Stig A. Schack Pedersen

Palaeocene–early Eocene inversion of the Phuquoc–Kampot Som Basin: SE Asian deformation associated with the suturing of Luconia

Abstract: The little explored Cambodian and Vietnamese Phuquoc–Kampot Som Basin is a Late Jurassic to Early Cretaceous foreland basin developed in response to the build-up of a palaeo-Pacific magmatic arc. A combination of seismic data, well data and outcrop geology complemented by fission track and U/Pb analysis is used to unravel the basin history. This reveals a hitherto unknown earliest Palaeogene basin inversion associated with the Luconian suturing to SE Asia and the shutdown of palaeo-Pacific subduction underneath SE Asia. The Phuquoc–Kampot Som Basin and the Khorat Basin in Thailand constitute the erosional remnants of a larger basin that covered large parts of SE Asia in Late Mesozoic time, and subsequently became segregated during earliest Palaeogene inversion and erosion. Inversion was focused along the several hundred kilometres long Kampot and Khmer–Chanthaburi fold belts that confine the Phuquoc–Kampot Som Basin and merge with the Mae Ping and the Three Pagodas fault zones. These connections, together with local NW–SE-trending sinistral transpressional faults offshore, indicate a link between initial SE Asian left-lateral strike-slip faulting and the Luconian suturing. The separation between the once unbroken Khmer–Chanthaburi Fold Belt and the Phetchabun Fold Belt in Thailand suggests a 50–100 km Cenozoic left-lateral offset across the Mae Ping Fault Zone.

Pollution-Induced Community Tolerance (PICT) in coastal phytoplankton communities exposure to copper

The toxic effect of copper to coastal phytoplankton communities was studied in 6 m3 enclosures during 15 days using the PICT (Pollution-Induced Community Tolerance) methodology. PICT, primary production, algal biomass, species composition and diversity in phytoplankton communities were measured in control enclosures and enclosures with 1, 3, 6 and 15 μg Cu l-1 added. Increased copper tolerances were induced in the enclosures with added copper and, related to the pooled mean value of the controls, the mean values for copper tolerance were significantly higher in enclosures with 1, 6 and 15 μg Cu l-1. In enclosures with 6 and 15 μg Cu l-1, photosynthetic activity was significantly depressed. Fundamental changes in taxonomic diversity and species composition occurred in enclosures with 15 μg Cu l-1. Algal biomass was not affected by the addition of copper. The distribution and concentration of copper in the enclosures showed that copper exposure was almost constant over time in the enclosures and was proportional to the amount of copper added to them. Our studies indicate that the PICT methodology is sensitive enough to detect even minor effects of copper on phytoplankton communities. The PICT measurements indicate effects from concentrations as low as 1 μg Cu l-1 in highly eutrophic coastal areas, where the bioavailability of copper is assumed to be low. Copper concentration in the fjord and control enclosures was high, about 0.5 μg Cu l-1, only a factor two below the effect concentration measured by PICT. These results are significant in view of the increased release of copper to the coastal marine environment as results of the substitution of copper-based ship paints for tri-n-butyltin (TBT) antifouling paints.

Landslide and Tsunami 21 November 2000 in Paatuut, West Greenland

A large landslide occurred November 21, 2000 at Paatuut, facing the Vaigat Strait onthe west coast of Greenland. 90 million m3 (260 million tons) of mainly basalticmaterial slid very rapidly (average velocity 140 km/h) down from 1,000–1,400 maltitude. Approximately 30 million m3 (87 million tons) entered the sea, creatinga tsunami with an run-up height of 50 m close to the landslide and 28 m at Qullissat,an abandoned mining town opposite Paatuut across the 20 km wide Vaigat strait. Theevent was recorded seismically, allowing the duration of the slide to be estimated tocirca 80 s and also allowing an estimate of the surface-wave magnitude of the slideof 2.3. Terrain models based on stereographic photographs before and after the slidemade it possible to determine the amount of material removed, and the manner ofre-deposition. Simple calculations of the tsunami travel times are in good correspondencewith the reports from the closest populated village, Saqqaq, 40 km from Paatuut, whererefracted energy from the tsunami destroyed a number of boats. Landslides are notuncommon in the area, due to the geology with dense basaltic rocks overlying poorlyconsolidated sedimentary rocks, but the size of the Paatuut slide is unusual. Based onthe observations it is likely at least 500 years since an event with a tsunami of similarproportions occurred. The triggering of the Paatuut slide is interpreted to be caused byweather conditions in the days prior to the slide, where re-freezing melt water inpre-existing cracks could have caused failure of the steep mountain side.

Palaeoproterozoic (1740 Ma) rift-related volcanism in the Hekla Sund region, eastern North Greenland: field occurrence, geochemistry and tectonic setting

Abstract Two Palaeoproterozoic volcanic successions, the Hekla Sund (HS) Formation and the Aage Berthelsen Gletscher (AaB) Gletscher Formation, occur within the Caledonian orogen of eastern North Greenland. They consist mainly of mafic pillow lavas, deformed and metamorphosed under greenschist-facies conditions during the Caledonian orogeny. Zircons from a rhyolitic ignimbrite in the HS Formation have yielded an age of 1740±6 Ma. In both formations the volcanic rocks are intercalated with immature sandstones and conglomerates that accumulated in the vicinity of active fault scarps; a shallow marine, rifted basin is implied. Relative concentrations of the more immobile minor and trace elements (Ti, Zr, Nb, Y and rare-earth elements) in both rock suites were unaffected by the metamorphism. Fractional crystallisation of olivine, clinopyroxene and, probably, plagioclase, as well as assimilation of crustal rocks was involved in the petrogenesis of the HS Formation. The AaB basalts have higher Mg, Ni and Cr and lower concentrations of incompatible elements than the rocks of the HS Formation, and they could be regarded as more primitive products of the same magmatic event. However, marked differences in incompatible trace element ratios in the two suites are unlikely to reflect either differences in fractionation histories or variable contamination, and suggest compositional differences in the mantle source rocks. Basalts from the two formations have distinct eNd values (−4.6 and −4.8 for the HS Formation, −5.9–−5.6 for the AaB Gletscher Formation), which is consistent with this interpretation. The volcanic rocks at HS and AaB Gletscher were erupted shortly after a long period of orogenic activity between 2000 and 1750 Ma ago. Following post-orogenic emplacement of granites at ca. 1750–1740 Ma, uplift and erosion took place, and accumulation of extensive immature sediments occurred simultaneously with formation of the volcanic rocks described in this paper. The magmatism that gave rise to the two formations may have been caused by melting during lithospheric extension.

Glaciodynamic sequence stratigraphy

Abstract The glaciofluvial deposits are by volume and permeability the most important unit in the terrestrial glacial successions, and they are the obvious target for groundwater as well as hydrocarbon reservoir exploration. The dominant glaciofluvial units are related to the proglacial setting in the foreland of an advancing ice margin, which results in a coarsening-upwards sequence with fine-grained beds at the base and glaciofluvial gravel at the top. In a complete sequence a till caps the unit, and at its base a glacitectonite is formed by shearing related to the development of the deformational layer below the ice. The glacial deposits laid down during the same glacial advance represent a glaciodynamic sequence. An important feature added to this is the proglacial glaciotectonic deformation. The glaciotectonic architectural elements comprise thrust faulting, folding of hanging-wall anticlines, thrust-sheet duplexes, hydrodynamic breccias and mud diapirs, the structural style of which define the glaciotectonic complex. The glaciodynamic sequence corresponds to the glaciodynamic event related to one major ice advance. The glaciodynamic processes representing the event comprise deposition as well as deformation, creating a glaciogenic sedimentary succession and a set of glaciotectonic structures. These constitute the elements to be recognized for defining a glaciodynamic sequence.

A healed strike-slip plate boundary in North Greenland indicated through associated pull-apart basins

Abstract In the North Atlantic, Laurentia–Eurasia break-up commenced in the Late Carboniferous, largely following the structural grain of the Caledonian Fold Belt. However, in the Arctic region, a 45° offset in the plate boundary between North Greenland and Svalbard was determined by a number of pre-Caledonian fundamental faults in North Greenland. As a result, this segment of the plate boundary experienced significant episodes of combined transtension and transpression, in part controlled by the movement of a temporarily independent Greenland Plate. Late Permian–Mesozoic deposits in the North Greenland Wandel Sea Basin record the plate-boundary history along this offset, in our view in a series of at least 20, variously disturbed, pull-apart basins, most of which can be assigned to four major episodes of pull-apart basin formation. The direction of the pre-existing fundamental faults, in combination with the regional variation in rock properties of both the basin floor and basin fill, explains the marked differences in tectonic style recorded along the plate boundary.

Cenozoic deformation and exhumation of the Kampot Fold Belt and implications for south Indochina tectonics

Latest Mesozoic to earliest Cenozoic deformation affected SE Asias Sundaland core. The deformation event bridges the Mesozoic SE Asian fusion with the Cenozoic era of rifting, translation, basin formation, and the creation of modern SE Asian oceans. Southern Cambodia and Vietnam are central to this shift, but geological investigations of the region are in their infancy. Based on apatite and zircon fission track analyses (AFTA and ZFTA), stratigraphic and structural observations, seismic data, thermal maturity, and igneous rock dating, the geological evolution of southern Cambodia and Vietnam is investigated. Diverse depositional styles, igneous activity, structural deformation and subsurface unconformities testify to a highly variable Phanerozoic tectonic setting. Major latest Cretaceous to Paleocene thrusting and uplift affected the Kampot Fold Belt and surrounding regions and the associated up to ~11 km exhumation probably exceeds earlier denudation events since at least Permian time. The present relief of the Bokor Mountains rising high above the Kampot Fold Belt represents an artifact after differential erosion and only 2.5–4.5 km of erosion affected this area. The latest Cretaceous to Paleocene orogenesis affected much of greater Indochina probably owing to plate collision along eastern Sundaland or a combination of collisions along both east and west Sundaland. AFTA and ZFTA data document protracted cooling of Cretaceous granites and locally elevated thermal gradients persisting a few tens of million years after their emplacement. The thermal gradient had stabilized by early Miocene time, and Miocene cooling probably reflects a renewed denudation pulse driven by either regional tectonism or climate-enhanced erosion.

An assessment of Palaeogene and Neogene clay deposits in Denmark as possible host rocks for final disposal of low- and intermediate-level radioactive waste

Abstract In Denmark, mapping and preliminary investigations of Palaeogene and Early Neogene clay deposits have been performed over the past 5 years. The goal was to locate potential host rocks for the final disposal of low- and intermediate-level radioactive waste from the Danish Research Centre Risø, which has to be decommissioned within the next 5–8 years. Five areas with low-permeability Paleocene and Oligocene clay formations, situated in northern Jylland, NE Fyn and southern Lolland, not far from the Baltic coast at Femern Belt, have been suggested. The clay formations are between 75 and 150 m thick, and have large lateral distribution. They are covered by thin layers of glacial clayey tills and the shallow depth to the clay formations is attractive, partly because they are easy to access and partly because there are no groundwater aquifers situated above or below the clay deposits. The paper gives an overall review of the characteristics of the six different clay formations within four of the areas.