Buried Quaternary valleys in the south-western Baltic Sea (BurVal-Baltic)
Final Report Abstract
The Burval-Baltic project strived for understanding the tectonic control on Buried Valley evolution. Buried Valleys (subglacial channels) are defined as deep channel-form features incised into the pre-Quaternary sedimentary record from glaciated terrains. These cut and fill structures have been a matter of intense debate in recent studies as they hold significant supplies of groundwater, they contain aggregate for construction and typically have a most complete sedimentary record of glacial geological processes and paleo-climate conditions. Their formation is generally attributed to subglacial melt-water transport incising the underlying strata during periods of glacial coverage. Several authors noticed a spatial correlation between Buried Valleys and tectonic faults beneath; however, a principle causative correlation was never established. For the suggested study, we processed and interpreted a dense profile grid comprising ca. 20.000 km of multi-channel data from the southwestern Baltic. In order to expand our knowledge of recent faulting in the southern Baltic, we studied first the local tectonic evolution of two different areas, which are the Carlsberg Fault Zone and the eastern Glückstadt Graben. In both studies, we combined marine air pulser with onshore vibrator seismics. We could show that the Carlsberg Fault System emerged at least in the Lower Triassic. Upper Cretaceous growth faulting contrast the Late Cretaceous to Paleogene inversion tectonics in the vicinity. High-resolution shear-wave seismic data strongly indicate that falting persist until present. In the eastern Glückstadt Graben we investigated faulting above a salt wall. Several observations strongly suggest that the faults continued developing during the Pleistocene until today: (i) the Pleistocene Unconformity is concave upwards and cut by faults; (ii) growth strata within the marine Holocene deposits above the graben imply recent tectonic movements; (iii) onshore high-resolution P-wave vibroseis data of the southeastern Eckernförde Bay suggest about 10 m of faulted Holocene strata; and (iv) marine seismic data show the faults piercing the seafloor. The combined interpretation of the entire data set enabled us to map buried valleys and shallow fault systems. Our results, however, are way beyond the primary goal of just mapping buried valleys and shallow faults. The valleys are less abundant than previously assumed, and we learned that the assumed, small salt anticlines are just velocity artifacts. Yet, the hypothesis that shallow faulting is abundant holds. In the salt floored North German Basin, three major fault trends are observed: NW-SE, N-S and NNE-SSW striking faults. Several of the faults are located directly above basement (sub-salt) faults and salt pillows. The majority of these faults are trending N-S to NNE-SSW and parallel the direction of the Glückstadt Graben faults. Basement tectonics controls supra-salt tectonics, but the ductile salt layer causes a shift between the sub- and supra-salt faults. In the salt free Pomeranian Bay, two major fault trends are found: NW-SE and NE-SW striking faults. The majority of these faults are located above basement faults following the direction of the Tornquist Zone. As a spin-off, we mapped contourites that developed in the Late Cretaceous chalk sea. We could show that two different bottom current systems controlled contourite deposition, a NW directed flow along the Tornquist Zone, and a SE directed flow west of it.
Publications
- (2019) Evolution of contourite systems in the late Cretaceous Chalk Sea along the Tornquist Zone. Sedimentology 66 (4) 1341–1360
Hübscher, Christian; Hseinat, Mu'ayyad Al; Schneider, Matthias; Betzler, Christian
(See online at https://doi.org/10.1111/sed.12564) - 2016. High-resolution shearwave seismics across the Carlsberg Fault zone south of Copenhagen–Implications for linking Mesozoic and late Pleistocene structures. Tectonophysics 682, 56-64
Kammann, J., Hübscher, C., Boldreel, L.O., Nielsen, L.
(See online at https://doi.org/10.1016/j.tecto.2016.05.043) - 2016. Triassic to recent tectonic evolution of a crestal collapse graben above a salt-cored anticline in the Glückstadt Graben / North German Basin. Tectonophysics 680, 50-66
Al-Hseinat, M., Hübscher, C., Lang, J., Lüdmann, T., Ott, T., Polom, U.
(See online at https://doi.org/10.1016/j.tecto.2016.05.008) - 2017. Late Cretaceous to recent tectonic evolution of the North German Basin and the transition zone to the Baltic Shield/southwest Baltic Sea. Tectonophysics 708, 28-55
Al Hseinat, M., Hübscher, C.
(See online at https://doi.org/10.1016/j.tecto.2017.04.021)
