Mikael Erlström

Structure and tectonic evolution of the Tornquist Zone and adjacent sedimentary basins in Scania and the southern Baltic Sea area

Abstract Southernmost Sweden, Bornholm and the surrounding Baltic Sea region are located on a large-scale releasing bend in the dextral strike-slip system of the Tornquist Zone, with its resulting pull-apart basins. The well constrained geology of Scania and Bornholm has been combined with detailed on- and offshore borehole data and three proprietary marine seismic surveys. This in conjunction with supplementary BABEL deep seismic reflection findings allows a combined 3D interpretation of sediment/structure interactions. As a result, a regional interpretation has emerged which gives a new understanding of the interplay between structural movement on a complex strike-slip fault system (Tornquist Zone) and its intrazonal depressions (Vomb Trough and Colonus Shale Trough) as well as the sedimentation history of associated areas of sediment accumulation (Ronne and Arnager Grabens, Hollviken Halfgraben, Hano Bay Basin and Skurup Platform). Detailed sequential litho- and seismo-stratigraphic descriptions have been possible by combination of the various data sets. This resulted in the clarification or recognition of previously unknown structural limits to sub-basins and highs in the study area. A 3D chronological (4D) model for the development of the region is proposed. This model takes into account the long-lived structural history combining elements of strike-slip, extension and inversion tectonics. The deep-seated faulting controlling these structures is integrated with the deep structure as revealed by the BABEL line in this area.

Micromorphology and petrography of Late Weichselian glaciolacustrine varves in southeastern Sweden

Abstract The purpose of this investigation is to describe and interpret the sedimentology and petrography of Late Weichselian varves in southeastern Sweden in order to determine their nature and origin. It is focused on the microscopic evidence for glaciolacustrine varve sedimentation in the Baltic Ice Lake and the possibilities of making a detailed facies classification of the sediments in an area with an established varve chronology. The material examined was cores taken from five representative localities in an area below the highest shoreline of the Baltic Ice Lake in the provinces of Skane and Blekinge, i.e., below an altitude of 55–65 m. The investigations included chemical analyses, XRD, microscopy (polarized) and SEM-EDX investigations of the summer and winter layers of the varves. The results of the chemical, clay mineralogy (XRD) and microscopic examinations of the bedrock and mineral fragments indicate that the material in the different facies of the varved clay is mainly produced by moderate alteration and erosion from the local bedrock of predominantly granitoid rocks and of residual kaoline deposits. It is possible to distinguish microscopic evidence of four varve types differing in texture depending on the water depth and how close to the ice the different facies were deposited, i.e., if they were deposited proximally, distally or extramarginally in relation to the ice margin. It is also possible to relate these differences to changes in the palaeoclimate during the deglaciation of the area in the Bolling and Older Dryas chronozones.

Intense and widespread seismicity during the end-Triassic mass extinction due to emplacement of a large igneous province

Multiple levels of earthquake-induced soft-sediment deformations (seismites) are concentrated in the end-Triassic mass extinction interval across Europe. The repetitive nature of the seismites rules out an origin by an extraterrestrial impact. Instead, this intense seismic activity is linked to the formation of the Central Atlantic magmatic province (CAMP). By the earliest Jurassic the seismic activity had ceased, while extrusive volcanism still continued and biotic recovery was on its way. This suggests that magmatic intrusions into sedimentary strata during early stages of CAMP formation caused emission of gases (SO 2 , halocarbons, polycyclic aromatic hydrocarbons) that may have played a major part in the biotic crisis.

The Upper Cretaceous clastic deposits of Ullstorp, Kristianstad basin, Scania

Abstract At Ullstorp, close to the fault of the Navlingeasen horst in northeastern Scania, Sweden, a 10 m thick Upper Cretaceous terrigenous clastic section underlies medium grained bioclastic limestones. The clastic section is interpreted as having been deposited rapidly in a nearshore environment. The interpretation is based on paleontological and lithological grounds. Two conglomerate beds in the section are interpreted as a result of storm events. A third conglomerate bed, composed of matrix supported angular clasts (many of them glauconite coated), is interpreted as a debris flow deposit. Negative sedimentation is indicated by a glauconite coated hardground near the top of the sequence. Changes in sea level are reflected in the composition of the foraminiferal fauna. Other faunal elements comprise benthic invertebrates of nearshore origin, including a large inoceramid specimen.

Lower Palaeozoic stratigraphy at Lyby and Tängelsås, sentral Scania, southern Sweden

Abstract Lithological and stratigraphical data from two new percussion borings at Lyby mosse and Tängelsås in central Scania, provide valuable information on the Middle Cambrian to Lower Ordovician succession. The drilling at Lyby mosse was stopped in the Alum Shale Formation at a depth of 55 m after penetrating a sequence of Upper Didymograptus Shale and Komstad Limestone. The stratigraphical assignment of the limestone is based on conodonts from cuttings. The conodont fauna is virtually the same as in the Komstad Limestone in SE Scania. The presence of a few Tremadocian specimens in the lower part of the limestone indicates either the existence of a very thin bed of the Bjørkåsholmen Formation, or the presence of an erosional residue of specimens between the Alum Shale Formation and the Komstad Limestone. Thus, there is a hiatus, including the Tøyen Shale and probably also the Bjørkåsholmen Formation, in the Lyby area of central Scania. This provides new evidence of differential movements and periods of local uplifts. The boring at Tängelsås reveals a previously unknown occurrence of Lower-Middle Cambrian strata along the Fyledalen Fault Zone. Below the Quaternary overburden, the boring entered a sequence of alum shale (53-110 m) resting on a Lower Cambrian quartzarenitic sandstone. The boring was stopped within the sandstone sequence at 140 m depth. Well preserved specimens of an agnostid trilobite, Ptychagnostus punctuosus (Angelin, 1851), from the depth interval 70-90 m, are indicative of a medial Middle Cambrian age.

Radiomagnetotelluric mapping of marlstone and limestone in the Silurian bedrock of Gotland

The Silurian of Gotland is composed of a series of stacked carbonate platforms. Airborne electromagnetic measurements show areas with high electrical resistivity, dominated by dense limestone, and areas with lower resistivity, dominated by marlstone. On Gotland, three main regional, up to 80 m thick, limestone-dominated bedrock packages overlie marlstone-dominated strata. The thickness of the limestone and the subsurface relationship between limestone and marlstone was investigated in the area of Ale–Ardre on central Gotland by use of the radiomagnetotelluric (RMT) method. A significant difference in resistivity between the limestone (1000–10 000 Ωm) and the marlstone ( < 100 Ωm) renders favorable RMT conditions. Four profiles, up to 4.3 km long, were measured across the upper part of the Klinteberg Formation and lower part of the Hemse Group (late Wenlock–early Ludlow). The results show a distinct change in resistivity at 50–80 m depth, correlating with the transition between biostromal–biohermal limestone and shelf marlstone–wackestone lithofacies, as observed in boreholes. The measurements were used to create resistivity models that make it possible to map the subsurface lateral relationship between limestone- and marlstone-dominated sequences. The results also provide important information on distribution and bedding, which give supporting information regarding the sequence stratigraphic model for the Klinteberg Fm–Hemse Group in the Ala–Ardre–Sigsarve area. The RMT method utilized in this study proved to be a very useful method for mapping subsurface bedrock in carbonate-dominated geological settings such as those on Gotland.

Campanian depositional settings in the Vomb trough, Scania, Sweden

Abstract In Scania, the southernmost province of Sweden, Upper Cretaceous strata are found in depositional basins associated with the Sorgenfrei‐Tomquist Zone which transects Scania in a NW‐SE direction. The Vomb Trough was developed during the Late Cretaceous as an isolated wedge‐shaped basin linked with the Danish Basin and the Polish Trough to the SW. Cretaceous strata are approximately 1000 m thick and include an up to 800 m thick Santonian‐Campanian sequence formed contemporarily with the peak of uplift movements in the Tornquist Zone. The Campanian deposits in the Vomb Trough consist of a variety of matrix‐rich greywackes, calcite cemented litharenites and conglomeratic lithofacies. The sedimentary characteristics of the investigated deposits verify a restricted inner shelf depositional environment strongly influenced by influx of terrigenous clastics from adjacent highs. Conglomerates with pebbles originating from the uplifted Palaeozoic Plateau to the NE occur frequently in the outcrops. An inner ...