Unusual Ca-Rich Formation-Waters from Devonian Aquifers in Western Canada: Possible Relict Seawater?
In this talk we present new data obtained from two producing wells in the Alberta Basin, plus new data collected from a potash mine-shaft in the Williston Basin, combined with unpublished data obtained from a Drill-Stem-Test in the Williston Basin, and compare these data to previously published (re-sampled and further analyzed) data from potash mine-shafts in the Williston Basin. These six samples are from aquifers of roughly similar stratigraphic age (Devonian; when seawater was reportedly of the Ca-Cl2 type) and are widespread across the Alberta-Williston Basins.
Results from across the basin are remarkably similar: calcium-chloride type brines (TDS > 425 g/L); calcium > 120 g/L; chloride >270 g/L; magnesium > 11 g/L; potassium >6 g/L; sodium < 10 g/L; bromine >6 g/L; and sulfate <100 mg/L. Using these data with stable isotopic measurements and analyses of the regional hydrogeology we conclude that each of these samples is relatively-unaltered evaporated Devonian seawater. If we assume that bromine was relatively conservative in seawater through time, we can calculate an evaporation factor, and then back-calculate the composition of the original Devonian seawater.
This talk will add new data to the discussion of secular changes in seawater chemistry as well as provide insights into a number of other paleo-hydrogeological processes in the Alberta and Williston basins.