Dakota Formation In New Mexico

Figure 7.32 Stratigraphic nomenclature for the Maastrichtian and Paleocene of parts of Alberta and southern Saskatchewan.

Figure 7.32 Stratigraphic nomenclature for the Maastrichtian and Paleocene of parts of Alberta and southern Saskatchewan.

North Dakota) lies within the upper part of magnetostratigraphic subchron C29r. The extinction of Aquilapollenites pollen marked the boundary. Lerbekmo (1985) repeated these results in the Frenchman Valley (Cypress Hills area; locality 75) in Saskatchewan.

Nichols et al. (1986) reported a K-T boundary at Morgan Creek in southern Saskatchewan (locality 76; Figure 7.34). Extinction of about 30% of the Maastrichtian palynoflora marks the boundary (Figure 7.35), and an iridium anomaly of 3 ppb, about 100 times the background level, is present at the top of the claystone layer, as is shocked quartz. Nichols et al. noted that differences in the composition of the palynofloras that disappeared at the extinction level in Saskatchewan and New Mexico were evidence that differing floras were simultaneously affected in much the same way by the impact event. They also noted that among the pollen taxa that survived the boundary event were two that are understood to have been produced by thermophilic (warmth-loving) plants; these were pollen of species of palms (Arecipites) and pandanus or screw pine (Pandaniidites). The persistence of this pollen across the boundary was seen as evidence that, if a period of darkness and cold resulted from an impact event as posited by Alvarez et al. (1980), it was of short duration, insufficient to kill off frost-sensitive plants. A fern-spore spike is present above the boundary. As reported by Nichols et al. (1986), the spike is composed of 96.5%

Figure 7.33 Photographs of the K-T boundary in the Scollard Formation at the Red Deer Valley locality in Alberta. Arrows point to the boundary in the distant (a) and close-up (b) views. In "b" a plastic spike has been driven into the boundary claystone layer, which is at the level of the arrow point and the hammer handle.

Figure 7.33 Photographs of the K-T boundary in the Scollard Formation at the Red Deer Valley locality in Alberta. Arrows point to the boundary in the distant (a) and close-up (b) views. In "b" a plastic spike has been driven into the boundary claystone layer, which is at the level of the arrow point and the hammer handle.

Laevigatosporites (but see results of subsequent studies in the vicinity of the Morgan Creek locality by Sweet and Braman 1992, discussed later). Nichols et al. (1986) took the presence of the fern-spore spike to confirm the work of Tschudy et al. (1984), who had concluded that the phenomenon was of continent-wide extent.

Beginning in 1986, a series of papers by Canadian palynologist Arthur Sweet and colleagues were published that described new localities in western Canada. Here we summarize the new data, and their interpretations that differ from those based on the studies from New Mexico, Colorado, Wyoming, Montana, and North Dakota.

146 Other North American records a

Figure 7.34 Photographs of the K-T boundary at the contact between the Frenchman Formation (below) and the Ravenscrag Formation (above) at the Morgan Creek locality in Saskatchewan. Arrows point to the boundary claystone layer seen at a distance (a) and close-up (b) and the basal coal bed of the Ravenscrag is visible a few centimeters above it in "b" (scale in centimeters and inches).

Figure 7.34 Photographs of the K-T boundary at the contact between the Frenchman Formation (below) and the Ravenscrag Formation (above) at the Morgan Creek locality in Saskatchewan. Arrows point to the boundary claystone layer seen at a distance (a) and close-up (b) and the basal coal bed of the Ravenscrag is visible a few centimeters above it in "b" (scale in centimeters and inches).

Jerzykiewicz and Sweet (1986) described the K-T boundary interval in drill cores from Coal Valley in the central Alberta Foothills, at the base of the coal zone in the upper part of the Coalspur Formation (locality 66; Figure 7.36). They documented a shift in palynofloras from a diverse Maastrichtian one, in which angiosperm pollen is prominent, to lower diversity Paleocene ones, dominated by gymnos-perm pollen and fern spores. They described a sequence of floral changes from latest Maastrichtian to earliest Paleocene time in Alberta and contrasted it with that documented by Tschudy et al. (1984) in New Mexico, Colorado, and Montana. In both Canada and the United States, a diverse latest Cretaceous angiosperm wcjccto

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