Columnar jointing in Paleoproterozoic carbon-bearing rocks (Onega Basin, NW Russia): implications for carbon migration in sedimentary rocks

Columnar jointing occurs commonly in igneous rocks and rarely in sedimentary rocks. We report the results of combined field and petrological studies, Raman spectroscopy and column geometry analysis of columnar jointing in Paleoproterozoic carbon-bearing rocks, Eastern Fennoscandian Shield, NW Russia. The columnar rocks occur near the contact with the saucer-shaped dolerite sill emplaced in the unconsolidated organic rich sediments. Columnar jointing aureole (1 to 7 m) and column architecture strongly depends on the contact morphology. Columnar jointing is caused by the contraction of organic-rich sediments due to generation and further release of gas and oil rich fluid. The results of integrated studies indicate that fluidization driving the jointing is associated with not only the dehydration, but also with the mobilization of gas and oil rich fluid due to the thermal maturation of organic matter. Columnar jointing is associated with intensive fluid circulation and devolatilization evidenced by the numerous veins, globules, and vugs filled with migrated carbonaceous matter and secondary minerals in the columnar rocks as well as high vesicularity of dolerites near the contact. The redistribution of the mobile elements (K, Rb, LREE) along with the significant enrichment of S near the contact also indicates the intensive fluid circulation. The study contributes to understanding of mechanism of columnar jointing in sedimentary rocks and formation the fracture networks in organic-rich sediments.