Some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins

Large volumes of carbon dioxide (i.e. up to 90 v/v%) have been encountered in sedimentary basins from various geological settings but their origins re main enigmatic. Evidence from carbon and noble gas isotope analyses indicat e a variety of interpretations for the origins of the CO2 including mantle degassing, metamorphic reactions or magmatic processes. The formation of la rge accumulations of large volumes of CO2 in sedimentary basins is discusse d with specific reference to published data from the Pannonian Basin, Hunga ry; the Cooper-Eromanga Basin, Australia; and the South Viking Graben, Nort h Sea. These basins have occurrences of large volumes (i.e. over 15 v/v%) o f isotopically heavy carbon dioxide (thought to be of inorganic origin), an d, although they differ somewhat in terms of sedimentary fill, all have maj or structural features close to the gas accumulations. The available geoche mical data are currently neither sufficient to confirm the specific origin( s) of the CO2 (e.g. mantle-derived, carbonate metamorphism) nor unscramble CO2 mixed from two or more sources: ongoing studies, especially those invol ving noble gas analyses, should provide fuller answers. (C) 1999 Elsevier S cience Ltd. All rights reserved.