Stratigraphic and geotechnical characterization of regionally extensive and highly competent shallow sand units in the southern North Sea

Abstract

A detailed stratigraphic and geotechnical investigation of the uppermost 50 m below the sea floor was carried out for parts of the German North Sea sector using combined information from shallow seismic reflection surveys, 50‐m‐long sediment cores and cone penetration tests covering an area of ~150 km2. While most recent studies concentrate on unusual features such as buried tunnel‐ or river‐valleys, this study focused on the less well understood, regionally dominant sand units deposited after the retreat of the last glaciers in this region. We identified two sandy units which dominate the late‐ to post‐Saalian geology: (i) the Upper Fluvial Member, believed to be derived from deposition of the Weser, Ems and Elbe palaeorivers as well as other tributaries of the Elbe Palaeovalley in the NE during the Saalian; and (ii) the Aeolian Member, which correlates with periglacial deposits of Weichselian age. Additionally, a Saalian Buried Valley Member believed to comprise fluvial deposit was also identified. Key stratigraphic units within the uppermost 50 m below the sea floor were also identified and mapped. Detailed geotechnical properties were obtained for each of the individual stratigraphic units. The regional extent of the Aeolian and Upper Fluvial Members was documented in the region west of the Elbe Palaeovalley and south of the Dogger Bank, where their geotechnical properties are important for foundation design. In conclusion, the study complements the established regional geotechno‐stratigraphy and offers new and detailed publically accessible information beneficial for offshore wind farm development within the region.

An integrated geological characterization of the Mid‐Pleistocene to Holocene geology of the Sørlige Nordsjø II offshore wind site, southern North Sea

“…2018; Fleischer et al . 2023). *Age correlations between geological era and Marine Isotope Stages from Shackleton (1969).…”

“…2019a, b; Prins & Andresen 2019; Fleischer et al . 2023). Ice sheets repeatedly advanced onto the continental shelf from the highlands of the UK and Scandinavia, compressing and deforming the underlying sediments, changing the pore pressure conditions within them (Piotrowski et al .…”

The submerged Palaeo-Ems River in the Quaternary stratigraphic context of the German North Sea

“…In the last couple of decades, many studies have aimed to reconstruct the Quaternary paleo-landscape architecture and stratigraphy of the North Sea Basin (Andresen et al, 2022;Bailey et al, 2020;Cohen et al, 2014;Cotterill et al, 2017aCotterill et al, , 2017bCoughlan et al, 2018;Fitch et al, 2005;Fleischer et al, 2022;Gaffney and Fitch, 2022;Gaffney et al, 2020;Hepp et al, 2012Hepp et al, , 2017Hepp et al, , 2019Huuse and Lykke-Andersen, 2000;Lohrberg et al, 2020;Phillips et al, 2017;Prins and Andresen, 2021;Spinney, 2008;van Heteren et al, 2014;Winsemann et al, 2020). The repeated glacialinterglacial and post-glacial reshaping of the Quaternary landscape of the North Sea resulted in complex and heterogenous morphological structures.…”

“…These structures which are now paleo-archives of past environmental changes can be related to various geological processes combined with major climatically-driven relative sea-level changes. In general, the Quaternary North Sea sub-surface is dominated by glacio-fluvial sands which are difficult to date and distinguish from each other due to strong similarities in material and grain characteristics (Fleischer et al, 2022). Thus, the identification of stratigraphic elements such as buried tunnel valleys, river channels, moraines, dunes, peats, and paleosols are important to unravel the Quaternary stratigraphic frameworks of the North Sea (Coughlan et al, 2018; Emery et al, 2020; Fleischer et al, 2022).…”

“…The abundance, distribution, orientation, size, morphology, and inferred age of buried tunnel valleys across the North Sea are well documented in literature (Coughlan et al, 2018; Hepp et al, 2012; Huuse and Kristensen, 2016; Kristensen et al, 2007; Lohrberg et al, 2020; Lutz et al, 2009; Ottesen et al, 2020; Prins and Andresen, 2019; Prins et al, 2020; Stewart et al, 2013; van der Vegt et al, 2012). These buried tunnel valleys, formed at ice sheet margins, were active under direct glacial conditions and their infills played a key role in reconstructing the offshore Quaternary stratigraphy of the North Sea (Coughlan et al, 2018; Fleischer et al, 2022).…”