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Cenomanian

Lower Zvitan Fm.

Lower Zvitan Fm.

Figure 8.10 Stratigraphie nomenclature for the Upper Cretaceous and Paleocene of the Amur region, Russian Far East, showing both older and newer names of units; the abbreviation SFm. stands for subformation, a stratigraphie rank used in Russian nomenclature (modified from Sun et al. 2002 with data from Geological Institute, Russian Academy of Sciences 2003). Reprinted by permission.

Figure 8.10 Stratigraphie nomenclature for the Upper Cretaceous and Paleocene of the Amur region, Russian Far East, showing both older and newer names of units; the abbreviation SFm. stands for subformation, a stratigraphie rank used in Russian nomenclature (modified from Sun et al. 2002 with data from Geological Institute, Russian Academy of Sciences 2003). Reprinted by permission.

areas. Beginning in 2000, Russian and Chinese workers have begun to collaborate and visit each other's sections (Sun 2002, 2004).

The earliest paper in the Russian palynological literature that directly relates to the K-T boundary is by Mtchedlishvili (1964), in which the author discussed the stratigraphic and geographic distribution of Triprojectacites pollen (Aquilapollenites and closely related genera). As discussed, this pollen group constitutes a major component of contemporaneous palynofloras of western North America and eastern Asia.

Mtchedlishvili (1964) stated that the most widely distributed species of Aquilapollenites in Russia is A. quadrilobus Rouse (which coincidentally is the type-species of the genus). This species is said to occur in various parts of Russia in rocks as old as Cenomanian and as young as early Paleocene. In North America, the occurrence of this species is restricted to the interval from the lower Campanian to the uppermost Maastrichtian (Tschudy and Leopold 1970, Nichols 1994) and it disappears at the K-T boundary. These dissimilar ranges are difficult to reconcile, given the wide distribution of the species on both continents. In Russia, Triprojectacites pollen has been recorded from the Santonian onward, which is in general agreement with the records from North America. The pollen group reached its peak of development in the Maastrichtian, and species of Aquilapollenites and related genera are found in rocks of that age in western Siberia, Yakutia, and the Russian Far East, where they are the characteristic forms at all localities. However, Mtchedlishvili also stated that Aquilapollenites is represented by even greater numbers of specimens, although fewer species, in rocks of Maastrichtian to Danian (Paleocene) age in western Siberia, and that triprojectate pollen is found as rare, isolated specimens in rocks as young as middle Eocene or early Oligocene. As the Paleogene records are inconsistent with those from North America, such records raise a fundamental question about stratigraphic occurrence data from Russia: how is it independently known that the age of a given deposit is any specific age? For the Cretaceous in most areas of western North America, the answer is that the ages of stratigraphic units are tied to ammonite biostratigraphy and/or radiometric dates (e.g., Nichols and Sweet 1993, Obradovich 1993). Such data are scarce or lacking in Russia, however, and thus we have become wary of the assignment of Russian terrestrial formations to standard Cretaceous or Paleogene stages.

Mtchedlishvili (1964) noted that Aquilapollenites subtilis Mtchedlishvili, which is common in the Maastrichtian in Russia, also occurs in the lower Paleocene. Mtchedlishvili observed that this species closely resembles, and may be the same as, the North American species A. spinulosus Funkhouser (Figure 8.11). In North America, A. spinulosus is unknown in the Maastrichtian and first occurs in

Figure 8.11 Aquiiapoiienites subtiiis Mtchedlishvili 1961 (Russia) and Aquiiapoiienites spinuiosus Funkhouser 1961 (North America). a - photomicrograph of holotype specimen of A. subtiiis (from Samoilovich et ai. 1961, Fig. 3a), b - drawing of holotype specimen of A. subtiiis (from Samoilovich et ai. 1961, Fig. 3b), c - photomicrograph of paratype specimen of A. subtiiis (from Samoilovich et ai. 1961, Fig. 4), d-f - photomicrographs of specimens of A. subtiiis (Tsagayan Formation, Russia), g-h - photomicrographs of holotype specimen of A. spinuiosus (from Funkhouser 1961, Figs. 4a-4b), i - photomicrograph of A. spinuiosus (Fort Union Formation, North Dakota), j-k - photomicrographs of A spinuiosus (Fort Union Formation, Wyoming). All specimens about 30 micrometers in greatest dimension.

Figure 8.11 Aquiiapoiienites subtiiis Mtchedlishvili 1961 (Russia) and Aquiiapoiienites spinuiosus Funkhouser 1961 (North America). a - photomicrograph of holotype specimen of A. subtiiis (from Samoilovich et ai. 1961, Fig. 3a), b - drawing of holotype specimen of A. subtiiis (from Samoilovich et ai. 1961, Fig. 3b), c - photomicrograph of paratype specimen of A. subtiiis (from Samoilovich et ai. 1961, Fig. 4), d-f - photomicrographs of specimens of A. subtiiis (Tsagayan Formation, Russia), g-h - photomicrographs of holotype specimen of A. spinuiosus (from Funkhouser 1961, Figs. 4a-4b), i - photomicrograph of A. spinuiosus (Fort Union Formation, North Dakota), j-k - photomicrographs of A spinuiosus (Fort Union Formation, Wyoming). All specimens about 30 micrometers in greatest dimension.

the middle Paleocene, after all other species of the genus are extinct. These two species (which may be one in the same) clearly have disparate ranges in eastern Asia and western North America, but migration from Asia to North America during middle Paleocene time could account for the sudden appearance of A. spinulosus, which has no direct ancestors in North America.

All species of Aquilapollenites disappeared from Russia and North America at some time in the Paleocene. Commenting on the cause of the ultimate extinction, Mtchedlishvili (1964) asserted that there were no data that would identify the factors responsible, but that climate change - in particular a drop in temperature during Paleocene time - may have been among the causes. The possible influence of climate change in the extinctions at the end of the Cretaceous was later reiterated by other Russian palynologists and paleobotanists.

A major early publication with specific reference to the palynology and paleobotany of the Russian Far East is that of Bratseva (1969). Her study area was along the Amur River near the city of Blagoveshchensk and the towns of Raichikhinsk and Arkhara, all of which became familiar to one of us (DJN) during field work conducted more than 30 years later, in 2003. Bratseva (1969) discussed how the age of the rich Tsagayanian megafossil flora in the Tsagayan Formation of the Zeya-Bureya Basin (Figure 8.10) was uncertain. The Tsagayanian flora was thought to be Danian (Paleocene) until palynological analyses conducted in the 1950s suggested that it was older and should be assigned either to the ambiguous "Maastrichtian-Danian" or that it might even be as old as Cenomanian. Bratseva set out to resolve the age dispute.

After analyzing 285 samples from 15 outcrops and 18 boreholes from the Aptian-Albian upward, Bratseva (1969) concluded that the Tsagayanian megaflora is Maastrichtian in age, and that deposits of Danian age begin with the Kivda coal-bearing beds in the Zeya-Bureya Basin (Figure 8.10). She noted that the palynofloras of the Tsagayan and Kivda beds differ strongly from one another in floristic composition. Triprojectate pollen predominates in the beds bearing the Tsagayanian megaflora, and most of those species are absent from the Kivda beds. Bratseva specifically compared the Tsagayanian palyno-floral assemblage with those from the Lance and Hell Creek formations in the western United States, stating that the species in common confirmed the Maastrichtian age of the Tsagayanian megafloral assemblage. In contrast, the Kivdian palynoflora is composed largely of pollen referable to the modern families Myricaceae, Juglandaceae, Fagaceae, Hamamelidaceae, and other tripo-rate pollen genera, and is similar to assemblages from the Paleocene deposits of the Tullock, Ludlow, and Cannonball members of the Fort Union Formation in

Stage

Palynozone

Bureya Depression

Danian

W Triatriopollenites plicoides-Comptonia sibirica

Lower Kivdinsa ya

Kl Wodehouseia fimbriata-Ulmipollenites krempii

UpperTsagayansa ya

Maastrichtian

K Orbiculapollis lucidus-Wodehouseia avita

Middle Tsagayansa ya

K Wodehouseia spinata-Aquilapollenites subtilis

Lower Tsagayansa ya

Figure 8.12 Palynostratigraphic zonation of the Maastrichtian and Danian of the Russian Far East (modified from Markevich 1994). Reprinted by permission of Elsevier.

Figure 8.12 Palynostratigraphic zonation of the Maastrichtian and Danian of the Russian Far East (modified from Markevich 1994). Reprinted by permission of Elsevier.

North America. Bratseva reported an abrupt and fundamental change in the composition of the palynofloras between the Tsagayan and Kivda assemblages, in which species of Aquilapollenites and other triprojectate pollen almost entirely disappear. She did not attribute a cause to this change, which was not the subject of her investigation.

From the studies published in the 1960s, we turn to studies of more recent date. From her summary of palynostratigraphic data from Lower Cretaceous through Paleocene nonmarine formations in five regions along the Pacific coast of Russia, Markevich (1994) identified 14 palynostratigraphic zones. Of these, four that are in the Zeya-Bureya Basin pertain to the K-T boundary in the Russian Far East (Figure 8.12). Three are in the "Tsagayanskaya" or Tsagayan Formation (now Tsagayan Group), which is divided into lower, middle, and upper parts or "subformations" (now known as the Udurchukan, Bureya, and Darmakan formations, respectively), and one is in the "Kivdinskaya" or Kivda beds (now upper part of the Darmakan Formation); see Figure 8.10. Markevich's findings are summarized in Figure 8.13.

All similarities and differences considered, data presented by Markevich (1994) demonstrate strong parallels in the palynostratigraphy of the uppermost Cretaceous and lower Paleocene of the Russian Far East and western North America. The dilemma is in determining which aspects of similar patterns are most important in defining the K-T boundary. It appears that the K-T boundary is between either palynozones XI and XII or XII and XIII. In either case, it is evident that the stratigraphic ranges of some palynomorph species that occur in both eastern Asia and western North America are not identical, and it is clear that some pollen species that disappear at the K-T boundary in North America persist into the lower Paleocene in Russia.

Figure 8.10 encapsulates the significant differences in interpretation we have with our Russian colleagues about changes in palynofloras, dinosaur extinction,

Zne

Formation

Age

Taxa ho wn in RFE and NA

Alternative Age

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