Polle Maastrichtian

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Lower Tsagayan (Udurchuan)

early Maastrichtian

Aquilapollenites conatus

Aquilapollenites quadrilobus

"Proteacidites" (Tschudypollis) thalmannii

Wodehouseia spinata

late Maastrichtian

Figure 8.13 Data on palynostratigraphic zones in the Zeya-Bureya Basin from Markevich (1994). Both the older and newer stratigraphic nomenclature (Figure 8.10) are shown. Palynomorph taxa listed are those that are known in both the Russian Far East (RFE) and North America (NA). Ages shown in the third column are from Markevich (1994); alternative ages shown in the fifth column are our interpretations based on occurrences of taxa in common between the RFE and NA. The K-T boundary may lie between either zones XI and XII or zones XII and XIII.

Figure 8.13 Data on palynostratigraphic zones in the Zeya-Bureya Basin from Markevich (1994). Both the older and newer stratigraphic nomenclature (Figure 8.10) are shown. Palynomorph taxa listed are those that are known in both the Russian Far East (RFE) and North America (NA). Ages shown in the third column are from Markevich (1994); alternative ages shown in the fifth column are our interpretations based on occurrences of taxa in common between the RFE and NA. The K-T boundary may lie between either zones XI and XII or zones XII and XIII.

and the position of the K-T boundary. In this stratigraphic chart, the Upper Cretaceous-Paleocene and Maastrichtian-Danian (K-T) boundary is within the Tsagayan Formation or Group, at the contact between the Bureya and Darmakan formations (= Middle Tsagayan and Upper Tsagayan subformations). That position agrees with the zonation published by Markevich (1994) because it is at the contact between palynozones XII and XIII, as discussed above. The chart also shows, however, that the "main dinosaur horizon'' is in the Udurchukan Formation (= Lower Tsagayan Subformation), with its top at a middle Maastrichtian-upper Maastrichtian boundary. Internationally, the Maastrichtian Stage is not formally subdivided, although Odin (1996) recommended dividing the Maastrichtian into two parts. In North America, the lower and upper parts of the Maastrichtian are informally recognized by many authors, but a middle Maastrichtian is not recognized. The apparent disappearance of the dinosaur fauna at the top of the "middle Maastrichtian" is a significant discrepancy and requires further investigation. If the position of the Maastrichtian-Danian boundary adopted by Russian stratigraphers (Figure 8.10) is to be accepted, it must be verified by the presence of iridium and shocked minerals, and supported by magnetostratigraphy and/or radiometric dating. None of these categories of supporting data are currently available in these sections.

Markevich et al. (2000) summarized evidence for vegetational change and dinosaur extinction in the Amur region and other localities in the Russian Far East, citing an abrupt change in climate and vegetation at the putative middle Maastrichtian-upper Maastrichtian boundary that resulted in the extinction of the dinosaurs. They presented palynological data to support the contention that climate change (cooling and increased humidity) occurred by the end of the mid Maastrichtian, as indicated by decreases in pollen of temperate plants and "unica" type pollen and increase in abundance of the Taxodiaceae. Markevich et al. concluded that dinosaur extinction was a global event that took place an estimated 2-3 million years before the end of the Cretaceous, in conjunction with the climatically induced change in vegetation. In support, they cited Nichols (1990), a paper mentioning that in the Lance and Hell Creek formations of Wyoming and Montana, dinosaur bones disappear 1-2 m below the K-T boundary. Presumably, Markevich et al. (2000) equated this small stratigraphic distance with their 2-3 million-year estimate, an equivalence that was neither implied by Nichols nor is supported by the data discussed here in Chapters 6 and 7. In fact, the 1-2 m interval represents only a tiny portion of the polarity subchron C29r and equates to between 10 000 and 100 000 years at the most. Markevich et al. reported that palynological assemblages similar to those in the Amur region are also present in the Chukotka region of Siberia and on Sakhalin Island, and that all of them are "middle Maastrichtian'' in age.

Markevich and Bugdaeva (2001) reiterated the assertion that both the vegeta-tional change and dinosaur extinction in the Russian Far East took place at the locally defined middle Maastrichtian-upper Maastrichtian boundary. They asserted that the tripartite division of the Maastrichtian Stage is based on paleontological data from marine invertebrates (inoceramids) and terrestrial vertebrates (dinosaurs), as well as from paleobotany (Golovneva 1994a, b) and palynology (Markevich et al. 1994).

A palynostratigraphic summary for Kundur (locality 97) in the Amur region published by Markevich and Bugdaeva (2001) and Bugdaeva (2001) (Figure 8.14)

System

Taxa

Stage

Aquilapollenites subtilis Kuprianipollis elegans K. santaloides Fothergilla gracilis Hamameliidaceae Fagaceae Yuglanspollenites Cranwellia striata C. aspera C.sp.

Aquilapollenites conatus Orbiculapollis globosus O. lucidus

Proteacidites bellus P. thalmanii Wodehouseia aspera Aquilapollenites insignis A. trilatus A. striatus A. amygdaloides Parviprojectus dolium Mancicorpus anchoriforme Wodehouseia gracile Liliacidites variegatus Fibulapollis mirificus Aquilapollenites asper A. quadrilobus A. cruciformis A. amurensis Mancicorpus tenue Wodehousia spinata Triatriopollenites radiatostriatus Tricolpites gracilis Erdmanipollenites albertensis Ulmipollenites krempii U. tricostatus U. planaeriformis Triatriopollenites aroboratus Triatriopollenites plectosus Quercites sparsus Myricapollenites imperfectus Comptonia sibirica Tricolpites aff. variegatus T. discus T. coryloides

System

Stage

Maastrichtian

-Rare f ossil pollen

-Ab undant fossil pollen shows a strong change in the composition of the angiosperm pollen assemblage occurring at their ' ' middle Maastrichtian-upper Maastrichtian boundary.'' In the list of species, we call particular attention to Aquilapollenites conatus, A. quad-rilobus, Cranwellia striata (= C. rumseyensis), Orbiculapollis lucidus, Proteacidites thal-mannii (= Tschudypollis thalmannii), and Wodehouseia spinata. All are species of the Wodehouseia spinata Assemblage Zone of the United States and Canada, which is late (not'' middle'') Maastrichtian in age (Nichols and Sweet 1993, Nichols 1994). The abrupt disappearance of these species (O. lucidus excepted) along with 16 other Russian species (55% of those listed) creates a pattern like that at the palynological K-T boundary in western North America. We would argue that those palynological extinctions at the Kundur locality of Bugdaeva (2001) and Markevich and Bugdaeva (2001) mark, not the middle Maastrichtian-upper Maastrichtian boundary, but the upper Maastrichtian-Paleocene (K-T) boundary.

A palynostratigraphic summary for Sinegorsk (locality 99) on Sakhalin presented by Markevich and Bugdaeva (2001) and reprinted in Bugdaeva (2001) shows much the same pattern (Figure 8.15). The angiosperm pollen assemblage there is similar to that at Kundur, although not identical in composition. At Sinegorsk, three ofthe same species named above disappear at the same level as 44% of the individual species listed. Here again, we would reason that the profound palynological change marks the K-T boundary, not the middle Maastrichtian-upper Maastrichtian boundary.

A palynostratigraphic summary for localities such as Beringovskoe (locality 98) in the Koryak Upland prepared by Markevich and Bugdaeva (2001) and Bugdaeva (2001) lists the same angiosperm taxa as for Kundur and Sinegorsk, but the pattern of occurrences is less clear (Figure 8.16). Only two of the species named above, Aquilapollenites quadrilobus and Proteacidites thalmannii, disappear at the middle Maastrichtian-upper Maastrichtian boundary; the other four either do not extend to that stratigraphic level or they transcend it. The extinction percentage at that horizon drops to 23%. Still, the change in assemblages may mark the K-T boundary in northeastern Siberia, but it is less clear than in the other regions of the Russian Far East.

The most complete exposition of the flora and dinosaurs at and near the K-T boundary in the Amur region is contained in a book edited by Bugdaeva (2001). In addition to the three range charts reproduced here as Figures 8.14 through 8.16, the book thoroughly documents the stratigraphy, flora, and fauna of the Zeya-Bureya Basin. A stratigraphic chart in the Bugdaeva (2001) book shows the palynozones of Markevich (1994) discussed here previously (Figure 8.12 and Figure 8.13). A difference is that zone XI, which Markevich had earlier maintained was in the lower Maastrichtian, is shown as both lower and middle

System

Taxa

Stage

Aquilapollenites subtilis Kuprianipollis elegans K. santaloides Fothergilla gracilis Hamameliidaceae Fagaceae Yuglanspollenites Cranwellia striata C. aspera C.sp.

Aquilapollenites conatus Orbiculapollis globosus O. lucidus

Proteacidites bellus P. thalmanii Wodehouseia aspera Aquilapollenites insignis A. trilatus A. striatus A. amygdaloides Parviprojectus dolium Mancicorpus anchoriforme Wodehouseia gracile Liliacidites variegatus Fibulapollis mirificus Aquilapollenites asper A. quadrilobus A. cruciformis A. amurensis Mancicorpus tenue Wodehousia spinata Triatriopollenites radiatostriatus Tricolpites gracilis Erdmanipollenites albertensis Ulmipollenites krempii U. tricostatus U. planaeriformis Triatriopollenites aroboratus Triatriopollenites plectosus Quercites sparsus Myricapollenites imperfectus Comptonia sibirica Tricolpites aff. variegatus T. discus T. coryloides

System

-Rare f ossil pollen

-Ab undant fossil pollen

Taxa

System

Stage

Aquiiapoiienites subtilis Kuprianipollis eiegans K. santaioides Fothergiiia graciiis Hamameiiidaceae Fagaceae Yugianspoiienites Cranweiiia striata C. aspera C.sp.

Aquiiapoiienites conatus Orbicuiapoiiis giobosus O. iucidus

Proteacidites beiius P. thaimanii Wodehouseia aspera Aquiiapoiienites insignis A. triiatus A. striatus A. amygdaioides Parviprojectus doiium Mancicorpus anchoriforme Wodehouseia graciie Liiiacidites variegatus Fibuiapoiiis mirificus Aquiiapoiienites asper A. quadriiobus A. cruciformis A. amurensis Mancicorpus tenue Wodehousia spinata Triatriopoiienites radiatostriatus Tricoipites graciiis Erdmanipoiienites aibertensis Uimipoiienites krempii U. tricostatus U. pianaeriformis Triatriopoiienites aroboratus Triatriopoiienites piectosus Quercites sparsus Myricapoiienites imperfectus Comptonia sibirica Tricoipites aff. variegatus T. discus T. coryioides

System

-Rare f ossil pollen I-Ab undant fossil pollen

Stratigraphic interval

Localities

Palynomorph assemblages

Danian (ones KM)/

Tsagayan Fm. stratotype at Belaya Gora

Pollen of the Betulaceae , Myr icaceae , and Juglandaceae dominates; Fagaceae , Salicaceae , and Ulmaceae pollen present; Aquilapollenites spinulosus and A. subtilis present in lower part of section , b ut Aquilapollenites and Wodehouseia disappear in upper part; Caryapollenites present

Upper Maastrichtian (one IC)

Mutnaya and Udurchuan River area and Belaya Gora

New species of Aquilapollenites appear,, b ut Aquilapollenites decreases in abundance; species of Triatriopollenites are characteristic; Orbiculapollis and Wodehouseia increase in abundance; Anacolosidites and Kurtzipites are present

Middle Maastrichtian (Zne I)

Blagoveshchensk area and stratotype of Tsagayan Fm., Russia , and Yuliangzi Fm. , China

Angiosperm pollen dominates all assemblages; gymnosperms also abundant; fern and moss spores diverse; ten species of Aquilapollenites present; Orbiculapollis lucidus, "Proteacidites" (Tschudypollis) and Wodehouseia spinata present

Lower Maastrichtian (Zne I)

Kundur area, 2 ya-Bureya Basin

Fern spores and gymnosperm pollen of Taxodiaceae and Gnetaceae common; angiosperm pollen (Triatriopollenites, Tricolpites, Tricoloporopollenites, and Triporopollenites)', Aquilapollenites and other tripropctates nominally present

Figure 8.17 A summary of palynostratigraphic data from Bugdaeva (2001). Note that Zone XI encompasses both the lower and middle Maastrichtian, and that the Danian, which is considered to be the entire Paleocene, includes Zone XIII in its lower part and Zone XIV in its upper part. Caryapollenites, which is reported from the lower Danian in the Zeya-Bureya Basin, is indicative of the upper Paleocene in North America.

Figure 8.17 A summary of palynostratigraphic data from Bugdaeva (2001). Note that Zone XI encompasses both the lower and middle Maastrichtian, and that the Danian, which is considered to be the entire Paleocene, includes Zone XIII in its lower part and Zone XIV in its upper part. Caryapollenites, which is reported from the lower Danian in the Zeya-Bureya Basin, is indicative of the upper Paleocene in North America.

Maastrichtian; zone XII is still shown as upper Maastrichtian. Palynologic data from Bugdaeva (2001) are summarized here in Figure 8.17.

In a discussion of the Maastrichtian Stage and correlation of plant-bearing deposits of the Russian Far East in Bugdaeva (2001), the palynofloras of the Lower Tsagayan Subformation (= Udurchukan Formation) are assigned to paly-nozone XI (Wodehouseia spinata-Aquilapollenites subtilis palynozone). Discoveries of dinosaur bones in the Lower Tsagayan and in the Yuliangzi Formation across the Amur River in China are reported and the dinosaur-bearing beds of the Amur region are palynologically correlated with their stratigraphic equivalent, the Yuliangzi Formation in Heilongjiang Province. A sharp reduction in floral diversity associated with the disappearance of the dinosaurs in the Amur and Heilongjiang regions is reported at the middle-upper Maastrichtian boundary. However, we would equate both events - floral change and dinosaur

Figure 8.18 View of the highwall at the Arkhara-Boguchan coal mine showing the upper part of the Middle Tsagayan and lower part of the Upper Tsagayan subformations.

extinction - with the Maastrichtian-Paleocene (K-T) boundary, as is the case in North America.

We have some data of our own to contribute to the debate about the ages of the lower, middle, and upper parts of the Tsagayan Group. One of us (DJN) collected palynological samples at the localities discussed by Markevich and Bugdaeva in Bugdaeva (2001). The localities include outcrops near the town of Kundur and coal mines near the towns of Raichikhinsk and Arkhara. Samples from the Lower Tsagayan Subformation (= Udurchukan Formation) near the town of Kundur yielded palynomorphs indicative of Maastrichtian age, which is partly consistent with the rather broad age range for the Tsagayan Group shown in Figure 8.10. As anticipated, samples from the Kivda beds of the Upper Tsagayan Subformation (= upper, coal-bearing part of the Darmakan Formation) in coal mines near Raichikhinsk yielded Paleocene palynomorphs. Our samples from the Arkhara-Boguchan coal mine (Figure 8.18) were the most interesting. They were from the upper part of the Middle Tsagayan and the overlying lower part of the Upper Tsagayan subformations (= Bureya and Darmakan formations of Figure 8.10) and were said by Russian geologists possibly to span the K-T boundary. However, sixteen samples collected through 24 m of exposure in the highwall of the mine yielded only Paleocene palynomorphs (Figure 8.19), including species of Momipites well known from numerous localities in western North America (Nichols 2003). Clearly, this

Mycelium Quatermary Lake Sediments

Figure 8.19 Fossil pollen of Paleocene age from the upper part of the Bureya Formation and lower part of the Darmakan Formation at the Arkhara-Boguchan coal mine; identifications based on closely similar or identical North American species. 1-4 - Momipites tenuipolus, 5 - Momipites sp. cf. M. wyomingensis, 6 - Paraalnipollenites confusus, 7 - Triporopollenites infrequens, 8 - ''Paliurus'' triplicatus, 9-11 - Aquilapollenites spinulosus (= A. subtilis).

Figure 8.19 Fossil pollen of Paleocene age from the upper part of the Bureya Formation and lower part of the Darmakan Formation at the Arkhara-Boguchan coal mine; identifications based on closely similar or identical North American species. 1-4 - Momipites tenuipolus, 5 - Momipites sp. cf. M. wyomingensis, 6 - Paraalnipollenites confusus, 7 - Triporopollenites infrequens, 8 - ''Paliurus'' triplicatus, 9-11 - Aquilapollenites spinulosus (= A. subtilis).

section does not include the K-T boundary. These results suggest that the K-T boundary lies below the sampled interval, near the boundary between the '' middle'' and upper Maastrichtian of Figure 8.10. They are also in general agreement with those of Markevich et al. (2004) and in complete agreement with the current interpretation of Valentina Markevich (personal communication, 2007).

There might appear to be a remaining obstacle with our reinterpreting the age of the Udurchukan Formation and the' ' main dinosaur horizon'' (Figure 8.10) in the Amur region as late Maastrichtian: the age of the dinosaur fauna associated with the palynomorph assemblages, but there is evidence in support of our opinion. Godefroit et al. (2003) concluded that a dinosaur from the lower part of the Tsagayan Formation (= Udurchukan Formation) at the Kundur locality was either '' middle'' Maastrichtian, in accordance with the Russian interpretations discussed previously, or - more likely - was late Maastrichtian in age. The dinosaur was found in association with palynomorphs that Godefroit et al. recognized as belonging to zone XI of Markevich (1994), the Wodehouseia spinata-Aquilapollenites subtilis palynozone. Van Itterbeeck et al. (2005) reached the same conclusion about the palynological age of the Udurchukan Formation being late Maastrichtian. Additionally, from a locality just across the Amur River in China, Godefroit et al. (2001) had previously determined the age of a dinosaur from the Yuliangzi Formation in Heilongjiang Province. The Yuliangzi Formation is the stratigraphic equivalent of the Udurchukan Formation and it contains the "main dinosaur horizon'' in that part of China (see Figure 8.9). Godefroit et al. (2001) identified the palynological assemblage from the Yuliangzi Formation as the Wodehouseia spinata-Aquilapollenites subtilis palynozone, and they equated it with assemblages from formations of "Lancian" (late Maastrichtian) age in North America. Based on our knowledge of the North American palynofloras of late Maastrichtian age, we are inclined to concur with Godefroit et al.'s (2001, 2003) interpretations and that of Van Itterbeeck et al. (2005).

Our colleagues Valentina Markevich and Eugenia Bugdaeva continue to assert (personal communication, 2007) that a palynozone of latest Maastrichtian age lies above the stratigraphic level from which Godefroit et al. (2003) collected the dinosaur. According to Markevich, this palynozone is characterized by distinctive species of Aquilapollenites and related triprojectate pollen that are not found in association with the dinosaurs of the Udurchukan Formation. For us, this debate remains unresolved because the key pollen species are endemic to the Russian Far East and unknown in western North America, and the strata of the overlying Bureya Formation have not yielded stratigraphically useful plant megafossils. Furthermore, it must be recognized that independent age indicators (paleontologic, geochronologic, or magnetostratigraphic) have yet to be found in the Maastrichtian strata of the Russian Far East. At best, the resolution of the K-T boundary in this region is at the stage level (see Section 2.1).

The Cretaceous and Paleocene megafloral record from the Russian Far East is extensive, and numerous Russian paleobotanists have expressed strong opinions concerning the nature of megafloral response to the K-T boundary. They are most recently summarized by Golovneva (1995), Herman and Spicer (1995, 1997), Krassilov (2003), and Akhmetiev (2004). All of these authors have argued against a catastrophic megafloral extinction and have posited climate or environmental change as causal factors. It is our opinion that these conclusions are somewhat premature because the K-T boundary itself has not been independently located at any site in the Russian Far East. Thus, many of the arguments for floral change across the boundary appear to be somewhat circular. We have already seen that there is a difference in the Asian and North American interpretations of the palynological K-T boundary, and for the moment, the interpretation of the megafloral record hangs on that of the palynofloral record. Resolution of this situation awaits the development of a reliable geochronology and magnetostratigraphy for the region and/or the discovery and documentation of the K-T boundary impactite itself.

Three primary areas have supplied the majority of the data for the discussion of the K-T boundary in the Russian Far East. These are the exposures along the forested north bank of the Amur River (Krassilov 1976, Kodrul 2004), a series of exposures in the tundra of the Koryak Uplands (Golovneva 1994a, 1994b, 1995, Herman and Spicer 1995, 1997), and beach cliff exposures on the western margin of Sakhalin Island (Krassilov 1978,1979, 2003).

The situation in the Amur is basically this: megafloras occur in association with dinosaurs in the Kundur Formation, they are essentially absent in the Lower Tsagayan Subformation (= Udurchukan Formation), and they occur with Paleocene palynofloras in the Middle and Upper Tsagayan subformations (= Bureya and Darmakan formations); Figure 8.10. This is essentially the same situation seen on the south bank of the Amur River in China, where the Taipinglinchang and dinosaur-bearing Yuliangze formations are separated from the leaf- and pollen-bearing Wuyun Formation by the poorly dated and poorly sampled Furao Formation (Figure 8.9). The Cretaceous megafloras from both the Kundur and Taipinglinchang formations are only preliminarily known (Golovneva et al. 2004), whereas the unambiguously Paleocene floras from the Wuyun and Upper Tsagayan (Darmakan) formations are well described (Krassilov 1976, Kodrul 2004). This is somewhat similar to the situation in the USA in the late 1980s before the flora of the upper Maastrichtian Hell Creek Formation was first described. The Paleocene flora was known, but the Cretaceous less so. In addition, the actual ages of the uppermost Cretaceous units in the Amur region are known only to the stage level. At best, this can be described as stage-level temporal resolution, and further understanding of these sections awaits the collection of more fossils and independent dating of the Furao Formation on the Chinese side and the Middle Tsagayan Subformation (Bureya Formation) on the Russian side.

In the Koryak Uplands, Golovneva (1994a, b) collected 124 megafloral localities from the 900-2000-m-thick Rarytkin Formation exposed along Rarytkin Ridge, a northeast trending range that is cut by the Anadyr River. From this formation, she described the middle Maastrichtian'' Gornorechensk floral assemblage (Gornorechenian floral stage) and the' ' late Maastrichtian-Danian'' Rarytkin floral assemblage (Rarytkinian floral stage). In these areas, it was not possible to measure stratigraphic sections and the relative stratigraphic positions of the mega-floral localities were extrapolated (Golovneva, personal communication, 2000). The Cretaceous age of the lower part of the section is constrained by marine mollusks and dinosaurs known from correlative beds in the Kakanut River Basin some 160 km to the south. Golovneva defined the position of the K-T boundary in Rarytkin Ridge by correlation of Cretaceous marine mollusks associated with Rarytkinian floral-stage fossils in the Khatyrka River Basin more than 180 km to the southwest. Based on these lengthy correlations, she interpreted the significant floral change at the Gornorechenian-Rarytkinian floral-stage boundary to occur at the middle Maastrichtian-upper Maastrichtian boundary. Based on this interpretation, Golovneva argued that floral change at the K-T boundary itself was insignificant. We would argue that the age control on this section is poor and that statements about megafloral change at the K-T boundary in this area are premature. Subsequent work by Herman and Spicer (1997) also used correlation of Cretaceous mollusks to argue for a Cretaceous age for the Rarytkinian floralstage megaflora; they provocatively titled their paper with a temporal tautology, "The Koryak flora: did the early Tertiary deciduous flora begin in the late Maastrichtian of northeastern Russia?'' This is not the first time that the Arctic has been implicated with the premature appearance of a floral stage, but as with past cases, the burden of proof is with the proposal, and independent age assessment is desperately needed before the relevance of these sections to the K-T boundary can be established.

On Sakhalin Island, Krassilov (1978,1979,2003) described the "Maastrichtian" Augustovian megaflora from the upper part of the Krasnoyoarka Formation in sections along the Augustovka River and an overlying "Maastrichtian-Danian" Boshnyakovian flora from the Boshnyakova Formation. In these sections as well, direct age control remains a significant concern and assertions about floral change at the K-T boundary should be treated as preliminary.

In general, it appears that the Russian paleobotanists have been too quick to assign global stage names and associated temporal significance to local and poorly dated terrestrial sections in the Russian Far East. These sections have clear potential, but to date it has not been realized, and it is premature to discuss the significance of these floras as if they were known to chron- or impactite-level resolution.

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