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(A) Location map. (B) Tengiz field on an isolated carbonate buildup that grew on a regional pre-Middle Devonian structural high. Dashed line shows position of seismic profile. (C) Seismic profile across the Tengiz buildup that grew more or less uninterrupted from Middle Devonian to early Bashkirian. The total thickness of carbonate is about 1.2 seconds TWT. The deepest borehole to date bottomed in the middle Famennian at 6032 m subsea, more than 2100 m below the top of the reservoir and 700 m below the Famennian SSB.