Araliaephyllum Polevoi

Hell Really Exists

Hell Really Exists

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R 106 w South R 105 W

Dakota

Figure 6.4 Geological map of the area in the vicinity of the town of Marmarth, southwestern North Dakota, showing locations of K-T boundary sites discussed in the text (modified from Nichols and Johnson 2002). T - township, R - range, Kp - Pierre Shale, Kfh - Fox Hills Formation, Khc - Hell Creek Formation, Tful - Ludlow Member of the Fort Union Formation. Reprinted by permission.

The Fossil Hunters Plants
Figure 6.5 A high-resolution sampling of the Hell Creek-Fort Union formation contact in North Dakota. In this case, the K-T boundary is located nearly 2 m above the base of the lignite bed that marks the formation contact, which is where the people are seated at the trench.

continental rocks: megaflora, palynoflora, iridium, and shocked quartz (for a comparison of K-T boundary localities based on definitive criteria, see Table 2.1). Leaf quarries that yielded Maastrichtian species below and Paleocene species above bracket the boundary level. Palynological collections made at a

Palynomorphs

Palynomorphs

Iridium (ppb)

Figure 6.6 Distribution and relative abundances of iridium and the most common palynomorphs in the K-T boundary section at Pyramid Butte (from Johnson et al. 1989). Khc, Hell Creek Formation; Tfu, Fort Union Formation. Numbers across top designate species of spores and pollen not individually named here: 1-3, bryophytes and ferns; 4-6, gymnosperms; 7-30, angiosperms. Reprinted by permission.

Iridium (ppb)

Figure 6.6 Distribution and relative abundances of iridium and the most common palynomorphs in the K-T boundary section at Pyramid Butte (from Johnson et al. 1989). Khc, Hell Creek Formation; Tfu, Fort Union Formation. Numbers across top designate species of spores and pollen not individually named here: 1-3, bryophytes and ferns; 4-6, gymnosperms; 7-30, angiosperms. Reprinted by permission.

finer stratigraphic scale between the boundary-bracketing leaf quarries served as a proxy for the megafossil flora and pinpointed the position of the K-T boundary, which was verified by the presence of an iridium anomaly. Megafloral turnover across the boundary was initially estimated to be 79%; palynological extinction at the boundary was estimated to be 30%. The difference between these numbers, both derived from plant fossils, is due to the different levels of taxonomic resolution of the kinds of plant fossils evaluated (see Section 3.3). At Pyramid Butte, the stratigraphically highest Maastrichtian pollen assemblages are present in a coal bed, and the lowermost Paleocene assemblages are present in mudstone just above the coal (Figure 6.6). This pattern is the reverse of that at most other localities in North America where the palynological extinction has been described, in which a coal bed overlies mudstone or shale at the K-T boundary. Prior to the discovery of the Pyramid Butte site, it could be speculated that the apparent replacement of an angiosperm-rich palynoflora by one dominated by ferns and sphagnum moss was due to the presence of a coal bed above the K-T boundary. At Pyramid Butte, characteristic Maastrichtian pollen is present in coal but is absent in the n 80 o

Figure 6.7 Biostratigraphic range chart for all megafloral taxa that occur at more than one stratigraphic level in the composite section in the Marmarth, North Dakota, area (from Johnson and Hickey 1990). Numbers across bottom designate leaf morphotypes; megafloral zone and subzone names are at the right (HC = Hell Creek, FU = Fort Union). Megafloral zone boundaries are indicated by dashed lines; subzone boundaries are indicated by dotted lines. Reprinted by permission.

Figure 6.7 Biostratigraphic range chart for all megafloral taxa that occur at more than one stratigraphic level in the composite section in the Marmarth, North Dakota, area (from Johnson and Hickey 1990). Numbers across bottom designate leaf morphotypes; megafloral zone and subzone names are at the right (HC = Hell Creek, FU = Fort Union). Megafloral zone boundaries are indicated by dashed lines; subzone boundaries are indicated by dotted lines. Reprinted by permission.

overlying mudstone facies, just above the level at which an iridium anomaly and shocked quartz are found.

In 1990, the second of the so-called "Snowbird conference" symposium volumes was published (for the complete set of publications in this authoritative series, see Silver and Schultz 1982, Sharpton and Ward 1990, Ryder et al. 1996, and Koeberl and MacLeod 2002). Two papers appeared in the 1990 volume that concerned the Marmarth area. Johnson and Hickey (1990) discussed the accumulated data from 57 Cretaceous and 30 Paleocene localities that had yielded 11 503 specimens assigned to 247 morphotypes of plant megafossils. They described four megafloral assemblage zones, three in the Hell Creek Formation and one in the Fort Union Formation. The extent of megafloral change across the K-T boundary (essentially the Hell Creek-Fort Union forma-tional contact) was presented as 79% and was based on a direct comparison of the composition of the uppermost Maastrichtian megafloral zone Hell Creek (HC) III with that of the lowermost Paleocene Fort Union (FU) I (Figure 6.7). Leo Hickey's coauthorship on this paper signified his conversion from the position of a skeptic of the K-T plant extinction story (see Section 4.5) to that of a supporter of the theory. The second paper of direct interest in the 1990 volume is that of Nichols and Fleming (1990). These authors reviewed the palynological data on the K-T boundary that had developed from 1982 to 1990 from sites that had both a palynological extinction horizon and an iridium anomaly. They a o o ra CL

Figure 6.8 Diagrams of stratigraphic relations of clastic rocks (gray), coal beds (black), and the K-T boundary (dashed line) at different localities in western North America (modified from Nichols and Fleming 1990). a - City of Raton, New Mexico; b - Morgan Creek, Saskatchewan; c - Sugarite, New Mexico; d - Pyramid Butte, North Dakota. With changes in vertical scale, these diagrams also pertain to other localities discussed later: a, Dogie Creek, Wyoming; b, Starkville South, Colorado, and localities in the Hell Creek area, Montana; c, Police Island, Northwest Territories. Reprinted by permission.

Figure 6.8 Diagrams of stratigraphic relations of clastic rocks (gray), coal beds (black), and the K-T boundary (dashed line) at different localities in western North America (modified from Nichols and Fleming 1990). a - City of Raton, New Mexico; b - Morgan Creek, Saskatchewan; c - Sugarite, New Mexico; d - Pyramid Butte, North Dakota. With changes in vertical scale, these diagrams also pertain to other localities discussed later: a, Dogie Creek, Wyoming; b, Starkville South, Colorado, and localities in the Hell Creek area, Montana; c, Police Island, Northwest Territories. Reprinted by permission.

summarized the data from the Pyramid Butte locality and compared it with patterns of extinction at the K-T boundary in three other areas in western North America (to be discussed later). Nichols and Fleming emphasized the independence of the palynofloral change at the K-T boundary from facies changes (mudstone to coal, or coal to mudstone) in their summaries of the localities; these relationships (Figure 6.8) also pertain to other localities, as will become evident in Chapter 7.

Johnson (1992) published additional information about the megaflora of the Hell Creek Formation in southwestern North Dakota. In that report, he showed that 90% of all the megafloral taxa (both Maastrichtian and Paleocene) were angiosperms. While other K-T boundary localities were being discovered in that area and detailed paleobotanical and palynological data were being gathered at them, a somewhat parallel study was undertaken in the Hell Creek and Fort Union formations farther to the east in the Williston Basin, in south-central North Dakota. Murphy et al. (1995) published the results of that study, which was more of a reconnaissance than were those in southwestern North Dakota. The K-T boundary was bracketed palynologically in 12 of 32 measured sections, within 30 cm at 8 of them, but closely spaced samples were not collected once the approximate position of the boundary had been determined. The K-T boundary layer with its iridium and shocked quartz was not found, and no paleobotanical collections were made. The palynoflora in south-central North Dakota is the same as that in the southwestern part of the state, and 16 familiar Cretaceous taxa were found in the Maastrichtian samples.

The most comprehensive and complete description of the K-T megaflora in southwestern North Dakota is published in the Geological Society of America Special Paper 361 (Johnson 2002). By 2002, the Williston Basin database included 158 localities (106 Maastrichtian and 52 Paleocene) and 13 571 specimens in 380 morphotypes or species (Figures 6.9 to 6.12). The stratigraphic context for these fossils had been delimited using palynostratigraphy, magnetostratigraphy, and vertebrate paleontology, all tied to the K-T boundary in a stratigraphic framework composed of 37 measured sections. Such a massive database is difficult to grasp, or even to portray graphically. Elimination of morphotypes present at only one locality or at only one or two stratigraphic levels left 98 stratigraphi-cally robust morphotypes to be plotted in 54 levels (Johnson 2002). Johnson defined five megafloral assemblage zones by subdivision of two of his three original Maastrichtian zones. He noted that extinction involved all of the numerically dominant plant taxa of the upper part of the Hell Creek Formation, and that survivorship appeared to be greatest among plants that had inhabited Maastrichtian mires. He discussed the effects of climate change (warming at the very end of the Maastrichtian) and base-level change (caused by brief re-advances of the regressing Western Interior seaway) on the terminal Cretaceous flora.

Kroeger (2002) analyzed the palynoflora of the Hell Creek Formation in northwestern South Dakota with relation to paleoenvironments. He distinguished three kinds of flood-basin deposits (lake, marsh, and crevasse-splay) and four kinds of meander-belt deposits (channel, point-bar, point-bar swale, and abandoned channel) in the Hell Creek Formation in his study area. Kroeger identified 44 palynomorph taxa in 34 samples from these deposits, and using detrended correspondence analysis, he identified six associations of taxa within certain deposits. Some of the taxa are somewhat more common in either the flood-basin or the meander-belt facies; others tend to occur preferentially in marsh or lake deposits. Hence, some influence of facies on occurrences of certain palynofloral species is evident, although certainly not enough to account for the extinctions at the K-T boundary (as clearly indicated in Figure 6.8).

The differences in relative abundance observed by Kroeger (2002) were interpreted as reflecting differing plant communities that characterized specific paleoenvironments. These results are highly significant because they may account for sample-to-sample variations in palynomorph content within closely spaced samples from a single measured section. Such variations are often

Maastrichtian Ferns

Figure 6.9 Representatives of the lobe-leafed Hell Creek megaflora (specimen catalogue numbers given in parentheses). a - Magnoliopsida HC 060 (DMNH 19233), b - Araliaephyllum polevoi (DMNH 8458), c - Erlingdorfia montana (DMNH 6253), d - "Artocarpus" lessigiana HC 179 (DMNH 13650), e - Magnoliopsida HC 199 (DMNH 13634), f - Cissites panduratus (DMNH 6240), g - Bisonia niemii (DMNH 16694). Scale bar is 1 cm.

Figure 6.9 Representatives of the lobe-leafed Hell Creek megaflora (specimen catalogue numbers given in parentheses). a - Magnoliopsida HC 060 (DMNH 19233), b - Araliaephyllum polevoi (DMNH 8458), c - Erlingdorfia montana (DMNH 6253), d - "Artocarpus" lessigiana HC 179 (DMNH 13650), e - Magnoliopsida HC 199 (DMNH 13634), f - Cissites panduratus (DMNH 6240), g - Bisonia niemii (DMNH 16694). Scale bar is 1 cm.

Maastrichtian Ferns

Figure 6.10 Representatives of the Hell Creek megaflora. a - "Artocarpus" lessigiana HC 179 (Pioneer Trails Regional Museum spec. 2559), b - Marmarthia pearsonii HC 162 (DMNH 7713), c - Dryophyllum tennesseensis HC 044 (YPM 6167), d - Palaeoaster inquir-enda HC 007 (YPM 6399), e - Platanites marginata HC106 (YPM 6234), f - Marmarthia trivialis HC 105 (DMNH 7395), g - Liriodendrites bradacii HC166 (DMNH 6889). Scale bar is 1 cm.

Figure 6.10 Representatives of the Hell Creek megaflora. a - "Artocarpus" lessigiana HC 179 (Pioneer Trails Regional Museum spec. 2559), b - Marmarthia pearsonii HC 162 (DMNH 7713), c - Dryophyllum tennesseensis HC 044 (YPM 6167), d - Palaeoaster inquir-enda HC 007 (YPM 6399), e - Platanites marginata HC106 (YPM 6234), f - Marmarthia trivialis HC 105 (DMNH 7395), g - Liriodendrites bradacii HC166 (DMNH 6889). Scale bar is 1 cm.

Figure 6.11 Representatives of the Hell Creek megaflora. a - Ginkgo adiantoides HC 114 (DMNH 18927), b - Nilssonia yukonensis HC 164 (Field Museum of Natural History spec. 6295), c - Taxodium olrikii HC 071 (YPM 6192), d - Fokieniopsis catenulata HC 137 (DMNH 19428), e - Glyptostrobus sp. #2 HC 009 (YPM 6133), f - Metasequoia sp. #2 HC 035, g - Metasequoia occidentalis FU 003 (YPM 6053). Scale bar is 1 cm.

Figure 6.11 Representatives of the Hell Creek megaflora. a - Ginkgo adiantoides HC 114 (DMNH 18927), b - Nilssonia yukonensis HC 164 (Field Museum of Natural History spec. 6295), c - Taxodium olrikii HC 071 (YPM 6192), d - Fokieniopsis catenulata HC 137 (DMNH 19428), e - Glyptostrobus sp. #2 HC 009 (YPM 6133), f - Metasequoia sp. #2 HC 035, g - Metasequoia occidentalis FU 003 (YPM 6053). Scale bar is 1 cm.

Figure 6.12 Representatives of the FUI megaflora from the central Great Plains. a - Penosphyllum cordatum (DMNH 20033), b - Zizyphoides flabella (DMNH 21874), c - ''Populus'' nebrascensis (YPM 7273), d - Browniea serrata (DMNH 22706), e -Cornophyllum newberryi (YPM 6078), f - Zizyphoides flabella (YPM 7289), g - Cornophyllum newberryi (DMNH 21891), h - Paranymphaea crassifolia (YPM 7266). Scale bar is 1 cm.

Figure 6.12 Representatives of the FUI megaflora from the central Great Plains. a - Penosphyllum cordatum (DMNH 20033), b - Zizyphoides flabella (DMNH 21874), c - ''Populus'' nebrascensis (YPM 7273), d - Browniea serrata (DMNH 22706), e -Cornophyllum newberryi (YPM 6078), f - Zizyphoides flabella (YPM 7289), g - Cornophyllum newberryi (DMNH 21891), h - Paranymphaea crassifolia (YPM 7266). Scale bar is 1 cm.

observed but seldom explained. Their importance is great in paleoecological studies, but less so in biostratigraphy. With respect to taxa that appear to become extinct at the K-T boundary in northwestern South Dakota, Kroeger noted that some are paleoenvironmentally sensitive, but others are not. Species in the extinction palynoflora Kroeger regarded as paleoenvironmentally sensitive (i.e., facies-controlled) include Liliacidites complexus, Orbiculapollis lucidus, and Tricolpites microreticulatus. Species of Aquilapollenites evidently are independent of paleoenvironmental influence, as their occurrence is not determined by sedimentary facies.

Nichols (2002a) based his description of the Hell Creek palynoflora on 110 000 specimens from 20 measured sections; he described 98 of about 115 palynofloral taxa, a few of which are illustrated here in Figures 6.13 and 6.14. The palynoflora is numerically dominated by angiosperm pollen, although it includes significant percentages of gymnosperm pollen and spores of ferns and other cryptogams. The palynofloral taxa Nichols described include 69 angio-sperms, 7 gymnosperms, 19 pteridophytes, and 3 bryophytes. Of these, 33 -about one-third of the most commonly occurring pollen species - do not occur in rocks of Paleocene age in the region. For this reason, they are called "K taxa.'' Five of the K taxa disappear within the Hell Creek Formation well below the K-T boundary, and their extinction cannot be attributed to the K-T boundary event. Three other K taxa are among the most commonly occurring taxa in the Hell Creek Formation. The K taxa whose disappearance marks the K-T boundary in the Williston Basin are listed in Table 6.1. The most commonly occurring taxa in the Hell Creek Formation, those present at 70% or more of the localities sampled in southwestern North Dakota, include ten taxa of angiosperm pollen, two of gymnosperm pollen, four of fern spores, and one of bryophyte spores (eight of these are genus-level taxa). The widespread occurrence of these palynomorph taxa suggests that, although angiosperms dominated the taxonomic diversity of the flora, ferns and bryophytes were also prevalent in the Hell Creek paleoeco-system, and certain gymnosperms were well represented. Nichols found that 25 of his Maastrichtian palynomorph species (K taxa) occur as much as 2.7 m above the top of the Hell Creek Formation, in a basal part of the Fort Union Formation that is Maastrichtian in age. This important observation further demonstrates that the position of the K-T boundary as defined by palynological extinctions is independent of the lithology and facies of Hell Creek and Fort Union formations.

Our joint paper on the palynology of the K-T boundary (Nichols and Johnson 2002) presents palynological and stratigraphic data from 17 measured sections that cross the boundary, including two in which its precise position is verified by geochemical and mineralogical evidence. Data from seven additional

Wodehouseia

Figure 6.13 Representatives of the Hell Creek palynoflora (species of Aquilapollenites 1-11 and Wodehouseia 12-13); many specimens photographed at two levels of focus. 1a, 1b - A. attenuatus; 2a, 2b - A. conatus; 3 - A. bertillonites, 4a, 4b - A. marmarthensis; 5a, 5b - A. collaris; 6 - A. delicatus, 7a, 7b - A. quadrilobus; 8a, 8b - A. reductus; 9,10 - A. quadrilobus; 11a, 11b - A. senonicus; 12a, 12b, 13a, 13b - W. spinata; symbol mm = micrometers (modified from Nichols 2002a). Reprinted by permission.

Figure 6.13 Representatives of the Hell Creek palynoflora (species of Aquilapollenites 1-11 and Wodehouseia 12-13); many specimens photographed at two levels of focus. 1a, 1b - A. attenuatus; 2a, 2b - A. conatus; 3 - A. bertillonites, 4a, 4b - A. marmarthensis; 5a, 5b - A. collaris; 6 - A. delicatus, 7a, 7b - A. quadrilobus; 8a, 8b - A. reductus; 9,10 - A. quadrilobus; 11a, 11b - A. senonicus; 12a, 12b, 13a, 13b - W. spinata; symbol mm = micrometers (modified from Nichols 2002a). Reprinted by permission.

Figure 6.14 Representatives of the Hell Creek palynoflora; many specimens photographed at two levels of focus. 1-6- Tschudypollis spp.; 7a, 7b-two specimens of Liliacidites complexus; 8 - Myrtipites scabratus; 9 - PorosipoUis porosus; 10a, 10b - Racemonocolpites formosus; 11 - Orbiculapollis lucidus; 12 - Retibrevitricolporites beccus; 13a, 13b - StriateHipollis striatellus; 14-16 - Tricolpites microreticulatus; 17,18 - Styxpollenites calamitas; 19 -Dyadonapites reticulatus; 20 - Arecipites columellas; 21a, 21b - Libopollisjarzenii; 22 - Kurtzipites circularis; 23 - Kurtzipites trispissatus; 24 - Pandaniidites typicus; 25 - Erdtmanipollis cretaceus; 26 - Leptopecopites pocockii (modified from Nichols 2002a) Reprinted by permission.

Figure 6.14 Representatives of the Hell Creek palynoflora; many specimens photographed at two levels of focus. 1-6- Tschudypollis spp.; 7a, 7b-two specimens of Liliacidites complexus; 8 - Myrtipites scabratus; 9 - PorosipoUis porosus; 10a, 10b - Racemonocolpites formosus; 11 - Orbiculapollis lucidus; 12 - Retibrevitricolporites beccus; 13a, 13b - StriateHipollis striatellus; 14-16 - Tricolpites microreticulatus; 17,18 - Styxpollenites calamitas; 19 -Dyadonapites reticulatus; 20 - Arecipites columellas; 21a, 21b - Libopollisjarzenii; 22 - Kurtzipites circularis; 23 - Kurtzipites trispissatus; 24 - Pandaniidites typicus; 25 - Erdtmanipollis cretaceus; 26 - Leptopecopites pocockii (modified from Nichols 2002a) Reprinted by permission.

Table 6.1 Palynomorph taxa whose extinctions mark the K-T boundary in the Williston Basin, North Dakota

Anacolosidites rotundus Stanley 1965

Aquilapollenites attenuatus Funkhouser 1961

Aquilapollenites collaris (Tschudy and Leopold 1971) Nichols 1994

Aquilapollenites conatus Norton 1965

Aquilapollenites delicatus Stanley 1961

Aquilapollenites marmarthensis Nichols 2002

Aquilapollenites quadricretaeus Chlonova 1961

Aquilapollenites quadrilobus Rouse 1957

Aquilapollenites reductus Norton 1965

Aquilapollenites senonicus (Mtchedlishvili 1961) Tschudy and Leopold 1971 Aquilapollenites turbidus Tschudy and Leopold 1971 Aquilapollenites vulsus Sweet 1986 Cranwellia rumseyensis Srivastava 1967

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

Leptopecopites pocockii (Srivastava 1967) Srivastava 1978

Libopollis jarzenii Farabee et al. 1984

Liliacidites altimurus Leffingwell 1971

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

Polyatriopollenites levis (Stanley 1965) Nichols 2002

Racemonocolpites formosus Sweet 1986

Retibrevitricolporites beccus Sweet 1986

Striatellipollis striatellus (Mtchedlishvili in Samoilovitch et al. 1961) Krutzsch 1969 Styxpollenites calamitas Nichols 2002

Tricolpites microreticulatus Belsky, Boltenhagen, and Potonie 1965 Tschudypollis retusus (Anderson 1960) Nichols 2002 Tschudypollis spp.

measured sections, which are near to but do not cross the boundary, supplement the data from the K-T sections, with respect to patterns of palynomorph occurrences. Our analysis is based on 700 000 specimens assigned to 110 taxa recovered from more than 350 samples. As noted above, the fundamental independence of extinction and paleoenvironment previously elucidated by Nichols and Fleming (1990) was verified within the Hell Creek-Fort Union transition. However, a ''facies effect'' on the palynoflora was found within a stratigraphic interval we designated as '' the Fort Union strata of Maastrichtian age'' (the Fort Union Formation is generally regarded as entirely Paleocene

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