Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States of America

The role of sulfur in chemical weathering and atmospheric CO2 fluxes: Evidence from major ions, δ13CDIC, and δ34SSO4 in rivers of the Canadian Cordillera

“…To test the sensitivity of the mass balance to the selected value of ␦ 34 S pyr , we performed the calculations using different values of ␦ 34 S pyr (Ϫ10‰ and 0‰ CDT ), which respectively apportion 61 and 81% of the riverine sulfate to sulfide oxidation, 33 and 14% to gypsum dissolution, with 5% coming from atmospheric deposition. Based on the studies of Taylor (2004) and Taylor and Beaudoin, 2000), the fact that no evaporite deposits have been mapped within the watersheds considered by this study (Wheeler and McFeely, 1991), and constraints imposed by carbon isotope systematics (described further on), we conclude that the average isotopic composition of sulfides in the study area must be closer to 0‰ CDT and therefore that 81% of the sulfate in the rivers originates from sulfide weathering. For rivers where the ␦ 34 S SO4 is more negative than 0‰ CDT , it is assumed that all non-atmospheric sulfate in these rivers can be attributed to pyrite oxidation.…”

“…Even though there are no mapped evaporite deposits within this watershed, it is possible that gypsum is present within the Paleozoic passive margin sediments of the Foreland Belt (the headwater regions of the Fraser watershed). Dolomites are common within these sediments (Wheeler and McFeely, 1991). Modern dolomites are known to form in sabkha plains such as around the Persian Gulf.…”

“…This process could be important in the headwater regions of the Fraser and North Thompson Rivers (Foreland Belt) where there are extensive carbonate and dolomite units (Wheeler and McFeely, 1991).…”

“…Evaporite mineral deposition is also common in such environments (see Holland, 1978). The Skeena and Nass watersheds are underlain by bedrock formed in tectonically active volcanic arc environments Wheeler and McFeely, 1991), where sabkha formation (and therefore evaporite deposition) would be highly unlikely.…”

“…Sulfur in chemical weathering and atmospheric CO 2 fluxes McFeely (1991), and . The Canadian Cordillera is a geologically complex region that makes up the northern portion of the western margin of North America.…”