Deposition or remobilization of the enigmatic Hefring Member sand, eastern North Sea – A multidisciplinary approach

Abstract

Abstract Sand remobilization is a well-known and well-studied phenomenon and seismic observations particularly from the North Sea Giant Sand Injectite Province (NSGSIP) combined with outcrop investigations have permitted a good understanding of the physical processes of sand remobilization, trigger mechanisms and resulting seismic geometries. The degree of remobilization and the distinction between depositional and remobilized/injected sand from seismic data alone are however still relatively unconstrained. In this study, we use a multidisciplinary approach based on seismic stratigraphy, petrography and biostratigraphy, to investigate an enigmatic and apparently isolated Eocene sandstone body, the Hefring Member, which in the seismic data shows characteristics of both depositional and remobilized origin. We use the available well logs, cutting samples and side-wall cores to investigate whether we can address the degree of remobilization from seismic data alone, by linking the mapped seismic facies with ‘remobilization degree’ as observed from the well data. In addition to addressing the degree of remobilization, we propose a model for the formation of the Hefring Member which includes laterally restricted submarine channel sand deposition and secondary remobilization with mainly upward and lateral injection. We infer, that the remobilization of the Hefring Member was controlled by local and rapid differential loading, potentially emphasized by activity in the nearby D-1 fault system and triggered by a significant drop in sea level. Understanding the origin and evolution of the Hefring Member is important for unravelling the geological development of the area and because the sand member represents a new reservoir unit comparable to the nearby prolific Siri Canyon sandstone.