Reflection of the Palaeoproterozoic Mid-Lithuanian Suture Zone in the overlying sedimentary cover

Abstract

The Mid-Lithuanian Suture Zone represents the first-order Palaeoproterozoic tectonic feature defined in the crystalline basement of Lithuania. It crosses the whole territory of Lithuania from the SW to NE. The vast basin sedimentation was established after more than 1.2 Ga years and persisted from Late Vendian to Quaternary. The geodynamic conditions were quite different during different geological periods. Accordingly, the structural pattern of the basin was also variable. Despite of the varying tectonic situation, the ancient Mid-Lithuanian Suture Zone showed a persisting impact on the sedimentation pattern and structuring of the overlying sedimentary layers. This influence is initially traced in the distribution of the Upper Vendian deposits, the western boundary of which is confined to the Mid-Lithuanian Suture Zone implying the subsidence trend east of the zone and erosion of the basement lithologies exposed on the surface in the west. The sedimentation pattern dramatically changed in the middle Early Cambrian time showing the transgression of the new marine basin from the west. The analysis of the thickness distribution of the trilobitic Cambrian deposits indicates the preservation of the controlling role of the Mid-Lithuanian Suture Zone on the local sedimentation variations. The zone is marked by the distinct depression characterised by increased thicknesses. Furthermore, it controlled the distribution of the lithofacies distribution. Some changes are recognised in the structural pattern during the Ordovician that reflect the changing tectonic situation. The southern part of the Mid-Lithuanian Suture Zone preserved the increased subsidence trend inherited from Cambrian, while the northern part is not discernible in the thickness variations. This can be related to different orientation of the southern and northern parts of the Mid-Lithuanian Suture Zone with respect to affecting tectonic forces. The dramatically increased subsidence and associated sedimentation rates mark the flexuring stage of the Baltic Basin evolution. The Mid-Lithuanian Suture Zone, however, is well defined in the lithofacies and thickness distribution. The zone is marked by transition from deep basin facies in the west to inner shelf shallow sedimentation in the east. The Mid-Lithuanian Suture Zone is not identified as the controlling feature in the Devonian sediments. However, the Mid-Lithuanian Suture Zone is well defined in the map of local structures. Application of the method of local residuals unraveled the local uplift confined to this zone. It suggests the post-Devonian formation of the Middle Lithuanian uplift. Furthermore, this uplift is well traced in the older Cambrian and Silurian layers. The amplitudes of the uplift are compatible for Cambrian, Silurian, and Devonian sediments that confirm the post-Devonian age of this feature. The later history of the Middle Lithuanian uplift cannot be restored due to absence of younger sediments straggling along the Mid-Lithuanian Suture Zone. The distribution of the Jurassic sediments makes a hint to persisting activity of the zone. It is implied that the Mid-Lithuanian Suture Zone represents the important feature of the Earth’s crust with specific mechanical properties that resulted in persistent activity under changing tectonic forces.