ABSTRACT

The Maastrichtian Whitemud Formation crops out in river cuts and in relatively elevated areas in the plains of Western Canada from about the Edmonton area to the southeasternmost corner of Saskatchewan. Its area of deposition probably covered most of southern Alberta and Saskatchewan. In Alberta it is conformably overlain by the lacustrine Battle Formation which has yielded radiometric age of 65 Ma. East of the Cypress Hills it is overlain disconformably or paraconformably by younger sediments.

The Whitemud strata are composed of sandstones, mudstones and thin interbedded lignite seams. Grain size and facies analyses of these fining upward sequences indicate deposition of sediments in meandering stream environments with extensive lacustrine and swampy conditions.

Petrological differences between the Whitemud strata of the Alberta plains and of Saskatchewan suggest different sources of sediment. In Alberta the sands contain abundant volcanic rock fragments which produced montmorillonite by diagenetic alteration. In Saskatchewan, kaolinite is locally abundant as alteration product of feldspars and metamorphic rock fragments and probably also as detrital clay.

Vegetal remains and coprolites are the only fossils found in the Whitemud Formation. The typical Whitemud microfossil assemblage consists of megaspore genera Azolla, Ghoshispora, Erlansonisporites, by seed cuticle genera Costatheca, Spermatites, Carpotheca, and by palynomorphs of the Wodehouseia spinata Zone. This typical microfossil assemblage, which is consistently found in the Whitemud Formation from the Red Deer River Valley of Alberta to southern Saskatchewan, suggests synchronous deposition of the unit over the whole region.

In southern Saskatchewan, floodplain mudstones of the Whitemud Formation contain abundant vertebrate faecal remains preserved as siderite and Fe-hydroxides. The coprolites can be grouped into nine morphological classes on the basis of style of coiling, shape, size, and surface striations. Their morphology is consistent with deposition of the faeces by terrestrial reptiles. The excellent preservation of the fossils can be attributed to early diagenetic precipitation of FeCO3 in loci where faecal matter was still bacterially fermenting.

Isotopic ઠ13C and ઠ18O ratios of coprolites are consistent with early diagenetic replacement of the faecal matter by siderite, followed by partial oxidation to Fe-hydroxide. 13C ratios of siderite spherulites and concretions from the Whitemud Formation in the Red Deer River Valley and in the Cypress Hills also reflect the influence of biogenic carbon in a reducing, methanic, diagenetic environment.