General Geology of Southern Kattegat, the Hesselø Wind Farm Area Desk Study Jørn Bo Jensen and Ole Bennike
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DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE General geology of southern Kattegat, the Hesselø wind farm area Desk Study Jørn Bo Jensen and Ole Bennike GEOLOGICAL SURVEY OF DENMARK AND GREENLAND DANISH MINISTRY OF CLIMATE, ENERGY AND UTILITIES DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE General geology of southern Kattegat, the Hesselø wind farm area Desk Study Report for Energinet Eltransmission A/S Jørn Bo Jensen and Ole Bennike GEOLOGICAL SURVEY OF DENMARK AND GREENLAND DANISH MINISTRY OF CLIMATE, ENERGY AND UTILITIES 1 Table of contents 1. Summary 3 2. Introduction 4 3. Data background 5 3.1 GEUS archive shallow seismic data and sediment cores ...................................... 5 3.2 IODP Site M0060 data types .................................................................................. 6 4. Existing knowledge of the region’s geology 7 4.1 General pre-Quaternary framework ....................................................................... 7 4.2 Pre-Quaternary surface ....................................................................................... 12 4.3 Glacial deposits and deglaciation ......................................................................... 14 4.4 Late glacial and Holocene .................................................................................... 19 5. Sequence stratigraphical model for southern Kattegat 21 5.1 Methods ............................................................................................................... 21 5.2 Seismic facies units ............................................................................................. 22 5.2.1 BR – Bedrock ................................................................................................... 22 5.2.2 GL – Glacial deposits ....................................................................................... 23 5.2.3 LG I – Older late glacial deposits ..................................................................... 24 5.2.4 LG II – Younger late glacial deposits ................................................................ 24 5.2.5 Distribution of late glacial deposits ................................................................... 26 5.2.6 H – Holocene deposits ..................................................................................... 27 5.2.7 Stratigraphy of southern Kattegat depositional sequences .............................. 28 6. IODP M0060 contribution to geological model 31 6.1 Unit I 0–6.00 m b.s.f. ............................................................................................ 31 6.2 Unit II 6.10–24.70 m b.s.f. .................................................................................... 31 6.3 Unit III 24.70-81.60 m b.s.f. .................................................................................. 32 6.4 Unit IV 81.60–85.70 m b.s.f.................................................................................. 32 6.5 Unit V 95.04–116.7 m b.s.f................................................................................... 32 6.6 Unit VI 116.70–146.10 m b.s.f. ............................................................................. 32 6.7 Unit VII 146.10–229.60 m b.s.f. ............................................................................ 33 6.8 Age–depth model ................................................................................................. 34 7. Seismic correlation to IODP site M0060 36 7.1 Stratigraphic correlation of 2002 seismic data and site M0060 ............................ 36 7.2 The DAN-IODP-SEIS survey ............................................................................... 36 7.2.1 DAN-IODP-SEIS line 8008 ............................................................................... 37 7.2.2 DAN-IODP-SEIS line 8002 ............................................................................... 38 7.2.3 DAN-IODP-SEIS line 8006 ............................................................................... 39 7.2.4 Acoustic indications of gas in sediments .......................................................... 40 G E U S 2 8. Geological model Hesselø OWF South and cable corridor 42 8.1 Late glacial marine sediments Hesselø OWF South and cable corridor .............. 42 8.2 Holocene transgression sediments Hesselø OWF South west and cable corridor 44 8.2.1 Hesselø OWF South west spit barrier and estuary .......................................... 44 8.2.2 Cable corridor, tidally dominated estuary ......................................................... 45 8.2.3 Palaeogeographical development of Hesselø OWF South west and cable corridor 47 9. Archaeological interests 48 10. Conclusions 50 11. References 51 12. Appendix A Site M0060 13. Appendix B Cruise report DAN-IODP-SEIS KAT2013 High Resolution 2D seismic survey i G E U S 3 1. Summary Energinet A/S has requested that GEUS undertakes a geological desk study of the Hesselø Offshore Wind Farm (OWF) region. The study has resulted in a general geological descrip- tion and establishment of a geological model. The study is based on existing data and is to be used as a background for future interpretations of new seismic data, geotechnical inves- tigations and an archaeological screening. In this study we have used a combination of published work, archive seismic data and sedi- ment core data to assess the general geological development of the southern Kattegat area, including the planned Hesselø OWF and the cable corridor. A geological description is provided, and a geological model has been developed. As a result of the geological desk study it has been possible to establish a relative late glacial and Holocene sea-level curve for the area and to describe the palaeo development relevant for an archaeological screening. The general geological description includes the complete geological succession from the general pre-Quaternary framework, the pre-Quaternary surface, glacial deposits, the degla- ciation and late glacial and Holocene deposits. The geological model of the southern Kattegat is based on sequence stratigraphical studies by Jensen et al. (2002) customized to the Hesselø OWF and cable corridor case. On the basis of the presented geological model the Integrated Ocean Drilling Program (IODP) Expedition 347 in September 2013 carried out a more than 200 m deep drilling at site M0060. The obtained sediment succession was divided into seven different lithostratigraph- ical units and description of lithology and downhole core logging were performed including physical parameters. A parallel scientific multichannel survey was carried out the same year and a detailed cor- relation has been carried out between the seismic data and core M0060. In the southernmost part of the Hesselø OWF area and the cable corridor, detailed studies of late glacial and early Holocene sea-level changes as well as the development of a Holo- cene barrier spit/estuary complex formed the basis for the evaluation of the geological model as well as input for construction of palaeo stratigraphical maps. The maps reveal late glacial and early Holocene archaeological interesting coastal com- plexes in the time period for the Ahrensburg and Maglemose cultures. while the area was transgressed by the sea during younger cultures. In relation to geotechnical challenges a number of focal points has been raised such as ne- otectonics, recent earthquakes, gas in sediments, glaciotectonic deformations, great thick- ness of weakly consolidated glaciomarine clay, Holocene sand and clay with high organic contents. G E U S 4 2. Introduction GEUS has been asked by Energinet to provide an assessment of the Hesselø Offshore Wind Farm (OWF) and the proposed cable transects, consisting of establishment of a geological model on basis of existing data as background for future interpretation of seismic data and a marine archaeological screening. (Figure 2.1). Figure 2.1. The location of the proposed Hesselø Offshore Wind Farm (polygon) and cable transects in the southern part of the Kattegat region. Bathymetry from Emodnet. G E U S 5 3. Data background As a background for the desk study, deep seismic information has been compiled from sci- entific papers, but the seismic data are available from the GEUS Oil and Gas database (http://data.geus.dk/geusmap/?mapname=oil_and_gas&lang=en#baslay=baseMapDa&opt- lay=&extent=-741060,5683270,1783060,6766730), while the GEUS Marta database (https://www.geus.dk/produkter-ydelser-og-faciliteter/data-og-kort/marin-raastofdatabase- marta/) is the main supply of shallow seismic data and vibro-core data (Figure 3.1). In addi- tion, scientific multichannel data not included in Marta have been used as well as data from IOPD core M0060. 3.1 GEUS archive shallow seismic data and sediment cores The Marta database includes available offshore shallow seismic data and core data in digi- tal and analog format. An increasing part of the seismic lines can be downloaded as SGY files from the web portal. Figure 3.1. Distribution of Marta database seismic grid and core data in the southern and central Kattegat region. IODP Site M0060 is located by a yellow star. The location of the proposed Hesselø Offshore Wind Farm (OWF) and cable transects is indicated by read lines. The bathymetry is from Emodnet. G E U S 6 3.2 IODP Site M0060 data types Important information about the sediment types in the Hesselø Windfarm area can be ob- tained from the nearby IODP core M0060 descriptions that can be downloaded from the IODP homepage (http://publications.iodp.org/proceedings/347/104/104_3.htm).