Paleozoic rocks structure versus Cenozoic cuesta relief along the Baltic Shield–East European Platform transect

Based on structural maps, the bedrock structure on the southern slope of the Baltic Shield is analysed. Gently southerly dipping (0.1–0.2°) Paleozoic layers from Estonia to the Swedish east coast form the Baltic Homocline (BH). Numerous monoclinal folds, forced by basement faulting, induce slight variations in bedrock attitude across the BH. Studies on faults exposed in Southern Finland suggest that many monoclinal folds inducing basement faults within the BH are of Precambrian origin and have been active in pulses. The present monoclines were shaped by the Caledonian Orogeny. Submeridional tectonic hinge-lines induce minor regional-scale changes in the structural setting and control trends/styles of the forced folds. From the west, the BH bounds with the Baltic–Bothnian mobile zone that has been intermittently active since Mesoproterozoic times. The evolving Baltic Syneclise in the Silurian rearranged the structural setting typical for the Ordovician Baltic Basin. The Cenozoic uplift of Scandinavia created a SE-to-E-dipping bedrock sequence around the Gotland–Öland area. As the latter area had a different attitude than the BH, two Cenozoic cuesta-sets started to evolve around the northern Baltic Proper. They both had an outlet to the N–S-flowing Eridanos River around the Gotska Sandön area, creating thus two independent sections of the Baltic Klint

The Ordovician-Silurian boundary beds between Saaremaa and Gotland, Baltic Sea, based on high resolution seismic data

New seismic profiles have been used to revise earlier interpretations of the Ordovician-Silurian bound ary beds be tween Saaremaa and Gotland. Atrans-Baltic reflector with erosional fea ures (S2) above the erosional Ordo vician-Silurian boundary reflector (S1) correlates with the bound ary between the Raikküla and Adavere stages. The sporadic reflector or2 below the S1 reflector off shore from Gotland represents the erosional boundary between the Pirgu and Porkuni stages. Three stratigraphic gaps occur in the Ordovician-Silurian boundary beds off shore from Gotland. The amount of eroded rocks between the Pirgu and Porkuni stages, the Ordovician and Silurian systems and the Raikküla and Adavere stages can change rapidly. Consequently, the thick ness and stratigraphy of the Ordovician-Silurian boundary beds around Gotland can change considerably across short distances. The O4-5-S1 unit off shore from Gotland, including carbonate build ups and erosional incisions infilled with Porkuni strata, belongs facially to the transi ional belt between the Estonian Shelf and the Livonian Tongue. The thick ness changes in the S1-S2 unit (Juuru and Raikküla stages) indicate an extensive subma rine erosional channel, streching from north of Estonia across the Baltic Sea and central Gotland, which developed in the Baltic Basin along a shelf to deep-basin transect dur ng Llandovery time

Structure and development of the Valmiera-Lokno Uplift – a highly elevated basement block with a strongly deformed and eroded platform cover in the East European Craton interior around the Estonian-Latvian-Russian borderland

Based on drillings, a number of geological cross-sections, and structure contour and isopach maps were composed to describe/analyse the structure and development of the Valmiera-Lokno Uplift (VLU), a basement block elevated up to 700 m with a heavily deformed and eroded platform cover in the East European Craton interior, along the regional Liepaja-Riga-Pskov Fault Zone (LRPFZ). Five isolated basement-cored anticlines (BCA), the Lokno, Haanja, Mõniste, Valmiera and Smiltene uplifts, arise in the platform cover on the VLU, whereas the downthrown LRPFZ side defines a complex monoclinal fold. The anticlines, straddling or occurring near the monocline, merge with it and thus have highly asymmetrical shapes. Thickness changes of stratigraphic units across the VLU reveal its complex history, reflecting regional tectonic activation pulses that varied noticeably even between neighbouring BCAs. In all, the latest Precambrian-earliest Ordovician initiation epoch of the VLU was followed by modest tectonic activity or a standstill period in the Middle Ordovician-Early Silurian. Intensifying tectonic movements culminated again in the prime of the Caledonian Orogeny in latest Silurian-earliest Devonian time, and faded thereafter towards the end of Early Devonian. The VLU has been reactivated occasionally since the latest Devonian and emerges as a crustal weakness in the recent movement and seismicity patterns. To decipher the origin of the VLU, hitherto factually undiscussed topics, a more detailed study of the LRPFZ, analysis of its fault pattern and kinematics alongside the regional tectonic setting/history is needed. A cursory look hints to a substantial Early Paleozoic sinistral strike-slip along the LRPFZ, allowing interpreting the VLU as a possible restraining bend structure

Seismic correlation of Palaeozoic rocks across the northern Baltic Proper – Swedish–Estonian project since 1990, a review

After a short historical review of the correlation of Palaeozoic rocks between Estonia and Sweden, this paper focuses on the results of marine seismic studies, achieved during the cooperative Swedish-Estonian project since 1990. The most recent seismic correlation scheme of the Cambrian, Ordovician, and Silurian strata and their distribution at the seafloor across the northern Baltic Proper are presented. Thickness changes and trends, as well as the sedimentary structures, reef bodies, and erosional features of different seismic units, are treated in connection with structural and facies changes in the Palaeobaltic Basin. The immediate background of this project is outlined and the locations of the seismic lines shot during the joint expeditions to the Baltic Sea are shown.</p