Nyhedsbrev nr. 4 • Marts 2003

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Indhold

  • Kommende arrangementer
  • Medlemskontingent 2003 – betal via PBS
  • Generalforsamling 2003
  • Nyt fra Nationalkomiteen for Geologi
  • Specielt for studerende!
Deadline for næste nummer af Nyhedsbrevet er:
30. april 2003

Evt indlæg kan sendes til redakt:ren


Kommende arrangementer

25. marts 2003
kl. 16.00
Petroleum systems in carbonate platforms: subsurface examples and outcrop analogs from the former Soviet Union
Harry E. Cook (U.S. Geological Survey)
DGF oliegeologisk foredragsrække – Læs mere
26. – 29. marts 2003 14. Ingeniørgeologiske Konference i Kiel
Se program og indbydelse.
8. april 2003
kl. 16.00
The se arch for hydrocarbons in the Fylla Area, offshore West Greenland
Richard M. Pegrum (RMP Geo-Exploration AS)
DGF oliegeologisk foredragsrække – Læs mere
24. april 2003
kl. 16.00
Sequence stratigraphy and facies architecture of deep-water reservoirs: new data, tools and concepts
Timothy R Garfield (ExxonMobil Exploration Co. )
DGF oliegeologisk foredragsrække – Læs mere
29 april 2003
kl. 16.00
Præsentation af Danmarks Geologipris 2002
Temamøde: Aktuel forskning på Dansk Lithosfærecenter
Læs mere
13. maj 2003
kl. 16.00
Upscaling: methods, pitfalls and consequences
Peter Frykman (GEUS)
DGF oliegeologisk foredragsrække – Læs mere
27. maj 2003
kl. 16.00
Stevns Klint og Cerithiumkalken: nyt fra det ældste tertiær
Claus Heinberg (RUC) og Jan Audun Rasmussen (GEUS)
Læs mere
18. september DGF Grundvandsmøde 2003: Prækvartære grundvandsmagasiner
Læs mere

Medlemskontingent 2003 – præmier til de hurtigste
Nu med mulighed for PBS

Nu nærmer tiden sig atter da medlemskontingentet skal betales. Prisen er den samme som sidste år, dvs sølle 240 kr for studerende, 480 kr for andre og900 kr for firmaer og institutioner.
Som noget nyt vil det være muligt at tilmelde kontingentet til PBS – det sparer både dig og foreningen for en masse besvær i fremtiden.Betalingsfristen er angivet på girokortet, og alle indbetalinger modtaget inden denne frist vil deltage i lodtrækningen om denne helt utroligt flotte fotobog – nogle vil sikkert mindes den fantastiske udstilling der blandt andet var på Kongens Nytorv sidste år. Har du tilmeldt dig PBS har du oven i købet en ekstra chancer for at vinde!

Af hensyn til adminstrationen vil bestyrelsen endvidere gøre opmærksom på at der i år – i modsætning til tidligere – kun vil blive udsendt to rykkere. Har man ikke betalt ved 2. rykkers frist, anses det for en udmeldelse af foreningen.

DERFOR! Skynd dig at betale og deltag i lodtrækningen om de 2 eksemplarer af dette pragtværk

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Generalforsamlingen 2003 – den nye bestyrelse

Generalforsamlingen 2003 er vel overstået – som sædvanligt uden det helt store drama. Regnskabet er godkendt og interesserede kan hente dette og referatet til nærmere granksning via foreningens hjemmeside.

Her kan dog godt røbes at den hidtige formand Peter Johannessen blev genvalgt med akklammation samt at der blev sagt tak for et stort arbejde til den afgående kasserer Ole Rønø Clausen og til bestyrelsens sekretær Rikke Bruhn der begge ikke ønskede genvalg. Desuden blev Walter Kegel Christensen, foreningens mangeårige redaktør af Bulletinen der døde pludseligt sidste efterår, mindet i kort tale af Svend Stouge.

Nyvalgte bestyrelsesmedlemmer er Flemming Jørgensen (Vejle Amt/Århus Universitet), Gunver Krarup Pedersen (Geologisk Institut, København) samt Arne Thorshøj Nielsen (Geologisk Museum). Bestyrelsen har konstitueret sig, og Bo Christiansen er kasserer mens Gunver Krarup Pedersen er bestyrelsens sekretær.

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Nyt fra Nationalkomiteen for Geologi

Komiteen har deltaget i debatten vedrørende den nye gymnasiereform. Sammen med Nationalkomiteen for Geografi har vi sendt et brev til Folketingets Uddannelsesudvalg og gjort opmærksom på behovet for et kendskab til geofagene i gymnasiet. Samtidig opfordrer vi til at geografi med geologimoduler inddrages i flere fagpakker og at faget forbliver er et tilvalgsfag på højniveau. Eventuelle spørgsmål til Gunver Pedersen, KU.

Komiteens projekt ’Danmarks Geologi på Internettet’ er nu godt på vej, og de første lokaliteter ligger på www.naturnet.dk . Planen er at der inden sommer skal være 100 lokaliteter. Målgruppen er naturinteresserede mennesker uden kendskab til geologi. Projektet udføres i et samarbejde mellem Midtsønderjyllands Museum, Skov- og Naturstyrelsen, GEUS og samtlige amter. Friluftsrådet bidrager med lønmidler. Eventuelle spørgsmål til Tove Stockmarr, Midtsønderlyllands Museum eller Lise Holm, Skov- og Naturstyrelsen.

Nationalkomiteens portal www.geologi.dk udbygges stadig. Vi modtager gerne ros og ris samt forslag til nye link. Henvendelse Erik Nygaard, GEUS.

Petroleum systems in carbonate platforms:
subsurface examples and outcrop analogs from the former Soviet Union

Harry E. Cook
U.S. Geological Survey • World Energy Resources • Menlo Park, California, 94025 USA

tirsdag d. 25. marts kl. 16:00
Geologisk Museum, Øster Voldgade 5–7

DGF – Oliegeologisk foredragsrække

Hent pdf -fil af udvidet abstract (135 kB)

Both shallow and deeper water and/or broad shelf sea (North Sea type) carbonates encompass several of the fundamental elements of petroleum systems. A fundamental difference exists between reservoirs comprising shallow water carbonates versus pelag ic chalks; i.e in rock type(s), architectures, depositional environments, porosity types, sequence stratigraphy, and diagenetic processes.

Carbonate platforms can be divided into a set of seven fairly predictable depositional environments. From shallow water to deeper water these depositional environments include: 1) tidal flats, 2) shelf lagoons, 3) middle shelf, 4) reef margin and/or a carbonate sand platform margin, 5) slope, 6) inner basin, and 7) a distal outer basin and/or broad shelf sea. The pattern expressed by these seven environments and their facies belts results from a combination of numerous factors including geotectonics, climate, shelf type, water depth, water energy, sea-level fluctuations, effects of local and regional slope, and geologic age as it determines the nature and types of carbonate constituents.

Source rocks: Devonian–Carboniferous shallow water carbonate platform reservoir oils in the North Caspian Basin are considered to be derived mainly from inner basin, organic rich argillaceous lime mud of Devonian and Carboniferous age. Thus, the source rock and reservoir rocks are laterally and genetically closely linked. In contrast, the North Sea Maastrichtian-Danian chalk oils are mainly sourced from older Kimmeridgian basin-floor mudstone.

Reservoir rocks: In shallow water carbonate platforms reservoir rocks are varied in their architecture and diagenetic attributes mainly due to early marine dolomitization, meteoric diagenesis and early marine cementation. Reservoir types can include tidal flat facies, inner-shelf lagoon wackestones and packstones, carbonate grainstones and reef boundstones on platform margins, and debris flow and turbidity current deposits on slopes and inner-basin settings.

Chalk reservoir rocks: These reservoirs are different than Bahamian-type shallow water carbonate reservoirs. Not only are their reservoir architectures determined by different factors than shallow water reservoirs but also they undergo different diagenetic alterations. Chalks occur in water depths normally not affected by meteoric diagenesis or early marine dolomitization. Also, most chalks are only moderately affected by seafloor cementation in contrast to shallow water carbonates, which can become cemented rapidly. Porosity loss by cementation in chalks is due to burial and/or postburial processes such as pressure solution and local reprecipitation.

Outcrop analogs and subsurface oil fields: Carbonate facies in the Bolshoi Karatau mountains of southern Kazakhstan provide good outcrop analogs for coeval reservoirs in supergiant oil and gas fields in the North Caspian Basin. Bolshoi Karatau carbonates record the development of a 4,500–m–thick carbonate platform that evolved close to the North Caspian Basin of western Kazakhstan during the Late Devonian and Carboniferous.

In the Bolshoi Karatau, thick stacks of upward–shallowing 3rd-order and 4th-order highstand sequences of dolomitized and karsted platform–margin and platform–interior ooid–bioclastic sands form potential reservoirs. Lower–slope and upper–slope Waulsortian skeletal mud mounds contain abundant marine cement and are relatively tight. Reservoir enhancement is related to early marine dolomitization and meteoric diagenesis. These geometric and diagenetic patterns are analogous to many of the reservoirs in the North Caspian Basin including the newest supergiant oil field discovered in 2000. Bolshoi Karatau studies provide important data on the characterization of reservoirs in terms of their facies types, spatial distribution on the platforms, sequence stratigraphy, and predictive diagenetic patterns. These outcrop studies are proving to be valuable for better understanding and predicting the subsurface characteristics and development of North Caspian Basin oil and gas reservoirs.

The presentation will be held in English. Non-DGF members are welcome.

Harry Cook has a Ph.D. degree in geology from the University of California at Berkeley. He started his career as a research geologist with Marathon Oil Company. Later, Harry went into academia where he was a Professor of Geology at the University of California. Since 1974 he has been a research geologist with the U.S Geological Survey in their World Energy Resources Program.

For the past 15 years Harry has focused on the geologic framework and petroleum geology of the Former Soviet Union where he conducts field expeditions in the mountains of Kazakhstan, Kyrgyzstan, and Russia. These expeditions involve studying Devonian through Permian carbonate reefs, platforms and basins that are the time-equivalent outcrop analogs for the super-giant carbonate oil and gas fields in the North Caspian Basin such as Tengiz, Karachaganak and Kashagan. These outcrop studies, which include developing predictive exploration and reservoir models, assisted in the recent discovery of the new supergiant Kashagan carbonate oil field in the North Caspian Basin. Harry’s studies have been part of industry-funded collaborative ventures with geoscientists from Agip/Eni, British Gas, British Petroleum, ChevronTexaco, ExxonMobil, Shell, and TotalFinaElf.

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The search for hydrocarbons in the Fylla Area,offshore West Greenland

Richard M. Pegrum
RMP Geo-Exploration AS • Stavanger, Norway

tirsdag d. 8. april kl. 16:00
Geologisk Museum, Øster Voldgade 5–7

DGF – Oliegeologisk foredragsrække

Hent pdf -fil af abstract (130 kB)

Seismic ‘flat-spots’ associated with thick sedimentary sequences in large, tilted fault blocks were first recognised in the Fylla area, offshore West Greenland, on regional 2D seismic lines shot by the GGU in 1992. Their interpretation as possible gas associated DHIs (Direct Hydrocarbon Indicators) led to the acquisition of a semi-regional 2D survey of approximately 1700 line kms by Nunaoil in 1994. This confirmed the presence of locally thick sedimentary sequences, confirmed the presence of large Mesozoic tilted fault blocks draped by Tertiary sediments and confirmed the widespread occurrence of the ‘Fylla flat-spot’. The latter seemed to be associated with a discrete stratigraphic interval and appeared to be confined within structural closures. All these observations strengthened the interpretation that the ‘flat-spot’ could represent a gas fluid interface within a porous reservoir sequence.

The occurrence of oil seepages and oil staining in Palaeocene volcanic lavas and hyaloclastites in the Disko and Nuusuaq areas, onshore in west central Greenland, have been well documented by GEUS. These data indicate the existence of several working petroleum systems in the underlying Cretaceous to Palaeocene fluvio-deltaic sequences. Significant wet-gas discoveries have been made on the Canadian margin, off the east coast of Labrador and the south coast of Ellesmere Island, in similar sedimentary basins. The possibility of gas accumulations in the Fylla area was therefore, in terms of regional geological understanding, not unreasonable. These considerations led to the Bureau of Minerals and Petroleum (BMP), in 1995, to designate the Fylla Bank area for petroleum exploration and to invite bids for exploration licences from the international petroleum industry.

From the outset, exploration activity focused on the ‘Fylla flat-spot’. If it truly represented a gas-fluid contact in porous sandstones, it was clear that potential gas volumes were extremely large. However economic screening studies had established that however large the volume, dry gas alone would not be commercially attractive due to the great water depths (1000 to 1500m), the remote location and distance from potential markets, and the lack of onshore infrastructure. Commercial viability depended on the discovery of rich, wet gas or the presence of a significant oil leg beneath the assumed gas cap.

This presentation reviews the exploration work carried out by the Statoil / Phillips / DONG / Nunaoil Group following the award of the Fylla Licence in 1996. The exploration programme culminated in the drilling of the Qulleq #1 exploration well in the summer of 2000. The well fully achieved its purpose in evaluating the ‘Fylla flat-spot’ and, although it failed to find oil or gas, it provides a key data point to assist in the ongoing exploration of the West Greenland offshore.

The presentation will be held in English. Non-DGF members are welcome.

Richard M. Pegrum graduated as a Geologist from University College, London in early 1960s and shortly after he became involved in the Great Train Robbery (unfortunately only as a Forensic Geologist working at Scotland Yard) and then worked with Conoco for ca.10 years onshore in Ireland and as a pioneer in the Southern North Sea gas play. He was one of the founding directors of ECL (Exploration Consultants Limited) in early 1970s and worked as a consultant on projects in North Sea, Africa and the Middle East. Worked with Statoil during the “golden age” of exploration in the Viking Graben and was involved in the initial mapping and exploration of Gullfaks, Troll, Oseberg and the Sleipner Complex. Became Exploration Manager with Statoil’s international division in the 1990s for the Middle & Far East (including Thailand, Vietnam and Australasia) and lived in Beijing, China for 3 years and returned to Norway in 1998 and had technical responsibility for the Fylla Licence during the last two years of the exploration programme. Richard is currently working as an independent consultant.

Sequence stratigraphy and facies architecture of deep-water reservoirs:
new data, tools and concepts

Timothy R. Garfield
ExxonMobil Exploration Co. • Houston, TX , USA

torsdag d. 24. april kl. 16:00
Geologisk Museum, Øster Voldgade 5–7

DGF – Oliegeologisk foredragsrække
Funded by the AAPG Foundation Dean A. McGee endowment

Hent pdf -fil af udvidet abstract (135 kB)

Understanding the stratigraphy and facies architecture of deep-water reservoirs has been historically linked to and dependent on technology development. Because direct observations of deep-ocean turbidity currents and debris flows was, until recently, impossible; conceptual understanding of how these sediments were transported and deposited had to await the development of new remote sensing tools and technologies.

In the 1970s and early ‘80s, several nearly identical models for submarine fans were developed, based largely on outcrop studies. Submarine fan models have evolved dramatically with the advent of high-resolution 3-D seismic, side-scan sonar and other water-bottom imaging tools developed in the 1980s and 90s. Extensive channel networks are now known to be persistent in deep-water systems and channelized flow more prevalent and important to the development of reservoir-grade sand deposits relative to unconfined flow. Channels play an important role in moving sands to even the most distal reaches of many submarine fans, whereas low density silts and muds are commonly stripped off the upper part of turbidity currents and deposited as overbank in more proximal to medial areas dominated by slope channels. This flow stripping process often results in an overall proximal to distal increase in the sand/mud ratio, the inverse of sediment distribution patterns depicted in the classic fan models.

Based on principals of accommodation, sequence stratigraphy has provided a conceptual framework to better understand and predict the stratigraphic occurrence, distribution and facies variability of deep-water reservoirs. Improved imaging using modern 3D seismic and the deep-water drilling activities of the 1990s has confirmed the fundamental principals of sequence stratigraphy and allowed the concepts to be applied to deep-water reservoir interpretation and prediction at increasingly higher levels of resolution. These data show that a lowstand cycle of sediment flux may generate early slope failure, slump and slide deposits associated with falling sea level. Early slope failure deposits are often overlain by coarser-grained distributary channel sands, which are primary reservoir targets. These sand-rich units are mostly deposited during peak lowstand times when sediment flux and shelf by-pass are at a maximum. Late-stage deposition of progressively finer-grained, levee-associated turbidites is a common product of waning coarse sediment supply to the upper slope as shelf accommodation increases during early transgression. This idealized sequence stacking pattern is predictive, but not always observed at every location along the depositional profile.

Many of the recent advancements in the data, tools and concepts applied to deep-water siliciclastics have been driven by the need to explore for and develop hydrocarbon reservoirs in the high-cost deep-water environment. For example, recent improvements in 3D-visualization technology have significantly enhanced our understanding of deep-water channel architecture. Previously unimagined, the complex vertical and lateral facies variations associated with temporally evolving and laterally migrating sinuous deep-water channel systems can now be imaged in great detail. This detailed understanding of channel architecture enables improved predictions of reservoir facies and net:gross, more accurate placement of reservoir properties in to 3D geologic models and more precise positioning of exploration and development wells.

The presentation will be held in English. Non-DGF members are welcome.

Timothy R. Garfield has an MS in geology from the University of Colorado, Boulder. After the studies, he worked as a well-site geologist for Continental Laboratories, Oklahoma City, as a staff geologist at Gallagher R&D Co., Lakewood, Colorado; Staff Geologist, and as project manager for RPI International Inc, Boulder, Colorado before he came to Exxon in 1990. At Exxon he has worked as research geoscientist, and has been Group-Leader for the Deep-Water Reservoirs Group. At present he is working as Upstream Geoscience, Stratigraphy Advisor.

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Upscaling: methods, pitfalls and consequences

Peter Frykman
GEUS

tirsdag d. 13. maj kl 16:00
Geologisk Museum, Øster Voldgade 5–7
DGF – Oliegeologisk foredragsrække

Hent pdf -fil af abstract (125 kB) As geological modelling develops an increasing ability to capture details in heterogeneity and therefore the flow properties, the demand for upscaling also increases. The growing disparity between the detailed models and the model-size limitations in full-field flow simulation can only be modified with appropriate upscaling techniques.

This presentation will first briefly present the geostatistical scaling laws that can be used within the geological modelling process itself, and secondly turn to the upscaling methods related to flow processes.

Flow upscaling procedures that can account for the geological heterogeneities will be presented for selected examples from both chalk reservoirs and from clastic reservoirs. Contrasts in permeability and other petrophysical properties will influence the distribution and flow of fluids that will cause anisotropy, cross-flow and break-through problems.

Upscaling of flow of only one fluid (or gas) phase seems fairly simple, but several different methods are available that are to be used depending on the geometry, scale and contrasts in the heterogeneity. Two- or three-phase upscaling will in addition depend on the saturation distribution.

One example will show that the permeability anisotropy in a layered reservoir chalk package can attain a value of 1:2 if single-phase upscaling is performed, while the anisotropy for the oil flow can increase to 1:5 if two fluid phases, oil and water, are present in the reservoir layers.

The presentation will be held in English. Non-DGF members are welcome.

Peter Frykman holds an M.Sc. and Ph.D. in geology from the University of Copenhagen. Since 1986, he has worked at the Geological Survey of Denmark and Greenland (GEUS). Peter Frykman is a reservoir geologist and is working within the broad field of GeoEngineering. His main interests are: reservoir characterisation from small to large scale; the connection between the different scales, mainly in chalk carbonate reservoirs; geostatistical modelling and the integration of petrophysical data to construct reservoir models, and the resulting consequences for the flow of fluids.

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Stevns Klint og Cerithiumkalken: nyt fra det ældste tertiær
Cerithiumkalkens biostatigrafi (planktoniske foraminifeer)og paleoøkologi (muslinger) som stratigrafisk værktøj

tirsdag d. 27. maj kl. 16:00
Geologisk Museum, Øster Voldgade 5–7

Hent pdf -fil af abstract (131 kB)

Planktoniske foraminiferer, muslinger og diakronitet, Cerithiumkalken, Stevns Klint

Claus Heinberg (Roskilde Universitetscenter)

Ved at anvende den kvantitative forhold mellem to morfotyper (serielle og spiralfoermede) af planktoniske foraminiferer op gennem de nederste par meter af Danienkalk ved Nye Kløv i Nordjylland som standart, har det været muligt at påvise at Cerithiumkalken bliver stadig yngre jo længere nordpå langs Stevns Klint man kommer. Den derved fremkomne chronotratigrafiske placering af de forskellige bassiner, fører til at et hidtil noget ukonsitent mønster hvad angår diversiteten af muslinger i Cerithiumkalken, erstattes af en gradient, hvor antallet af arter stiger systematisk fra syd mod nord. Da der samtidig er en stigning i diversitet opad i de enkelte bassiner, fås en smuk diversitetsgardient fra nul arter i bunden til ca 25 arter i toppen, altså er typisk ‘recovery’ mønster.

Metodemæssigt kan studiet siges at være et eksempel på hvordan en i øvrigt ikke tilladelig cirkulær argumentataion, kan bruge konstruktivt. De to gradienter (planktoniske foiraminiferer og muslinger) bekræfter gensidigt hinanden i den forstand at de tilsammen producerer klare mønstre, samt en uddvikling som i øvrigt harmonerer med den generelle biologiske udvikling efter K/T grænsen.

Biostratigrafi og planktoniske foraminferer i Cerithiumkalken (basale Danien) på Stevns

Jan Audun Rasmussen (Danmarks og Grønlands Geologiske Undersøgelse)

Den op til ca. 0,80 m mægtige Cerithiumkalk er den næstnederste litologiske enhed fra Danien på Stevns og underlejres af Fiskeleret. Det er på baggrund af dinoflagellatcyster blevet påvist, at Kridt/Palæogen grænsen er placeret nogle få centimeter over basis af Fiskeleret, hvorimod der hidtil kun har været et beskedent kendskab til Cerithiumkalkens interne, biostratigrafiske opdeling. Dette hænger især sammen med, at enheden almindeligvis er meget fossilfattig. I modsætning til det fossilrige, underliggende Skrivekridt, som opbygges af hovedsaglig kokkolitter, blev det foreslået for over 10 år siden, at Cerithiumkalken overvejende udgøres af kemisk udfældet kalk.

Gennem et omfattende prøveindsamlings- og sorteringsarbejde er det lykkes at tilvejebringe mere end 3000 planktoniske foraminiferer fra 5 lokaliteter langs Stevns Klint. Individerne er små (typisk mellem 40 og 125 my-m) og artsdiversiteten meget lav i prøverne fra Cerithiumkalken.

De ca. 15 planktoniske foraminiferarter, som hidtil er identificeret, giver nu mulighed for at korrelere enheden med den internationale biozonering. Det påvises, at enheden korrelerer med Palfa og P1a zonerne. Cerithiumkalkens foraminiferer afslører dog markante laterale, zoneringsmæssige variationer og det er påfaldende, at såkaldte survivor-arter fra Kridttiden er langt hyppigere i den sydlige del af klinten end i den nordlige.

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29 april 2003: Præsentation af Danmarks Geologipris 2002

Prisen overrækkes til:

Hans Christian Larsen – Dansk Lithosfærecenter

Geologisk Museum, Øster Voldgade 5–7, kl. 16-18

I anledning overrækkelsen af Danmarks Geologipris 2002 til Hans Christian Larsen, leder af Dansk Lithosfærecenter afholdes en temaeftermiddag hvor Lithosfærecenteret præsenterer nogle af deres mest aktuelle arbejdsområder og forskningsresultater. Programmet ser ud som følger:

kl. 16:00 Martin Ghisler (GEUS): Velkomst og overrækkelse af Danmarks Geologipris 2002
kl. 16:15 Hans Christian Larsen: Introduktion
kl. 16:20 Hans Christian Larsen: Characteristic features of volcanic rifted margins: what can we learn about rifting and deep mantle processes?
kl. 16:50 John R. Hopper: Characteristic features of non-volcanic rifted margins: what can we learn about rifting and shallow mantle processes
kl. 17:10 Joel Baker: New frontiers in isotope geochemistry
kl. 17:30 Martin Bizzarro: Early History of Earth’s crust-mantle system inferred from Hafnium isotopes in chondrite
kl. 17: 50 Hans Christian Larsen: Afslutning med efterfølgende reception

Hent pdf-fil af program og abstracts (125 kB)

Characteristic features of volcanic rifted margins: what can we learn about rifting and deep mantle processes?

Hans Christian Larsen – Danish Lithosphere Centre

A new class of rifted margins, volcanic rifted margins, were first discovered in the North Atlantic during the 1980s. Through a number of later studies including ocean drilling, large scale geological sampling and deep crustal seismic studies, the East Greenland margin is now a global type locality for this margin structure. The igneous (oceanic) crust that accreted along this margin during breakup was 3-5 times thicker than normal oceanic (igneous) crust, and it formed above or at sea-level for several million years. Given the globally very uniform thickness of oceanic crust (ca. 6 km) and an average depth of oceanic rifts (spreading ridges) of ca. 2.7 km, these anomalies in crustal thickness and rift elevation are remarkably distinct and requires, in a plate tectonic context, unusual conditions of formation. A possible link to the Iceland hot-spot was already made early on, but requires this to have been an order of magnitude larger during breakup than at the present day. Furthermore, similar margin structures have now also been identified along large sections of the central and south Atlantic margins, off Antarctica and north-west Australia, and possibly within the Red Sea region. Can we from this infer that such giant hot-spots exist and are needed in order to initiate the plate-tectonic cycle through continental breakup? Alternatively, can rifting itself drive special, transient mantle convection leading to excessive magmatism? In other words, is it a bottom-up or top-down driven process?

The North Atlantic is the only region so far where critical data encompassing chronology, crustal thickness variations, rates of melting, and melt compositional variations in time and space exists in sufficient amounts to address this fundamental question. In addition, the still active Iceland hot-spot uniquely allows comparative study of the ancient margins with active processes in Iceland. As usual in science, things are not that black and white. So the answer is: It is a bottom-up and top-down process. And in that order, both in terms of geological time and importance. If you want the details, attend the talk!

In the broader perspective, the massive and sudden mantle upwellings, referred to as mantle plumes, that can be inferred from volcanic rifted margins represent deep mantle convection working in parallel with the more steady state plate tectonic mantle convection and perhaps have more in common with the rare, but extreme events of mantle convection inferred for Venus. Likewise, the steady state plate tectonic mantle convection is now seen more and more as a very much top-down driven process preferentially being controlled by the cool lithospheric plates. Thus, while the plate-tectonic paradigm probably is as healthy as ever, our understanding of the driving forces are changing.

Characteristic features of non-volcanic rifted margins: what can we learn about rifting and shallow mantle processes

John R. Hopper, Thomas Funck and Hans Christian Larsen – Danish Lithosphere CentreIt is recognized now that rifted margins form a spectrum of types, primarily categorized by how much magmatism is associated with final breakup and the initiation of seafloor spreading. One end member shows almost no melting and volcanism. Extension proceeds through progressive thinning of the continental crust until there is effectively nothing left, exposing the underlying mantle to the surface. While at first glance, this seems like a simple and straightforward idea, the mechanics of how this occurs have proven difficult to understand. In the last decade, a key component of rifted margin research has been the collection of new data to characterize thinned continental crust and lithosphere to test ideas about their formation. Complicated structural patterns imaged on the Galicia Bank and Iberia margins suggest that detachment surfaces may exist at the base of the lower crust, despite the high shear stresses required to form them. Large scale asymmetries have been hypothesized that make predictions about the pattern of strain that should be seen in the other half of the rift, in this case off the coast of Newfoundland. Studies on Galicia Bank and Iberia have also shown that mantle can be brought to the surface without undergoing decompression melting. Instead, it is mechanically unroofed where it interacts with seawater to form a thin layer of serpentinized crust that is neither continental, nor igneous oceanic crust. How important these processes are on other rifted margins or in other tectonic environments remains largely unknown. In collaboration with Institutes in the US and Canada, we collected new seismic reflection and refraction data off Newfoundland to examine the nature of rifted continental crust conjugate to the well studied areas off Iberia. This new data, which will be briefly summarized in this talk, shows remarkable new images of thin crust off a continental margin and has important implications for understanding the final stages of breakup and the onset of seafloor spreading in the North Atlantic.

New frontiers in isotope geochemistry

Joel Baker1, Martin Bizzarro1,2, Ingrid Ukstins1 and Tod Waight1

1 Danish Lithosphere Centre, 2 Geological Museum

Plasma-source mass spectrometers differ from older generation mass spectrometers in that samples are ionised in an argon plasma at temperatures equivalent to those on the surface of the sun. This allows: (1) Elements that were difficult to ionise by conventional mass spectrometry (e.g., W, Hf, Zr, Fe) to be readily analysed and utilised in earth, environmental and space sciences (2) A laser to be directly coupled to the mass spectrometer for in situ analysis of rocks or minerals. (3) precise analysis of new stable isotopic systems like Mg, Fe, Cu or Zn, and much improved precision for radiogenic isotope systems like Pb. Recent tungsten isotope studies, based on the decay of the now extinct 182Hf (t1/2 = 9 Myr), shows that Earth’s core formed within 30 Myr of the accretion of the planet and that core formation in smaller planets progressively decreases with planet size. Precise Lu-Hf isotopic data for meteorites produced at the DLC demonstrate that crustal differentiation on Earth took place very early, perhaps starting within 200-400 Myr of accretion from the solar nebula. Laser ablation Pb isotope work at the DLC has shown that is possible to date minerals like apatite, sphene, monazite and rutile in situ with relative precisions << 1%, which were previously only obtainable after time-consuming chemical separation of Pb. Moreover, in situ Pb isotopic analysis can be used as a tracer for oceanographic and volcanological processes. The potential of new “heavy” stable isotopic systems to complement and extend the cosmochemical and paleoenvironmental information routinely extracted from oxygen and carbon isotopes is illustrated by recent magnesium isotopic studies. Magnesium isotopes in chondrites, basaltic rocks from the angrite and eucrite parent bodies, Mars and Earth, and low-temperature terrestrial samples display a range in Mg isotope ratios of 6 per mil. Unlike the different oxygen isotopic arrays defined by meteorite samples, all our data recently acquired for these samples lie on a single mass fractionation line in Mg isotopic space. Intriguingly, basaltic rocks are systematically lighter than the chondritic reservoir commonly assumed to represent the starting material for building planets. Despite the long residence time of Mg in the oceans, Fe-Mn nodules display larger Mg isotopic variations (3 per mil) than any other stable isotopic systems in these materials. With more than 50 new isotopic systems now analysable in our laboratory there remains much to understand in these rapidly developing fields of isotope geochemistry!

Early history of Earth’s crust-mantle system inferred from hafnium isotopes in chondrites

Martin Bizzarro1, 2, Joel Baker1, Henning Haack2, David Ulfbeck1 and Minik Rosing2,1

1 Danish Lithosphere Centre, 2 Geological Museum

The DLC mass spectrometry laboratory has placed itself in the international forefront by developing a new technique for precise determination of the Lu-Hf system in ultra low concentration samples like chondrite meteorites (Nature, 27/02/03). With a half-life of about 37,000 million years, the decay series from 176-lutetium (Lu) to 176-hafnium (Hf) is both a precise geochronometer and a powerful tool for studying early planetary differentiation processes. The interpretation, however, of Lu–Hf isotope data requires accurate knowledge of the radioactive decay constant of 176Lu, as well as bulk-Earth reference parameters. Chondrite meteorites are among the most primitive objects derived from the solar nebula, and are considered to represent our best estimate of the average composition of the Solar System. Therefore it is commonly accepted that the average evolution of the chondritic Lu–Hf system also represents its evolution in the terrestrial planets as a whole. Deviation from the chondritic evolution is thus a measure of planetary differentiation processes such as mantle melting and solidification of these melts into crustal or mantle reservoirs. In order to precisely re-define the decay constant of 176Lu and bulk-Earth reference parameters, we have measured Lu–Hf concentrations and Hf isotope ratios on a number of chondrite meterorites. Our results provide a new and clear picture of the early Earth, indicating that the differentiation of our planet into a first persistent crust and residual mantle occurred very early in its history, approximately 320 million years after accretion. This is as much as ca. 400 million years before the oldest, large crustal fragments (e.g., Isua in West Greenland) known on Earth. A rapid timescale for differentiation of Earth suggests that it may have had an early history similar to other planetary bodies such as the Moon, Mercury and Mars.

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DGF Grundvandsmøde 2003

Prækvartære grundvandsmagasiner

18. september i Torvehallerne, Vejle

Væsentlige dele af det danske drikkevand indvindes fra prækvartære magasiner. I det østlige og nordlige Danmark er det primært Danien kalksten, som udgør magasinerne, mens der mange steder indvindes fra miocæne sandmagasiner i det vestlige Danmark. På Bornholm er der endvidere en række prækvartære magasiner, som ikke findes andre steder i Danmark.

Mødet vil fokusere på den nyeste viden om disse prækvartære magasiner. Hvordan kortlægges de, hvordan er de opbygget, hvordan er vandkvaliteten og er der tale om fremtidens ressourcer?

Mødet afholdes som et heldagsmøde i Torvehallerne, som ligger tæt på jernbanestationen i Vejle.

Program for mødet og oplysning om tilmelding annonceres i næste nyhedsbrev.

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