Multiple magnetizations in Ordovician–Devonian carbonates in the Williston Basin (Manitoba, Canada)

Abstract

AbstractPalaeomagnetic and rock magnetic data collected from the Upper Ordovician Red River, Silurian Interlake and Devonian Winnipegosis, Souris River and Birdbear carbonates in one well from southwestern Manitoba (Canada) reveal a complex magnetization history for the north-eastern Williston Basin. Rock magnetic analysis (thermal demagnetization, anhysteretic remanent magnetization (ARM)/saturation isothermal remanent magnetization (SIRM), S-ratios, partial ARM (pARM), SIRM crossover curves and points and coercivity) show three magnetic carriers for different magnetizations seen in this well. An Early–Mid-Jurassic remagnetization observed in the lower Red River and Souris River formations is carried by single-domain to pseudo-single-domain (SD–PSD) magnetite and was probably produced by basement fluids circulating along fractures and faults created by the Hartney impact/volcanic structure and/or tectonic movements along the Superior Boundary Zone. In the Winnipegosis Formation a possible primary depositional or early depositional magnetization (Devonian age) is carried by PSD pyrrhotite. In the Birdbear Formation two different magnetizations of uncertain age are present: one carried in hematite in the upper strata, possibly originating from the younger Amaranth Formation, and magnetite dominates in the lower strata. The upper Red River and Interlake formations contain both magnetite and pyrrhotite; however, the weaker palaeomagnetic data reveal little in terms of a magnetization age.