism, which led to the development of complex stratigraphy and highly variable successions, the elucidation of which is aided by the recognition of correlation of the J sequences. Marine sedimentation dominated the Callovian to Berriasian interval, with the development of multiple sandstone units, comprising reservoir units in many hydrocarbon fields, charged by marine source rocks (e.g., the Kimmeridge Clay Formation). Each of these units is subdivided and correlated by a succession of J sequences. Several sequences are renumbered (e.g., J54, J55, J65, J66), some sequence definitions are amended or their basal boundaries recalibrated chronostratigraphically (J52, J54, J72, J73, J74, J76) and new sequence subdivisions are recognised (J64a, J64b, J72a–J72c, J73a, J73b). Significant unconformities are recognised at the bases of the J54, J55, J62, J63, J64, J71 and J73 sequences. The top of J70 (J76) equates to the major “Base Cretaceous Unconformity” seismic sequence boundary.