Genesis of honeycomb buildups in the Permian Zechstein Group, Southern North Sea

Abstract

Seismic interpretation has revealed a hitherto unreported honeycomb pattern of carbonate buildups within the Orchard Platform (Southern North Sea). The Z2 Stassfurt Halite Fm. onlaps the southern margin of the Orchard Platform and is also found infilling Z2 intra-platform lagoons to form salt lakes. Post Z2 evaporation, the deeper Z3 water column drowned the Orchard Platform inhibiting the platform recovery attempted by the Z3 Plattendolomit Fm. The palaeobathymetric variability of the drowned Orchard Platform was sufficient to bring parts of the seafloor into the photic zone allowing for the sporadic growth of the Z3 Plattendolomit Fm. However, the palaeobathymetric lows remained beneath the photic zone ensuring an incomplete regeneration of the Orchard Platform with the creation of a high-frequency network of intra-platform lagoons which mimic the polygonal texture of a honeycomb. Whilst previously accepted as collapse structures or karst systems, this study correlates the development of the honeycomb buildups to variations in seafloor palaeobathymetry which in turn mimic the structural lineaments of the Zechstein subcrop. Syn-depositional instability in the Zechstein subcrop caused the topsets of the Z2 salt lakes to become warped. The warped halite provided seed points for Z3 Plattendolomit Fm. growth which allowed for linear ridges of carbonate to traverse the Z2 salt lakes and eventually connect with the honeycomb buildups. Deposition in the Mesozoic lead to loading of the Zechstein. Halite-filled Z3 lagoons accommodated this loading, which caused a pinching effect on the Z3 honeycomb buildups. The sedimentological understanding provided by this study not only de-risks frontier exploration but also provides insight into carbonate growth in restricted platform recovery scenarios.