Archaeology in the North Sea - a paleo landscape and geo archaeological approach

01 January 2014 → 31 December 2017
Regional and community funding: IWT/VLAIO
Research disciplines
  • Humanities
    • Archaeology
    • Theory and methodology of archaeology
    • Other history and archaeology
archeology Northsea marine spatial plan underwater heritage
Project description

The Belgian Continental Shelf is the smallest exclusive economic zone of the North Sea and is bounded by the French, British and Dutch Continental Shelves, however the number of economic and societal claims is very large, comprising fishing, military defence, sand extraction, maintenance dredging, shipping, wind farms, pipelines and cables. On top of that, the scarce economic resource of the Quaternary sediments of the Belgian Continental Shelf is thin and fragmented, which is the main reason why it has been so difficult up to now to produce a coherent reconstruction of the Quaternary evolution of the BCS. Moreover, the limited thickness of the Quaternary cover makes its entire section potentially vulnerable to the economic claims. Marine spatial planning hence exists to accommodate these various economic interests. It is a process to allocate the space available on sea to certain actors within a certain time frame and at the same time to ensure that all ecological, economic and social objectives are achieved. An ecosystem vision and involvement of all stakeholders (science, industry, policy) are hereby of great importance. Within the Marine Spatial Plan of 2014 it is recognised that next to shipwrecks all traces of human presence, be it cultural, historic or archaeological, belong to the submerged heritage. However, the marine spatial plan does not elucidate on how this submerged heritage is to be protected from damage or destruction that comes forth from these economic claims. Furthermore, it does not elaborate on palaeontological bone material, which is inherently connected to past human activities and use of the land and is therefore a fundamental part of this submerged heritage (from here on, submerged heritage refers to drowned palaeolandscapes, prehistoric archaeology and palaeontological bone material). An efficient policy at sea is therefore imperative. A first step to achieve a more efficient policy was developed by the SeArch project (2013–2016). The project offered solutions to improve the offshore policy by: 1) providing stakeholders with new and improved remote sensing technologies and an efficient survey methodology for the assessment of submerged heritage; 2) to provide stakeholders with a new, sustainable management framework regarding submerged heritage, and including marine spatial planning; 3) to provide practical guidance for the stakeholders on how to implement the new methodology and management approach. The one thing that remains underrepresented to provide the necessary tools for an efficient offshore policy is a thorough overview of the Quaternary stratigraphy of the BCS and what geological formation processes lie at its base. This is a pivotal step to understand why and where submerged heritage may be preserved within the Quaternary deposits, i.e. the preservation potential. The first objective of this research was to further complement and refine the growing database of seismic reflection and sediment core information regarding the geomorphology of the base of the Quaternary deposits (Chapter 4). In this perspective additional seismic surveys were performed between 2013 and 2017 to provide a denser seismic grid for the whole BCS. Complementary information from sediment cores and vibrocores resulted  in a high-resolution depth-converted structure map of the base of the Quaternary, also known as the top of the Paleogene substratum. This pre-Quaternary surface is an important polygenetic unconformity that truncates older strata of the Paleogene and to a smaller extent some of Neogene age from the overlying Quaternary deposits. The represented surface has been diachronously shaped and reworked through Middle and Late Pleistocene times by different geological processes (e.g. fluvial, marine, estuarine, periglacial). Additionally, the offshore surface has been attached to the landward pre-Quaternary surface and was transformed into a uniform three-dimensional surface allowing new and better interpretations to be used in fundamental and applied research underpinning both scientific purposes (e.g. geology, archaeology, palaeogeography), and commercial applications (e.g. wind farm construction, aggregate extraction, dredging). A geomorphological analysis of this surface revealed that its structure is highly complex and consists of two striking incised palaeochannel orientations bounded by escarpments: 1) a southeast-northwest orientation stretching from the Coastal Plain to the Inner and Middle Shelves (Chapter 5); 2) the second orientation of palaeochannels has a north to south-southwest orientation and is confined to the Outer Shelf (Chapter 6). The formation of the Middle Shelf is considered influenced by both geological processes that formed these two dominating palaeochannel incision orientations. The second objective of this research was to understand the landscape evolution and the formational processes of the different landforms and depositional environments preserved on the Belgian Continental Shelf (Chapters 5 and 6). Chapter 5 demonstrates that the BCS and its coastal plain occupy a key position between the depositional North Sea Basin and the erosional area of the Dover Strait as it is an area where erosional landforms and fragmented sedimentary sequences provide new evidence on northwest European landscape evolution. The Coastal Plain-Inner Shelf area host 20–30 m thick penultimate to last glacial sand-dominated sequence that is preserved within the buried palaeoix Scheldt Valley. Here, we build on the results of previous seismo- and lithostratigraphical studies, and present new evidence from biostratigraphical analysis, OSL dating and depthconverted structure maps, together revealing a complex history of deposition and landscape evolution controlled by climate change, sea-level fluctuations and glacio-isostasy. This study presents new supportive evidence on the development, incision and infilling of the incised palaeo-Scheldt Valley landform that became established towards the end of the penultimate glacial period (MIS 6: Saalian) as a result of glacio-isostatic forebulge updoming, proglacial lake drainage and subsequent relaxation of a forebulge between East Anglia and Belgium following ice-sheet growth, disintegration and retreat in areas to the north. The majority of the incised-valley fill is of estuarine to shallow marine nature, and its age constrains the transgression and high-stand to the last interglacial (MIS 5e: Eemian). A thin upper part of the valley fill consists of last glacial (MIS 5d-2: Weichselian) fluvial sediments that show a gradual decrease and retreat of fluvial activity to inland, upstream reaches of the valley system until finally the valley ceases to exist as the combined result of climate-driven aeolian activity and possibly also glacio-isostatic adjustment. Thus, strong contrasts exist between the palaeo- Scheldt Valley and estuarine systems of the Penultimate Glacial Maximum to Last Interglacial (Saalian to Eemian), the beginning of the Last Glacial (Weichselian Early Glacial and Early- Middle Pleniglacial), and the Last Glacial Maximum to Holocene. Chapter 6 discusses the Middle-Outer BCS in the southern North Sea. This area is characterised by a series of north to south-southwest-oriented buried, elongated and interconnected palaeodepressions, eroding last interglacial marine deposits. Despite the fact that these erosional/sedimentary features have been studied by several authors, their origin and interrelationship remained largely unknown. Here, we re-evaluate their formation and relationship by combining a large set of sediment cores with a tight high-resolution seismic grid, and by comparing their combined interpretation with recent palaeoclimatic/palaeogeographic reconstructions of northwest Europe. The sedimentary record evidences the formation of an early last interglacial shallow marine embayment that was to the south controlled by a late penultimate glacial Meuse River terrace. These sediments are truncated by the buried elongated palaeodepressions, which we interpret as erosional features carved within a floodplain of the Axial Channel trunk valley that was subjected to one or several episodes of major flooding during the Last Glacial. These episodes may have been produced by massive meltwater discharges into the North European Plain drainage system that entered the southern North Sea at the Danish–German continental shelf during time intervals when icesheets merged across the North Sea Basin. These meltwater pulses might have promoted icex sheet destabilisation, releasing icebergs into the same drainage system, which may have included a large proglacial lake located in the Dutch-Danish–German continental shelf. This lake and drainage system is interpreted as the transportation medium of erratic clasts from the Scottish Grampian Highlands and the British East Coast that are currently found scattered along the southern North Sea and the Middle-Outer BCS. Indeed, erratic clasts from these locations could have reached the southern North Sea during episodes of rapid ice melting, which may have induced GLOFs, transporting icebergs and debris in the direction of the Dover Strait. The final objective of this research is to understand and visualise the preservation potential for submerged heritage on the BCS (Chapters 7 and 8). Detailed knowledge about the distribution and formational process characteristics of the characterised depositional environments can now be used to assess, for the first time ever, the preservation potential of any form of submerged heritage (Chapter 7). The BCS shares geomorphological affinities with the northern part of Belgium (Flanders): 1) both areas have a thin and fragmented Quaternary cover thereby exposing the Paleogene substratum; 2) platforms, such as the Campine area, are comparable to the Inner, Middle and Outer BCS; and 3) the Flemish Valley system is connected to the downstream palaeo-Scheldt Valley, that extends to the Inner and Middle BCS. This geological affinity between both areas provides the unique opportunity to expand the current state-ofknowledge of onshore Flanders to the now submerged area of the shelf. The final result is two maps that visualise the preservation potential of submerged heritage, one for archaeology and one for palaeontology (Chapter 8). The archaeological potential map indicates areas from which period archaeological material can be expected, while the palaeontological potential map highlights areas where certain types of faunas can be expected. These maps are tools that can be used to develop a sustainable management policy for submerged heritage in the near future. This way both the scientific, industry and policy communities can benefit from each other.