Sedimentology and depositional environments of the Lund Diamicton, southern Sweden

The Lund Diamicton (earlier named Lund Till) in SW Skåne, S. Sweden, is a glacioaquatic sediment consisting of clay and massive and laminated diamictons. It is characterized by clasts derived from the Baltic depression and its depositional history can be summarized as follows: After deglaciation, large fields of stagnant ice remained in the area and a periglacial land surface with ice-wedge polygons and wind-abraded clasts was developed in ice-free areas. A transgression followed and a clay/diamicton sediment was deposited, partly on top of stagnant ice and against a coastal barrier of stagnant ice along large parts of the basin boundary. This sediment is the Lund Diamicton. The main depositional processes were: fall-out of clay from suspension, sediment gravity flow from stagnant ice and icebergs and rain-out of debris from floating icebergs. The unit was extensively deformed by escaping pore water, loading, flow and due to melting of buried ice. The Lund Diamicton is the equivalent in this area of the classical 'Low Baltic till', which has been interpreted as a basal till deposited by the 'Low Baltic ice stream'. The present study concludes that this unit is instead a glacioaquatic sediment deposited during a transgression in the Öresund area. Its boundary represents the highest coastline and not the margin of a glacier.     

Observations on the vegetation and vascular plants of Hopen

The vascular plant flora of the small arctic island of Hopen, located in the Barents Sea, was inventoried during a visit in the summer of 1982. Eighteen vascular plant species were observed and mapped, and the vegetation described.     

Impact-related clastic injections in the marine Ordovician Lockne impact structure, Central Sweden

Clastic injections generated in connection with the formation of impact craters show many similarities to injections created by other geological processes. However, circumstances such as their position relative to the impact structure and the evidence of forceful processes indicate an impact origin. The Ordovician Lockne impact structure was formed in a marine environment with both sedimentary (Cambrian and Ordovician) and underlying crystalline (Proterozoic) target rocks. Sea water played a substantial part in the cratering process, especially in the modification of the newly formed crater as the water surged back into the structure. In the Lockne area clastic dykes and sills have long been known and have earlier been interpreted as neptunian dykes and conglomerates. So far seven cases of dykes and sills are known in the area. In this work these are interpreted as clastic injections formed in connection with the Lockne impact. The clastic injections occur in the crystalline basement and the sedimentary sequence. The material in the injections comes from all local lithologies (both sedimentary and crystalline) but the sedimentary sequence dominates as a source. The dykes and sills were injected simultaneously with the fracturing and dilation of the host rock in the cratering process, and occur at different stratigraphic levels. In some dykes, clasts from the host rock wall can be fitted back to their original position; the clasts are slightly rotated and surrounded by exotic material. Quartz grains with planar deformation features were observed in the injected material. Most of the sills within the bedded Ordovician limestone are restricted to marly beds, except for the feeder dykes which cut through the overlying beds. This circumstance demonstrates how the decompression has opened the strata along weaker layers and that the underpressure created subsequently sucked the material down. Laminar flow is a conspicuous internal structure in the dykes and sills and indicates viscous flow of injected material. The lamination in the injected material is parallel to the walls in each case. The material was lithified prior to the event and was crushed, mobilized in a water/sediment slurry and injected as dykes and sills.     

Carbonate platforms as recorders of high-amplitude eustatic sea-level fluctuations: the late Albian appenninica-event

The mid-Cretaceous was a time in which rapid vertical carbonate accumulation alternated with intervals of world-wide crisis on carbonate platforms. Next to the well-known mid-Valanginian, mid-Aptian and Cenomanian/Turonian event, the late Albian Rotalipora appennirjica-7.one is a period of severe platform crisis which is reflected differently on different platforms in the Tethys, the Pacific and the Atlantic Ocean. On the Dinaric Platform in western Slovenia (Tethys) karstification and subsequent temporary drowning of parts of the platform is recorded in sediment infillings of a cave system in a reef along the northern edge of the open ocean platform. Biostratigraphic analysis indicates that vertical aggradation, karstification, short-term pelagic influx and subsequent shallow-water carbonate production all took place in the late Albian. Simultaneous, but complete drowning can be observed in the north-west Pacific which is an area where the demise of reefs is most obviously expressed by numerous sunken atolls. New sedimentological and palaeontological data, as well as seabeam and seismic data from several cruises, suggest a dramatic fall of sea level prior to a rise of even higher amplitude in the Rotalipora appenninica-zone. This sea-level rise led to the deposition of a drowning succession and the formation of terminally drowned barrier reefs, rimming the top of many guyots. Karstification and drowning during the same biozone is also recorded on an isolated, shelf-attached platform in the Basco-Cantabrian Basin (North Atlantic) which shows similar cavity systems, infilling sediments and a thin drowning succession. Another example of late Albian platform drowning is the Maracaibo Platform in north-west Venezuela. Thus, carbonate platforms can be used as recorders of high-amplitude sea-level changes, providing quantitative data on magnitude of fluctuations and their nature (relative vs. eustatic). In the case of the appenninica-extnt, they also provide evidence that even during Cretaceous greenhouse climate period(s), dramatic disturbance of climatic equilibrium linked with short-term high-amplitude regressive-transgressive cycle(s) occurred. The reason for this eustatic sea-level fluctuation is yet unclear but could ultimately be triggered by volcanotectonic processes.     

Chronological calculation of the varve zero in Sweden

A revised calculation of the age of the zero in the Swedish time scale by the aid of published varve diagrams (Eiden 1913; Borell & Offerberg 1955) confirms the earlier calculation by E. Nilsson (1960, 1968). The age of the zero, including 365 additional years for the extension of the time scale to present time (Cato 1985), should be historical – 7,288 (9,238 B.P.).     

An alternative Weichselian glaciation model, with special reference to the glacial history of Skåne, South Sweden

A revised lithostratigraphy of Skåne, South Sweden, constitutes the basis of an alternative Weichselian glaciation model for southern Scandinavia, progressively anchored to the stratigraphy. Skåne was not glaciated during the Weichselian until 21,000 B.P. The concepts, outlet surge and marginal dome (the main tools of the model) are defined. The palaeogeography of the Baltic and Kattegatt basins during the Mid-Weichselian are reconstructed. Shorelines, during the advance stage, are calculated from an inferred proglacial depression. Outlet surges, which occurred in three basins of the Baltic, guided the ice sheet during its growth. The growth of marginal domes on the outlet surge lobes resulted in changes in the configuration of the ice sheet and in the lowering of its surface profile. The South Scandinavian ice divide became located over a former outlet surge lobe NNE-NE of the island of Gotland in the northern Baltic. This gave the main ice in South Sweden and Denmark a NE ice movement during the whole glaciation until the deglaciation of SE Sweden. The Kattegatt Ice Lake was formed due to damming in the Skagerack area. Surging ice tilled in the basin resulting in the formation of vast areas of stagnant ice in front of the advancing NE-ice. Marginal domes were formed on these giving rise to the early glacial episodes in the southwest of Sweden and Denmark. During the deglactanon, tnree pnases of marginal dome formation are recorded in the soutnern Baltic area and the growth of these domes resulted in the East Jylland advance, the Bælthav readvance and the Simrishamn readvance. The marginal domes were formed on vast fields of stagnant ice left behind by the receding main ice. Baltic erratics, englacially present in the main ice as well as in the stagnant ice in front of it, were transported (stepwise) towards the west and northwest, partly by the advancing marginal domes and partly by ice streams formed between the marginal domes and the main (NE-) ice. It is argued that the classical, so-called Low Baltic ice stream in the sense of a readvancing glacier lobe never existed. The first two marginal domes collapsed due to starvation and the ice movement returned gradually to the independent NE ice movement of the main ice. The third marginal dome collapsed due to a downdraw caused by a large transgression recorded in the Kattegatt and the Öresund regions. The transgression took place roughly around 13,300 B.P. and was possibly caused by damming of the Kattegatt basin in the north in connection with a marine downdraw. The collapse of the third marginal dome and the subsequent ‘ice lake downdraw’ of the dome centre NNE-NE of Gotland took place during a cold period of the deglaciation. This resulted in an extremely high recessional rate on the Swedish cast coast compared with the west coast and a contemporaneous westwards displacement of the South Scandinavian ice divide. After the downdraw, the recession rate on the east coast slowed down markedly and became more or less equal to that of the west coast. Pure dynamic causes for the extremely high recession rate in SE Sweden are expected because the decrease in this rate coincides with the onset of a recorded, marked climatic amelioration at around 12,600 B.P. Formation of the marginal domes during the deglaciation indicates periods of increased cyclon activity at the southwest margin of the Weichsclian Scandinavian ice sheet alternating with periods of ice sheet starvation. Detailed modelling of the marginal domes is therefore expected to have significant palaeoclimatic implications. The marginal dome concept is believed to he useful also in the reconstruction of earlier glaciations.