Bulletin of the Geological Society of Denmark • Volume 47/1
 | ContentsGarde, A.A., Friend, C.R.L., Nutman, A.P. & Marker, M.:
Rapid maturation and stabilisation of middle Archaean continental crust: the Akia terrane, southern West Greenland
Bruton, D.L. & Harper, D.A.T.:
A mid-Cambrian shelly fauna from Ritland, western Norway and its palaeogeographical implications
Schovsbo, N.H.:
Environmental fluctuations in the Olenus Zone (Upper Cambrian), southern Scandinavia: A geochemical approach
Hansen, T. & Hansen, J.:
The echinoid Brissopsis lyrifera from the Danish Upper Miocene Gram Formation
Konradi, P.B.:
Biostratigraphy and environment of the Holocene marine transgression in the Heligoland Channel, North Sea
Christensen, W.K., Hancock, J.M., Peake, N.B. & Kennedy, W.J.:
The base of the Maastrichtian
Dybkjær, K. & Rasmussen, E.S.:
Palynological dating of the Oligocene – Miocene successions in the Lille Bælt area, Denmark
Book review
Landvik, J.Y.: Molluscs and the formation of the Arctic
Editor’s Column Christensen, W.K.: Change in Bulletin format
|
Rapid maturation and stabilisation of middle Archaean continental crust: the Akia terrane, southern West Greenland Garde, Adam A., Friend, R.L., Nutman, A.P. & Marker, M. 2000: Rapid maturation and stabilisation of middle Archaean continental crust: the Akia terrane, southern West Greenland. Bulletin of the Geological Society of Denmark, Vol. 47, pp. 1–27, Copenhagen.
New ion probe U-Pb zircon analyses of twelve samples of grey orthogneiss, granite and post-kinematic diorite from the Akia terrane, southern West Greenland, supported by Sm-Nd isotope geochemistry, document its middle Archaean accretional history and provide new evidence about the location of its northern boundary. Zircon populations in grey gneiss and inherited zircons in granite show that magmatic accretion of new continental crust, dominated by intrusion of tonalite sheets in a convergent island arc setting, occurred between c. 3050 and 3000 Ma, around and within a c. 3220 Ma continental core. In the central part of the terrane, tonalite sheets were intercalated with older supracrustal rocks of oceanic affinity by intrusion, thrusting and folding during the Midterhøj and Smalledal deformation phases of Berthelsen (1960). Continued tonalite injection led to a thermal maximum with granulite facies conditions at c. 2980 Ma, dated by metamorphic zircons in grey gneiss. The metamorphic maximum was contemporaneous with upright, angular folds of the Pâkitsoq deformation phase. Within a few million years followed high-grade retrogression and intrusion of two large dome-shaped tonalite-granodiorite complexes, granites s.l. derived from remobilisation of grey gneiss, and post-kinematic diorite plugs. Whereas the relative chronology of these events is firmly established from field observations, zircons from the post-granulite facies intrusions all yielded statistically indistinguishable emplacement ages of c. 2975 Ma. These results show that crustal growth occurred in several short-lived events starting at c. 3220 Ma, and that final maturation and stabilisation of new, thick continental crust took place rapidly (within c. 20 Ma) at c. 2975 Ma.
Key words: Archaean, southern West Greenland, Akia terrane, continental crust, deformation, granulite facies, zircon, ion probe, U-Pb, Sm-Nd..
Addresses: A.A. Garde, Geological Survey of Denmark and Greenland, Thoravej 8, 2400 Copenhagen NV, Denmark. C.R.L. Friend, Department of Geology, Oxford Brookes University, Headington, Oxford, Oxon OX3 0BP, UK. A.P. Nutman, Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia. M.Marker, Norges Geologiske Undersøkelse, Leiv Eirikssons Vei 39, Postboks 3006 - Lade, 7002 Trondheim, Norge. 13 April 1999.0. |
 Get pdf-file of paper (656 kB)
A mid-Cambrian shelly fauna from Ritland, western Norway and its palaeogeographical implications
Bruton, D.L. & Harper, D.A.T. 2000: A mid-Cambrian shelly fauna from Ritland, western Norway and its palaeogeographical implications. Bulletin of the Geological Society of Denmark 47, pp. 29–51. Copenhagen.
A new mid-Cambrian shelly fauna from Ritland, western Norway, significantly extends the known development of the Andrarum limestone facies to the edge of the Baltic craton. The assemblage includes the trilobites Axagnostus fallax (Linnarsson), Solenopleura bucculenta Grönwall, Anomocare cf. laeve (Angelin) and abundant, etched specimens of the linguliformean brachiopod Treptotreta? socialis (von Seebach) together with Dictyonina ornatella (Linnarsson); the fauna indicates the presence of the Jincella brachymetopa Zone and also includes hyoliths, bradoriid crustaceans and sponge spicules. Elsewhere the trilobites and brachiopods have widespread distributions in amphicratonic settings during this part of the mid-Cambrian; the Scandinavian faunas signal the inshore migration of these more cosmopolitan elements, tracking the shallower-water development of calcareous facies of the Andrarum Limestone.
Key words: Trilobites, brachiopods, facies, Cambrian, Norway.
David L. Bruton [
], Paleontologisk Museum, Sars gate 1, Oslo, Norway; David A.T. Harper [
], Geologisk Museum, Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark. 4 April 2000.0.
Get pdf-file of paper (496 kB)
Environmental fluctuations in the Olenus Zone (Upper Cambrian), southern Scandinavia: A geochemical approach
Schovsbo, N.H. 2000: Environmental fluctuations in the Olenus Zone (Upper Cambrian), southern Scandinavia: A geochemical approach. Bulletin of the Geological Society of Denmark, Vol. 47, pp. 53–61. Copenhagen.
The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) was deposited under generally low bottom water oxygen levels. In the formation there is a covariance between faunal composition and the level of trace element enrichment caused by their mutual dependence upon changes in the bottom water oxygen levels. A detailed profile of the V/(V+Ni) ratio through the Upper Cambrian Olenus Zone in the Gislövshammar-2 core, Scania, Sweden, is described. Environmental information from this zone is particularly relevant since the Olenus species in the zone apparently undergo iterative changes in morphology that may be linked to environmental changes. Moreover, the occurrences of Olenus species and Homagnostus obesus are almost mutually exclusive. The results indicate that the trilobitic intervals coincide with increases in oxygen levels as monitored by the V/(V+Ni) ratio. Peak oxygen levels do not appear at the base of each interval, suggesting that colonisation of the sea-floor took place when the oxygenation level reached a certain threshold but before maximum oxygen levels were reached. The distribution patterns of Olenus and Homagnostus are interpreted as reflecting differences in substrate preference since samples containing Homagnostus have statistically significantly higher TOC levels. The V/(V+Ni) variations in the Olenus bearing intervals suggest that oxygen levels fluctuated more than would be expected from morphological changes apparent in the Olenus species.
Key words: Alum Shale, Gislövshammar-2, olenids, agnostids, evolution, dysoxic, substrate, V/(V+Ni).
Niels H. Schovsbo [
], Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark. 3 May 2000.
Get pdf-file of paper ( 1100 kB)
The echinoid Brissopsis lyrifera from the Danish Upper Miocene Gram Formation
Hansen, T. & Hansen, J. 2000: The echinoid Brissopsis lyrifera from the Danish Upper Miocene Gram Formation. Bulletin of the Geological Society of Denmark, Vol. 47, pp. 63–69. Copenhagen.
The irregular echinoid Brissopsis is described for the first time from the type locality of the Upper Miocene Gram Formation at Gram, Denmark. The specimens are conspecific with the Recent Brissopsis lyrifera Forbes, 1841. Futhermore they show remarkable resemblance to the Danish forms of B. lyrifera.
Key words: Brissopsis lyrifera, Upper Miocene, Gram Formation, Denmark.
Thomas Hansen & Jesper Hansen, Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark. 1 June 1999.
Get pdf-file of paper (93 kB)
Biostratigraphy and environment of the Holocene marine transgression in the Heligoland Channel, North Sea
Konradi, P.B. 2000: Biostratigraphy and environment of the Holocene marine transgression in the Heligoland Channel, North Sea. Bulletin of the Geological Society of Denmark, Vol. 47, pp. 71–79. Copenhagen.
A 51 m deep borehole in the outer Heligoland Channel, south-eastern North Sea, penetrated 17 m of marine Holocene, laminated, clayey silt and silty fine sand followed by 34 m of Pleistocene, fluvial sand. Samples from the two units were investigated for their content of foraminifers. The fluvial sand yielded only reworked foraminifers and, based on these is divided into two parts that can be related to differences in lithology. Based on the study of the foraminiferal assemblages in 20 samples, the marine unit is divided in five foraminiferal assemblage zones reflecting the marine inundation into this part of the North Sea after the last glaciation. The basal part of the unit is strongly influenced by freshwater and the lowermost part is dated to c. 11.0 cal. ka BP. The freshwater influence diminishes uphole with deposition of beds characteristic of a tidal flat environment in an estuarine setting with slowly increasing sedimentation depth. A subsequent sudden change in the fauna indicating higher salinity and a more open-marine environment is interpreted to reflect a change in the hydrographic situation. The basal part of this zone is dated to c. 8.6 cal. ka BP. A continuation of this trend is observed in the following zones with further increasing sedimentation depth. The fauna in the topmost assemblage zone indicates an environment comparable to the present conditions in this area of the North Sea.
Key words: Foraminifera, biostratigraphy, environment, radiocarbon dating, sea level, Quaternary, Holocene, North Sea
Peter B. Konradi [
], Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark. 10 March 2000.
Get pdf-file of paper (242 kB)
The base of the Maastrichtian
Christensen, W.K., Hancock, J.M., Peake, N.B. & Kennedy, W.J. 2000: The base of the Maastrichtian. Bulletin of the Geological Society of Denmark, Vol. 47, pp. 81–85, Copenhagen.
At the Brussels Symposium on Cretaceous Stage Boundaries in 1995, the Maastrichtian Working Group decided to recommend the first occurrence of the ammonite Pachydiscus neubergicus in the Tercis quarry near Dax in the Landes, southwest France as the boundary stratotype for the base of the Maastrichtian stage. On the basis of the echinoid genus Echinocorys the Campanian-Maastrichtian boundary beds of Tercis are correlated with the succession in north Norfolk, England, which in turn is correlated with the succession at Kronsmoor, northwest Germany on the basis of belemnites and brachiopods. If the possible correlation between Tercis and northwest Germany is true, the P. neubergicus and Belemnella lanceolata standards for the base of the Maastrichtian stage are not separated by more than 0.2 m.y.
Key words: Maastrichtian stage, base, Tercis, SW France, correlations.
Walter Kegel Christensen [
], Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark. Jake M. Hancock [
], T.H. Huxley School, Imperial College, Prince Consort Road, London SW7 2BP, U.K. Norman B. Peake, 30 St. Benedict’s Street, Norwich NR2 4AQ, U.K. William James Kennedy [
], Geological Collections, Oxford University Museum, Parks Road, Oxford OX1 3PW, U.K. 11 August 2000.
Get pdf-file of paper (
84 kB)
Palynological dating of the Oligocene – Miocene successions in the Lille Bælt area, Denmark
Dybkjær, K. & Rasmussen, E.S. 2000: Palynological dating of the Oligocene – Miocene successions in the Lille Bælt area, Denmark. Bulletin of the Geological Society of Denmark, Vol. 47, pp. 87–103, Copenhagen.
A new geological model for the succession outcropping in the Lille Bælt area, Denmark, is proposed. The model is based on dinoflagellate cyst stratigraphy on the three sections at Hindsgavl, Hagenør and Rønshoved combined with earlier biostratigraphic studies and sequence stratigraphic correlation of outcrops and borings.
Our results indicate that there have been two periods with lagoonal and nearshore marine deposition in the Lille Bælt area separated by a hiatus of at least 3.5 million years. The first period occurred in Late Oligocene or earliest Early Miocene (early Aquitanian) time and is represented by the deposits at Hindsgavl. The second period occurred in Early Miocene (early to mid-Burdigalian) time and is represented by the deposits at Hagenør and Rønshoved.
The deposits at Hindsgavl are time equivalent with the lagoonal upper part of the Vejle Fjord Formation and the overlying nearshore marine sand at Hvidbjerg. The deposits at Hagenør and Rønshoved correlate with the lower part of the offshore marine Arnum Formation and thus represent part of the coastline during the early to mid-Burdigalian.
Key words: Palynology, sequence stratigraphy, Late Oligocene, Early Miocene, Hagenør, Hindsgavl, Rønshoved, Lille Bælt, Denmark..
Karen Dybkjær [
] & Erik Skovbjerg Rasmussen [
], Geological Survey of Denmark and Greenland (GEUS), Thoravej 8, DK-2400 Copenhagen NV, Denmark. 3 April 2000.
Get pdf-file of paper (252 kB)
|
|
Publications
 |
