Volume 10, numéro 4, december 1983

EN :

Paleomagnetism is a useful tool for geologists. It gives simple data on remanent and induced magnetizations in rocks, which may help to distinguish or characterize them, determine their structural relationships with respect to other units, unravel their geological histories and infer their latitude of formation. Magnetic parameters separately, together or combined with density may also be used to identify and map various primary and secondary geological processes. In view of the utility of paleomagnetic methods, geologists and paleomagnetists should become routinely involved in joint projects.

EN :

The redox state of iron, (Fe,2/Fe,), in rocks is a useful Indicator of hydrothermal alteration. In general, rocks are resistant to shifts in (Fe,2/Fe,) unless large volumes of fluid or high concentrations of exotic reactants such as H2 or O2 are present. The earth's surface in equilibrium with the atmosphere is an oxidizing environment; surface waters carry in solution O2 plus SO42. Laboratory experiments conducted at high temperatures reveal that water in the presence of ferrous minerals tends to dissociate and yield free hydrogen. At depths exceeding a few kilometres, waters are hot and reducing with H2 H20 = 1 30 to 1/60. In a hydrothermal convection cell, rocks along the descending limbs will be oxidized whereas rocks along the ascending limbs will be reduced by the circulating water.

EN :

Both J. W. Dawson and G. M. Dawson, father and son, wrote about glaciation in Canada in the late nineteenth century, but their philosophies and contributions often are misidentified. J. W. Dawson was a proponent of the deposition of glacial drift from floating ice, but believed that ice caps covered some highland areas. Hisson, G. M. Dawson, was indoctrinated with the floating ice theory, but his field studies in western Canada convinced him that glaciers deposited most of the drift there. Both the Cordilleran and Laurentide Ice Sheets were named by him. He reserved final judgement concerning the origin of the drift on the prairies because it contained foraminifera that he correctly identified as Cretaceous, but which an English micropaleontologist, considered to be an expert on Cretaceous forms, misjudged to be recent forms.