Channel structures formed by contour currents and fluid expulsion: Significance for Late Neogene development of the central North Sea basin

Channel horizons delimiting a major Pliocene sedimentary prism in the central North Sea basin have been investigated in the context of oceanographic climatic and tectonic controls using 3D seismic and well data from the UK and Norwegian sector. Aggrading channel structures forming 700-2500 m wide and 75-150 m deep linear to arcuate troughs superimpose the truncated distal part of the prism in the northern Central Graben. The origin of the aggradational channel and prism complex is related to differential deposition and erosion by contour currents that intensified as tectonic subsidence formed a deep marine basin (>600 m) with open connections to the Atlantic and Norwegian Sea. The largest channel troughs appear to be filled with consolidated sediments and emerge from areas where the Neogene strata is pierced by salt diapir chimneys. From Early Pleistocene (c. 2.5 Ma) the channels were subject to progressive burial by rapid clinoform progradation. Based on the seismic observations a depositional model is proposed that relates contourite channel dev elopment to fluid expulsion from salt diapir structures and fracture zones extending from lower Miocene strata. The sedimentary prism accumulated over a Late Miocene/Early Pliocene Unconformity marked by incised channels that are reminiscent of a northward diverging drainage system. This erosive low-stand development is probably related to late Alpine compression which promoted uplift in the British Isles and the Channel region. The ensuing subsidence of the central North Sea associated with concomitant uplift of the Norwegian-Danish Basin generated the present vsouthwestward dip of 0.5-0.8° of the basal unconformity. The Late Miocene compressional phase followed by rapid basin depending during Pliocene to early Pleistocene suggests that present concepts of North Sea basin development have to be re-evaluated.