The Hanklit Gaciotectonic Thrust Fault Complex, Mors, Denmark

The Hanklit cliff section is a classical glaciotectonic locality where an excellent cross-section through a thrust fault complex is exposed. The thrust imbrications were thrust from north to the south during a Late Weichselian glacier advance. Three thrust sheets with thickness of more than 50 m are involved in the thrust fault complex. The deposits exposed in the cliff-section comprise ca. 39 m diatomite with ash layers of Paleocene-Eocene age (the Fur Formation), overlain by up to 27 m of Quaternary glacigenic sediments. Common structural features related to compressional thrust fault helts, are recognizable in the glaciotectonic complex, which shows a lateral shortening of more than 40%. Structures created by soft sedimentary deformation due to high water pressure occur in relation to the thrust fault zones. The structural framework is described with the terminology of thin-skinned tectonics and flats, ramps and hanging-wall anticlines are identified in the cliff-section. A balanced cross section has been constructed. Based on this construction the structural model is verified and the glaciotectonic development is interpreted. A geoelectrical investigation has been made to support the construction of the 3-dimensional framework of the thrust complex. This demonstrates that the impressive Hanklit thrust sheet extends for more than 1 km along the strike and is displaced more than 200 m to the south. Superimposed extentional structures, situated above the sole of the Hanklit Thrust Sheet, are interpreted to be related to Tertiary subsidence tectonics.

Palaeozoic tectonic and sedimentary evolution and hyrdrocarbon prospectivity in the Bornholm area

The present distribution of Palaeozoic sediments in the Bornholm area is a consequence of several different tectonic regimes during the Phanerozoic eon. This development may be divided into three main evolutionary phases: A Caledonian to Variscian phase encompassing the Lower Palaeozoic sediments. The sediments are assumed originally to have showed a gradual thickness increase towards the Caledonian Deformation Front located to the south. This pre-rift development may be further subdivided into three sub-phases: A period of slow sedimentation on a relatively stable platform as recorded by the uniformly low thicknesses of the Cambrian to Lower Silurian sediments. A period of foreland-type rapid sedimentation commencing in the Llandoverian to Wenlockian, continuing in the Ludlovian and possibly into the Devonian. The period is characterized by /olding and uplift of the Caledonides to the south causing tectonic loading of the foreland and resultant rapid sedimentation in the foreland basin. A period of gravitational collapse causing minor erosion during the Devonian. The transition to the second major phase in the Phanerozaic structural development, during which the Sorgenfrei-Tornquist zone came into existence, is recorded by regional deposition of Carboniferous sediments. These sediments are, however, mostly removed by tater erosion. A syn-rift phase characterized by sedimentation in graben areas and expanding basins commencing in the Rotliegendes and continuing through the Triassic, Jurassic and Lower Cretaceous. This phase was probably initiated by a Late Carboniferous- Early Permian tensional dominated right-lateral wrench fault system within the Sorgenfrei-Tornquist zone. A Post-rift development phase dominated by Late Cretaceous carbonate sedimentation. During Late Cretaceous and Early Tertiary times the Bornholm area was strongly affected by inversion tectonism caused by compressional strike-slip movements. This resulted in reverse faulting and uplift and erosion of former basinal areas. Understanding the two latter phases is important for understanding the present distribution of the Palaeozoic. A key to understanding the hydrocarbon potential of the area is the maturation of the organic matter in the main potential source, the Ordovician Upper Alum Shale. Maturity was mainly achieved during the Silurian to Late Palaeozoic time, and little further maturation took place later. The Upper Alum Shale is accordingly expected to be overmature in the main part of the study area and mature in the Hano Bay Basin. This reflects the assumed primary uniform thickness of the Lower Palaeozoic, with a general thinning towards the northeast. A Caledonian to Variscian phase encompassing the Lower Palaeozoic sediments. The sediments are assumed originally to have showed a gradual thickness increase towards the Caledonian Deformation Front located to the south. This pre-rift development may be further subdivided into three sub-phases: A period of slow sedimentation on a relatively stable platform as recorded by the uniformly low thicknesses of the Cambrian to Lower Silurian sediments. A period of foreland-type rapid sedimentation commencing in the Llandoverian to Wenlockian, continuing in the Ludlovian and possibly into the Devonian. The period is characterized by /olding and uplift of the Caledonides to the south causing tectonic loading of the foreland and resultant rapid sedimentation in the foreland basin. A period of gravitational collapse causing minor erosion during the Devonian. The transition to the second major phase in the Phanerozaic structural development, during which the Sorgenfrei - Tornquist zane came into existence, is recorded by regional deposition of Carboniferous sediments. These sediments are, however, mostly removed by tater erosion. A syn-rift phase characterized by sedimentation in graben areas and expanding basins commencing in the Rotliegendes and continuing through the Triassic, Jurassic and Lower Cretaceous. This phase was probably initiated by a Late Carboniferous- Early Permian tensional dominated right-lateral wrench fault system within the Sorgenfrei-Tornquist zone. A Post-rift development phase dominated by Late Cretaceous carbonate sedimentation. During Late Cretaceous and Early Tertiary times the Bornholm area was strongly affected by inversion tectonism caused by compressional strike-slip movements. This resulted in reverse faulting and uplift and erosion of former basinal areas. Understanding the two latter phases is important for understanding the present distribution of the Palaeozoic. A key to understanding the hydrocarbon potential of thearea is the maturation of the organic matter in the main potential source, the Ordovician Upper Alum Shale. Maturity was mainly achieved during the Silurian to Late Palaeozoic time, and little further maturation took place later. The Upper Alum Shale is accordingly expected to be overmature in the main part of the study area and mature in the Hano Bay Basin. This reflects the assumed primary uniform thickness of the Lower Palaeozoic, with a general thinning towards the northeast.

Depositional environments of coal and associated siliciclastic sediments in the Lower and Middle Jurassic of Denmark. The Øresund -5, -7, -13, -15 and -18 wells

Five cored wells located in the Fennoscandian Border Zone in the Øresund area, Denmark, encountered Lower or Middle Jurassic coal-bearing strata; the coal seams are Lignite to Sub-bituminous A/High Vol. Bituminous C in rank. A number of shallowing-upward units are recognized in the five wells. Each unit is capped by a coal seam. Correlation of these shallowing-upward units between wells is difficult on the basis of available biostratigraphy and log data. Seven of the coal seams result from establishment of peatforming conditions due to infilling of freshwater lakes, whereas the last two of the coal seams result from peat accumulation on top of restricted brackish lagoon or bay sediments. However, only one of the latter two seams accumulated in an environment influenced by saline water. Hence, the investigated coals represent almost entirely freshwater peat-forming environments. Three main types of environments are defined: 1) Type 1 is a sparsely vegetated open water swamp; it is represented by a limnic facies. The deposit is typically a carbonaceous claystone with a high content of allochthonous organic matter; 2) Type 2 is a densely vegetated rheotrophic, nutrient-rich and anoxic swamp; it is represented by a limnotelmatic to telmatic facies. The coal has a very high content of humified organic matter; 3) Type 3, subdivided into the types 3a and 3b, is the driest environment of the three types. Type 3a is a desiccated ombrotrophic raised bog represented by a terrestrial facies. It is strongly influenced by a fluctuating watertable. The coals contain a high content of inertinite that generally shows a low reflectance. Type 3b is a mesotrophic to ombrotrophic domed bog; the environment alternates between dry oxidizing conditions and wet conditions. It is represented by a telmatic to terrestrial facies. In general, the three types of environments form ecosystems characterized by the groundwater influence, nutrient supply, and vegetation. Successions representing the hydrological evolution towards drier conditions due to vertical peat accretion are recognized in some of the seams. The vegetation was small-statured and consisted of a prominent herbaceous type of flora, shrub-like plants, smaller arboreous plants and, to a lesser extent, larger plants.

Megaspore assemblages from the Jurassic and lowermost Cretaceous of Bornholm, Denmark

There are more than 600 slides containing megaspores in "Helge Gry's collection", housed at the Geological Survey of Denmark in Copenhagen. The majority of the specimens are unnamed, all are from the Danish island of Bornholm in the Baltic Sea, and none has been described hitherto. The stratigraphic distribution of 22 of the taxa was, however, taken into account in a paper by Gry, published in 1969, and 16 of these were illustrated by small line drawings. He considered the lithology, areal extent and depositional history of what were thought at the time to be only Jurassic strata on Bornholm. The youngest part of the succession he discussed, the "Purbeck beds" (Rabekke and Robbedale Formations), are, however, now known to be mainly, if not entirely, of earliest Cretaceous age. In the present paper Gry's megaspore records are brought up to date so that they can be used more effectively along with other microfossils in drawing biostratigraphical and palaeoenvironmental conclusions. All 22 taxa to which he referred are discussed and illustrated, mostly with scanning electron micrographs, and their nomenclature emended where necessary. Descriptions and figures of an additional 15 forms encountered in the collection are included. Three of these arc new species of megaspores and one is a palynomorph of uncertain origin, named Henrisporites bornholmensis, Paxillitriletes kristinae, P. rasmusii and Aneuletes discus respectively. Most, if not all, of the megaspores in Gry's collection are likely to have selagincllalean or isoetalcan affinities. There is no evidence of the presence of heterosporous water ferns. The assemblages differ significantly in composition according to their relative ages, with several forms being of considerable biostratigraphic value. There is, however, still room for greater precision in determining local stratigraphic ranges, and also a need to apply occurrence data to palaeoenvironmental interpretations. This will require carefully documented collecting of new samples.

Palynological zonation and palynofacies investigation of the Fjerritslev Formation (Lower Jurassic - basal Middle Jurassic) in the Danish Subbasin

A detailed study of the palynology and palynofacies of the Fjerritslev Formation (Lower Jurassic - basal Middle Jurassic) has resulted in the definition of four spore/pollen zones and four dinoflagellate cyst zones. The spore/pollen zones are the Corollina - Ricciisporites Zone (Late Rhaetian), the Cerebropollenites macroverrucosus Zone (Sinemurian - Pliensbachian), the Spheripollenites - Leptolepidites Zone (Toarcian), and the Perinopollenites elatoides Zone (Middle Jurassic). The dinoflagellate cyst zones are the Rhaetogonyaulax rhaetica Zone (Rhaetian), the Dapcodinium priscum Zone (latest Rhaetian - earliest Sinemurian), the Liasidium variabile Zone (Sinemurian), and the Nannoceratopsis gracilis Zone (Late Pliensbachian - ?Bajocian/Bathonian). These zones, and the Pinuspollenites - Trachysporites Zone Lund 1977 (Hettangian), are proposed for use in the Danish Subbasin. The combined spore/pollen and dinoflagellate cyst zonation has resulted in a detailed biostratigraphical subdivision of the sequences studied. A new combination, Manumia delcourtii (Pocock 1970) nov. comb. et emend., is proposed here, and the species description emended. New photographs of the holotypes of some of the species erected by Nilsson (1958) are included in the plates. The kerogen assemblages recorded from the Fjerritslev Formation, indicate a marine depositional environment, with a high but variable influence of terrestrially-derived organic particles. Stratigraphic variation in the kerogen assemblages generally correlate with the lithostratigraphical subdivision, and support previous environmental interpretations of the Fjerritslev Formation. Indications of strongly reducing conditions in the bottom waters were found in the Stenlille-2 borehole, in samples here referred to the Early Toarcian. The variations in the kerogen assemblages in the sequence investigated from the Gassum-1 borehole are not correlatable with the other boreholes, but seem primarily to reflect a distinct decrease in bioturbation in the Late Sinemurian. The Fjerritslev Formation does not generally represent a potential source rock for oil. Some levels (parts of the F-111 member) show, however, the characteristics of a fair to good source rock. The organic matter is generally immature or only at the earliest stage of maturity.

Deep wells in Denmark 1935-1990. Lithostratigraphic subdivision

The lithostratigraphic data presented here represent the mid-1991 status of the lithostratigraphic database at the Geological Survey of Denmark. The database comprises basic well information such as well location, company, completion date, depths and seismic two-way travel times to top and base of lithostratigraphic units recognized in the wells. Well location maps, a stratigraphic scheme and a list of selected references are included in the present publication. The aim of the presentation is to make these abundant data available to those working with subsurface geology in Denmark and adjacent areas. The key information are depths and seismic two-way travel times to top and base of lithostratigraphic units. The units are primarily recognized by means of petrophysical wireline logs measured in the wells. The boundaries of the units are indicated by significant changes in log pattern and readings as defined in the relevant publications (see reference list). The stratigraphic subdivision of the individual wells has been undertaken over the years by various geologists at the Survey and the level of subdivision thus depends on the data and time available when the subdivision was made. The database is, however, continuously revised as new wells or further work increase our knowledge of the subsurface. The database contains all exploration and appraisal wells drilled on Danish territory. The wells are included irrespective of whether the purpose was exploration for hydrocarbons, geothermal energy, or investigation of possible sites of waste-deposits or gas-storage. However, the wells drilled on the Tostrup salt structure are not included nor are production, observation and injection wells from oil or gas fields since the additional stratigraphic information provided by such wells is generally limited. Wells related to exploration and production of rock salt are not included in the database; most of these were drilled before 1953 and are dealt with in Sorgenfrei & Buch (1964, Table 1, p. 14-17). Further information concerning available logs, reports, and geological samples obtained from the wells, together with information on casings, bit sizes, and test intervals can be found in the Well Data Summary Sheets, vol. 1-16. These can be ordered from the Geological Survey of Denmark. Exploration data in Denmark are in most cases, subject to a 5-year confidentiality period. Therefore, the tables of wells drilled after mid-1986 only show data released by the Danish Energy Agency, such as location, total depth and lithostratigraphic unit at total depth. A few new wells have been released, however, due to relinquished concessions. These wells (Borg-1, Felicia-I, lbenholt-1, Mejrup-1) are presented with full data sets. Furthermore, DONG has permitted release of data from the Stenlille-2, -3, -4, -5, and -6 wells. The authors acknowledge the work of their colleagues who contributed to the database, especially Ole Vejbæk and Jens Jørgen Møller who initiated the data base together with Jens Christian Olsen. Heinke Andersen, Bent Katz, and Uli Heyden are thanked for technical assistance. Jon Ineson (Geological Survey of Denmark) and Olaf Michelsen (University of Arhus) made valuable comments on the manuscript.

Well records on the Phanerozoic stratigraphy in the Fennoscandian Border Zone, Denmark. Hans-1, Sæby-1, and Terne 1 wells

The Hans-1, Sæby-1, and Terne-1 wells are located within the Danish part of the Fennoscandian Border Zone and provide significant new data pertaining to the evolution of this important tectonic belt. All three wells encountered Palaeozoic rocks; the Terne-1 well extended into the lower Palaeozoic. Two of the wells are located in the Danish waters of the Kattegat, and thus yield the first deep well data from this part of the border zone. The wells encountered Cambrian to Silurian, Carboniferous to Zechstein and Triassic to Upper Cretaceous successions. The Cambrian to Lower Silurian section is interpreted to represent shelf and shallow marine deposits comparable to those known from Scania and Bornholm. The inferred Upper Silurian section is calculated to be up to 2600 m thick and may represent the fill of a foreland basin in front of the Caledonian 4 deformation front. A hiatus comprising the Devonian to Lower Carboniferous is inferred. A 550 m thick Rotliegende sequence was drilled in the eastern part of the Sorgenfrei-Tornquist Zone; changes in structural dip indicate a syn-depositional faulting. Palaeozoic tectonism is also indicated by Late Carboniferous intrusive and extrusive volcanic rocks. Reworked volcanic rocks characterize the Rotliegende elastic sequence. A thin siliciclastic Zechstein sequence is recognized. The lithology and stratigraphy of the Mesozoic sections are in accordance with well data from the Danish Subbasin. The presence of a Middle Jurassic depocenter within the Sorgenfrei-Tornquist Zone may indicate a tectonically controlled subsidence of the zone. The occurrence of a Late Cretaceous to Early Tertiary inversion tectonism is supported by these new data.

Upper Cretaceous (Cenomanian-Santonian) inoceramid bivalve faunas from the island of Bornholm, Denmark. With a review of the Cenomanian-Santonian lithostratigraphic formations and locality details

The inoceramid bivalve faunas from the Arnager Greensand, Arnager Limestone, and Bavnodde Greensand Formations of the island of Bornholm, Denmark are described. The fauna from the basal part of the Arnager Greensand s. str. is from the Lower Middle Cenomanian and includes Inoceramus crippsi Mantell, /. crippsi hoppenstedtensis Trager, and I. schoendorfi Heinz. The Arnager Limestone at its type locality immediately west of Arnager yielded a diverse fauna, including /. waltersdorfensis cf. hannovrensis Heinz, /. lusatiae Andert, I. cf. rotundatus Fiege, /. striatoconcentricus Gumbel, I. (Heroceramus) cf. hercules Heinz, I. cf. wandereri Andert, I. cf. annulatus Goldfuss, I. cf. renngarteni Bodilevski & Schulgina, and/. (Mytiloides) incertus Jimbo. This fauna is Lower Coniacian. I. cf. lusatiae and /. cf. guerichi Heinz are recorded from the top part of the formation east of Horsemyre Odde, which is Lower Coniacian. /. (Cremnoceramus) schloenbachi Bohm from the upper Lower Coniacian is reported from the Arnager Limestone Formation at Muleby. /. (Volviceramus) koeneni Muller and /. (V.) alievimussensis lvannikov occur in 4 the top part of the Arnager Limestone Formation at Stampe A; this fauna is probably Lower Middle Coniacian. The fauna of the Bavnodde Greensand Formation at the type locality consists of /. (Sphenoceramus) pachti cf. pachti Arkhangelsky and /. (S.) cardissoides Goldfuss which are Lower, but not lowest, Santonian. At Risenholm, the formation yielded I. (S.) subcardissoides Schluter, I. (S.) cardissoides, I. (S. ?) bornholmensis n. sp., /. (S.) sp. ex gr. pachtilcardissoides, and incomplete, poorly preserved inoceramids possibly belonging to the I. (Magadiceramus) subquadratus group; this fauna is basal Santonian. The fauna of the formation at Jydegard comprises I. (S. ?) bornholmensis n. sp. and /. (S.) sp. ex gr. pachti/cardissoides, and the formation here is lowest Santonian and possibly highest Coniacian. The Cenomanian-Santonian lithostratigraphic formations of Bornholm are reviewed and their ages are discussed with regard to various fossil groups, including inoceramid bivalves, ammonites, belemnites, and foraminifera. Locality details are given.

Upper Triassic-Lower Jurassic tidal deposits of the Gassum Formation on Sjælland, Denmark

Three deep wells on the Danish island of Sjælland penetrate the Upper Triassic - Lower Jurassic Gassum Formation. The formation has been the subject of a facies analysis of cored sediments and interpretation of petrophysical logs. The principal part of the work presented is based on data from the Stenlille-1 well. The sediments were deposited in a NW-SE trending, microto mesotidal, prograding coastal zone and the adjacent fluvial hinterland. In the Stenlille-1 well, the coastal progradation is recorded as a thick, coarse-grained sandstone unit deposited within a barrier island complex. This basal part of the formation is overlain by four stacked regressive sequences consisting of finegrained sandstones and mudstones deposited on tidal flats. A thin transgressive sandstone sheet terminates the formation and marks the boundary to marine claystones of the Fjerritslev Formation.

Revision of the Jurassic lithostratigraphy of the Danish Subbasin

The lithology and stratigraphy of the Jurassic sequence in the Danish Subbasin is described from 5 wells situated in the central region of the Danish Subbasin. The chronostratigraphic subdivision of the Lower Jurassic Fjerritslev Formation is discussed and modified in the light of new biostratigraphical and lithostratigraphical data from the five well sections. The Jurassic lithostratigraphic subdivision is amended. The F-Ia, F-lb, F-II, F-III, and F-IV members of the Fjerritslev Formation are redescribed and defined in relation to the reference section in the Hyllebjerg-1 well. The Haldager and Bream Formations are abandoned. The Haldager Sand, Flyvbjerg, Borglum, and Frederikshavn Members are elevated to the rank of formations.