Lower Carboniferous igneous intrusions within the crystalline basement of the Baltic Basin (SW edge of the East European Craton, Poland) – insight based on seismic data interpretation and seismic forward modelling

Abstract. The deep, high-resolution regional-scale seismic profiles of the PolandSPAN® survey provided a unique insight into the extensive system of inferred igneous intrusions imaged within the crystalline basement of the Baltic Basin (SW part of the East European Craton). These intrusions, that continue laterally for 100+ km, are located at depth of c. 6–7 – 19–20 km, and are far beyond the reach of the deepest wells. They are represented by packages of strong seismic reflectors, sometimes saucer-shaped, and are often characterized by step-wise geometry, sometimes diverging into several separate branches. Forward seismic modelling was used in order to provide insight – “educated guess” – regarding their lithology, exact lateral extent, and lateral thickness variations. It was concluded that most probably these are doleritic intrusions of thickness in the range of 60 to 200 m. Due to lithological coherence and close spatial relation to shallow sills and massifs recognized in wells, they have been interpreted as Mississippian (early Carboniferous) intrusions belonging to the recently recognized Lublin-Baltic Igneous Province. Developed methodology that combines quantitative assessment of seismic data resolution and estimation of tuning thickness with 2D seismic forward modelling based on geological constrains might be used to better understand, or estimate, parameters characterizing deep intrusions that are beyond reach of deep wells.