14 The Mid Black Sea High comprises two en-echelon basement ridges, the 15 Archangelsky and Andrusov Ridges that separate the western and eastern Black Sea 16 basins. The sediment coverage above these ridges has extensive seismic reflection 17 coverage, but the crustal structure beneath is poorly known. We present results from 18 a densely sampled wide-angle seismic profile, coincident with a pre-existing seismic 19 reflection profile, which elucidates the crustal structure. We show that the

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... ement 20 ridges are covered by c. 1-2 km of pre-rift sedimentary rocks. The Archangelsky 21 Ridge has higher pre-rift sedimentary velocities and higher velocities at the top of 22 basement (~6 km/s). The Andrusov Ridge has lower pre-rift sedimentary velocities 23 and velocities less than 5 km/s at the top of the basement. Both ridges are underlain 24 by c. 20-km thick crust with velocities reaching c. 7.2 km/s at their base, interpreted 25 as thinned continental crust. These high velocities are consistent with the geology of 26 2 the Pontides, which is formed of accreted island arcs, oceanic plateaux and 27 accretionary complexes. The crustal thickness implies crustal thinning factors of ~1.5-28 2. The differences between the ridges reflect different sedimentary and tectonic 29 histories. 30 31