Geological Survey of Denmark and Greenland Bulletin 25 - 2011

Upper Cretaceous chalk facies and depositional history recorded in the Mona-1 core, Mona Ridge, Danish North Sea

​Kresten Anderskouv and Finn Surlyk

Upper Cretaceous – Danian chalks form important hydrocarbon reservoirs in the North Sea, contributing significantly to the national economies of Denmark, Norway and the United Kingdom. Understanding the process of chalk sedimentation thus has implications not only for charting the evolution of the Cretaceous chalk sea, but also for predicting the distribution and nature of potential reservoir chalks in the subsurface. In particular, North Sea chalk reservoirs commonly include a range of redeposited chalk facies types, yet rigorous documentation of such facies is scarce in the published literature.

This bulletin presents a detailed analysis of chalk deposits from an exceptionally well-cored borehole (Mona-1) in the northern Danish Central Graben. Chalk sedimentation in this area in the Late Cretaceous was strongly influenced by active intrabasinal tectonics, controlling sea-floor morphology and the location of depocentres. Chalk ooze was commonly remobilised, creating a wide spectrum of chalk facies types that record processes ranging from suspension settling to slumping and debris flow.