palynological assemblages, not on the extinction event. Sweet and Braman documented occurrences and relative abundances of some individual species and several broader groups of palynomorphs (pollen, spores, and algal cysts) through the stratigraphic intervals at all 12 of their localities. They proposed a sweeping revision of the interpretation of the K-T boundary event and its effects on plants. Their new scenario centered on emplacement of the boundary clay-stone layer, which they interpreted to have preceded the extinction and to have consisted of more than one depositional event. From this they concluded that multiple impacts might have occurred at or around the K-T boundary.

In their 1992 paper (and subsequently), Sweet and Braman contended that palynological extinctions were not abrupt but gradual or even stepwise in pattern, approaching the K-T boundary. They stated that within the last tens of centimeters below the K-T boundary, individual samples usually yield fewer specimens and fewer species of pollen typical of the late Maastrichtian than do underlying samples. Despite this, Sweet and Braman noted that if species records from several Canadian localities are summed, most of these late Maastrichtian species are found to range up to or into the boundary claystone. That observation would appear to reinforce the concept of a significant extinction at the K-T boundary. That observation is the basis for Table 7.4.

In the late 1990s, Sweet and his colleagues were involved in a major endeavor to gather lithostratigraphic, palynostratigraphic, magnetostratigraphic, and geo-chemical data relevant to events at the end of the Maastrichtian and beginning of the Paleocene. This was the Canadian Continental Drilling Program Cretaceous-Tertiary (K-T) Boundary Project. In this effort, three long cores were drilled in southern Canada: the Elkwater core in southeastern Alberta, the Wood Mountain core in south-central Saskatchewan, and the Turtle Mountain core in southwestern Manitoba. Sweet and colleagues presented previous research on these cores and some adjacent outcrop localities in a series of nine papers in a special issue of the Canadian Journal of Earth Sciences (CJES). Three of them put forward new data concerning the plant fossil record; they are reviewed here.

In one of the three pertinent papers in the CJES special issue, Braman and Sweet (1999) outlined the palynostratigraphy of the three cores. They described nine biozones or subzones from the lower Maastrichtian to the middle Paleocene, which they recognized in all three cores. The definitions of most of these palynostratigraphic biozones or subzones were compiled from previously published work, but one zone and two subzones were based on new data from the cores. The position of the K-T boundary - arguably the most significant palynostratigraphic datum in North America - is obscure in Braman and Sweet's stratigraphic scheme. It lies without emphasis between two subzones within a previously described palynostratigraphic zone (Figure 7.37).

Table 7.4 Palynomorph taxa whose extinctions mark the K-T boundary in western Canada

Aquilapollenites amicus Srivastava 1968

Aquilapollenites augustus Srivastava 1969

Aquilapollenites attenuatus Funkhouser 1961

Aquilapollenites collaris (Tschudy and Leopold 1971) Nichols 1994

Aquilapollenites conatus Norton 1965

Aquilapollenites oblatus Srivastava 1968

Aquilapollenites quadricretaeus Chlonova 1961

Aquilapollenites quadrilobus Rouse 1957

Aquilapollenites reductus Norton 1965

Aquilapollenites sentus Srivastava 1969

Aquilapollenites vulsus Sweet 1986

Bratzevaea amurensis (Bratzeva) Takahashi 1982

Cranwellia rumseyensis Srivastava 1967

Echiperiporites sp.

Ephedripites multipartitus (Chlonova 1961) Yu, Guo and Mao 1981

Equisetosporites lajwantis Srivastava 1968

Gabonisporis cristata (Stanley 1965) Sweet 1986

Leptopecopites pocockii (Srivastava 1967) Srivastava 1978

Liliacidites complexus (Stanley 1965) Leffingwell 1971

Marsypiletes cretacea Robertson 1973 emend. Robertson and Elsik 1978

Myrtipites scabratus Norton in Norton and Hall 1969

Orbiculapollis lucidus Chlonova 1961

Proteacidites globisporus Samoilovich 1961

Racemonocolpitesformosus Sweet 1986

Retibrevitricolporites beccus Sweet 1986

Senipites drumhellerensis Srivastava 1969

Siberiapollis occulata (Samoilovich 1961) Tschudy 1971

Striatellipollis radiata Sweet 1986

Striatellipollis striatellus (Mtchedlishvili in Samoilovitch et al. 1961) Krutzsch 1969 Tricolpites microreticulatus Belsky, Boltenhagen, and Potonie 1965 Wodehouseia octospina Wiggins 1976 Wodehouseia quadrispina Wiggins 1976

In a second paper in the CJES special issue, Sweet et al. (1999) summarized data on relative abundances of pollen and spores from boundary localities in western Canada. They reached new conclusions about post-boundary fern-spore spikes, survival floras, and recovery floras. Adhering to views first expressed by Sweet et al. (1990), Sweet et al. (1999) concluded that the shifts in composition of pre-boundary, boundary, and post-boundary palynofloras and multi-layered boundary claystone

Stages/ Ages

Palynological Onal Scheme

Alberta/Sasatche wan /Manitoba



Aquilapollenites spinulosus


0 0

Post a comment