Structural, Sedimentologic, and Sea-Level Controls on Sand Distribution in a Steep-Clinoform Asymmetric Wave-Influenced Delta: Miocene Billund Sand, Eastern Danish North Sea and Jylland

Abstract

Abstract The lower Miocene Billund sand of Jylland, Denmark, provides an excellent opportunity to study the distribution of sands and the types of clinoform generated by a wave-dominated delta prograding into a deep shelf environment. In particular seismic sections, the sand-rich parts correlate with parallel clinoformal seismic facies, in which the clinoforms dip 7° to 10°. The stacking pattern of this seismic facies also indicates whether the progradation occurred during rising or falling sea level by displaying an ascending or descending shoreline trajectory, respectively. The Billund delta was deposited in the eastern North Sea Basin during the early Miocene and is on the available data recognized as a NW to SE trending feature. It forms a wave-dominated delta with thick sand bodies deposited in relatively deep waters (> 100 m) at the river mouth and in the up-drift area of newly formed delta lobes. Sands and muds associated with a spit complex or a lagoonal complex dominated the down-drift area. In the distal delta-front area, alternating sands and muds were laid down, the sands associated mainly with storm events. Progradation of the studied part of the delta occurred during high sea level and a subsequent fall in sea level that was caused by a eustatic fall during the mid Aquitanian (early Miocene). Although sand intervals 10 to 20 m thick are common throughout the delta complex, the thickest (up to 100 m) and cleanest sand is found in units deposited in narrow bands within structural lows and during periods of forced regression. The Billund delta may be an excellent analogue for hydrocarbon-bearing, wave-dominated deltas, and seems to exhibit similarities to Jurassic deposits in the North Sea area.