Upper Cenozoic sequences in the southeastern North Sea Basin

Abstract

The Upper Cenozoic deposits, which cover the "mid-Miocene unconformity" in the southeastern North Sea Basin are subdivided into thirty-one sequences. Progradation from the east to the west is observed. The lowstand systems tracts appear seismically as prograding wedges. The top lowstand surface is recognized as a toplap surface in areas where high-angle progradation dominates the stratal pattern, indicating the presence of a bypass zone formed during lowstand progradation. The maximum flooding surface is identified on logs as a maximum gamma ray peak, which separates an upward fining from an upward coarsening trend. The two trends represent the transgressive and the highstand systems tracts, respectively. Sequence boundaries are commonly associated with widespread erosion. The presence of both fluvial and submarine erosion is interpreted on the basis of the orientation of incision and the position of erosion relative to the depositional shoreline break of the preceding sequence. In Late Miocene times the Ringkøbing-Fyn High partly separated the southeastern North Sea into two embayments, which were connected by a deep seaway towards the west. Sediment accumulation rates seem to have culminated during periods with decreasing palaeo-temperatures. During relatively cold periods, the sequences were deposited as prograding wedges with a limited lateral extent. Two periods with maximum palaeotemperatures are time-equivalent with the two most distinct maximum flooding surfaces and intervals characterized by low sediment accumulation rates.

Tunnel valleys in the southeastern North Sea: more data, more complexity

“…Different incision mechanisms have been described for TVs, and there has long been a debate about whether the incision could be explained with fluvial erosion (Donovan, 1972;Salomonsen, 1995;Sørensen and Michelsen, 1995) or whether pressurized subglacial erosion is the more likely mechanism (Jentzsch, 1884;Kuster and Meyer, 1979;Piotrowski, 1994). Our high-resolution longitudinal profiles along a single-incision TV show that the incision has overcome significant morphological highs of over 75 m over a 500 m distance, which is a significant gradient when compared to earlier studies by Stewart et al (2013), who showed a maximum gradient of approx.…”