The late Holocene coastal dunefield at Vejers, Denmark: characteristics, sand budget and depositional dynamics

Abstract

The coastal dunefield at Vejers (west coast of Jutland), which is now stabilized by vegetation, covers an area of approximately 120 km 2 and occurs in a very high-energy wind regime. Along the coastline a narrow belt of 5–15 m high dune ridges occur. The dune ridges are gradually replaced inland by 10–20 m high parabolic or irregular dune forms. In the central part of the dunefield a large aeolian sand plain (ca. 50 km 2) occurs at the windward side of a large and up to 20 m high parabolic dune. The 3D structure of the dunefield deposits have been studied by geomorphological analysis, sedimentological facies analysis of borings, trenches and natural exposures, and most importantly by georadar mapping. The aeolian deposits which overlie a middle to late Holocene barrier spit depositional system can be divided into a Lower unit that drapes the underlying barrier system topography, and an Upper unit that includes the present dunes. The boundary between the two aeolian units is a well-developed Phragmites peat. The Lower aeolian unit is composed of two aeolian subunits separated by an organic-rich horizon. Also the Upper unit is composite and composed of a basal aeolian sand cover and overlying dune or sand plain deposits. The dune deposits locally are composed of up to four depositional subunits separated by immature soils. The base of the Lower aeolian unit formed around 300 A.D., whereas the Phragmites peat at the base of the Upper aeolian unit has been dated to ca. 1000 A.D. From historical sources we know that the present dunefield primarily formed between 1550 and 1850 A.D. The sand content in the Upper unit is estimated to 550 × 10 6 m 3, which yields sand transport rates between 25 m 3 (m width) −1 yr −1 (accumulation in 1000 years), and 83 m 3 (m width) −1 yr −1 (accumulation in 300 years). The sand in the dunefield originated from beach deposits. A large but pulsating supply of sand was supplied to the beaches by southwards running coastal currents. The composition of the Vejers dunefield deposits indicate that periods of dunefield growth alternated with periods of dunefield stabilization during the last ca. 1700 years. The final and most important phase of dunefield growth took place during ‘the Little Ice Age’. This period was characterized by an overall cold and stormy climate and a relative low sea level, and resulted in an increased availability of sand in the shorezone and a high influx of sand into the dunefield. Short periods of decreased storminess are recorded by the immature soils. Dunefield growth prior to 1000 A.D. was also linked to cold and stormy climatic intervals.