Pseudo-toplap in seismic models of the Schlern-Raibl contact (Sella platform, northern Italy)

In the Sella platform of the Dolomite Alps, the horizontal beds of the Raibl Formation directly overlie the Upper Schlern Dolomite (Cassian Dolomite of some authors). The Schlern Dolomite comprises steep clinoforms, together with a few tens of metres of horizontal topset beds in the platform interior. Two-dimensional seismic modelling techniques were used to determine the seismic-response of this interesting situation. To perform this, two different lithological models were constructed based on outcrops of the Sella south face. The first model is that of a rapidly prograding platform with slow aggradation in the platform interior. The second model shows clinoforms toplapping against the topset beds of the platform interior. P-wave velocities and bulk densities were assigned to the lithostratigraphical units in accordance with values from a similar study, involving the same formations. The vertical-incidence method was used to construct perfectly migrated time sections and depth sections of reflectivity. These were convolved with zero-phase Ricker wavelets of different peak frequencies to produce the final synthetic seismic sections. Using conventional, low frequencies (e.g. 25 Hz), the seismic response of the two models is almost identical. The topset beds and the Schlern-Raibl contact appear as one event. In a real seismic survey, both sections would be interpreted as toplap of Schlern clinoforms against the Raibl Formation. At higher frequencies (75 Hz), however, differences are revealed. The angle of progradation in the progradation & aggradation model becomes visible, as opposed to the horizontal surface in the progradation & toplap model. Topset beds are resolved separate from the Raibl Formation, but still appear to form a single dipping pseudo-toplap surface. Another modelling technique, simulating unmigrated sections, shows few differences between the two models even at high frequencies. In addition, the clinoforms are disturbed by the refraction of rays. This study demonstrates that, even under ideal acquisition and processing conditions, the seismic tool can introduce a pseudo-toplap. This implies that toplap in a seismic section is not necessarily toplap in outcrop.     

Maximum extent of the Eurasian ice sheets in the Barents and Kara Sea region during the Weichselian

Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17 000 calendar years ago. During the Late Weichselian (25 000-10 000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation.     

The Fossvogur marine sediments in SW Iceland - confined to the Allerød/Younger Dryas transition by AMS 14 C dating

An exhaustive ¹⁴C dating programme of molluscs from the Fossvogur sediments in Reykjavik. Iceland is presented. For the first time all the fossiliferous units of the sediments are dated. The results confirm earlier conclusions of a widespread occurrence of marine sediments of Allerød age in Reykjavik. The set of dates from the Fossvogur sediments shows a narrow ¹⁴C age distribution (standard deviation of ±235 years) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional ¹⁴C age is 11,400 BP. Assuming a reservoir effect of 400 years. this corresponds to a reservoir-corrected age of I1,000 BP. i.e. the Allerød- Younger Dryas transition for the sampled units, These new ¹⁴C dates from Fossvogur confirm the need for a revision of the Upper Pleistocene chronology of the Reykjavik region. They also have a bearing on the Late Weichselian record of glacier readvances and sea-level changes in the area. The dates suggest that the marine units in Fossvogur accumulated within a restricted time-span of a few hundred years. The sediments in Fossvogur are of volcaniclastic origin and are extremely lithified, indicating local geothermal activity soon after their deposition. This may explain anomalously high D/L amino acid ratios measured in molluscs from the Fossvogur sediments. δ¹³C and δ¹⁸O results suggest that temperatures may have ranged up to 60°C.     

Late Holocene glacier variations and climate at Jan Mayen

Jan Mayen is a small (373 km²) remote island in the Norwegian Sea. One third of it is covered by glaciers, all located on the Beerenberg volcano. There have been at least two Holocene periods of glacier expansion at Jan Mayen. The first may have taken place around 2500 B.P. Some glaciers had their maximum extent during the second period, around 1850 A.D. They have subsequently shown an oscillating retreat, with marked expansion around 1910, and with a minimum extent around 1950. Many glaciers advanced again around 1960. The advance of Sørbreen probably culminated around 1965. The climate appears to have been more arctic-continental than today during these two periods of glacier advances, caused by expanded pack ice cover in the East Greenland current and strong influence from the Greenland-Arctic high pressure area. The interplay between the high pressure area and the low pressure tracks in the North Atlantic Ocean determines the climate over the north-western part of the Atlantic, and this results in parallel climate and glacier variations within this region. We conclude, contrary to previous reports, that the advances of the glaciers around 1960 were caused by reduced summer temperatures and ablation, and not by increased precipitation.     

Duration of ship-following by Kittiwakes Rissa tridactyla in the Barents Sea

Ship-following Kittiwakes Rissa tridactyla were caught and dye-marked with picric acid on three occasions from a ship trawling in the Barents Sea in August 1986. The ship trawled regularly every 20-30 nautical miles and most of the trawl contents were fed to the birds accompanying the ship. Kittiwakes followed the ship for an average of 480-591 min. Between trawl-stations the birds rested on lifeboats and on the rail of the ship, and resting birds showed aggressive behaviour towards neighbours and intruders. The mean departure rate ranged from 4.2 to 5.1% per hour, and the turnover rate was 32 hours. It is obvious that the Kittiwakes behaved opportunistically and had adapted to exploit the waste from the commercial fisheries in the area.     

Weichselian stratigraphy and palaeoenvironments at Bellsund, western Svalbard

A coastal cliff facing the ocean at the west coast of Spitsbergen has been studied, and seven formations of Weichselian and Holocene age have been identified. A reconstruction of the palaeoenvironment and glacial history shows that most of the sediments cover isotope stage 5. From the base of the section, the formation 1 and 2 tills show a regional glaciation that reached the continental shelf shortly after the Eemian. Formation 3 consists of glacimarine to marine sediments dated to 105,000–90,000 BP. Amino acid diagenesis indicates that they were deposited during a c . 10,000-year period of continuous isostatic depression, which indicates contemporaneous glacial loading in the Barents Sea. Foraminifera and molluscs show influx of Atlantic water masses along the west coast of Svalbard at the same time. Local glaciers advanced during the latter part of this period, probably due to the penetration of moist air masses, and deposited formation 4. A widespread weathering horizon shows that the glacial retreat was succeeded by subaerial conditions during the Middle Weichselian. Formation 5 is a till deposited during the Late Weichselian glacial maximum in this area. The glaciation was dominated by ice streams from a dome over southern Spitsbergen, and the last deglaciation of the outer coast is dated to 13,000 BP. A correlation of the events with other areas on Svalbard is discussed, and at least two periods of glaciation in the Barents Sea during the Weichselian are suggested.     

Soft-bedded subglacial meltwater channel from the Welzow-Süd opencast lignite mine, Lower Lusatia, eastern Germany

An excellent section in the Welzow-Süd open-cast lignite mine in Lower Lusatia, eastern Germany, provided a rare opportunity to study a small (5 m deep), buried subglacial meltwater channel of Saalian age. The channel is steep-sided and distinctly U-shaped. It is separated from undeformed outwash deposits in which it is incised by a sharp erosional contact and it is filled with meltwater sand and till. The till was possibly squeezed into the channel from the adjacent ice/bed interface. Directly beneath the channel, there is a partly truncated diapir of clayey silt, evidencing sediment intrusion into the channel from below. During channel formation, the pressure gradient was oriented from the surrounding sediments into the channel, so that the channel served as a drainage conduit for groundwater from the adjacent subglacial aquifer. The substratum consists largely of sandy aquifers with a total thickness of about 100 m, separated by two aquitards. Channel formation was initiated when hydraulic transmissivity of the bed did not suffice to evacuate all the subglacial meltwater as groundwater flow. As the Welzow-Süd channel belongs to a dense network of subglacial channels in eastern Germany, temporary ice-sheet instability in this region prior to channel formation seems possible.     

Early Holocene drowned lagoonal deposits from the Kattegat, southern Scandinavia

Shallow seismic profiling indicated the presence of a drowned lagoon-barrier system formed during the transgression of the southern Kattegat, and investigations of core material have confirmed this. Studies of plant and animal macrofossils show that the lagoonal sediments contain a mixture of marine, brackish, lacustrine, telmatic and terrestrial taxa, and analyses of foraminifers indicate brackish-water conditions. Low oxygen isotope values obtained on shells of marine molluscs also point to lowered salinity. The lagoonal sediments are situated at depths between 24 and 35 m below present sea level. They are dated to between c. 10.5 cal. ka BP and c. 9.5 cal. ka BP, and reflect a period characterized by a moderate relative sea level rise. The lagoonal sediments are underlain by lateglacial glaciomarine clay and silt, which are separated from the Holocene deposits by an unconformity. The earliest Holocene sediments consist of littoral sand with gravel, stones and shells; these sediments were formed during the transgression of the area before the barrier island-lagoon system was developed. The lagoonal sediments are overlain by mud, which contains animal remains that indicate increasing water depths.     

Perceptions of water in a changing hydrological and ecological context: the case of the Logone flood plains in Cameroon

We look at the beliefs of the population in North Cameroon concerning water, fish and water spirits in the context of the construction of a dam (1979) and of a flood embankment for a rice irrigation scheme financed by the World Bank. These operations caused a drought that had severe effects on the environment and the inhabitants' economic activities. Acknowledging the new approaches within development and ecological development thinking, we emphasize that local people are part of their environment, and that the environment and people's use of the ecosystem ought to be regarded as a functional unit. Our main argument is that the success of environmental strategies requires that the unequal power relations between the different actors and agencies and the perceptions of policymakers and NGOs be analysed and examined regularly in the course of a project to test their aims and integrity. In addition, the positions of beings and cosmological entities, which in the eyes of the population are 'actors of power to be reckoned with', like the water spirit, should also be included. The hidden agendas of all actors can be as difficult as the water spirit ( Maama Waata ) itself, by which we mean that hidden agendas are equally a part of reality as is the water spirit, even if they are not visible at first.