The geological framework for Hvideklint, south-east Denmark, using glaciodynamic sequence stratigraphy

Glaciodynamic sequence stratigraphy provides a practical model for grouping and classifying complex geological data to aid interpretation of past climatic and environmental development in Quaternary successions. The principles of glaciodynamic sequence stratigraphy are applied here to summarise the complex glacial geological framework of Hvideklint on the island of Møn, south-east Denmark. The framework of the superimposed deformed Hvideklint is presented in a reconstructed geological cross-section of Hvideklint. For the construction of the architecture of the glaciotectonic complex, the interpretation of structures below sea level was based on a detailed new survey of the cliff section combined with construction of successive approximation balanced cross-sections. The new description is supported by drill hole data from the Jupiter database. Where chalk is not glaciotectonically deformed, the constructed depth to the top-chalk-surface is generally located about 30 m below sea level. In Hvideklint, thrust sheets with chalk are exposed 20 m above sea level, and the balanced cross-section constructions indicate that the décollement surface for a Hvideklint glaciotectonic complex is located about 80 m below sea level. Between the décollement level and the top of the complex, two or more thrust-fault flat-levels and connecting ramps add to the complex architecture of Hvideklint

Prediction and risk evaluation of chalk cliff collapse: the PROTECT project

A major cliff collapse took place at Store Stejlebjerg in the southern part of Møns Klint on 5 July 2003 (Fig. 1). This cliff collapse was one in a number of rock falls that has affected Møns Klint with a frequency of about one per five years. Geological investigations of the rock fall at Store Stejlebjerg were carried out by the Geological Survey of Denmark and Greenland (GEUS) after the Danish Forest and Nature Agency had asked for advice and help concerning security regulations for public access to the site. GEUS was prepared for this type of investigation due to the Survey’s engagement in the European Union project PROTECT, which aims at prediction of chalk cliff collapses. In this project a number of sites in northern Europe have been selected for detailed investigation, among which two are situated at Møns Klint, southeast Denmark (Fig. 1). This report provides a short description of the 2003 cliff collapse at Møns Klint and a brief description of the PROTECT project and its practical implications for cliff collapse evaluation

Kortbladsbeskrivelse, Geologisk kort over Danmark, 1:50 000, Møn Dele af 1511 I, 1511 IV og 1512 II: With a summary in English

Det geologiske kortblad Møn omfatter Møn med de tilgrænsende øer Langø, Lindholm og Nyord samt mindre dele af Sjælland og Falster. Kortet består af dele af de topografiske kortblade 1511 I og 1512 II samt 1511 IV med randområder af tilgrænsende kortblade mod vest og nord. Møn opdeles i tre geomorfologiske områder: det stærkt kuperede Høje Møn mod øst, det småbakkede landskab omkring Stege Nor mod vest, og det flade marine forland omkring Nyord og Ulfshale. Høje Møn opbygges af opskudte skiver af skrivekridt og kvartære aflejringer, som det ses i Møns Klint. Skiverne er op til 80 m tykke, hvoraf skrivekridtet udgør ca. 50 m. Under hele Møn består prækvartæroverfladen af Maastrichtien skrivekridt i en dybde omkring kote –25 til –40 m. Mindre skiver af glacialtektonisk forstyrret skrivekridt optræder også omkring Stege Nor og langs sydkysten af det vestlige Møn ved Hvideklint. De ældste kvartære aflejringer er moræneler fra Saale-istiden og sand og ler fra Eem-mellemistiden. Derefter følger fluviale aflejringer og nedskylslag fra Tidlig Weichsel. Disse lag efterfølges af moræneler fra Ristinge Klint Till Formationen med over- og underliggende smeltevandsaflejringer fra Mellem Weichsel dannet under Ristinge Isfremstødet for ca. 55 000–50 000 år siden. Den næste enhed er Kraneled Formationen (ny formation), som efterfølges af moræneler tilhørende Klintholm Till Formationen (justeret formation) fra Klintholm Isfremstødet for 35 000–32 000 år siden. Formationen overlejres af mere end 10 m tykke enheder af gråt til olivengråt issøler med dropsten, smeltevandssand og lamineret fint sand samt diamikte aflejringer i Kobbelgård Formationen (ny formation). Denne formation blev aflejret i en issø, som dækkede store dele af Østersøen i en mildningsperiode for 32 000– 28 000 år siden. Denne enhed overlejres af eller er øverst sammenflettet med sand og grus tilhørende Stubberup Have Formationen (ny formation). Moræneler tilhørende den Midtdanske Till Formation blev aflejret under NØ-Isfremstødet for 23 000–20 000 år siden. Efter at NØ-Isen var smeltet tilbage fra østersøområdet, rykkede den Ungbaltiske Is frem fra den østlige del af Østersøen, hvorunder bl.a. Møns Klint og Hvideklint blev deformeret. En tilhørende strukturel enhed, Møns Klint Glacialdynamiske Kompleks, er defineret med fire sekvenser. Hele Hjelm Bugt dannede en glacial lobe, og nord herfor dannedes et randmorænestrøg. Radialt ud fra loben dannede smeltevandet store afløbskanaler fra gletsjerporte i den Ungbaltiske Is. Aflejring af sand og grus tilhørende Ny Borre Formationen (ny formation) skete i dette tidsrum. Under det Ungbaltiske Isfremstød blev Lolland Till Formationen aflejret som et relativt tyndt lag af moræneler. Ved slutningen af Weichsel-istiden for ca. 17 000 år siden smeltede den Ungbaltiske Is tilbage. Et residualt isdække i området nordøst for Møn sendte et genfremstød til det østlige Møn, som medførte en reorientering af skrivekridtskiverne i Møns Klint. I Sen Weichsel (17 000–11 700 år før nu) fandtes søbassiner på det sydlige Møn ved Hjelm og Tøvelde samt på Høje Møn, hvor en række ferskvandslag blev dannet, og aflejringen fortsatte et stykke ind i Holocæn. I Holocæn blev de tidligere afløbskanaler transgrederet under den atlantiske havstigning, hvorved fjorde skar sig ind fra nord og nordvest til midt på Møn. Herefter begyndte udbygningen af marine forlande, især mod nord i området Ulvshale og Nyord. De tidligere fjorde voksede til med planter, som omdannedes til tørveaflejringer. Den sidste sedimentationsfase skete langs kysterne, hvor strandvolde blev akkumuleret, og kystklitter af flyvesand blev dannet

Pilespidsstrukturer

Intet resum

Rubjerg Knude, Rubjerg, Klint, Rubjerg Klit

Intet resum

Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, Northern Denmark

The Rubjerg Knude Glaciotectonic Complex is a thin-skinned thrust-fault complex that was formed during the advance of the Scandinavian Ice Sheet (30 000 – 26 000 B.P.); it is well exposed in a 6 km long coastal profile bordering the North Sea in northern Denmark. Theglaciotectonic thrust-fault deformation revealed by this cliff section has been subjected to detailed structural analysis based on photogrammetric measurement and construction of a balanced cross-section. Thirteen sections are differentiated, characterising the distal to proximal structural development of the complex. The deformation affected three stratigraphic units: the Middle Weichselian arctic marine Stortorn Formation, the mainly glaciolacustrine Lønstrup Klint Formation and the dominantly fluvial Rubjerg Knude Formation; these three formations are formally defined herein, together with the Skærumhede Group which includes the Stortorn and Lønstrup Klint Formations. The Rubjerg Knude Formation was deposited on a regional unconformity that caps the Lønstrup Klint Formation and separates pre-tectonic deposits below from syntectonic deposits above.In the distal part of the complex, the thrust-fault architecture is characterised by thin flatlying thrust sheets displaced over the footwall flat of the foreland for a distance of more than 500 m. Towards the proximal part of the complex, the dip of the thrust faults increases, and over long stretches they are over-steepened to an upright position. The lowest décollement zone is about 40 m below sea level in the proximal part of the system, and shows a systematicstep-wise change to higher levels in a distal (southwards) direction. The structural elements are ramps and flats related to hanging-wall and footwall positions. Above upper ramp-hinges,hanging-wall anticlines developed; footwall synclines are typically related to growth-fault sedimentation in syntectonic piggyback basins, represented by the Rubjerg Knude Formation. Blocks and slump-sheets constituting parts of the Lønstrup Klint Formation were derived from the tips of up-thrusted thrust sheets and slumped into the basins. Mud diapirs are a prominent element in the thrust-fault complex, resulting from mud mobilisation mainly at hanging-wallflats and ramps.Shortening during thrust-fault deformation has been calculated as 50%. Only about 11% of the initial stratigraphic units subjected to thrust faulting has been lost due to erosion. The thrust-fault deformation was caused by gravity spreading of an advancing ice sheet. Overpressured mud-fluid played an important role in stress transmission. The average velocity of thrust-fault displacement is estimated at 2 m per year, which led to compression of a 12 kmstretch of flat-lying sediments, c. 40 m in thickness, into a thrust-fault complex 6 km in length. The thrust-fault complex is truncated by a glaciotectonic unconformity, formed when the advancing ice sheet finally overrode the complex. When this ice sheet melted away, a hilland-hole pair was formed, and meltwater deposits derived from a new ice-advance (NE-Ice) filled the depression. The NE-Ice overran the complex during its advance to the main stationary line situated in the North Sea. When this ice in turn melted away (c. 19 000 – 15 000 B.P.), the glacial landscape was draped by arctic marine deposits of the Vendsyssel Formation (new formation defined herein)

Thrust-fault architecture of glaciotectonic complexes in Denmark

Cross sections of glaciotectonic complexes are exposed in coastal cliffs in Denmark, which allow structural studies of the architecture of thin-skinned thrust-fault deformation (Pedersen 2014). However, the basal part of the thrust-fault complex is never exposed, because it is located 50 to 100 m below sea level. It is in the basal part the most important structure – the décollement zone – of the complex is found. The décollement zone constitutes the more or less horizontal surface that separates undeformed bedrock from the displaced thrust-sheet units along the décollement level. One of the most famous exposures of glaciotectonic deformations in Denmark is the Møns Klint Glaciotectonic Complex. The structures above sea level are well documented, whereas the structures below sea level down to the décollement level are poorly known. Modelling of deep structures was carried out by Pedersen (2000) but still needs documentation. A glaciotectonic complex affecting comparable rock units, such as the chalk at Møns Klint, was recently recognised in seismic sections from Jammerbugten in the North Sea (Fig. 1). These sections provide an excellent opportunity for comparable studies of the upper and lower structural levels in thin-skinned thrust-fault deformation, which is discussed in this paper with examples from three major glaciotectonic complexes