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An Interpretation of the Basement Structure and Formation of the Black Sea Based on Deep Seismic Data and Gravity Modelling

Abstract

It is widely accepted that the Black Sea consists of two separate back arc basins which opened at different times during the Cretaceous driven by northward subduction of the Neo-Tethys Ocean. The paucity of well data, complex geometries and seismic imaging challenges mean that questions remain regarding the basement architecture though most authors accept that, at least in part, both these basins are floored by oceanic crust, even though there a no magnetic stripes. Interpretation of deep, long offset SPAN seismic data (imaging to more than 30km) and integrated modelling of gravity data support the presence of oceanic crust and allow its distribution and that of stretched continental crust to be mapped in both the West and East Black Sea. We also investigate the architecture of the transitional zone between continental and oceanic realms and how it changes across the Black Sea. We note the absence of seaward dipping reflectors and only limited areas where there is good evidence for exposure of sub-continental mantle and discuss the implications this may have on the nature of Black Sea opening within the regional tectonic framework. The Black Sea is surrounded by fold and thrust belts. We will show some evidence to suggest that the beginnings of subduction of the oceanic crust can be seen beneath part of the mid Black Sea high, and that the original oblique outer marginal detachment on which the ocean opened is beginning to be inverted as a subduction zone with contractional deformation of the volcano-sedimentary pile in the outer marginal trough. Deep crustal structure is an important element in hydrocarbon maturation. The quantity of radiogenic heat generated by the upper continental crust depends on its thickness, and is therefore a direct function of the amount of stretching and the rift architecture. Other terrains provide generally much less heat into the base of the sedimentary system. We present maps of heat flow and radiogenic heat production which could provide direct and important inputs into petroleum systems models.