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Megafloral change in the early and middle Paleocene in the Williston Basin, North Dakota, USA
... The best records of this extinction in plants are from North America (e.g., Nichols and Johnson, 2008). The postextinction North American record documents a major restructuring of terrestrial ecosystems, a destabilization of terrestrial food webs, and a prolonged recovery that extended at least into the middle Paleocene (Hickey 1980;Wing et al. 1995;McIver 1999;Dunn 2003;Wilf and Johnson 2004;Wilf et al. 2006;Peppe 2010;Blonder et al. 2014). Thus, reconstructions of patterns of plant community diversity and composition in the early Paleocene are necessary to fully understand both local and regional ecosystem recovery following the K/Pg mass extinction. ...
... Extensive early Paleocene megafloral collections have been made in North America for over 150 years (e.g., Newberry 1868;Lesquereux 1878;Brown 1962;Hickey 1980;Wolfe and Upchurch 1987;Wing et al. 1995;Johnson 2002;Barclay et al. 2003;Peppe 2010). The majority of these studies have focused on the Northern Great Plains (NGP) of North America (Fig. 1A) (e.g., Newberry 1868;Lesquereux 1878;Brown 1962;Hickey 1980;Barclay et al. 2003;Dunn 2003;Wilf and Johnson 2004;Peppe 2010), with large collections of floras from the first 300,000 years of the Paleocene being primarily from the Denver Basin (DB) of central Colorado (Barclay et al. 2003; Johnson et al. 2003) and the Williston Basin (WB) of North Dakota (e.g., Johnson 1989Johnson , 2002Johnson and Hickey 1990;Wilf and Johnson 2004;Peppe 2010). ...
... Extensive early Paleocene megafloral collections have been made in North America for over 150 years (e.g., Newberry 1868;Lesquereux 1878;Brown 1962;Hickey 1980;Wolfe and Upchurch 1987;Wing et al. 1995;Johnson 2002;Barclay et al. 2003;Peppe 2010). The majority of these studies have focused on the Northern Great Plains (NGP) of North America (Fig. 1A) (e.g., Newberry 1868;Lesquereux 1878;Brown 1962;Hickey 1980;Barclay et al. 2003;Dunn 2003;Wilf and Johnson 2004;Peppe 2010), with large collections of floras from the first 300,000 years of the Paleocene being primarily from the Denver Basin (DB) of central Colorado (Barclay et al. 2003; Johnson et al. 2003) and the Williston Basin (WB) of North Dakota (e.g., Johnson 1989Johnson , 2002Johnson and Hickey 1990;Wilf and Johnson 2004;Peppe 2010). Early Paleocene plant communities from the NGP are characterized by low diversity and are dominated by long-lived, cosmopolitan, mire-adapted taxa (Hickey 1980;Johnson 2002;Barclay et al. 2003;Peppe 2010). ...
Earliest Paleocene megafloras from North America are hypothesized to be low diversity and dominated by long-lived cosmopolitan species following the Cretaceous/Paleogene (K/Pg) mass extinction. However, megafloras used to develop this hypothesis are from the Northern Great Plains (NGP) of North America, and relatively little is known about floras from southern basins. Here, we present a quantitative analysis of an earliest Paleocene megaflora (<350 kyr after K/Pg boundary) from the Ojo Alamo Sandstone in the San Juan Basin (SJB), New Mexico. The megaflora, comprising 53 morphotypes, was dominated by angiosperms, with accessory taxa composed of pteridophytes, lycophytes, and conifers. Diversity analyses indicate a species-rich, highly uneven, and laterally heterogeneous flora. Paleoclimate estimates using multivariate and univariate methods indicate warm temperatures and relatively high precipitation consistent with a modern tropical seasonal forest.
When compared with contemporaneous floras from the Denver Basin (DB) of Colorado and the Williston Basin (WB) of North Dakota, the SJB flora had significantly higher species richness but lower evenness. Paleoclimate estimates from the SJB were 7–14°C warmer than the estimates for the DB and WB, indicating a shift from a temperate forest in the NGP to a tropical forest in the SJB. These results demonstrate the presence of a latitudinal floral diversity and paleoclimatic gradient during the earliest Paleocene in western North America. We hypothesize that the warm, wet conditions in the earliest Paleocene SJB drove rapid rates of speciation following the K/Pg boundary, resulting in a diverse and heterogeneous flora.
... Stratigraphic and paleobotanical reconstructions of early Paleocene terrestrial ecosystems from the Williston, Bighorn, Hanna, and Denver Basins contemporaneous with this mammalian turnover suggest climate was relatively stable during this time (e.g. Hickey, 1980;Barclay et al., 2003;Dunn, 2003;Johnson et al., 2003;Wilf et al., 2003;Peppe, 2010;Peppe et al., 2011); however, studies detailing the paleoclimatic and paleoenvironmental conditions in the early Paleocene in the San Juan Basin, which best document the Pu2-Pu3 faunal turnover, are lacking. ...
... Although they are not from the same deposits as the Photopan Outcrop, the Ojo Alamo floras are at most a few hundred thousand years older (Flynn et al., 2014). Paleoclimate estimates for the earliest Paleocene across North America indicate that climate was relatively stable (e.g., Hickey, 1980;Barclay et al., 2003;Dunn, 2003;Johnson et al., 2003;Wilf et al., 2003;Peppe, 2010;Peppe et al., 2011). This suggests that the paleoclimate estimates from the Ojo Alamo floras (Flynn et al., 2014) are likely representative of climate in the San Juan Basin during the earliest Paleocene, and thus are useful for comparison with the paleosol estimates from the Photopan Outcrop. ...
... 4; Table 2). These temperatures are similar to paleobotanical estimates (10.25 ± 2.97°C) from the Williston Basin, located 1600 km north of the San Juan Basin (Peppe, 2010), and to high latitude, deep ocean temperatures (Zachos et al., 2001). Additionally, the occurrence of crocodiles (Williamson, 1996) and fossil palms (Flynn et al., 2014;Peppe et al., 2015) in the Arroyo Chijuillita Member indicate a minimum MAT of N 14°C (Markwick, 1998) and winter temperatures above freezing (Larcher and Winter, 1981;Sakai and Larcher, 1987;Wing and Greenwood, 1993), respectively. ...
... Paleocene floras of the Western Interior U.S.A. typically had low diversity and were dominated by widespread species [12][13][14]. For ca. 10 million years following the K-Pg extinction, floral diversity was depressed compared to the latest Cretaceous and finally began to increase during the latest Paleocene and early Eocene [15][16][17]. ...
... There are 17 documented dicotyledonous angiosperm leaf species overall (Table 1), and one unknown monocot leaf species. The most common leaf species at Mexican Hat also are widespread throughout the Western Interior USA during the early Paleocene [14]. Fruits include the aforementioned Polyptera manningii; Joffrea speirsii (Cercidiphyllaceae), the presumed fruits of the local C. genetrix [36]; Nordenskioldia (Trochodendraceae), which has been correlated with Zizyphoides leaves [37]; and two unidentified fruits. ...
... These specimens are housed at DMNH and YPM. Collections made by DJP from early to middle Paleocene strata in the Williston Basin in North Dakota (2916 specimens at YPM [14,39] [31] and sedimentation rates from [30]) were examined for insect damage for the first time in this study. For broader regional and temporal context, the leaf fossils from early late Paleocene localities in Wyoming (59.0-57.5 Ma) collected by PW and CCL and scored for insect damage in [19] were also reexamined. ...
Plant and associated insect-damage diversity in the western U.S.A. decreased significantly at the Cretaceous-Paleogene (K-Pg) boundary and remained low until the late Paleocene. However, the Mexican Hat locality (ca. 65 Ma) in southeastern Montana, with a typical, low-diversity flora, uniquely exhibits high damage diversity on nearly all its host plants, when compared to all known local and regional early Paleocene sites. The same plant species show minimal damage elsewhere during the early Paleocene. We asked whether the high insect damage diversity at Mexican Hat was more likely related to the survival of Cretaceous insects from refugia or to an influx of novel Paleocene taxa. We compared damage on 1073 leaf fossils from Mexican Hat to over 9000 terminal Cretaceous leaf fossils from the Hell Creek Formation of nearby southwestern North Dakota and to over 9000 Paleocene leaf fossils from the Fort Union Formation in North Dakota, Montana, and Wyoming. We described the entire insect-feeding ichnofauna at Mexican Hat and focused our analysis on leaf mines because they are typically host-specialized and preserve a number of diagnostic morphological characters. Nine mine damage types attributable to three of the four orders of leaf-mining insects are found at Mexican Hat, six of them so far unique to the site. We found no evidence linking any of the diverse Hell Creek mines with those found at Mexican Hat, nor for the survival of any Cretaceous leaf miners over the K-Pg boundary regionally, even on well-sampled, surviving plant families. Overall, our results strongly relate the high damage diversity on the depauperate Mexican Hat flora to an influx of novel insect herbivores during the early Paleocene, possibly caused by a transient warming event and range expansion, and indicate drastic extinction rather than survivorship of Cretaceous insect taxa from refugia.
... In contrast, Wing et al. (1995) found a gradual increase in plant diversity in the early to mid-Paleocene, and little correspondence between trends in plant and mammal diversity. Studies of macrofloras from the Paleocene-Eocene Denver Basin in North America, however, have demonstrated considerable diversity gradients within a regional context , matching results for Cretaceous dinosaurs in the same area (Vavrek and Larson 2010) and suggesting that high diversity might also be facilitated by local to regional level environmental factors, such as precipitation patterns and topography (Peppe 2010). ...
... In contrast to Peppe (2010), we do not see a correlation between declining MAT and declining diversity, although the Williston Basin study encompasses a much longer time period (millions, rather than thousands, of years) and so may be tracking trends at a broader scale. In addition, Peppe (2010) notes that local environmental factors may modulate the climate-diversity relationship, as seen in other parts of North America, such as the Denver Basin. ...
... This pattern is not evident at Falkland, as the unit with the highest diversity is associated with the coolest MAT, and diversification in the Okanagan Highlands appears to be centered on temperate plant families, rather than on tropical inmigration. Perhaps a better analogy is the Denver Basin, where variation in topography and precipitation is linked to regional differences in plant diversity Peppe 2010). Microhabitat diversity has been suggested based on pollen evidence from Falkland and may best explain the intra-site variation in diversity, in combination with the disturbance regime. ...
The early Eocene fossil localities of the Okanagan Highlands in British Columbia, Canada, and Washington State, USA, span
the Early Eocene Climatic Optimum, the warmest period of the Cenozoic, and reflect mild but equable upland climates (mean
annual temperature <15°C, cold month mean temperature >0°C). The Okanagan Highlands region has been identified as a centre
of temperate plant family diversification in the northern hemisphere during the early Eocene. Here, we test the hypothesis
of mid-latitude high diversity through rarefaction analysis of unbiased census collections from the Okanagan Highlands Falkland
fossil locality, demonstrating levels of diversity similar to those documented at hyperdiverse Eocene sites in South America
when adjusted for sample size. An explanation for this diversity may lie in the upland character of the Falkland site, as
altitudinal gradients provide a mosaic of microhabitats through interacting effects of topography and climate. Fine-scale
trends are also examined within the Falkland site, demonstrating a shift in plant community composition over time to a more
diverse flora, although the dominant taxa persist through the section in varying levels of abundance. Intra-site patterns
in plant community structure and composition are attributed to a combination of environmental factors, including disturbance
and microhabitat diversity.
KeywordsFossil flora–Okanagan Highlands–British Columbia–Early Eocene Climatic Optimum–Diversity–Rarefaction
... 66 Ma; Peppe, 2003;Peppe et al., 2007; Table 1). We grouped these taxa by floral zone following Peppe (2009Peppe ( , 2010. Specimens used in this study are housed at the Yale Peabody Museum in New Haven, Connecticut, USA. ...
... First, high-latitude deep-sea temperatures were c. 10°C at this time (Zachos et al., 2001) and are incompatible with low-elevation, mid-latitude MATs of c. 10°C. Second, the presence of palm fossils in floral zone Williston Basin I (Peppe, 2009(Peppe, , 2010 suggests a MAT > 10°C (Larcher & Winter, 1981;Sakai & Larcher, 1987;Wing & Greenwood, 1993;Greenwood & Wing, 1995). Third, crocodilian fossils are present throughout the Paleocene sequence in the Williston Basin and across the Western Interior of North America, implying a MAT of ‡ 14°C (Markwick, 1998). ...
... . Specimens are stored at the North Dakota Heritage Center in Bismarck, North Dakota, USA, and at St Lawrence University in Canton, New York, USA.The Fort Union Formation floras (Williston Basin I, II, and III) are from the Fort Union Formation in the Williston Basin of southwestern North Dakota, USA (65.5 to c. 58.5 Ma;Peppe, 2009Peppe, , 2010 ...
• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. • We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. • Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.
... In contrast, composite studies of megafloral records from New Mexico to Alberta show consistent extinction on the order of 50e75% of morphospecies across the KPB (Wolfe and Upchurch, 1986;Johnson et al., 2003;Barclay et al., 2003). However, these studies typically focus on individual megafloral localities (e.g., Wing et al., 1995;Johnson and Ellis, 2002;Dunn, 2003;Peppe, 2010) and are frequently biased towards Paleogene megafloras (e.g., Davies-Vollum, 1997;Dunn, 2003;Barclay and Johnson, 2004;Peppe, 2010;Flynn and Peppe, 2019). Therefore, they do not allow evaluation of the lead-up to the mass extinction or the role of biogeography in shaping patterns of floral change (i.e., local extirpation versus extinction). ...
... In contrast, composite studies of megafloral records from New Mexico to Alberta show consistent extinction on the order of 50e75% of morphospecies across the KPB (Wolfe and Upchurch, 1986;Johnson et al., 2003;Barclay et al., 2003). However, these studies typically focus on individual megafloral localities (e.g., Wing et al., 1995;Johnson and Ellis, 2002;Dunn, 2003;Peppe, 2010) and are frequently biased towards Paleogene megafloras (e.g., Davies-Vollum, 1997;Dunn, 2003;Barclay and Johnson, 2004;Peppe, 2010;Flynn and Peppe, 2019). Therefore, they do not allow evaluation of the lead-up to the mass extinction or the role of biogeography in shaping patterns of floral change (i.e., local extirpation versus extinction). ...
The Cretaceous-Paleogene (K/Pg) boundary marks a mass extinction resulting in global biotic turnover. Exposures of the Hell Creek Formation in northeastern Montana contain some of the most well-studied vertebrate localities recording this mass extinction; however, very little is known of the floral record in this area. As part of an effort to reconstruct floral changes across the K/Pg in northeastern Montana, this study presents a taxonomically diverse flora from the Seafood Salad locality, located ∼ 65 m below the K/Pg boundary in the Hell Creek Formation, Garfield County, Montana. Leaves, stems, and reproductive structures (e.g., cones and seeds) are preserved as compression and impression fossils in massive, bedded siltstones and very fine sandstones. Seafood Salad is significant in that it is represents a “pre-disaster” community approximately 1.3 m.y. before the K/Pg mass extinction. We interpret the plants in these deposits as reflecting a local riparian community. The vegetation was taxonomically diverse and dominated by angiosperm trees; it also included abundant conifer specimens of a few taxa and relatively few ginkgoes and ferns. We describe 34 morphotypes and propose taxonomic affinities to modern groups and to fossil taxa from contemporaneous-age deposits in Montana and North Dakota. The Seafood Salad flora shares several taxa with other Late Cretaceous floras of the Western Interior, but substantial differences in taxonomic composition and relative abundances among these assemblages indicate that regional plant communities in the latest Cretaceous were spatially heterogeneous, rapidly changing, or both.
... Some of the best evidence for the terrestrial response to the Cretaceous/Paleogene (K/Pg) mass-extinction event comes from the highly fossiliferous outcrops in the Williston Basin of the Western Interior of North America (e.g., Brusatte et al., 2015;Nichols and Johnson, 2008;Pearson et al., 2002). The conformable succession of the Hell Creek Formation (Hell Creek, upper Cretaceous) and the overlying Fort Union Formation (Fort Union, Paleocene) preserve an extraordinary record of terrestrial vertebrates, plants and insects across the extinction interval (Fastovsky, 1986(Fastovsky, , 1987Johnson et al., 1989Johnson et al., , 2000Johnson et al., , 2002Johnson, 1992Johnson, , 2002Nichols et al., 2000;Pearson et al., 2001Pearson et al., , 2002Hartman et al., 2002;Nichols and Johnson, 2002;Labandeira et al., 2002aLabandeira et al., , 2002bWilf et al., 2003;Wilf and Johnson, 2004;Bercovici et al., 2008Bercovici et al., , 2009Peppe, 2010;DePalma et al., 2010DePalma et al., , 2019Chin et al., 2013;Vajda et al., 2013;Carvalho et al., 2014;Donovan et al., 2014;Fastovsky and Bercovici, 2016). In addition to the exceptional paleontological record, these successions also contain in situ ejecta and geochemical indicators from the Chicxulub-impact event, which allows for high-resolution analysis of the pace and tempo of responses to the environmental perturbation, especially for a terrestrial deposit (e.g., Bohor et al., 1984;DePalma et al., 2019;Fastovsky and Bercovici, 2016;Fastovsky et al., 1989;Hildebrand and Boynton, 1988;Johnson et al., 1989;Kring, 2000Kring, , 2007Nichols and Johnson, 2008;Renne et al., 2013;Sprain et al., 2015Sprain et al., , 2018. ...
... Ichnology has been demonstrated as a versatile tool for refining the sedimentological history and stratigraphic relationships across the K/Pg boundary globally (Ekdale and Bromley, 1984;Savrda, 1993Savrda, , 2018Ekdale and Stinnesbeck, 1998;Twitchett and Barras, 2004;Rodríguez-Tovar et al., 2004, 2010Rodríguez-Tovar, 2005;Rodríguez-Tovar and Uchman, 2008;Kę dzierski et al., 2011;Sosa-Montes de Oca et al., 2013Alegret et al., 2015;Horner et al., 2016). Quantitative ichnology has also revealed insight into widespread nature of the Lilliput effect in response to the K/Pg extinction (Labandeira et al., 2016;Łaska et al., 2017;Wiest et al., , 2016Wiest et al., , 2018. ...
The Hell Creek Formation and overlying Fort Union Formation record a geologically rapid base-level rise that was approximately contemporaneous with the K/Pg extinction and deposition of Chicxulub-impact indicators. An outstanding question that remains is whether this base-level rise is attributable to: 1) a multi-thousand-year transgression adjacent to a relatively low-relief coastal plain, causing a rise in the water table; or 2) catastrophic flooding due to upland denudation, rapid channel accretion, and hydrologic reorganization resulting from wildfires/deforestation consequential of the impact. Herein we aim to address which of these hypotheses is most consistent with a paleolandscape reconstruction at Mud Buttes, a locality where the boundary clay (BC) is coincident with the Hell Creek-Fort Union contact. One hundred twenty-seven trenches were examined laterally across ∼2 km transect of K/Pg boundary. The uppermost Hell Creek is comprised of three pedotypes: Pale-Silt Inceptisol (PSI), Olive-Clay Vertisol (OCV), and Chocolate-Clay Vertisol (CCV), which range from moderately well-drained, to variable to poorly drained, to very poorly drained, respectively. All of the BC occurs superjacent to the CCV, despite this pedotype accounting for only ∼50% of the pre-event landscape. The edaphic features preserved in the CCV pedotype are not attributable to Paleogene overprinting, which indicates that hydromorphic conditions began prior to the impact. Furthermore, 46% of BC is overlain by lignite, despite lignite occurrence on 17% of the earliest Paleogene landscape. This reveals that the poorest-drained landscape positions of the latest Cretaceous persisted across the boundary. These relationships are most consistent with a non-catastrophic base-level rise.
... Whereas there is no high-resolution plant record for the K-Pg boundary from the Big Bend area, records from across North America, including from the geographically proximate Raton Basin, document a 30 to > 50% extinction of plant taxa at the K-Pg boundary followed by a short-lived interval dominated by fern taxa (the "fern spike") and then a prolonged recovery dominated by angiosperms (Vajda and Bercovici, 2014, and references therein). When compared to their Cretaceous counterparts, Paleocene floras were lower in diversity and were dominated by a few species that were geographically widespread (e.g., Wing et al., 1995;Wilf and Johnson, 2004;Peppe, 2010). Given that this pattern has been observed across North America, it is very likely that the Big Bend region experienced a similar extinction of plants and plant community response across the K-Pg boundary. ...
... Trace-fossil analysis has been demonstrated previously as an effective tool for refining the sedimentological history and stratigraphic relationships at other K-Pg exposures (Ekdale and Bromley, 1984;Savrda, 1993;Ekdale and Stinnesbeck, 1998;Twitchett and Barras, 2004;Rodríguez-Tovar et al., 2004, 2010, 2016Rodríguez-Tovar, 2005;Chin et al., 2013;Sosa-Montes de Oca et al., 2013, 2016Horner et al., 2016). Thus, in the absence of diagnostic K-Pg boundary indicators, we propose that the trace fossil dataset herein can be used to refine the stratigraphic position of the K-Pg event in the Dawson Creek section. ...
Recent research has demonstrated that the Lilliput effect (reduction of body size in response to a mass extinction) affected all trophic levels in the marine realm following the Cretaceous-Paleogene (K-Pg) event. However, it is unclear if this size change was strictly a marine signal, or a global phenomenon that also affected continental ecosystems. Herein we present the results of an ichnological proxy for body size of soil-dwelling insects across the K-Pg boundary in Big Bend National Park, Texas, U.S.A. Quantitative efforts focused on Naktodemasis isp., which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci. These traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments. As an approximation for the body size of the subterranean insects, this dataset indicates that a smaller Naktodemasis diameter (DN) is statistically correlated (α < 0.05) with several edaphic factors including poor drainage and weak development (Entisols). Additionally, the DN in strata immediately superjacent to the highest Cretaceous-specific taxa is smaller by 23% (5.6 ± 1.8 mm) in comparison to DN within the subjacent Cretaceous interval (7.3 ± 2.7 mm). This abrupt shift occurs in a well-drained Inceptisol, and cannot be attributed to facies changes, drainage, or paleosol maturity. Furthermore, a reduced DN (6.6 ± 2.3 mm) persists above this anomalous shift for at least 20 stratigraphic meters within chron 29r. The cause for this negative response in body size within soil-dwelling biota may be attributed to plant-community shifts in taxonomic composition and ecological strategies, which would have caused fundamental alterations to the diet of the herbivorous, subterranean insects. This study provides empirical evidence that the Lilliput effect was not restricted to marine environments during the aftermath of the K-Pg event.
... to their Cretaceous counterparts, Paleocene floras were lower in diversity and were dominated by a few species that were geographically widespread (e.g., Wing et al. 1995;Wilf and Johnson 2004;Peppe 2010). Given that this pattern has been observed across North America, it is very likely that the Big Bend region experienced a similar extinction of plants and plant community response across the K-Pg boundary. ...
... Trace-fossil analysis has been demonstrated previously as an effective tool for refining the sedimentological history and stratigraphic relationships at other K-Pg exposures (Ekdale and Bromley 1984;Savrda 1993;Ekdale and Stinnesbeck 1998;Twitchett and Barras 2004;Rodríguez-Tovar et al. 2004, 2010Rodríguez-Tovar 2005;Chin et al. 2013;Sosa-Montes de Oca et al. 2013Horner et al. 2016). Thus, in the absence of diagnostic K-Pg boundary indicators, we propose that the trace fossil dataset herein can be used to refine the stratigraphic position of the K-Pg event in the Dawson Creek section. ...
... ISSN The Paleocene flora of the Rocky Mountains and Great Plains region is known from more than 500 collection sites spreading from New Mexico to Alberta and has been treated collectively in many publications (summarized in Brown, 1962;Hickey, 1977;Peppe, 2010;Pigg and DeVore, 2010;Manchester, 2014). Relatively few individual sites have been treated in detail to provide glimpses of particular settings and times. ...
We investigated leaf, cone and fruit impressions preserved in a siltstone deposit between coal seams in the late Paleocene Tongue River Member near Otter, southeast Montana, to assess the floristic diversity and composition. We document the presence of Taxodium based on seed cone scales as well as foliage branches and associated pollen cones, and a low-diversity angiosperm assemblage of about 15 genera dominated by Platanaceae (Platanus, Macginitiea, Macginistemon) and Cornales (Cornus, Davidia, Amersinia, Browniea), cf. Trochodendraceae (Zizyphoides, Nordenskioeldia), augmented by Aesculus, Trochodendroides, Ulmites and Porosia. Most of these genera were widespread in the Paleocene of the Northern Hemisphere. The low diversity of this florule is consistent with that of Tiffanian assemblages elsewhere in Montana and Wyoming. The leaf known as Phyllites demoresii Brown is proposed as a likely candidate to correspond with the extinct fruits called Porosia verrucosa (Lesquereux) Hickey emend. Manchester et Kodrul.
... grandei, living within thousands of years after the K-Pg, would have coexisted with small-bodied (body size less than 1 kg) mammalian 'disaster' faunas (e.g. [27]) and depauperate forests that represented an early wave of ecosystem succession in the early Palaeocene [49][50][51][52][53]. With an estimated total length of 1.4-1.5 m, the new gar is therefore one of the largest freshwater vertebrates to appear on the North American landscape directly after the impact. ...
The Cretaceous–Palaeogene (K–Pg) mass extinction was responsible for the destruction of global ecosystems and loss of approximately three-quarters of species diversity 66 million years ago. Large-bodied land vertebrates suffered high extinction rates, whereas small-bodied vertebrates living in freshwater ecosystems were buffered from the worst effects. Here, we report a new species of large-bodied (1.4–1.5 m) gar based on a complete skeleton from the Williston Basin of North America. The new species was recovered 18 cm above the K–Pg boundary, making it one of the oldest articulated vertebrate fossils from the Cenozoic. The presence of this freshwater macropredator approximately 1.5–2.5 thousand years after the asteroid impact suggests the rapid recovery and reassembly of North American freshwater food webs and ecosystems after the mass extinction.
... This floral work in Montana is ongoing, but preliminary trends can be compared with prior work in North America. Early Paleocene floras from elsewhere in the Williston Basin (e.g., North Dakota; Wilf and Johnson 2004;Peppe 2010) and farther south in the Western Interior (e.g., Hanna Basin, San Juan Basin, Denver Basin; Dunn 2003, Flynn and Peppe 2019 present differing patterns of plant recovery during this interval. These works broadly present two alternative hypotheses for the pattern of plant recovery: that floras regained pre-extinction diversity within the earliest~300 ka of the Paleocene or that floras remained homogeneous and depauperate for at least 1 Ma (Wilf and Johnson 2004). ...
The Hell Creek region of northeastern Montana is an excellent study system to explore the rise to dominance of mammalian faunas after the Cretaceous-Paleogene (K-Pg) mass extinction. The Tullock Member of the Fort Union Formation exposed in that region was deposited during the first 1.2 Ma after the Chicxulub bolide impact. Some aspects of post-K-Pg mammalian succession remain obscure, however, due to a lack of finer stratigraphic resolution between vertebrate fossil localities. Here, we present a new stratigraphic model for the lower and middle Tullock and identify a stratigraphic succession of five mammal-bearing sedimentary units that span the first~900 ka of the Paleocene. Most notably, we find that middle Tullock fossil localities, which were previously thought to be deposited by a single, large fluvial channel complex, are derived from two temporally and lithologically distinct sedimentary units: the Biscuit Springs unit (BS) and the Garbani channel (GC). The top of the GC is stratigraphically above the top of the BS, but in some places cuts through the entirety of the BS, a relationship that previously complicated interpretations of their relative age. This cross-cutting relationship reveals that the BS is older than the GC. Thus, the BS local fauna represents a potential intermediate between the older local faunas from the post-K-Pg 'disaster' interval and the younger, more taxonomically/ecologically diverse GC local fauna. This new stratigraphic framework sets the stage for future studies focused on the pattern and timing of biotic recovery in the aftermath of the K-Pg mass extinction.
... Amongst land plants, angiosperms display the highest rate of extinction at the K-Pg boundary as evident from the macrofloral and palynofloral record in North America (Wilf and Johnson 2004;Nichols and Johnson 2008;Vajda and Bercovici 2014). After the K-Pg mass extinction event, plant communities gradually recovered Peppe 2010;Vajda and Bercovici 2014;Lyson et al. 2019) and many angiosperm clades diversified (Nichols and Ott 1978;Magall on et al. 2019). Hence, we focus on angiosperm diversity during the early Palaeocene as the vegetation recovered. ...
The lower Goodlands Member of the Turtle Mountain Formation is exposed in a streambank outcrop on the western flank of Turtle Mountain, south-western Manitoba, Canada (49°0′2″N, 100°14′51″W). This outcrop was sampled for a 1.5 m section of microfossil-rich non-marine clay and coal-rich sediments deposited in a coastal plain environment during the early Palaeocene. These sediments were deposited 65.4–65 Ma and thus offer an opportunity to reconstruct terrestrial palaeoecology 0.6 to 1 Ma after the Cretaceous–Paleogene boundary (K–Pg) extinction event. We use quantitative palynology to reconstruct terrestrial plant ecology and explore ecological patterns of recovery and succession of these communities on a millennial time scale. Quantitative palynological analyses shows that at the time of deposition of the Goodlands Member the landscape on the coastal plain of the Western Interior Seaway – in what is now south-western Manitoba – was covered in a forested canopied swamp with tall standing swamp cypress and other conifers, Juglandaceae (walnut family), birch, alder, elms and other angiosperms, with an understory of ferns and ground cover of Sphagnum moss. Notably, palms were present but scarce, indicating a relatively warm climate. No successional pattern of diversity and community composition is evident in the samples; all samples showed high plant diversity (33–54 taxa/sample, H′ 2–3). Vegetation in Manitoba recovered within 0.6 to 1 Ma following the K–Pg extinction event or was predominantly influenced by local environmental patterns independent of time.
... This floral work in Montana is ongoing, but preliminary trends can be compared with prior work in North America. Early Paleocene floras from elsewhere in the Williston Basin (e.g., North Dakota; Wilf and Johnson 2004;Peppe 2010) and farther south in the Western Interior (e.g., Hanna Basin, San Juan Basin, Denver Basin; Dunn 2003, Flynn and Peppe 2019 present differing patterns of plant recovery during this interval. These works broadly present two alternative hypotheses for the pattern of plant recovery: that floras regained pre-extinction diversity within the earliest~300 ka of the Paleocene or that floras remained homogeneous and depauperate for at least 1 Ma (Wilf and Johnson 2004). ...
... Census collections were made in July 2018 following established protocols (e.g., Johnson, 2002;Wilf and Johnson, 2004;Peppe, 2010). For census collections, all specimens were assigned to morphotypes in the field, and the number of specimens per "field morphotype" were tallied. ...
The lower Miocene of Rusinga Island (Lake Victoria, Kenya) is best known for its vertebrate fossil assemblage but the multiple stratigraphic intervals with well-preserved fossil leaves have received much less attention. The Hiwegi Formation has three fossil leaf-rich intervals, which span the entire formation from oldest to youngest: Kiahera Hill, R5, and R3. Here, we describe new fossil collections from Kiahera Hill and R3 and compared these floras to previous work from R5, as well as modern African floras. The oldest flora at Kiahera Hill was most similar to modern tropical rainforests or tropical seasonal forests and reconstructed as a warm and wet, closed forest. This was followed by a relatively dry and open environment at R5, which was reconstructed as a woodland to open tropical seasonal forest. The youngest flora at R3 was most similar to modern tropical seasonal forests and was reconstructed as a warm and wet spatially heterogenous forest. Floral composition of all three floras differed, but the Kiahera Hill and R3 floras were more similar to each other than either flora was to the R5 flora. The Kiahera Hill flora had few monocots or herbaceous taxa, was dominated by large leaves, and had higher species richness and greater evenness than the R3 flora. Our work, coupled with previous studies, suggests that the R3 landscape consisted of both closed forest areas and open areas with seasonal ponding. The absence of morphotypes from the R5 flora that were present in the Kiahera Hill and R3 floras provides evidence for local extirpation during the R5 time interval. Thus, this work indicates that the Hiwegi Formation on Rusinga Island samples multiple environments ranging from more closed tropical forests to more open woodlands in the Early Miocene and provides important context for the evolution and habitat preference of early apes.
... As much as 90% of pre-extinction palynomorphs reappeared during the Danian (66 to 61.6 Ma) in Patagonia and New Zealand (6,7), and species-rich Danian megafloral assemblages with diverse types of insect damage indicate rapid recovery of diversity in Patagonia (8,9). By contrast, palynofloral extinction was up to 30% in the Northern Great Plains of North America (10), and floral and insectdamage diversity may not have reached preextinction levels until the latest Paleocene or early Eocene [ (11,12); but see (3)]. ...
The birth of modern rainforests
The origin of modern rainforests can be traced to the aftermath of the bolide impact at the end of the Cretaceous. Carvalho et al. used fossilized pollen and leaves to characterize the changes that took place in northern South American forests at this time (see the Perspective by Jacobs and Currano). They not only found changes in species composition but were also able to infer changes in forest structure. Extinctions were widespread, especially among gymnosperms. Angiosperm taxa came to dominate the forests over the 6 million years of recovery, when the flora began to resemble that of modern lowland neotropical forest. The leaf data also imply that the forest canopy evolved from relatively open to closed and layered, leading to increased vertical stratification and a greater diversity of plant growth forms.
Science , this issue p. 63 ; see also p. 28
... In turn, Flynn and Peppe (2019) argued that fundamental climatic differences between the northern Great Plains and the southern Western Interior of North America were primarily responsible for disparity among plant communities in these regions following the K/Pg mass extinction event-an argument that parallels earlier observations by Johnson and Ellis (2002), Ellis et al. (2003), Wilf and Johnson (2004), and Peppe (2010). However, the depauperate nature of some earliest Danian plant assemblages, coupled with a lack of high-frequency sampling, taxonomic bias, and other factors, has made it difficult to use leaf physiognomic methods to reliably estimate mean annual temperature or precipitation at many of these low-diversity sites (Nichols and Johnson 2008;Flynn and Peppe 2019;Lyson et al. 2019;Berry 2020b). ...
Premise of research. A two-phase fern spike occurred immediately after the Cretaceous-Paleogene (K/Pg) mass extinction event. Solely on the basis of palynological evidence, researchers have traditionally attributed the first phase of this spike to the proliferation of a single species of a Cyathea-like fern in the earliest Danian. This traditional perspective is challenged by recent investigations linking Anemia-like fern foliage with Cyathidites spores at K/Pg boundary localities in the Raton Basin, where the fern spore spike was first discovered by R. H. Tschudy. Although evidence emerging from neighboring basins appears to corroborate this new perspective, it remains to be seen whether this generalization applies to the northern Great Plains. Methodology. A comprehensive list of the most common fern megafossils collected from earliest Danian plant localities across western North America was compiled to determine the number and potential identity of Cyathiditesproducing ferns. Pivotal results. Three K/Pg survivors commonly collected from basal Paleocene strata in western North America conceivably produced psilate, trilete (Cyathidites) fern spores essentially identical to those observed at the K/Pg boundary fern spore spike: Anemia elongata (Newberry) Knowlton, Dennastra sorimarginata McIver et Basinger, and the Coniopteris-like fern “Dennstaedtia” americana Knowlton. Conclusions. Arborescent ferns were not among the first plants in western North America to thrive in the immediate wake of ecological collapse at the K/Pg boundary. Basal polypod ferns can be linked to Cyathidites spores in the northern Great Plains, perhaps because of a latitudinal climatic gradient. These results could explain taxonomic inversion in the dual-phase fern spore spike between western North America and New Zealand.
... For the three Williston Basin floras, several lines of evidence suggest that MAT should be >10 C (Larcher and Winter, 1981;Greenwood and Wing, 1995;Zachos et al., 2001;Peppe, 2010), while one other suggests ≥14 C (Markwick, 1998). The MLR estimates (Peppe et al., 2011) were all ≥15 C (15.7, 15.0, 16.3, ± 4.0 C), while our MAT estimates of these floras were all >12 C (13.1, 13.6, 12.5, ± 3.5 C; Table 6). ...
Digital leaf physiognomy (DLP) is considered as one of the most promising methods for estimating past climate. However, current models built using the DLP data set still lack precision, especially for mean annual precipitation (MAP). To improve predictive power, we developed five machine learning (ML) models for mean annual temperature (MAT) and MAP respectively, and then tested the precision of these models and some of their averaging compared with that obtained from other models. The precision of all models was assessed using a repeated stratified 10‐fold cross‐validation. For MAT, three combinations of models ( R ² = .77) presented moderate improvements in precision over the multiple linear regression (MLR) model ( R ² = .68). For log e (MAP), the averaging of the support vector machine (SVM) and boosting models improved the R ² from .19 to .63 compared with that of the MLR model. For MAP, the R ² of this model combination was 0.49, which was much better than that of the artificial neural network (ANN) model ( R ² = .21). Even the bagging model, which had the lowest R ² (.37) for log e (MAP), demonstrated better precision ( R ² = .27) for MAP. Our palaeoclimate estimates for nine fossil floras were also more accurate, because they were in better agreement with independent paleoclimate evidence. Our study confirms that our ML models and their averaging can improve paleoclimatic reconstructions, providing a better understanding of the relationship between climate and leaf physiognomy.
... This floral work in Montana is ongoing, but preliminary trends can be compared with prior work in North America. Early Paleocene floras from elsewhere in the Williston Basin (e.g., North Dakota; Wilf and Johnson 2004;Peppe 2010) and farther south in the Western Interior (e.g., Hanna Basin, San Juan Basin, Denver Basin; Dunn 2003, Flynn and Peppe 2019 present differing patterns of plant recovery during this interval. These works broadly present two alternative hypotheses for the pattern of plant recovery: that floras regained pre-extinction diversity within the earliest~300 ka of the Paleocene or that floras remained homogeneous and depauperate for at least 1 Ma (Wilf and Johnson 2004). ...
... A basin-scale examination of fossil flora preserved within the Paleocene sediments of the Fort Union Formation indicates that this area was covered with lowland swamp vegetation extending for over ca 300 kilometres, from the Cannonball Sea in the east to the foothills of the Rocky Mountains in the west (Brown, 1962). A basin-scale quantitative analysis of the megafloral record shows that vegetation was dominated by dicotyledonous angiosperm species, i.e. one major group of flowering plants, for 79 % (Peppe, 2010). The brackish water tongues of the Cannonball Member, exposed along the Little Missouri River (Fig. 3.1B), are composed of dark black-brown mudstones that were likely deposited in lagoons during terrigenous inflow of clay and silt, derived from rivers draining a low-gradient coastal plain (Van Alstine, 1974). ...
The work in this thesis has corroborated that fluvial sedimentary rocks may have partly been formed under the influence of orbital-forced climate changes. The identification of astronomical control on fluvial deposition could, therefore, provide us important new insights on how global and regional climate change may impact fluvial environments. There may be regular and hierarchic stratigraphic patterns in fluvial successions hinting towards Milankovitch cycles, but they do not necessarily have to be. Flume experiments show that autogenic processes including channel avulsion and lateral
migration can produce clastic compensational stacking patterns resembling the regularity and hierarchy of Milankovitch cyclicity (Hajek and Straub, 2017). Disentangling orbital from autogenic controls on stacking patterns within fluvial deposits solely dominated by clastic deposition is therefore a high challenge or, even, an endless task. The game changes when channel-induced clastic stratigraphy bears pronounced intercalations of lower-energy overbank soil facies such as red palaeosols (Abels et al., 2013) and coals (Fielding and Webb, 1996; Noorbergen et al., 2018). The architecture and lateral extent of such overbank soil facies, namely, can provide an important criterion to disentangle autogenic from allogenic control (Chapter 2). In case of autogenic compensational stacking the accumulation of overbank sediments is synchronous to channel bed
aggradation resulting in the channel lithofacies gradually passing into the lateral overbank facies. When this architecture is not found and when the channel-soil facies stratigraphically succeed one another at Milankovitch timescales, an orbital control on such alternations can be rectified (Chapters 2, 3, and 4). The application of this time-architecture dual-criterion has most potential in soil-bearing fluvial successions that can be well dated while their outcrops are regionally wellexposed (Chapter 4). In the studied successions of north-eastern Montana (USA), coal-bearing fluvial deposits of the lower Paleocene Fort Union Formation are spectacularly exposed and contain
multiple chronostratigraphic marker levels. The successions have proven to be excellent archives for detailed sedimentological and chronostratigraphical analyses (Chapters 2, 3, and 4) as well as they appeared highly valuable for the generation of high-resolution geochemical proxy records within coal (Chapter 5). They allowed for testing challenging research hypotheses such as the role of orbital forcing in building coal-bearing fluvial stratigraphy as well as the potential implication of orbital control on widespread peat formation to global carbon cycle dynamics (Zachos et al., 2010).
... A basin-scale examination of fossil flora preserved within the Palaeocene sediments of the Fort Union Formation indicates that this area was covered with lowland swamp vegetation extending for over ca 300 km, from the Cannonball Sea in the east to the foothills of the Rocky Mountains in the west (Brown, 1962). A basin-scale quantitative analysis of the megafloral record shows that vegetation was dominated by dicotyledonous angiosperm species, i.e. one major group of flowering plants, for 79% (Peppe, 2010). The brackish water tongues of the Cannonball Member, exposed along the Little Missouri River (Fig. 1B), are composed of dark black-brown mudstones that were likely deposited in lagoons during terrigenous inflow of clay and silt, derived from rivers draining a low-gradient coastal plain (Van Alstine, 1974). ...
Aggradation and fluvial incision controlled by downstream base‐level changes at timescales of 10 to 500 kyr is incorporated in classic sequence stratigraphic models. However, upstream climate control on sediment supply and discharge variability causes fluvial incision and aggradation as well. Orbital forcing often regulates climate change at 10 to 500 kyr timescales while tectonic processes such as flexural (un)loading exert a dominant control at timescales longer than 500 kyr. It remains challenging to attribute fluvial incision and aggradation to upstream or downstream processes or disentangle allogenic from autogenic forcing, because time control is mostly limited in fluvial successions. The Palaeocene outcrops of the fluvial Lebo Shale Member in north‐eastern Montana (Williston Basin, USA) constitute an exception. This study uses a distinctive tephra layer and two geomagnetic polarity reversals to create a 15 km long chronostratigraphic framework based on the correlation of twelve sections. Three aggradation–incision sequences are identified with durations of approximately 400 kyr, suggesting a relation with long‐eccentricity. This age control further reveals that incision occurred during the approach of – or during – a 405 kyr long‐eccentricity minimum. A long‐term relaxation of the hydrological cycle related to such an orbital phasing potentially exerts an upstream climate control on river incision. Upstream, an expanding vegetation cover is expected because of an increasingly constant moisture supply to source areas. Entrapping by vegetation led to a significantly reduced sediment supply relative to discharge, especially at times of low evapotranspiration. Hence, high discharges resulted in incision. This study assesses the long‐eccentricity regulated climate control on fluvial aggradation and incision in a new aggradation–incision sequence model.
... Age justification. Dipteronia brownii occurs within the P4 Pollen Zone in the type section of Nichols and Ott [67], which falls fully within Magnetic Anomaly Zone C26r [68], the end of which is dated to 59.24 Ma in the combined age model of Vandenberghe et al. [50]. [69]. ...
The explosive increase of molecular sequence data has produced unprecedented opportunities for addressing a number of evolutionary problems. Specially, the species divergence time estimation is fundamental because our understanding of history of life depends critically on knowledge of the ages of major clades. This thesis explores the use of molecular data (genome-scale datasets), combined with statistical summaries of the fossil record, to date the origin of angiosperms (flowering plants) and the divergence times of its major groups in an attempt to resolve the apparent conflict between the molecular dates and fossil evidence. Moreover, because fossil calibrations are the major source of information for resolving the distances between molecular sequences into estimates of absolute times and absolute rates in molecular clock dating analysis, several strategies for converting fossil calibrations into the prior on times are evaluated. Chapter one introduces the diversity and evolution of angiosperms, reviews the current literature that is based predominantly on systematics, phylogenetics, palaeobotany and plant molecular evolution. In introducing the early evolution of angiosperms this chapter highlights the questions associated with the origin of angiosperms and presents aims of the thesis. Chapter two focuses on molecular clock dating methods. It discusses different approaches for estimating divergence times, with emphasis on Bayesian molecular clock dating methods. Chapter three uses a powerful Bayesian method to analyze a molecular dataset of 83 genes from 644 taxa of vascular plants, combined with a suite of 52 fully-justified fossil calibrations to disentangle the pattern of angiosperm diversification. The results indicate that crown angiosperms originated during the Triassic to the Jurassic interval, long prior to the Cretaceous Terrestrial Revolution. This analysis demonstrates that even though many sources of uncertainty are explored, attempts to control for these factors still do not bring clock estimates and earliest confident fossil occurrences into agreement. A post-Jurassic origin of angiosperms was rejected, supporting the notion of a cryptic early history of angiosperms. The main factors affecting the estimates in this study are also discussed. Subsequently, in chapter four different strategies for summarizing fossil information to construct calibration priors were assessed employing an a priori procedure for deriving accurate calibration densities in Bayesian divergence dating. In general, truncation has a great impact on calibrations so that the effective priors on the calibration node ages after the truncation can be very different from the user-specified calibration densities. The different strategies for generating the effective prior also had considerable impact, leading to very different marginal effective priors. Arbitrary parameters used to implement minimum-bound calibrations were found to have a strong impact upon the prior and posterior of the divergence times. The results highlight the importance of inspecting the joint time prior used by the dating program before any Bayesian dating analysis. Finally, chapter five draws together key finding from chapters three and four, and reviews how this work advances our understanding of the origin and evolution of angiosperms and on molecular clock dating using fossil calibrations. This chapter also highlights new gaps in our understanding of early evolution of angiosperms and in the implementation of fossil calibrations in Bayesian molecular clock dating, and discusses several areas for future research. Overall, this thesis highlights that more room for improvement might lie in refining our knowledge and use of fossil calibrations, the resulting improvements to molecular estimates of timescales will lead to a better understanding of angiosperm evolution. I speculate that these results will also shed light on dating discrepancies in other major clades.
... The Tongue River Member consists of poorly consolidated sandstone, mudstone, thick beds of lignite and small lenses of limestone (Hickey, 1977;Jacob, 1976). An unconformity with an age gap of~2 Myr probably exists at the contact between the Ludlow and Tongue River members, and the Tongue River Member was likely deposited from~61 to~58.5 Ma, based on a megaflora study (Peppe, 2010). The Sentinel Butte Member has a similar lithology as the Tongue River Member, except that this member is better consolidated by carbonate cement and the mudstone contains zones of dense discoidal siderite concretions (Hickey, 1977;Jacob, 1976). ...
Detrital zircon U-Pb provenance in the northern Great Plains reveals histories of drainage reorganization of the paleo-Missouri River in response to Cenozoic tectonic and magmatic processes in the central North American Cordillera. During the latest Cretaceous, sediment provenance was confined to the Cordilleran hinterland in central Idaho and southwestern Montana, probably due to the existence of a subtle paleohydraulic divide in northwestern Montana. During the early to middle Paleocene, the paleodrainage was expanded to cover the Belt Supergroup in northwestern Montana in response to the eastward propagation of the Cordilleran thrust belt. During the late Paleocene to early Eocene, the final movement of the thrust belt and the initial extension of the Cordilleran hinterland shifted the drainage divide to the orogenic front and caused focused erosion of the upper Lower to Upper Cretaceous rocks to the east. During the middle Eocene to early Oligocene, a significant increase of Archean grains suggests renewed exhumation of the Laramide province and sediment delivery by the paleo-Yellowstone River originated in the central Rocky Mountains. The presence of middle Eocene to early Oligocene zircons during this stage also suggests headwater erosion of the paleo-Upper Missouri River into the Dillion volcanic field in southwestern Montana. These interpretations indicate that a drainage pattern similar to that of the modern Missouri River was established during middle Eocene to early Oligocene time. The detrital zircon maximum depositional ages also improve the chronostratigraphic framework of the Paleogene strata. Our study demonstrates that orogenic processes can be well archived in sedimentary records far away from orogenic systems.
... Age justification. Dipteronia brownii occurs within the P4 Pollen Zone in the type section of Nichols and Ott[67], which falls fully within Magnetic Anomaly Zone C26r[68], the end of which is dated to 59.24 Ma in the combined age model of Vandenberghe et al.[50].Node 878 | SG Ailanthus plusCitrus | MRCA: Ailanthus-Swietenia | 51.83 Ma. Fossil taxon and specimen. ...
Fig. S1 Maximum likelihood (ML) phylogenetic tree from plastid 1st–2nd codon positions for 643 taxa.
Fig. S2 Maximum likelihood (ML) phylogenetic tree from mitochondrial 1st–2nd codon positions for 515 taxa.
Fig. S3 Maximum likelihood (ML) phylogenetic tree from nuclear RNA genes for 540 taxa.
Fig. S4 RAxML phylogenetic tree from the 83 genes and 644 taxa of tracheophytes.
Fig. S5 Chronogram of 644 taxa of tracheophytes (from SA‐IR‐3P).
Fig. S6 Calibration, prior and posterior densities for 52 calibrated nodes in the tree and for the five calibration strategies.
Table S1 List of genes included in the dataset
Table S2 Basic information of data partitions
Table S3 Summary of fossil calibrations used in this study in million years before the present
Table S4 The 95% high posterior density (HPD) limits of posterior divergence times for selected nodes in the vascular plant tree under the five calibration strategies in millions of years before the present
Table S5 The 95% high posterior density (HPD) limits of posterior divergence times, in millions of years before the present, for selected nodes in the vascular plant tree under different partition strategies, autocorrelated rates (AR) model, birth–death parameters and excluding lycophytes and ferns
Notes S1 Justification of fossil calibrations.
... Fig. 2.2; e.g.,Lehman 1990;Nordt et al. 2003;Atchley et al. 2004; Lehman and Busby 2007;Cobb 2016; Leslie et al. in press).Trace-fossil analysis has been previously demonstrated as an effective tool for refining the sedimentological history and stratigraphic relationships at other K-Pg exposures(Ekdale and Bromley 1984;Savrda 1993;Ekdale and Stinnesbeck 1998;Twitchett and Barras 2004;Rodríguez-Tovar et al. 2004;2010;Rodríguez-Tovar 2005;Chin et al. 2013;Sosa-Montes De Oca et al. 2013;2016;Horner et al. 2016). Thus, in the absence of diagnostic K-Pg boundary indicators, we propose that the trace fossil dataset herein can be used to refine the stratigraphic position of the K-Pg event in the Dawson ...
The assemblage of Pleistocene megafauna at Waco Mammoth National Monument (WMNM) and the terrestrial Cretaceous-Paleogene (K-Pg) boundary at Big Bend National Park are just two examples that demonstrate the peril effects of an extreme environmental perturbation on ancient ecosystems. Ichnology is the study of traces that are generated by organismal behavior; therefore, analyzing major die-offs through an ichnological lens can provide a unique perspective to understand the ethology of the survivors. At WMNM trace-fossil analysis was combined with taphonomy, which revealed that the Columbian mammoth herd was subjected to extensive vertebrate and invertebrate scavenging. These findings necessitated a re-evaluation of the causal mechanisms responsible for the death of the herd, as well as demonstrated that scavenging organisms out-survived, at least for some time, the large herbivores in this case. The application of ichnology to the terrestrial K-Pg boundary revealed new findings about the surviving organisms in response to the end-Cretaceous extinction. Herbivorous, soil-dwelling insects, as evidenced from analogous traces, were significantly reduced in body size (Lilliput effect) following the aftermath of the event. These findings, in conjunction with research on marine-organism responses, provide empirical evidence that the Lilliput effect was a phenomenon that affected surviving organisms across highly disparate trophic levels and ecosystems. Lastly, a hybrid approach of ichnology and zooarchaeology was used to develop morphological criteria for taphonomic analysts to differentiate between carnivore traces and unintentional, preparator air-scribe marks, which can be more similar than one might imagine. Utilization of an ichnological perspective to study survival behaviors from the ancient past may one day help address some of the decisions regarding our current mass extinction.
... This low-diversity recovery macrofloral assemblage was coined FUI by Johnson (2002). The FUI and other time-equivalent assemblages (Peppe et al., 2009;Peppe, 2010) are composed of taxa that survived the mass extinction event, yet, were only marginal components of the HCF floral assemblages, generally most common in mire facies (Johnson, 2002). This survival pattern may therefore represent the existence of an important local ecological filter in the recovery process. ...
... Much of the synoptic view of the megafl ora of the latest Cretaceous and early Paleocene in the western interior of North America comes from intensively studied areas in southwestern North Dakota, southeastern Montana, central Colorado, and southern Alberta (Brown, 1939;Shoemaker, 1966;Johnson et al., 1989Johnson and Hickey, 1990;Johnson, 1992Johnson, , 2002McIver and Basinger, 1993;Johnson and Ellis, 2002;Barclay et al., 2003;Ellis et al., 2003Ellis et al., , 2004Wilf et al., 2003Wilf et al., , 2006Barclay and Johnson, 2004;Wilf and Johnson, 2004;Peppe et al., 2007;Peppe, 2010;Hartman et al., this volume). These areas have abundant, rich, and well-preserved megafl oras that have been studied by a small army of professionals and amateurs over the last two decades. ...
The Hell Creek Formation in eastern Montana has yielded well-preserved leaf megafossil localities that provide insight into the vegetation and climate of the latest Cretaceous. Among the most basal, the PDM locality (UCMP [University of California Museum of Paleontology] PB99057 = MOR [Museum of the Rockies] HC-278) occurs in channel sandstones ∼10 m above the underlying Fox Hills Formation. The locality represents a fluvial/estuarine environment. Leaf megafossil impressions were preserved on clay drapes within the channel. Angiosperms dominated the flora (13 of 17 morphotypes). Dryophyllum subfalcatum and "Vitis" stantoni, two common morphospecies in the Hell Creek Formation, are well represented. Gymnosperms including Metasequoia, Glyptostrobus, Cupressinocladus, and Ginkgo are rare; ferns and cycadophytes are absent. Univariate leaf-margin analysis produced mean annual temperature (MAT) estimates of ∼7-11 °C (5-14 °C including overlapping estimation errors). The Climate Leaf Analysis Multivariate Program (CLAMP) produced a MAT value of 11-12 °C ± 2 °C. Leaf area analysis produced mean annual precipitation (MAP) estimates of 197 cm (+152/-86 cm) and 191 cm (+161/-87 cm), while CLAMP produced a growing season precipitation estimate of 82-90 ± 48 cm. The wetter MAP values are consistent with paleosols near the base of the formation, which lack paleosol carbonate. CLAMP results further suggest seasonality in both temperature and precipitation. Some PDM morphotypes are familiar from the Hell Creek I floral zone of North Dakota, and several are not, suggesting greater spatial and/or temporal heterogeneity in the Hell Creek Formation flora than has been previously appreciated.
... Overall phytolith morphotype diversity (Fig. 5) is not directly linked to vegetation diversity, as redundancy and multiplicity are common among phytolith morphotypes (Piperno, 2006); however, significant changes in the relative abundance of functional groups, as observed through this section (Fig. 4), can signal major shifts in ecosystem composition (Strömberg et al., 2007). While the number of diagnostic morphotypes (n = 12) in this middle Paleocene section is low compared to other Cenozoic assemblages in South America (e.g., Strömberg et al., 2013), it is important to note that: 1) overall plant diversity during the mid-Paleocene was likely substantially lower than at other times during the Cenozoic (Wing et al., 1995;Peppe, 2010), even in the relatively higher-diversity South American floras (Jaramillo et al., 2006;Iglesias et al., 2007), and 2) the number of phytolith morphotypes increases dramatically through time with the introduction and spread of grasses, which produce more diagnostic morphotypes than other plant groups (Strömberg, 2003;Piperno, 2006). Due to both the limited abundance of grasses and the generally lower overall floral diversity of the middle Paleocene, the low number of morphotypes in this section is likely not a result of preservational biasing, and the observed trends in vegetation composition during the MPBE intervals are likely robust. ...
... The Paleogene was a time of profound reorganization of the biosphere, following the Cretaceous-Paleogene mass extinction (Vajda et al., 2001;Benton and Harper, 2009), which was followed by the loss of major Mesozoic lineages and low-diversity fl oras during the Paleocene (Wappler et al., 2009;Wing and DiMichele, 1995;Peppe, 2010). Here, we explore new evidence of ferns and fl owering plants in the early Paleogene drill-core macrofossil record of the Boltysh meteorite impact crater (Kelley and Gurov, 2002;Gurov et al., 2006), which provides a unique window into Paleocene vegetation. ...
We analyzed the plant macro- and mesofossil records deposited in the Paleocene oil shales of the Boltysh crater (Ukraine) in terms of leaf morphology and its implication for reconstruction of the vegetation and paleoecology of the region. During the early Cenozoic, the Boltysh astrobleme formed a geothermal crater lake that accumulated sediments, preserving a record from the Paleocene to the early middle Eocene. These sediments contain fossil leaf fragments of ferns and angiosperms that grew close to the lake. The occurrence of the Mesozoic fern Weichselia reticulata is of importance. This discovery suggests the survival of this Jurassic to Cretaceous fern into the early Paleogene in the refugial geothermal ecosystem of the Boltysh crater area. Our finding is the youngest record of this fern, although it was a widespread and common element of secondary vegetation during the Cretaceous. The local survival of this fern may have been fostered by the unique combination of edaphic environmental factors of the Boltysh hydrothermal area. Other plant fossils include fragments of leaves that represent ferns likely belonging to lineages that diversified in the shadow of angiosperms, as well as remains of the flowering plants Pseudosalix, Sorbus, Comptonia, and ?Myrica leaf morphotypes.
Accepted 31 January 2014.
© Geological Society of America
https://books.google.ru/books?id=dqFmBAAAQBAJ&pg=PA163&lpg=PA163&dq=Comptonia+dryandrifolia+...&source=bl&ots=b8_kYbhan2&sig=aqR6yPlktHSBcjyifJS7F5tCE_k&hl=ru&sa=X&ei=dWXmVPLHGKnoywPC2IEQ&ved=0CDwQ6AEwBQ#v=onepage&q=Comptonia%20dryandrifolia%20...&f=false
... The first occurrence of a typical Paleocene taxon is Paranymphaea crassifolia, which is recorded a few meters above the K-Pg boundary (Johnson, 2002;Bercovici et al., 2008). The distribution of major Paleogene vegetation types was also discussed by Macrofloristic diversity remained low in some North American ecosystems for several million years following the end-Cretaceous event and did not reach end-Cretaceous values until the Eocene (Johnson and Ellis, 2002;Barclay et al., 2003;Barclay and Johnson, 2004;Peppe, 2010). However, the vegetation in other areas recovered much faster and exceeded Cretaceous diversity levels, only 1 Ma after the K-Pg event. ...
Changes in pollen and spore assemblages across the Cretaceous–Paleogene (K–Pg) boundary elucidate the vegetation response to a global environmental crisis triggered by an asteroid impact in Mexico 66 Ma. The Cretaceous–Paleogene boundary clay, associated with the Chicxulub asteroid impact event, constitutes a unique, global marker bed enabling comparison of the world-wide palynological signal spanning the mass extinction event. The data from both hemispheres are consistent, revealing diverse latest Cretaceous assemblages of pollen and spores that were affected by a major diversity loss as a consequence of the K–Pg event. Here we combine new results with past studies to provide an integrated global perspective of the terrestrial vegetation record across the K–Pg boundary. We further apply the K–Pg event as a template to asses the causal mechanism behind other major events in Earths history. The end-Permian, end-Triassic, and the K–Pg mass-extinctions were responses to different causal processes that resulted in essentially similar succession of decline and recovery phases, although expressed at different temporal scales. The events share a characteristic pattern of a bloom of opportunistic “crisis” tax followed by a pulse in pioneer communities, and finally a recovery in diversity including evolution of new taxa.
Based on their similar extinction and recovery patterns and the fact that the Last and First Appearance Datums associated with the extinctions are separated in time, we recommend using the K–Pg event as a model and to use relative abundance data for the stratigraphic definition of mass-extinction events and the placement of associated chronostratigraphic boundaries.
... Uncertainties for CLAMP MATs are 2.0°C for the MET dataset and 2.1°C for the GRID dataset. Data from Axelrod, 1966;Wolfe, 1971;Turner et al., 1983;Triplehorn et al., 1984;Wehr, 1987 andWing et al., 1991;Greenwood, 1993;Wing and Greenwood, 1993;Burnham, 1994;Manchester, 1994;Wolfe, 1994;Greenwood and Wing, 1995;Wilf, 1997;Smith et al., 1998;Wolfe et al., 1998;Graham, 1999;Wilf, 2000;Wolfe and Dilcher, 2000;Evanoff et al., 2001;Kester, 2001;Meyer, 2001;Malchus et al., 2002;Myers, 2003;Wolfe et al., 2003;Fricke and Wing, 2004;Retallack et al., 2004;Warwick et al., 2004;Dillhoff et al., 2005;Greenwood et al., 2005;Mathewes and Greenwood, 2007;Henry, 2008;McLean, 2009;Devore and Pigg, 2010;Lovelock, 2010;Peppe, 2010;Peppe et al., 2011;Sunderlin et al., 2011 Greenwood, 1993 (continued on next page) after the Slide Member (Breedlovestrout, 2011). Tilia first occurs in the Slide Member and is present in the Maple Falls and Padden members (Breedlovestrout, 2011). ...
The Chuckanut and Manastash formations were deposited in a lowland fluvial environment in western Washington during the Paleocene–Eocene. We provide a thorough paleotemperature analysis using the physiognomic characteristics from the fossil dicotyledonous leaves from these formations using two techniques, Leaf Margin Analysis (LMA) and Climate Leaf Analysis Multivariate Program (CLAMP). This work differs from previous analyses by 1) analyzing more localities and including the assessment of the never-before described Taneum Ridge Body and Manastash Main Body within the Manastash Formation and the Maple Falls Member of the Chuckanut Formation, and 2) using two different techniques to decipher mean annual temperatures through time. In this study, mean annual temperatures (MAT) were determined from 125 distinct morphotypes and are several degrees higher at each locality than previously reported. MAT values derived from LMA ranged from 17.0° to 28.8 °C for the lowermost and 13.4° to 19.5 °C for the uppermost Chuckanut Formation. The Manastash Formation had MATs ranging from 17.1 °C to 29.1 °C. Using CLAMP, paleotemperatures ranged from 15.3° to 19.4 °C for the lowermost and 12.3° to 15.6 °C for the uppermost Chuckanut Formation and 15.8 to 21.3 °C for the Manastash Formation. These data are compared to other Eocene–Paleocene formations in the western US; the Chuckanut and Manastash formations record some of the warmest paleotemperatures in the Paleogene in the western US because of their low-elevation locations. These paleotemperatures may reflect the terrestrial signal of paleoclimate optima defined in marine rocks during the Paleocene–Eocene.
... Quereuxia is widely known in Eurasia from the Late Cretaceous Cenomanian to the end of the Paleogene (Lee & Li, 1959;Golovneva, 1991Golovneva, , 2000Moiseeva, 2010) and in North America from the Late Cretaceous Campanian and Maastrichtian to the Eocene (e.g. Peppe, 2010). In North America, early paleobotanists consistently employed the synonym Trapa? ...
The Lythraceae (Myrtales) are a family of 28 genera and ca. 600 species constituting with the Combretaceae and sister family Onagraceae a major lineage of the Myrtales and including the former Sonneratiaceae, Duabangaceae, Punicaceae, and Trapaceae. The fossil record of the family is extensive and significant new discoveries have been added to the record in recent years. This review provides a vetted summary of fossils attributed to the Lythraceae, their geographic distributions, and their stratigraphic ranges. It anticipates the use of the information to generate robustly dated molecular phylogenies to accurately reconstruct the evolutionary and biogeographic history of the family. Fossils of 44 genera or form genera have been attributed to the Lythraceae; 24 are accepted here as lythracean. Fourteen of the 28 modern genera have fossil representatives: Adenaria, Crenea, Cuphea, Decodon, Duabanga, Lafoensia, Lagerstroemia, Lawsonia, Lythrum, Pemphis, Punica, Sonneratia, Trapa, and Woodfordia. Ten extinct genera are recognized. The most common kinds of fossil remains are seeds and pollen. The only fossil flower confidently accepted in the family is the extinct genus Sahnianthus from the Early Paleocene of India. The oldest confirmed evidence of the Lythraceae is pollen of Lythrum/Peplis from the Late Cretaceous (early Campanian, 82−81 Ma) of Wyoming. Seeds of Decodon from the late Campanian (73.5 Ma) of northern Mexico are next oldest. Sonneratia, Lagerstroemia, and extinct Sahnianthus first appear in the Paleocene of the Indian subcontinent; extinct Hemitrapa fruits first occur in the Paleocene of northwestern North America. Diversification of the Lythraceae occurred primarily during two major periods of global temperature change, during the Paleocene-Eocene Thermal Maximum and from the middle Miocene forward when temperatures decreased markedly and seasonality and dry-adapted vegetation types became more prominent. Fossils of the Lythraceae from South America and Africa are limited in number. The few dates available for South American genera are comparatively young and diversification of the largest genus, Cuphea (ca. 240 species), was mainly a Quaternary event. A phylogeny of the family is briefly explored and examples of specialized characters occurring in the oldest known genera are noted. The fossil record of the Lythraceae is presently too fragmentary to confidently reconstruct the early history of the family. The record indicates, however, that the family was well-diversified and widely dispersed globally over a wide latitudinal range by the end of the Paleocene.
Some of the most extensive terrestrial biomes today consist of open vegetation, including temperate grasslands and tropical savannas. These biomes originated relatively recently in Earth’s history, likely replacing forested habitats in the second half of the Cenozoic. However, the timing of their origination and expansion remains disputed. Here, we present a Bayesian deep learning model that utilizes information from fossil evidence, geologic models, and paleoclimatic proxies to reconstruct paleovegetation, placing the emergence of open habitats in North America at around 23 million years ago. By the time of the onset of the Quaternary glacial cycles, open habitats were covering more than 30% of North America and were expanding at peak rates, to eventually become the most prominent natural vegetation type today. Our entirely data-driven approach demonstrates how deep learning can harness unexplored signals from complex data sets to provide insights into the evolution of Earth’s biomes in time and space. The expansion timing and dynamics of open vegetation are disputed. Here, the authors present a model of paleovegetation changes in North America, showing open vegetation beginning around 23 million years ago and accelerating at 5 million years ago to become the most prominent natural vegetation type in North America today.
Open vegetation today constitutes one of the most extensive biomes on earth, including temperate grasslands and tropical savannas. Yet these biomes originated relatively recently in earth history, likely replacing forested habitats as recently as the second half of the Cenozoic, although the timing of their origination and the dynamics of their expansion remain uncertain. Here, we present a new hypothesis of paleovegetation change in North America, showing that open habitats originated between 25 and 20 Ma in the center of the continent, and expanded rapidly starting 8 Ma to eventually become the most prominent vegetation type today. To obtain space-time predictions of paleovegetation, we developed a new Bayesian deep learning model that utilizes available information from fossil evidence, geologic models, and paleoclimate proxies. We compiled a large dataset of paleovegetation reconstructions from the peer-reviewed literature, which we used in combination with current vegetation data to train the model. The model learns to predict vegetation based on the learned associations between the vegetation at a given site and multiple biotic and abiotic predictors: fossil mammal occurrences, plant macrofossils, estimates of temperature and precipitation, latitude, and the effects of spatial and temporal autocorrelation. Our results provide a new, spatially detailed reconstruction of habitat evolution in North America and our deep learning model paves the way for a new quantitative approach to estimating paleovegetation changes.
We travel back in time through this chapter and take a field trip to western North America during the Paleocene– Eocene Thermal Maximum (PETM), some 56 million years ago. Here, plant-and-animal fossils were discovered in the warmest interval of the last 500 million years, a condition that lasted only 200,000 years. We provide a brief review of what may have caused a massive influx of atmospheric carbon detected during the PETM. We contrast the PETM to similar ongoing thermal events that began during the Industrial Revolution and persist today. We discuss the tools that paleobotanists have devised to interpret climate from fossil leaf, pollen, and wood records, and present a brief overview of floral changes that occurred in western North America before, during, and right after this thermal maximum. Lastly, we explore how fossil data can be incorporated with ecological and systematic information into biogeographical models to predict how plants respond to climate change.
Sedimentary basins throughout the North American Western Interior contain a record of Late Cretaceous through Eocene deposition related to the Laramide orogeny. The typical stratigraphic progression includes an uppermost Cretaceous fluvio-deltaic geologic formation that is unconformably overlain by an alluvial or paludal Paleocene geologic formation. The Paleocene unit is usually characterized by drab overbank facies, and overlain by an interval of amalgamated fluvial sand bodies. The overlying Eocene geologic units are characterized by red bed overbank facies. These major stratigraphic changes have been variably linked to long-wavelength dynamic subsidence, local uplift, and climatic shifts. Herein, we evaluate the depositional history of the Huerfano Basin of south-central Colorado in this overarching context. Our study presents a detailed lithofacies analysis of the Poison Canyon, Cuchara, and Huerfano Formations integrated with a new bulk (1) organic carbon isotope record, n = 299 measurements (Data Supplement 1A); and (2) magnetic record, n = 247 measurements (Data Supplement 1B). We interpret that the Paleocene Poison Canyon Formation was deposited by a braided or coarse-grained meandering river system with relatively poorly drained floodplains. The Eocene Huerfano Formation was likely deposited by a coarse-grained meandering river system with a comparatively well-drained floodplain. This pattern mirrors other Laramide basins, and is likely related to a regional drying pattern linked to long-term warming during the early Paleogene. Age of the intervening Cuchara Formation is poorly resolved, but is an anomalously thick and coarse-grained fluvial unit, with evidence for extensive reworking of floodplain deposits and a moderate coarsening-upward pattern. The Cuchara Formation is associated with magnetic trends that suggest greater oxidation and weathering, and greater variability in rainfall patterns, as well as a subtle negative shift in carbon isotope values. This pattern indicates a period of widespread progradation within the basin, potentially related to a major Laramide uplift event that affected Colorado’s Wet Mountains, Front Range, and Sangre de Cristo Mountains.
Six fossil leaf species are described from impression fossils collected from the Paleocene Fort Union Formation in the Williston Basin in southwestern North Dakota, USA. They are Meliosma vandaelium sp. nov., Meliosma thriviensis sp. nov., Ternstromites paucimissouriensis sp. nov., Macginitiea nascens sp. nov., Dicotylophyllum horsecreekium sp. nov. and Dicotylophyllum han-sonium sp. nov. These species represent some of the elements of the Fort Union Formation that are biostratigraphically important megafloral zone taxa or are species that demonstrate an evolutionary relationship to floras from the Eocene Golden Valley Formation. Some of the species described here suggest that new species endemic to the Williston Basin evolved through the Paleocene and into the Eocene. If the pattern of the origination of endemic daughter species seen in the Williston Basin is consistent across the Western Interior basins of North America, it might have driven up gamma diversity through the Paleogene. This provides a possible explanation for the relatively steep vegetation diversity gradients seen in mid-and high-latitude pollen floras in North America during the late Paleocene and early Eocene.
The Paleocene megafossil flora of the Rocky Mountains and Great Plains region in the United States of America, including leaves, cones, fruits, and seeds, monographed by Roland W. Brown in 1962, has been reevaluated and updated to include subsequent taxonomic revisions. The scope of this investigation included thousands of specimens from more than 450 localities of the Fort Union, Evanston, Ferris, Raton, Bear, Lebo, Melville, Ludlow, Tongue River and Sentinel Butte strata of New Mexico, Colorado, Wyoming, Montana and North and South Dakota. A large number of floristic elements remain uncertain as to their modern familial affinities due to limited diagnostic characters, or insufficient comparative investigations. Nevertheless, many of Brown’s determinations have been upheld and several newly recognized genera and families have strong support. The flora includes greater diversity of Platanaceae and Cornales than Brown had recognized. These, together with Fagales (particularly Betulaceae and Juglandaceae), Saxifragales (Trochodendroides, Archeampelos and Nyssidium), are widespread and prominent members of the flora. New combinations introduced here include Ensete goldianum (LESQUEREUX) comb. nov., Macginitiea nobilis (NEWBERRY) comb. nov., Platanites raynoldsii (NEWBERRY) comb. nov., Trochodendroides genetrix (NEWBERRY) comb nov., Cucurbitaciphyllum lobatum (KNOWLTON) comb. nov., and Mciveraephyllum nebrascense (SCHIMPER) comb. nov. Georeference data are provided for all of the localities cited by Brown. © 2014, Acta Musei Nationalis Pragae, Series B - Historia Naturalis. All right reserved.
We analyzed paleomagnetic samples and documented the stratigraphy from two sections near Miles City, Montana to determine the geomagnetic polarity stratigraphy and to constrain the age and duration of the Lebo and Tongue River Members of the Fort Union Formation in the northeastern Powder River Basin. The resulting polarity sequence can be correlated to subchrons C29n–C26r of the geomag-netic polarity time scale. By interpolating measured sediment accumulation rates from the base of C28r to the top of C27n, and then extrapolating to the top of the Tongue River Member and the bottom of the Lebo Member, we developed two age models to estimate the durations of the Lebo and Tongue River Members. Based on the first model, which uses different sedimentation rates for the Lebo and Tongue River Members, we estimate the duration of deposition of the Lebo to be between 1.30 and 1.74 million years and of the Tongue River to be between 1.42 and 1.61 million years. Using the second model, which uses the same sedimentation rate for the Lebo and Tongue River Members, we estimate the duration of deposition of the Lebo to be between 1.33 and 1.76 million years and of the Tongue River to be between 1.00 and 1.25 million years. Our results indicate a decrease in sediment accumulation rates in C27r, which is likely the result of a 0.26 to 0.62 million-year long depositional hiatus in the middle of C27r, represented by the Lebo–Tongue River contact. This unconfor-mity occurs 2 million years earlier than previously suggested and is likely contempo-raneous with unconformities in the Williston Basin and in southwestern Alberta, suggesting that it may be regionally significant.
Joseph H. Hartman, editor Table of Contents.
A North Dakota Geology Field Trip Primer. Joseph H. Hartman.
Hell Creek Formation Stratigraphy and Paleontology at the Stumpf Site Natural Area, Morton County, South-Central North Dakota. John W. Hoganson
Mud Buttes – A Cretaceous–Tertiary boundary section in southwestern North Dakota. Dean A. Pearson.
The Brown Ranch Locality area, “mid” Paleocene mammals and the tongues of the Cannonball Formation, Slope County, North Dakota. John P. Hunter and Joseph H. Hartman
The Late Paleocene Judson Local Fauna, North Dakota. Allen J. Kihm and Joseph H. Hartman
Stratigraphy and Paleontology of the White River Group, Little Badlands, Stark County, North Dakota. John W. Hoganson.
The Medicine Pole Hills Local Fauna, North Dakota. Allen J. Kihm.
[Document derived from and reviewed from 2003 SVP Guidebook.]
The Paleocene Tongue River Member of the Fort Union Formation contains trace-fossil associations indicative of marine influence in otherwise freshwater facies. The identified ichnogenera include: Arenicolites, Diplocraterion, Monocraterion, Ophiomorpha, Rhizocorallium, Skolithos linearis, Teichichnus, Thalassinoides, and one form of uncertain affinity. Two species of the marine diatom Coscinodiscus occur a few meters above the base of the member. The burrows occur in at least five discrete, thin, rippled, fine-grained sandstone beds within the lower 85 m of the member west of the Cedar Creek anticline (CCA) in the Signal Butte, Terry Badlands, and Pine Hills areas. T wo discrete burrowed beds are found in the lower 10 m of the member east of the CCA in the little Missouri River area. Abundant freshwater ostracodes include Bisulcocypridea arvadensis, Candona, and Cypridopsis. Freshwater bivalves include Plesielliptio and Pachydon mactriformis. We recognize four fossil assemblages that represent fluvio-Iacustrine, proximal estuarine, central estuarine, and distal estuarine environments. Biostratal alternations between fresh- and brackish-water assemblages indicate that the Tongue River Member was deposited along a low-gradient coastal plain that was repeatedly inundated from the east by the Cannonball Sea. The existence of marine-influenced beds in the Tongue River Member invalidates the basis for the Slope Formation.
To assess the degree to which forest litter reflects the source forest, three 1-ha plots of temperate deciduous forest were mapped and litter accumulating in these forests was sampled. Identity, position, and diameter of all stems 2 cm or larger diameter at breast height are known for each forest. Composition of the leaf litter is governed by two key factors: (1) abscised leaves are deposited primarily on the forest floor directly underneath the canopy that produced them, and (2) the leaf mass of a species is highly correlated with its stem cross-sectional area. These factors produce autochthonous litter samples that correspond closely in composition to the forest within a circle of canopy-height radius or less. Even relatively small litter samples (350 leaves) consistently contained all the common species in the local area. However, the rarer tree species were seldom recovered in the litter samples. Correlation coefficients for litter mass and basal area by species are typically over .80.
These observations have three important implications for interpreting autochthonous compression-fossil assemblages. First, approximate relative abundances of locally dominant and subdominant forest taxa can be obtained from relatively small samples of autochthonous compression-fossil assemblages. Second, representation of rare forest species, even in large fossil samples, will be fortuitous. For this reason, complete species lists and consistent estimates of richness cannot be derived directly from most existing samples of autochthonous compression-fossil assemblages. Third, the strong tendency for leaves to fall beneath the canopy of the tree that sheds them suggests that properly sampled autochthonous fossil leaf assemblages may yield information on crown size of individual trees and the spatial distribution of individuals and species, aspects of vegetational structure that have been thought accessible only in well-preserved “fossil forests” with standing trunks.
Comparisons of Tertiary floras of North America with those of Europe and Asia document a long history of floristic interchange. The stratigraphic and geographic ranges of selected conifer and angiosperm genera that are easily recognized in the fossil record provide a basis for discerning patterns in the routes and timings of intercontinental dispersals through the Tertiary.
A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
The warmest global temperatures of the Cenozoic Era occurred in early Eocene time, following a warming trend that started in late Paleocene time. The greater Green River Basin of southwestern Wyoming is one of the best areas in the Rocky Mountains for paleobotanical investigation of the Paleocene-Eocene climatic transition. Intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the Tiffanian, Clarkforkian, Wasatchian, and Bridgerian land mammal "ages." The leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate Paleocene-Eocene climates. Following cool humid conditions in the Tiffanian, the Clarkforkian was humid and subtropical, and several plant families with modern tropical affinities appeared. However, as in the Tiffanian, Clarkforkian floras had low diversity and were dominated by a single species in the birch family. Mean annual temperature (MAT) rose from an estimated 12 °C in the Tiffanian to 19 °C in the Clarkforkian, while mean annual precipitation (MAP) for the Tiffanian and Clarkforkian is estimated to have been 130-150 cm. Little fossil plant material is preserved from the latest Clarkforkian or the earliest Wasatchian, which is thought to have contained an interval of cooling and drying followed by renewed warming. By the middle Wasatchian, the time of the Cenozoic thermal maximum, the inferred MAT was about 21 °C, and the MAP was near 140 cm. A second influx of plant families with tropical affinities appeared in the area, and diversity increased significantly, but most plant families known from the Clarkforkian persisted. Species turnover from the Clarkforkian to the Wasatchian was greater than 80%. A second turnover of more than 80% of species (but not families) from the Wasatchian to the early Bridgerian accompanied drying and increased seasonality of precipitation. The early Bridgerian MAT is inferred to have been near 20 °C and the MAP to have been about 80 cm. Except for the Tiffanian and possibly portions of the early Wasatchian, paleoclimates during the study interval were predominantly frost free. Although the moderating influence of the Green River lake system has been suggested as a possible explanation for mild Eocene winters in Wyoming, this study shows that virtually frost-free climates existed in the area prior to and independent of significant lake development.
We present a quantitative analysis of megafloral turnover across the Cretaceous/Paleo- gene boundary (K/T) based on the most complete record, which comes from the Williston Basin in southwestern North Dakota. More than 22,000 specimens of 353 species have been recovered from 161 localities in a stratigraphic section that is continuous across and temporally calibrated to the K/T and two paleomagnetic reversals. Floral composition changes dynamically during the Cre- taceous, shifts sharply at the K/T, and is virtually static during the Paleocene. The K/T is associated with the loss of nearly all dominant species, a significant drop in species richness, and no subse- quent recovery. Only 29 of 130 Cretaceous species that appear in more than one stratigraphic level (non-singletons) cross the K/T. Only 11 non-singletons appear first during the Paleocene. The sur- vivors, most of which were minor elements of Cretaceous floras, dominate the impoverished Pa- leocene floras. Confidence intervals show that the range terminations of most Cretaceous plant taxa are well sampled. We infer that nearly all species with last appearances more than abou t5mb elow (approximately 70 Kyr before) the K/T truly disappeared before the boundary because of normal turnover dynamics and climate changes; these species should not be counted as K/T victims. Max- ima of last appearances occur from 5 t o3mb elow the K/T.Interpretation of these last appearances at a fine stratigraphic scale is problematic because of local facies changes, and megafloral data alone, even with confidence intervals, are not sufficient for precise location of an extinction horizon. For this purpose, we rely on high-resolution palynological data previously recovered from continuous facies in the same sections; these place a major plant extinction event precisely at the K/T impact horizon. Accordingly, we interpret the significant cluster of last appearances less tha n5mb elow the K/T as the signal of a real extinction at the K/T that is recorded slightly down section. A max- imum estimate of plant extinction, based on species lost that were present in the uppermost 5 m of Cretaceous strata, is 57%. Palynological data, with higher stratigraphic but lower taxonomic res- olution than the megafloral results, provide a minimum estimate of a 30% extinction. The 57% estimate is significantly lower than previous megafloral observations, but these were based on a larger thickness of latest Cretaceous strata, including most of a globally warm interval, and were less sensitive to turnover before the K/T. The loss of one-third to three-fifths of plant species sup- ports a scenario of sudden ecosystem collapse, presumably caused by the Chicxulub impact.
Field surveys of the Upper Cretaceous Hell Creek Formation in southwestern North Dakota since 1986 have produced a total of 10 124 specimens from 42 vertebrate microsites and an additional 41 dinosaur skulls or partial skeletons or skulls from separate sites representing 61 taxa of vertebrates dominated by fish, dinosaurs, turtles, and crocodilians. Common elements of this diverse fauna occur to within 2.37 m of the Cretaceous-Tertiary (K-T) boundary. The stratigraphically highest fossil in the study is a partial ceratopsian skeleton 1.77 m below the K-T boundary in the basal Fort Union Formation. All dinosaurs that occur at more than two sites also occur at the highest level that yielded more than 500 specimens (8.40 m below the K-T boundary). The fine-grained uppermost 2 m of the Hell Creek is nearly devoid of all fossils, including taxa known to occur in the overlying formation. The absence of channel deposits in this part of the formation may be the reason for the absence of fossil localities. The presence of marine-tolerant taxa suggests that the study area may have been adjacent to a previously unidentified seaway of latest Cretaceous age. Rarefac-tion analysis indicates no evidence for a decline in vertebrate diversity through the formation or dinosaurian diversity in the 3 m below the K-T boundary. Our results are not compatible with gradual vertebrate extinction at the end of the Cretaceous.
Palynology is used to bracket or pinpoint the Cretaceous-Tertiary (K-T) boundary in 17 measured sections near the contact of the Hell Creek Formation and the Ludlow Member of the Fort Union Formation in southwestern North Dakota. Palynostratigraphy is the most reliable method for locating the K-T extinction horizon - which defines the K-T boundary - in nonmarine rocks. The palynological database includes 110 taxa for which relative abundance or presence or absence data were recorded in more than 350 samples based on surveys of more than 700 000 specimens. These data from laterally extensive outcrops in the badlands along the Little Missouri River provide a temporal framework for concurrent studies in the area on megafossil paleobotany, vertebrate paleontology, lithostratigraphy, magnetostratigraphy, and chemostratigraphy. Palynology demonstrates extinction of 30% or more of the Maastrichtian palynoflora, including characteristic Maastrichtian taxa ("K taxa"), at the K-T boundary. Most of the palynomorph taxa discussed probably represent higher-level plant taxa (botanical genera or families). The K-T boundary is shown to be coincident with the Hell Creek-Fort Union formational contact at only two localities; it is as much as 2.7mabove the base of the Fort Union Formation at others. Thus, a distinctive interval of Fort Union strata of Cretaceous age is recognized that is characterized by occurrences of numerous K taxa, usually in low percentage abundance, up to the K-T boundary. This interval documents a regional paleoenvironmental change that is independent of the extinction event and that is important to understanding the K-T transition throughout western North America.
The Hell Creek Formation of North Dakota preserves a rich and varied palynoflora including pollen, spores, and algal cysts; this palynoflora provides insight into the nature of plant life in the region in late Maastrichtian time. This palynological record supplements extensive data from the same ancient vegetation preserved in the megafloral record, and it provides background biostratigraphic data necessary to determine the nature of the Cretaceous-Tertiary (K-T) boundary event. This study of the Hell Creek palynoflora is based upon occurrences of palynomorphs in 71 samples from 20 measured sections in Bowman and Slope Counties, southwestern North Dakota. The palynoflora documented includes 115 or more palynomorph species, 98 of which are described. Three new genera are proposed, three new species are described, and five new nomenclatural combinations are made. The new taxa are Palaeoisoetes gen. nov., Styxpollenites gen. nov., Tschudypollis gen. nov., Aquilapollenites marmarthensis sp. nov., Osmundacidites stanleyi sp. nov., Styxpollenites calamitas sp. nov., Polyatriopollenites levis (Stanley 1965) comb. nov., Palaeoisoetes subengelmannii (Elsik 1968) comb. nov., Triporopollenites triplicatus (Anderson 1960) comb. nov., Tschudypollis retusus (Anderson 1960) comb. nov., and Tschudypollis thalmannii (Anderson 1960) comb. nov. The palynofloral taxa include 67 angiosperms, eight gymnosperms, 19 pteridophytes, and three bryophytes. Of these, 33 are regarded as characteristically uppermost Cretaceous taxa (K taxa). A few of the K taxa do not range all the way to the K-T boundary. Extinction of the Hell Creek palynoflora at the K-T boundary is ∼30%. The Hell Creek Formation is within theWodehouseia spinata Assemblage Zone.
The Hell Creek and Fort Union Formations in southwestern North Dakota and northwestern South Dakota have yielded a diverse megaflora of 380 species from 158 quarry sites. These sites are situated in a stratigraphic framework, delimited by palynology, magnetostratigraphy, and vertebrate paleontology, that contains both the Cretaceous-Tertiary (K-T) boundary event horizon and stratigraphic evidence for rapid base-level increase. The late Maastrichtian Hell Creek flora is dominated by angiosperms; ferns, fern allies, cycads, ginkgo, and conifers represent <10% of total taxa and specimens. Megafloral extinction at the K-T boundary is extensive, effectively eliminating all dominant plant taxa of the upper Hell Creek Formation. K-T survivorship appears to be greatest in plants that occupied Cretaceous mire facies. The Hell Creek megaflora is heterogeneous with respect to stratigraphic position and sedimentary facies, allowing the recognition of three superposed megafloral zones and two facies-controlled megafloras. Hell Creek vegetation represents an angiospermdominated woodland composed of small-to medium-sized trees, often with lobed leaves. One exception is a diverse angiosperm-dominated herbaceous vegetation associated with large paleochannels in the middle of the formation. The uppermost Hell Creek megaflora zone (HCIII) first occurs near the base of magnetic polarity subchron C29R. The HCIII megaflora is significantly more diverse than earlier Hell Creek floras, and foliar physiognomy suggests a significant climate warming during the final 300-500 k.y. of the Cretaceous. The Paleocene megaflora is depauperate, less heterogeneous than the Cretaceous megaflora, and dominated, in all facies, by taxa that were most common in Cretaceous mire facies.
A -1.5% to -2% carbon isotope shift in surface ocean dissolved inorganic carbon has been reported stratigraphically above the Cretaceous-Tertiary (K-T) boundary in the global stratotype section at El Kef, Tunisia, and in many other marine sections worldwide. Because a change in the δ13C value of paleoatmospheric CO2 would have accompanied the marine surface carbon isotope shift, the K-T carbon isotope anomaly can be used to diagnose and correlate the boundary in terrestrial sections as well. We use this shift and other secular variation in the carbon isotope signature from the Hell Creek and Fort Union Formations to correlate four sections in Slope County, North Dakota. At Pyramid Butte, the K-T boundary is marked by a -2.8% carbon isotope shift approximately 10 cm above the iridium-bearing impact clay. This shift is larger in magnitude than might be expected by plant vital effects or taphonomic variation. The Pyramid Butte carbon isotope shift allowed correlation to the Bobcat Butte (shift of -2.1%), Terry's Fort Union Dinosaur (shift of -1.1% to -1.6%), and the New Facet Boundary (shift of -2.3%) sections, where an iridium enrichment was not preserved. An interval of carbon isotope fluctuation marks the transition from HCII to HCIII megafloral zones in the Bobcat Butte section, suggesting that some instability in the physical environment was correlated with the observed vegetation change. These data demonstrate that carbon isotope chemostratigraphy can provide an additional line of evidence that is largely independent from taxonomic extinction for correlating fossil-bearing terrestrial sections. Chemostratigraphic interpretations may also recognize incomplete or condensed sections, which will aid interpretation of the fossils found in them.
In North Dakota, the Hell Creek Formation is a Laramide clastic wedge of primarily nonmarine strata intercalated with marine and brackish facies. The formation ranges in thickness from 100 to 60 m on a west to east transect across the southern portion of the state and tongues within the Hell Creek represent the youngest Cretaceous marine strata in the Western Interior. Hell Creek strata consist of poorly cemented fine-grained sandstone, siltstone, and carbonaceous-rich shale, mudstone, claystone, and rare lignite. These sedimentary rocks were deposited primarily in laterally accreting fluvial channel systems and associated flood plains. Although localized stratigraphic patterns were recognized within the 76 sections measured for this study, no regional trends or marker horizons were observed. The marine Breien Member, formally proposed in 1942, maintains its integrity in outcrop over an area of at least 6000 km2 in south-central North Dakota and is the only valid member of the Hell Creek Formation. The Cantapeta Tongue, a marine brackish-water tongue characterized by Ophiomorpha and named herein, is present 16 m below the top of the Hell Creek Formation (40 m above the Breien Member and 20 m below the base of the Paleocene Cannonball Member [Fort Union Formation]). These occurrences of marine or brackish-water strata near both the base and top of the Hell Creek Formation in south-central North Dakota suggest that the Fox Hills Sea may not have withdrawn completely from the area before the advance of the Cannonball Sea in Paleocene time. Dinosaur remains are found throughout the Hell Creek Formation in North Dakota but are clustered within 20 m of the base of the formation in the south-central portion of the state where the fossils are concentrated a few meters above and below the Breien Member.
This report details a statistical analysis of palynological change across iridiumenriched claystones defining the Cretaceous-Tertiary (K-T) boundary in the Cretaceous Hell Creek Formation and Tertiary Tullock Member of the Fort Union Formation, eastern Montana, United States. The results strongly support the bolide impact model of terminal Cretaceous extinctions. Chi-square analysis of presence and abundance below and above the iridium datum was used to define characteristic Cretaceous and Tertiary palynomorph species. There is no statistical support for gradual decline in Cretaceous species below the iridium datum, although the presence and abundance of certain Cretaceous species decline somewhat, and the presence of Tertiary species increases slightly, 0-3 m below the iridium datum. An estimated 15%-30% of the Hell Creek palynoflora disappear 0-2 cm above the iridium datum, and another 20%-30% undergoes a significant decline in abundance. Palynoflorules directly overlying the iridium datum are characteristically depauperate. Partial recovery of the palynoflora occurs within 10-20 cm of the boundary, but species richness remains depressed throughout the lower Tullock Member compared to the Hell Creek Formation. Palynoflorules from rare Hell Creek coals contain significantly fewer Cretaceous and significantly more Tertiary species, relative to those of flood-plain deposits, suggesting that perhaps 30%-40% of affected Hell Creek species disappear or decline due to facies change. Greenhouse warming from impact-generated atmospheric CO2 and consequent increased soil water saturation, combined with still uncertain mass-kill mechanisms, best fit the available data to explain the pattern of change in vegetation at the K-T boundary throughout the Western Interior.
A quick dip into the literature on diversity reveals a bewildering range of indices. Each of these indices seeks to characterize the diversity of a sample or community by a single number. To add yet more confusion an index may be known by more than one name and written in a variety of notations using a range of log bases. This diversity of diversity indices has arisen because, for a number of years, it was standard practice for an author to review existing indices, denounce them as useless, and promptly invent a new index. Southwood (1978) notes an interesting parallel in the proliferation of new designs of light traps and new permutations of diversity measures.
Fossil palynomorphs were recovered from fluvial meander-belt and flood-basin sediments of the Maastrichtian Hell Creek Formation. Subenvironments represented within the meander-belt deposits include point-bar, abandoned channel lake and marsh, and point-bar swale. Flood-basin subenvironments include lake, marsh, and crevasse splay. Analyses of the occurrence and relative abundance of 44 palynomorph taxa or groups of taxa allow recognition of numerous taxa that have limited paleoenvironmental distribution. Detrended correspondence analysis demonstrates that the greatest paleoenvironmental distinction occurs among the lacustrine, marsh, swale, and point-bar subenvironments. An additional paleoenvironmental trend, in which taxa occur more commonly in either meander-belt or flood-basin settings, is also evident. Although many factors affect the relative abundance of palynomorph taxa that are preserved in sediments, comparisons to palynomorph distribution in modern environments suggest that the palynomorph assemblages recovered frommarsh deposits were primarily produced by the local flora of the Late Cretaceous marshes. The lake deposits contain palynomorphs that may represent mixtures of local, extra-local, and regional pollen rain. Point-bar sediments probably contain a mixture of locally produced, transported, and reworked palynomorphs. The differences in palynomorph assemblages between meander-belt and flood-basin deposits represent local paleofloral differences due to drier edaphic conditions within the meander-belt paleoenvironments.
The patterns of marine magnetic anomalies for the Late Cretaceous through Neogene (C-sequence) and Late Jurassic through Early Cretaceous (M-sequence) have been calibrated by magnetostratigraphic studies to biostratigraphy, cyclostratigraphy, and a few radiometrically dated levels. The geomagnetic polarity time scale for the past 160 myr has been constructed by fitting these constraints and a selected model for spreading rates. The status of the geomagnetic polarity time scale for each geological period is summarized in Chapters 11–22 as appropriate. PRINCIPLES Magnetic field reversals and magnetostratigraphy The principal goal of magnetostratigraphy is to document and calibrate the global geomagnetic polarity sequence in stratified rocks and to apply this geomagnetic polarity time scale for high-resolution correlation of marine magnetic anomalies and of polarity zones in other sections. The basis of magnetostratigraphy is the retention by rocks of a magnetic imprint acquired in the geomagnetic field that existed when the sedimentary rock was deposited or the igneous rock underwent cooling. The imprint most useful for paleomagnetic directions and magnetostratigraphy is recorded by particles of iron oxide minerals. Most of the material in this chapter is updated from summaries in Harland et al. (1990) and Ogg (1995). Excellent reviews are given in Opdyke and Channell (1996) for magnetostratigraphy and McElhinny and McFadden (2000) for general paleomagnetism.
Exposures of the Hell Creek and Tullock formations in eastern Montana and the Ludlow Formation in western North Dakota allow detailed reconstruction of the paleoenvironments associated with the Cretaceous-Paleogene (K-P) faunal transition in the Western Interior of North America. Facies associations demonstrate an ancient meandering fluvial environment in which gleization in unstable, poorly drained flood plains modified incipient soils. Sedimentologic and pedologic features indicate that concurrent with the faunal transition that occurred in the region, the amount of standing water increased dramatically, changing the earliest Paleogene soils and landscape. Depositional environment imposes taphonomic constraints on interpretations of K-P faunas and floras. Contrary to recent reports, fossil assemblages in Hell Creek channel deposits are reworked; bone and sediment clasts of the channel fills have been subject to traction transport. Age estimations based on supposedly unreworked fossils in channel deposits are thus unreliable. The chronostratigraphic resolution of the sediments under study is to date simply not comparable to the resolution required by researchers of the K-P boundary. - from Author
THEORIES that explain the extinctions characterizing the
Cretaceous/Tertiary (K/T) boundary1-3 need to be tested by
analyses of thoroughly sampled biotas. Palynological studies are the
primary means for stratigraphic placement of the terrestrial boundary
and for estimates of plant extinction4-12, but have not been
combined with quantitative analyses of fossil leaves (megaflora).
Megafloral studies complement palynology by representing local floras
with assemblages capable of high taxonomic resolution13, but
have previously lacked the sample size and stratigraphic spacing needed
to resolve latest Cretaceous floral history5,14-18. We have
now combined megafloral data from a 100-m-thick composite K/T boundary
section in North Dakota with detailed palynological analysis. Here the
boundary is marked by a 30% palynofloral extinction coincident with
iridium and shocked-mineral anomalies and lies ~2 m above the highest
dinosaur remains. The megaflora undergoes a 79% turnover across the
boundary, and smaller changes 17- and 25-m below it. This pattern is
consistent with latest Cretaceous climatic warming preceding a bolide
impact.
The Paleocene Cannonball Formation is a marine, non-lignitic-bearing clastic sequence in the lower part of the Fort Union Group. It is overlain by the lignite-bearing Tongue River Formation in places and both overlain and underlain by the lignite-bearing Ludlow Formation in places. The Cannonball crops out primarily in southwest-central North Dakota and probably occurs throughout the western one-half of the state. It occurs also in northwestern South Dakota and may extend into parts of Saskatchewan and Manitoba. Poorly consolidated, very fine- to fine-grained, light to medium brownish yellow-weathering sandstone and light gray-weathering, sandy mudstone are the principal types of lithology. Mudstone generally predominates in North Dakota whereas sandstone seems to predominate in South Dakota. Although uranium in the Williston basin has been found almost entirely in lignite and nonmarine carbonaceous rocks, its occurrence in the marine Cannonball Formation is possible. If the Cannonball, Ludlow, Tongue River, and Sentinel Butte Formations are at least partly penecontemporaneous, a variety of depositional environments were in areal juxtaposition during the Paleocene. Streams originating or passing through coastal plain bogs could have carried uranium ions (derived from volcanic materials) to the Cannonball sea where they were deposited syngenetically. Epigenetic uranium may occur in Cannonball mudstones or sandstones that directly underlie the Ludlow Formation, which is known to contain volcanic materials.
Sequential morphologic changes in pollen of the Momipites‐Caryapollenites lineage from Paleocene strata in the Wind River Basin of Wyoming appear to reflect evolution within the family Juglandaceae. The stratigraphic occurrence of the species within this complex permits the establishment of six biostratigraphic zones that can be correlated between outcropping and subsurface sequences within the basin and to surrounding areas.Trends involving changes in shape and size of the pollen and in structure of exine at the poles proceed from a basic form of Momipites to six other distinguishable species. The genus Caryapollenites appears to have been derived from the basic form of Momipites by changes in size and development of heteropolarity in pore position.Species of Momipites described as new are M. wyomingensis, M. waltmanensis, M. ventifluminis, M. actinus, M. anellus, and M, leffingwellii. The genus Caryapollenites is redescribed and C. prodromus, C. imparalis, C. inelegans, and C. wodehousei are described as new.
A very diverse, early Paleocene (63.8 ± 0.3 Ma) fossil leaf site located in Castle Rock, Colorado represents nearly autochthonous burial of a rainforest floor. This is an unusual fossil flora preserved in an unusual manner. The site, on the western margin of the Denver Basin in synorogenic sediments associated with the rise of the Laramide Front Range, is dated using multiple methods. Leaves are preserved in three distinct units overlying a poorly developed paleosol that contains in situ tree trunks. Fossil-bearing units are continuous along 150 m of outcrop. The leaves were apparently preserved as a result of rapid deposition of sand and mud onto the floor of a mature rainforest via overbank flooding. Five quarries were excavated and the leaves from these quarries were segregated by morphotype and scored for leaf area and margin type. From 1030 specimens, we document 93 unique dicotyledonous angiosperm leaf types, three cycads, three ferns, two conifers, and seven seed types. There is little taxonomic variation among leaf-bearing units of a single quarry, but the taxonomic composition varies significantly among laterally spaced quarries, suggesting that the fossil leaf litter reflets the original growth positions of the source trees. We compare the fossil leaf litter to leaf litter of modern forests and show that the Castle Rock flora has numerous features in common with extant equatorial rainforests, including dominance by angiosperms, high species richness, large leaves that often have smooth margins and drip tips, and high spatial heterogeneity from quarry to quarry.
Late Cretaceous and Paleogene plant fossils collected at 149 localities in the Denver Basin, Colorado, are placed into a stratigraphic
framework based on palynostratigraphy, magnetostratigraphy, vertebrate paleontology, geochronology, sequence stratigraphy,
electric well logs, and two cored wells. Between 69 and 54 Ma, the Denver Basin accumulated sedimentary rocks that recorded
the withdrawal of a seaway, the uplift of a mountain range, and evidence of the Cretaceous-Tertiary and Paleocene-Eocene boundary
events. Fossil floras deposited in the Denver Basin record these events as variations of floral composition, species diversity,
and leaf margin and size (used to estimate mean annual temperature and precipitation, respectively). Attention to these details
and to the position of the floras relative to the basin margins and sedimentary facies allows for the recognition of six megafloral
associations (K-L, K-D1, P-D1-West, P-D1-Central, P-D1-East, and E-D2). Preliminary comparison of these assemblages documents:
floral change at the K-T boundary; a strong paleoenvironmental gradient probably associated with increased topographic relief
along the basin margin in the early Paleocene; and a warmer, drier Eocene vegetation.
The recovery and subsequent prolific radiation of mammals in the northern Western Interior of North America following the Cretaceous-Paleogene (K-P) boundary is well documented in rocks attributed to the Puercan Land Mammal Age. The most complete Puercan record is that of the Tullock Formation, which overlies the dinosaur-bearing Hell Creek Formation and consists of a stratigraphic series of channel and overbank deposits from which well-preserved Puercan faunas have been collected. These channel deposits are typically bracketed by widespread coal beds. The IrZ- and Z-coals mark the base of the Puercan at the K-P boundary. The IrZ-Coal is overlain sequentially by the Z-, HFZ-, Y-, W-, and U-coals. 40Ar/39Ar dating of single crystals of sanidine separated from bentonites in the IrZ-, Z-, HFZ-, W-, and U-coals has yielded high-precision ages with standard errors of 0.1%. Replicate analyses of single crystals of sanidine yield weighted mean ages for bentonites in the following coals: IrZ, 65.16 ± 0.04 Ma; Z, 65.01 ± 0.03 Ma; HFZ, 64.77 ± 0.06 Ma; W, 64.11 ± 0.02 Ma; and U, 63.90 ± 0.04 Ma. These ages provide detailed calibration of Puercan through earliest Torrejonian land mammal ages and provide crucial calibration for the nonmarine K-P boundary and the Early Paleogene portion of the geomagnetic polarity time scale. -from Authors
Intensive collecting of Maastrichtian and early Paleocene plant megafossils (primarily leaves) in the northern Rocky Mountains and Great Plains has resulted in a database of nearly 25,000 specimens from more than 200 localities in eight areas. The most completely sampled section is at Marmarth, in southwestern North Dakota, where 57 latest Cretaceous and 30 early Paleocene localities (11,503 specimens) span the Cretaceous/Tertiary (K/T) boundary. Zonation of the Marmarth megaflora based on floral composition and relative abundance results in four zones: HC I, HCII, HC in, and FU I. This megafloral zonation appears to be applicable to terrestrial sediments across the northern Great Plains and Rocky Mountains and to correlate with the Western Interior ammonite zonation. The zones reflect major megafloral changes before and at the K/T boundary. Megafloral change at the boundary is large (79 percent) and is characterized by the disappearance of most of the Upper Cretaceous dicotyledonous angiosperm taxa. It coincides with a peak in palynofloral extinctions and iridium content and with the occurrence of shocked mineral grains, all of which have become accepted as the characteristic signature of the K/T boundary and as indications of an abrupt causal mechanism. In contrast, the megafloral changes before the boundary appear to have been caused by a regional climate warming. The fact that the megafloral zones are not reflected by palynostratigraphy argues for using an integrated approach to biostratigraphy that combines the high stratigraphic resolution of palynomorphs with the high taxonomic resolution of megafossils. Results of this analysis of the terrestrial plant record are compatible with the hypothesis of a biotic crisis caused by extraterrestrial impact at the end of the Cretaceous.
The western interior of North America has the only known non-marine sections that contain the iridium-rich clay interpreted as the Cretaceous–Tertiary (K–T) boundary1–7. Because vegetation and climate can be directly inferred from physiognomy of leaves8–15 and because leaf species typically represent low taxonomic categories, studies of leaf floras in these sections provide data on the effects of a terminal Cretaceous event on the land flora, vegetation and climate. A previous study based on detailed sampling of leaves and their dispersed cuticle16 in the Raton Basin provides a framework for interpretation of other leaf sequences over 20 degrees of latitude. We conclude that at the boundary there were: (1) high levels of extinction in the south and low levels in the north; (2) major ecological disruption followed by long-term vegetational changes that mimicked normal ecological succession; (3) a major increase in precipitation; and (4) a brief, low-temperature excursion, which supports models of an ‘impact winter’
Paleosols occur in exposures of the latest Cretaceous Hell Creek and Paleocene Tullock (=Ludlow) Formations in Montana and western North Dakota. The paleosols indicate that changes in ancient soil development occurred concomitantly with the better-known faunal transition. Features suggest that throughout the Cretaceous-Paleogene transition pedogenic processes in the region produced immature profiles, an observation consistent with the unstable, fluvial setting in which the ancient soils formed. Gleization was a dominant process in this setting, and podzolization modified some sandy soils. The assocation of the features enables recognition of O, A/E, Btg, Bhs, Bg, BC, Cg, and C horizons. During middle Hell Creek time, soils formed in a poorly drained setting that was only stable enough to permit incipient pedogenesis. The bulk of the pedogenesis occurred in levee and flood-plain deposits; soils also occurred on point-bar and crevasse-splay deposits. In topographically depressed regions, organic accumulations formed with minimal soil development. Matted plant debris is the product of this environment. Gley features and segregations of iron oxides around voids suggest fluctuation of the water table. By latest Hell Creek time, the mean level of the water table rose, and in the lowest Tullock (Ludlow) exposures, extensive ponded deposits are preserved. Vegetation accumulated at a rate sufficient for coal formation. The amount of fluctuation apparently was reduced, and pedogenesis was further inhibited, as indicated by the virtual absence of illuviated clays in the sediments.-from Authors
Facies analysis of the Ludlow and Tongue River Members of the Palaeocene Fort Union Formation provides an understanding of the relationship between fluviodeltaic environments and associated coal deposition in the south-western Williston Basin. The Ludlow Member consists of high-constructive delta facies that interfinger with brackish-water tongues of the Cannonball Member of the Fort Union Formation. The lower part of the Ludlow Member was deposited on a lower delta plain that consisted of interdistributary crevasse and subdelta lobes. The upper part of the Ludlow Member was deposited in meander belts of the upper delta plain. The delta plain facies of the Ludlow Member is overlain by alluvial plain facies consisting of swamp, crevasse-lobe, lacustrine, and trunk meander belt deposits of the Tongue River Member. The Ludlow delta is believed to have been fed by fluvial systems that probably flowed from the Powder River Basin to the Williston Basin undeterred by the Cedar Creek Anticline. However, the evidence indicates that the Cedar Creek Anticline was prominent enough, during early Tongue River Member deposition, to cause the obstruction of the regional fluvial system flowing from the SW, and the formation of local drainage.The Ludlow Member contains 18 coal beds in the area studied, of which the T-Cross and Yule coals are as thick as 4 m (12 ft). Abandoned delta lobes served as platforms where coals formed, which in turn, were drowned by mainly fresh water and subordinate brackish water. Repetition of deltaic sedimentation, abandonment, and occupation by swamp led to preservation of the T-Cross and Oyster coals in areas as extensive as 260 km2 (< 100 miles2).
Seven fossil leaf species are described from impression fossils collected from the Upper Cretaceous (Maastrichtian) Fox Hills Formation in south-central North Dakota, USA. They are Marmarthia johnsonii n. sp., Nilssoniocladus yukonensis n. comb., Nilssoniocladus comtula n. comb., Mesocyparis borealis, Rhamnus salicifolius, Paloreodoxites plicatus, and Zingiberopsis magnifolia. These species represent some of the elements of the Fox Hills flora that have paleogeographic ranges to the northwest (N. yukonensis, N. comtula, and M. borealis) and to the southwest (M. johnsonii, R. salicifolius, P. plicatus, and Z. magnifolia) of the Fox Hills type area. The identification and reappraisal of these species represent an effort to understand the biogeographic relationships of Late Cretaceous floras across the Northern Hemisphere.