Detailed morphology of the Top Chalk surface in the eastern Danish North Sea

A detailed time-structure map of Top Chalk in the eastern Danish North Sea is presented, based on conventional seismic and well data, and 5800 km of n ew multi-channel, high resolution seismic data. Several factors influenced the present-day topography of Top Chalk at various scales: Cenozoic regiona l differential subsidence/uplift, reactivation of late Palaeozoic-Mesozoic structures, salt structures in the Norwegian-Danish Basin, collapse structu res along the Ringkobing-Fyn High, mounds on the Ringkobing-Fyn High, erosi onal valleys, and possible karstification in parts of the Norwegian-Danish Basin. Erosional valleys and karst topography suggest that the Top Chalk was subae rially exposed in the eastern North Sea in mid-Paleocene times. The valleys probably acted as conduits for deposition of potential reservoir sands in the middle to late Paleocene. The interpretation of karst topography indica tes that carbonate dissolution may have affected the reservoir properties o f the uppermost part of the Chalk Group in the eastern North Sea.