Dunkirk transgression
In the course of the Holocene sea level rise in the North Sea region, the Dunkirk transgression is a series of several transgression pulses that occurred over a period of around 3000 years throughout the subatlantic and had a lasting impact on human settlement history.
Type locality
The Dunkirk transgression was after its type locality , of the English Channel located northern French city of Dunkirk named.
history
The term Dunkirk transgression was first introduced into the literature in 1948 by the Belgian geologist R. Tavernier. It was preceded by studies of the Belgian Quaternary coastal plain by G. Dubois in 1924, J. Cornet in 1927 and A. Briquet in 1930, these authors having eliminated the Calais transgression that preceded the Dunkirk transgression .
stratigraphy
The Dünkirchen transgression follows an extended Torfhorizont , the so-called Oberflächentorf ( engl. Surface peat ), the sandy covers deposits of Calais transgression. However, the transgression was not a one-off event, but took place in several phases. In general, the following stages, separated from regressions , can be identified (from young to old):
- Dunkirk IIIb transgression
- Dunkirk IIIa transgression
- Dunkirk II transgression
- Dunkirk Ib Transgression
- Dunkirk Ia transgression
Below the Dunkirk Ia transgression, FR Moormann had also introduced a Dunkirk 0 transgression. Karl-Ernst Behre described the rise in sea level from 1700 as the Dunkirk IV transgression .
Temporal course
The time division of the Dunkirk transgression into its individual stages essentially follows Behre (2007):
Dunkirk Ia transgression
The Dünkirchen Ia transgression follows the beginning of the Subatlantikums / end of Subboreal (period 1000-800 v. Chr.) To the foregoing, very clearly marked regression 2 , which in the Netherlands and in Northern Germany left Torfhorizont a widely used and powerful ( possibly correlatable with the surface peat of the Belgian coast mentioned above ). The so far oldest German marching settlement from the late Bronze Age , which was excavated in recent years near Rodenkirchen on the Lower Weser , comes from this stage; it indicates a mean tidal high water (MThw) of 1.40 meters below today's NN . A little later in the period from 650 to 550 BC. Settlements laid out on the left bank of the Ems . They make clear that up to 400 BC Chr. Continuous regression 3 with a slight drop in sea level to - 1.60 meters below sea level.
Dunkirk Ib Transgression
The Dunkirk Ib transgression follows in the period 400 to 150 BC. On the regression 3. This transgression pulse was very strong (with a sea level rise from 2.20 meters to +0.60 meters) and so all settlements existing at that time were destroyed. New bays tore down. From the 1st century BC onwards, the embankments surrounding them, piled up by the storm surge sediments. Next phase settlements built. This first large-scale marsh colonization had benefited from the sea retreat during regression 4 . The archaeological state surveys for Lower Saxony record numerous flat settlements that were created during this time. They point to an MThw of −0.65 m above sea level, which was 1.25 m lower than during the peak of the previous transgression.
Dunkirk II transgression
The also quite strong Dunkirk II transgression began in the 1st century AD (and extended over the period 50 to 350 AD). The sea level had risen by 1.50 meters to + 0.85 meters above sea level. As a consequence, some of the newly created flat settlements were abandoned, but most remained occupied and were raised to sausages to withstand the storm surges. In the period that followed, however, these sausages had to be continuously increased. In some residential mounds there were therefore up to seven layers of settlement on top of each other. This is the first major Wurten period in the German March.
Around 350 AD, houses on the flanks of the Wurten were moved lower down again, as studies by the Feddersen Wierde have shown. At this time regression 5 had occurred, the storm surge level had sunk and the MThw had fallen to +0.50 m above sea level. The Wurten was abandoned during the Migration Period , and a general gap in the settlement followed.
After the turmoil of the Great Migration, the repopulation of the marshland in the early Middle Ages was able to take advantage of the favorable conditions of regression 5 (period 350 to 700 AD) in the form of flat settlements. An example of this is Oldorf im Wangerland , which was founded in 630 AD.
Dunkirk IIIa transgression
As early as 700 AD, the Dunkirk IIIa transgression led to a renewed rise in sea levels. This transgression pulse, which was very weak at 30 centimeters, was only of relatively short duration (up to 850 AD). Nevertheless, he induced the settlers to transform their former flat settlements into Wurten. This is the second German Wurten phase, in the course of which numerous large village Wurten emerged, especially in Lower Saxony, which often form the core of today's places. Around 850 AD, regression 6 began, which lasted until 1100 AD and equalized the current level with a drop of 80 centimeters.
Dunkirk IIIb transgression
The again quite strong Dunkirk IIIb transgression (1.40 meters sea level rise) extended over the period AD 1100 to 1450. Its beginning is marked by the construction of dykes , which had already started in the late 11th century and then in the 13th century . Century represented a closed winter dike line. With the time approximately equal to the LIA extending regression 7 (from 1450 to 1700 n. Chr.), The level fell again by a meter to + 0.40 above sea level. In parallel to the general increase in temperature, the sea level has risen by a further 1.30 meters in the last 300 years and is currently 1.70 above sea level.
The Dunkirk transgression achieved a total sea level rise of 3.30 meters since the beginning of the subatlantic. This corresponds to a rate of 1.1 millimeters / year.
Individual evidence
- ↑ Tavernier, R .: De jongste geologische geschiedenis de Vlaamse kustvlakte . In: Handelingen der Maatschappij voor Geschiedenis en Oudheidkunde te Gent . tape 3: 2 , 1948, pp. 107-115 .
- ^ Dubois, G .: Recherches sur les terrains quaternaires du nord de la France . In: Mémoires de la Société Géologique du Nord . tape 8 . Lille 1924.
- ^ Cornet, J .: Leçons de géologie . Maurice Lamertin, Brussels 1927.
- ^ Briquet, A .: Le littoral du nord de la France et son évolution morphologique . Paris 1930.
- ^ Moormann, FR: De bodemgesteldheid van het oudland van Veurne-Ambacht . In: Natuurwetenschaapelijk tijdschrift . tape 33 , 1951, pp. 3-124 .
- ^ Behre, K.-E .: A new Holocene sea-level curve for the southern North Sea . In: Boreas . tape 36 , 2007, p. 82-102 .
- ↑ Strahl, E .: Rodenkirchen . In: Reallexikon der German. Antiquity, 2nd edition, volume 25 , 2003, p. 55-58 .
- ^ Schmid, P .: The medieval resettlement of the Lower Saxon marches . In: M. Bierma, OH Harsema & W. van Zeist (eds.): Archeologie en Landschap. Festschrift HT Waterbolk . Groningen 1988, p. 133-164 .