Interpretation of the Silurian Basin of Central and Eastern Europe as a Pro-Foreland Flexural Basin:Implications for Shale Gas Exploration

摘要

The present day collage of various Silurian basin fragments in Central and Eastern Europe(CEE)is the result of several orogenic and rifting/drifting episodes.The proper paleogeographic reconstruction of a single,very large Silurian foredeep basin in the context of regional geology has a major impact on the ongoing unconventional shale gas exploration efforts in the region,including Poland,Ukraine,Romania and Moldova. The distal segments of a large Silurian foreland basin associated with the Caledonian collisional orogene,along the perimeter of the East European Craton,can be reasonably followed along strike from NW to SE,from Poland all the way to the Ukrainian Black Sea coast.The foredeep basin sequence onlaps to the NE the various pre-Silurian and crystalline basement units.The Silurian basin of the CEE is interpreted here as a pro-foreland basin,with short-lived(less than 15 m.y.)and extremely rapid(locally more than 1,500 m per m.y.!),accelerating subsidence histories recording a portion of the orogenic history of the broader Caledonian orogeny.Besides the typical subsidence curves and the very prominent onlap of successive Silurian lithostratigraphic units onto the craton,the flexural origin is also supported by the general lack of normal-faulting within the basin,contradicting some interpretations suggesting deposition on the extensional continental margin of the Rheic Ocean.The map-view distribution of the lithofacies within the basin,such as clastic turbidites in the southwestern perimeter of the basin,deepwater shales in the center and neritic carbonates on the northeastern foreland margin,is also consistent with the flexural basin interpretation.