Abstract

In the Paleozoic Elk Point Basin, Saskatchewan, Canada, hematite in evaporite rocks of the Middle Devonian Prairie Formation records two magnetizations that are very different from those expected when the evaporites were originally deposited. The first (X magnetization) corresponds to Cretaceous or Cenozoic paleofield directions and contains both normal and reversed polarities. The second (Y magnetization) appears to be a composite of Cretaceous–Cenozoic and late Paleozoic (Kiaman) reversed polarity directions. The X magnetization occurs in anomalous ores and is associated with fine-grained hematite occurring predominantly along grain boundaries. The Y magnetization occurs in normal ore and is associated with sylvite that has hematite both along grain boundaries and within sylvite crystals, the latter inferred to be of Kiaman age. K–Ar ages of the host sylvites are also composite, and are consistent with those inferred from paleomagnetic directions. Stable isotopic compositions of fluid inclusions in halite and the associated hematite in the Prairie Formation indicate that the hematite carrying the X magnetization formed at low temperature (about 60 °C) by fluids similar to those currently resident in overlying formations. The hematite carrying the inferred late Paleozoic magnetization was also formed at low temperatures by fluids having δD and δ18O values significantly lower than Paleozoic seawater. Paleomagnetic, petrographic, and isotopic data, and K–Ar ages indicate that evaporites in the Elk Point Basin have been affected by major fluid events that occurred during the late Paleozoic and Cretaceous–Cenozoic. These fluids are most probably related to brines mat have their origins within the basin, which were mobilized by major tectonic events.

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