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Tectonic control on the distribution of depositional environments in the back arc syn-rift setting of eastern part of Drava Depression in Croatian part of Pannonian Basin: implications on exploration and regional assessment of CO2 storage resources

Syn-rift rock infill and tectonic control on depositional environment distribution in the eastern part of Drava Depression were reconstructed based on 3D seismic data interpretation, integration of exploration wells’ data and making use of tectonostratigraphic approach to sequence stratigraphy. Rift phase in the study area is characterized by the formation of half-graben, graben, sag, and supradetachment basins as well as by synthetic transfer zone and structural highs. The syn-rift rock infill was subdivided into sequences of different order that correspond to rift stages characterized by different rates of extension or to local rift migration. Unlike the ones formed in the early rift stage, the rift climax structures were predefined by tectonic transport along extensional detachments, which represent the principal syn-rift normal fault system in study area. Complex structural evolution controlled various depositional processes. Early rift stage was characterized by continental deposition in alluvial fan, fan delta and lacustrine environments. Rift climax stage corresponded with marine deposition in shallow water, fan delta, subaquatic fault aprons and deep marine environments, followed by intense volcanic activity. Syn-rift tectonics exerted primary control on the sedimentary infill. Synthetic transfer zone, slopes of subsided hanging wall fault blocks and fault scarp slopes presented main sediment transfer zones for deposition in form of alluvial fans, fan-deltas and subaquatic fault aprons. Main depocenters can be structurally correlated with synforms in extensional detachments. Research structured in this way could be effective for regional assessment of prospective reservoirs in syn-rift rocks within the continental (passive) rift system. Due to the complexity of the sediment infill, as well as the structure of the syn-rift basin, various well data, reliable seismic data and understanding of tectonic control on syn-rift sedimentary characteristic are needed. Interpretation of rift tectonostratigraphic boundaries that can be correlated with the activity of normal faults, mapping of seismic facies and lithofacies as well as analysis of paleostructural relationships enables the mapping of depositional environments and locations of prospective sites for HC accumulation and CO2 storage. Correlation with petrophysical properties together with spatial distribution of CO2 density in reservoir conditions enables to model CO2 storage capacity potential.

tectonostratigraphic interpretation, syn-rift, seismic data, Drava depression, geological storage of carbon dioxide

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