Eocene boundary section in the Williston Basin, North Dakota, USA

Palaeogeography, Palaeoclimatology, Palaeoecology 226 (2005) 214 – 232 www.elsevier.com/locate/palaeo

Palynology and organic-carbon isotope ratios across a terrestrial Palaeocene/Eocene boundary section in the Williston Basin, North Dakota, USA Guy J. Harrington a,b,*, Elizabeth R. Clechenko c, D. Clay Kelly c b

a Department of Paleobiology, Smithsonian Institution, 10th and Constitution Avenue NW, Washington, DC 20560-0121, USA School of Geography, Earth and Environmental Sciences, Aston Webb Building, University of Birmingham, Birmingham, B15 2TT, UK c Department of Geology and Geophysics, 1215 W. Dayton Street, University of Wisconsin-Madison, Madison, WI 53706, USA

Received 7 October 2004; received in revised form 12 May 2005; accepted 23 May 2005

Abstract The Palaeocene–Eocene Thermal Maximum (PETM) at 55 Ma marks the Palaeocene/Eocene (P/E) boundary and represents a discrete period of abrupt, transient global warming. There are few vegetation records from within the PETM and such an absence of data prevents modelling of the vegetation response to climate warming. Outcrops exposing the Sentinel Butte member (upper Fort Union Formation) and the Golden Valley Formation (Bear Den and lower Camels Butte members) within the Williston Basin of western North Dakota, USA are known to span the P/E boundary. Pollen and spore floras at the Farmers Butte locality (Stark County, North Dakota; 46.928 N 102.118 W) record changes in abundance of some reed, fern and understorey plants across the Sentinel Butte–Bear Den contact but no other composition changes occur until the arrival of Eocene immigrants Platycarya spp. (walnut/pecan family) and Intratriporopollenites instructus (linden/sterculia/cotton tree families) at the top of the Bear Den member, c. 11 m above the change in co-occurrence and relative abundance patterns of range-through taxa. The exact stratigraphic level at which these Eocene marker taxa first occur is unclear owing to the heavily weathered nature of Bear Den strata below the Alamo Bluff lignite. This pattern of stratigraphic change may be correlative to the well documented bfloral gapQ of PETM records in Wyoming. Though bulk d 13Corg ratios decrease by 2.4x across the Alamo Bluff lignite, degradation of organic carbon within the upper Bear Den member partially masks full expression of the carbon isotope excursion associated with the PETM. Hence, strata around the Alamo Bluff lignite may represent a new terrestrial record of the PETM. In agreement with terrestrial PETM records from other U.S. western interior localities, palynological data indicate no floral extinction and little composition change across the Palaeocene/Eocene boundary. D 2005 Elsevier B.V. All rights reserved. Keywords: Palaeocene–Eocene Thermal Maximum; Organic carbon isotopes; Palynology; North Dakota; Golden Valley Formation; Fort Union Formation

* Corresponding author. School of Geography, Earth and Environmental Sciences, Aston Webb Building, University of Birmingham, Birmingham, B15 2TT, UK. E-mail address: [email protected] (G.J. Harrington). 0031-0182/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2005.05.013

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1. Introduction The responses of plant communities to climate warming during the Palaeocene–Eocene Thermal Maximum (PETM; c 55 Ma) are perplexing (Wing and Harrington, 2001; Crouch and Visscher, 2003; Harrington, 2003; Wing et al., 2003). Major restructuring of terrestrial plant communities did not occur during this transient c 100 ky interval of significant climate warming at the Palaeocene/Eocene boundary (Ro¨hl et al., 2000; Bowen et al., 2001; Farley and Eltgroth, 2003). This pulse of global warming entailed c. 8 8C warming of sea-surface temperatures at high latitudes (Kennett and Stott, 1991; Zachos et al., 2001) and an increase of land temperatures by c. 4– 6 8C in warm-temperate, continental North America (Fricke et al., 1999; Fricke and Wing, 2004). But so far, massive regional extinction and compositional changes among terrestrial floras have not been documented during the PETM (Crouch and Visscher, 2003; Wing et al., 2003), although some immigration of plant taxa in Early Eocene floras has been noted at all latitudes (Rull, 1999; Wing and Harrington, 2001; Harrington, 2003; Harrington et al., 2004). However, the earliest Eocene is marked by altered co-occurrence patterns of plants that range-through the Palaeocene/ Eocene boundary (e.g. Wing and Harrington, 2001; Harrington, 2001a). These results contrast with those from modelling of Holocene plant dynamics, which predict massive, rapid turnover of plants in their different vegetation types with a deleterious, long-term impact on biodiversity and biome composition as a response to global warming. The lack of floral change is especially surprising given the degree to which steady-state carbon cycling was perturbed during the PETM. This perturbation is evidenced by a pronounced, negative carbon isotope excursion (CIE) in the d 13C compositions of all phases of terrestrial and marine carbon (e.g. Kennett and Stott, 1991; Koch et al., 1992; Bowen et al., 2001; Zachos et al., 2001; Steurbaut et al., 2003; Magioncalda et al., 2004). Various lines of chronostratigraphic evidence, such as linearly interpolated sedimentation rates, astronomically tuned cyclostratigraphies, and cosmogenic 3He fluxes, indicate that the initiation of the CIE took less than a few 103 years (Kennett and Stott, 1991; Norris and Ro¨hl, 1999; Ro¨hl et al., 2000; Farley and Eltgroth, 2003). Catastrophic

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outgassing of large volumes of 12C-enriched, biogenic/thermogenic methane from deep-sea sediments is the most parsimonious mechanism proposed that accounts for both the rapidity and magnitude of this distinctive isotopic signal (Dickens et al., 1995; Katz et al., 1999; Dickens, 2004; Svensen et al., 2004). The release and subsequent oxidation of this methane further exacerbated greenhouse-gas induced PETM warmth, and has been estimated to have elevated atmospheric pCO2 levels by nearly 1500 ppmv (Shellito et al., 2003; Zachos et al., 2003). Moreover, the presence of the CIE in both marine and terrestrial materials reflects rapid carbon exchange between the oceanic and atmospheric reservoirs with this methaneoxidatively derived CO2 being incorporated into the terrestrial organic carbon pool via land-plant photosynthesis (Koch et al., 1992, 1995). Thus, C3 vegetation should reflect this global isotopic shift (e.g., Arens et al., 2000; Jahren et al., 2001; Arens and Jahren, 2002; Hesselbo et al., 2000; 2002). Nevertheless, the use of bulk organic carbon derived from terrestrial vegetation to detect the CIE has proven problematic (Koch et al., 2003; Collinson et al., 2003). Plants have important reciprocal interactions with the carbon cycle and pedogenic processes (e.g., Bazzaz, 1996; Ko¨rner, 2000, 2004; Clark, 2004). Hence, understanding the responses of plants to rapid warming is important because a perturbation of the global carbon cycle should have strongly affected land plants by changing the composition and taxonomic diversity of vegetation types in all biomes. However, a paucity of plant data from within the PETM stratigraphic interval is a major obstacle to recording the vegetation response to the PETM. The short duration of the PETM means that it is extremely difficult to locate in many stratigraphic sections, especially in the absence of other fossils, such as mammals, with which to independently date the rock record. So far, only a few localities that unequivocally record the PETM have also yielded plant fossils (Harrington, 2003; Harrington et al., 2004). To date, the best sections are the terrestrial Powder River Basin, Wyoming (Wing et al., 2003) which yielded two pollen samples from within the PETM, and Tawanui in New Zealand (Crouch and Visscher, 2003) which is marine and contains twelve samples from within the PETM. Both of these PETM sections show no apparent changes in pollen floral composition.

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Here we report on the palynology of a stratigraphic section exposed in the Williston Basin of western North Dakota, USA that spans the Palaeocene–Eocene (P/E) boundary. A bulk-organic d 13C record was generated for this section to provide a chemostratigraphic framework within which to evaluate the palynofloral record. We have chosen a section in the Williston Basin of North Dakota because there are numerous buttes exposed here that span the P/E boundary (Hickey, 1977). Many of these buttes yield fossil plants and have potential for expanding our knowledge on the vegetation response to the PETM. Isotope data are lacking from these sections identified by Hickey (1977) and no major investigations have been undertaken on the Palaeocene/Eocene floras from North Dakota since this time. The terrestrial sections exposed in western North Dakota require thorough re-evaluation. We seek answers to two principal questions: (1) Is there a terrestrial PETM record in North Dakota? and (2) How does vegetation change across the exposed interval spanning the Palaeocene/ Eocene boundary?

2. General geology and stratigraphy Throughout the Williston Basin of western North Dakota, the uppermost Fort Union Formation is locally referred to as the Sentinel Butte member, while the overlying Golden Valley Formation is split into a

lower Bear Den member and an upper Camels Butte member (Hickey, 1977) (Fig. 1). Outcrops exposing Late Palaeocene sediments of the upper Fort Union Formation and the latest Palaeocene–earliest Eocene Golden Valley Formation occur discontinuously in this region (Fig. 2). These non-marine sequences consist of swamp to fluvio-deltaic sedimentary complexes deposited during the progressive infilling of the Williston Basin during the early Palaeogene. Most information on the Golden Valley Formation is derived from the seminal work of Hickey (1977). 2.1. Sentinel Butte member (uppermost Fort Union Formation) The Sentinel Butte member consists of sombrecoloured (buff brown to olive grey) lacustrine/palustrine shales, siltstones and sandstones that are intercalated with seams of lignite and coal. Petrified tree stumps preserved in growth position are common in some beds. The clay-mineral fraction of this stratigraphic unit is composed predominantly of montmorillonite (Freas, 1962). The thickness of the Sentinel Butte member varies from 91 m up to 204 m throughout the region (Hickey, 1977); only the upper 7 m of this unit were sampled. Vertebrate fossils are extremely rare in the Sentinel Butte member, but its megaflora indicates a Late Palaeocene age mainly because it lacks diagnostic Eocene indicator plants such as Salvinia preauriculata and Platycarya spp. (Brown,

Fig. 1. Diagrammatic stratigraphy of the upper Fort Union Formation and Golden Valley Formation redrawn from Hickey (1977) showing the major lithological units and informal colour zonations. The Palaeocene–Eocene boundary is placed at the Alamo Bluff lignite on the basis of pollen and megafloral data (Hickey, 1977; Bebout, 1977).

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Fig. 2. Map of the area over which the Golden Valley Formation is exposed in western North Dakota, USA. The Farmers Butte section is near Hebron in Stark County and marked by a white star.

1948a,b; Hickey, 1977). A Late Palaeocene age is also indicated by the co-occurring palynoflora (Nichols, 1999; Robertson, 2002). 2.2. Bear Den member (lower division of Golden Valley Formation) At most localities, the Bear Den member rests conformably above the Sentinel Butte member, except where localized channels have cut down into the underlying Sentinel Butte member (Hickey, 1977). The thickness of the Bear Den member varies from 6 m up to 11 m, but can change in an abrupt, nonuniform manner where channels are present. It differs

from the underlying Sentinel Butte member in having a tripartite colour zonation, high kaolinite content, and fewer lignite seams (Hickey, 1977). Hickey (1977) utilized the tripartite colour zonation to subdivide the Bear Den member into three informal subunits. The lower bgray zoneQ is fluvially derived and forms two lithofacies. The first, the channel lithofacies, is cross-bedded, lenticular, and sandy. This lithofacies also incorporates levees and channel fills that fine upward. The second, the interchannel lithofacies, is most prevalent and generally parallel bedded or laminated, with greater lateral exposure, and is generally finer grained. These interchannel sediments can contain abundant megaflora that were

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deposited in standing water on floodplains and backswamp ponds. The overlying borange zoneQ is an ironstained, kaolinitic claystone/siltstone that is massive and slightly sandy in character. It is often leached of organic matter and lacking sedimentary structures, suggesting it has been subjected to intense palaeoweathering (Murphy, 2001). The uppermost subunit is the bcarbonaceous zoneQ which is composed of purplish-grey to brown, carbonaceous claystone/siltstone. This zone becomes increasingly carbonaceous culminating in a thin cap of lignite/carbonaceous shale referred to as the Alamo Bluff (AB) lignite at the top of the Bear Den member (Fig. 1). In other areas, a silicified unit called the Taylor Bed is present instead of the AB lignite but this bed still separates the Bear Den from the Camels Butte members of the Golden Valley Formation. Contacts between the different colour zones and between the different members are typically transitional with no apparent evidence for disconformity. The fossil flora from within the Bear Den member suggests a Late Palaeocene age; the first Eocene plant fossils, which include the aquatic fern Salvinia preauriculata and the weedy tree Platycarya spp. occur within the AB lignite (Hickey, 1977). Pollen found in the Bear Den member also indicates a Late Palaeocene age (E.B. Leopold in Hickey, 1977; Bebout, 1977). However, the AB lignite is palynologically Eocene because it contains both Platycarya and the Tilia-type pollen Intratriporopollenites instructus (E.B. Leopold in Hickey, 1977; Bebout, 1977). These two distinctive pollen taxa are first present in other Western Interior basins immediately after the CIE in the Early Eocene (Wing and Harrington, 2001; Wing et al., 2003). 2.3. Camels Butte member (upper division of Golden Valley Formation) The Camels Butte member is gradational from the underlying Bear Den member and represents channel and interchannel sediments. In some areas, these channels have eroded down through the underlying Bear Den member and into the Sentinel Butte member. Sediments in the Camels Butte member include soft micaceous yellow montmorillonitic claystones, siltstones and sandstones. Some local lignites are also present. Unlike the Bear Den member, siderite

concretions are present in some interchannel facies. Plants and vertebrates are found in the Camels Butte member, including Eocene mammal fossils belonging to the orders Perissodactyla, Artiodactyla, and Primate (Jepsen, 1963; West, 1973). Though these vertebrate faunas are sparse, they indicate the Early Eocene Graybullian (Jepsen, 1963) or Lysitean (Lucas, 1998) subzones of the Wasatchian land mammal age.

3. Study section and sample collection The study section is located approximately 5 km northwest of Hebron in Stark County, North Dakota at 46.928 N, 102.118 W (Fig. 2). Hickey (1977) referred to this area as the Farmers Butte locale and designated this particular section as USNM locality number 14058. A total of 20 m is exposed on the butte and represents a gradational section that ranges from the uppermost Sentinel Butte member of the Fort Union Formation through the Bear Den and lower Camels Butte members of the Golden Valley Formation. Four sections were studied in close proximity to one another on the butte and provide a composite section (Fig. 3). Individual sections within this composite stratigraphy were traced laterally from one another to form a comprehensive sampling transect through the butte. The Harnisch lignite, a locally prominent lignite/ coal (Hickey, 1977), occurs just below the contact separating the Fort Union and Golden Valley formations at Farmers Butte. It is approximately 1.8 m thick at Farmers Butte. The lithology within the interval designated the bHarnisch ligniteQ varies up-section from a basal carbonaceous claystone to lignite that, in turn, grades upwards into sub-bituminous coal. It is easy to recognise but, in practice, the tripartite colour zonation of the Bear Den member is sometimes difficult to recognise; in the Farmers Butte section we estimate that the bgray zoneQ accounts for c7 m of section, followed by c 3.5 m of borange zoneQ and a thin (b 1 m thick) interval belonging to the bcarbonaceous zoneQ. This uppermost zone of the Bear Den member merges into the overlying AB lignite. Plant fossils are found in some layers of the section and include mats of monocotyledon debris and also abundant Equisetum remains at the top of

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Fig. 3. Measured stratigraphic sections at Farmers Butte indicating the 45 pollen and 47 organic-carbon sampling horizons. The arrows and measurements above the four individual sections (GV04, GV05, GV06, and GV07) indicate the distance from each other on the side of the butte. The composite section is 20 m through the upper Fort Union Formation (Sentinel Butte member) and Golden Valley Formation and drafted on the left of the diagram.

the Fort Union Formation. The AB lignite near the top of the section also contains thin monocotyledon mats but also the Eocene floating-fern, Salvinia preauriculata (Hickey, 1977). The Farmers Butte section therefore ranges through the Palaeocene/Eocene boundary.

4. Methods 4.1. Pollen samples A total of 45 samples were studied for pollen and spores from the upper Fort Union Formation to

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the lower Camels Butte member of the Golden Valley Formation. The majority of these samples are from the Bear Den member, and in particular the lower bgray zoneQ (Fig. 3). Processing for fossil pollen and spores followed a basic procedure of maceration with mortar and pestle, chemical digestion of carbonates (HCl) and silicates (HF), followed by light oxidation in Schultes’s solution to remove amorphous organic material. Residues were stained with safranin and mounted onto glass slides. Between most stages, residues were sieved with a 10 Am mesh. A count size of 300 pollen and spores was aimed for in each sample, but this was not always possible in the less organic-rich samples. Hence, count sizes vary between different samples. After a count was completed, the remaining slide was scanned for taxa that were not encountered in the count. This procedure was only carried out on samples with abundant palynomorphs. These were scored separately in the data matrix as an bxQ. We are interested in the changes in taxonomic composition throughout the section and have used detrended correspondence analysis (DCA) as a means to quantify and graphically describe floral changes. Ordination was undertaken on relative abundance sporomorph (pollen and spore) data as well as on presence–absence data; the two matrices document different aspects of the data. Presence–absence data provide an estimate of the co-occurrence patterns of taxa (i.e. what taxa are found together regardless of their abundance within a sample) whereas relative abundance data show the changes in numerical proportion of the different taxa within a sample, or group of samples. In the presence–absence matrix, taxa encountered within the main count, as well as from scans outside the main count, were scored as either b1Q if present or b0Q if absent. Taxa therefore have an equal weighting in the ordination. For the relative abundance ordination, only those taxa encountered in the main count are included and rare taxa are downweighted. Rare taxa are categorized as those present in b 20% of samples. In addition, singletons of any particular taxon were culled from both types of matrix. We used rarefaction analysis to study changes in within- and among-sample diversity. Rarefaction is necessary because the samples have different count

sizes and this will have a direct affect on taxonomic diversity estimates within a sample or groups of samples (Birks and Line, 1992; Miller and Foote, 1996). Rarefaction can also consider the evenness component in a sample more effectively than metrics such as the Simpson and Shannon–Wiener indices (Birks and Line, 1992). Statistical significance of our results were tested, where appropriate, using the nonparametric Mann–Whitney U-test and the Kolmogorov–Smirnov D-test (Sokal and Rohlf, 1980). 4.2. Stable isotope analysis of bulk organic carbon Bulk-sediment samples from 47 separate stratigraphic horizons through 19.75 m of the exposed section were used for stable isotope analyses (Table 1). This stratigraphic series ranges from the base of the section within the Sentinel Butte member of the Fort Union Formation, up through the Bear Den member and into the lower part of the overlying Camels Butte member. The suite of geochemical samples is composed of several different lithologies with highly variable organic carbon contents, ranging from silty claystone to coal. Rock samples weighing on average c10 g were oven-dried at 40 8C and powdered using a porcelain mortar and pestle. Each powdered sample was then treated with 1.2 M HCl for 4 h to remove carbonates and then centrifuged with distilled water until neutral (Gro¨cke, 1998). This step in sample processing indicated that the original sediments were largely devoid of pedogenic/diagenetic carbonate. The carbonate-free powder was oven-dried at 60 8C overnight. Total organic carbon (TOC) of these treated samples was measured using a LECO carbon analyser (Table 1). The quantity of bulk organic residue (0.5–60 mg) required for each isotopic analysis was gauged on the basis of TOC. Bulk organic carbon was combusted in the presence of excess CuO and elemental silver (to remove sulphur) in sealed, preannealed quartz tubes at 900 8C for 3 h. Carbon dioxide was cryogenically purified before gas extraction for mass spectrometry, and sample gases were measured with a Finnigan MAT 251 mass spectrometer. Replicate analyses of an in-house standard (UW-Graphite; Dunn and Valley, 1992) yielded an analytical precision of 0.1x. Carbon isotope ratios are expressed using the d

G.J. Harrington et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 226 (2005) 214–232 Table 1 Isotopic summary of d 13Corg values in the Farmers Butte section, North Dakota, USA Sample

Lithology

wt.%Corg

GV07-14 GV07-12 GV07-11 GV07-10 GV07-09 GV07-08 GV07-08 GV07-05 GV07-04 GV07-02 GV06-73 GV06-71 GV06-69 GV06-68 GV06-67 GV06-67 GV06-66 GV06-66 GV06-64 GV06-63 GV06-57 GV06-52 GV06-48 GV06-43 GV06-38 GV06-34 GV06-29 GV06-24 GV06-20 GV06-19 GV06-19 GV06-18 GV06-17 GV06-16 GV06-13 GV06-11 GV06-07 GV06-05 GV06-05 GV06-04 GV06-03 GV06-02 GV06-01 GV05-15 GV05-15 GV05-13 GV05-13 GV05-08 GV05-08 GV05-01 GV05-01 GV04-05 GV04-04

Clayst Clayst Carb sh Carb sh Carb sh Carb sh Carb sh Clayst Clayst Clayst Clayst Clayst Clayst Clayst Carb sh Carb sh Lignite Lignite Clayst Clayst Clayst Clayst Clayst Clayst Clayst Clayst Clayst Clayst Lignite Lignite Lignite Lignite Lignite Mudst Mudst Mudst Mudst Carb sh Carb sh Carb sh Carb/mudst Carb sh Coal coal/lignite Lignite Coal Coal Lignite Lignite Siltstn Siltstn Carb sh Carb sh

3.11 3.24 4.07 3.65 5.56 13.05 13.05 3.20 3.16 3.20 3.17 3.17 3.30 3.33 12.10 12.10 29.99 29.99 3.37 3.44 3.34 3.36 3.45 3.64 3.49 3.48 3.39 3.64 54.90 6.68 6.68 35.93 15.36 3.73 3.58 3.42 4.41 4.45 4.45 4.31 3.98 8.83 53.36 29.38 29.38 79.34 79.34 74.37 74.37 5.26 5.26 3.80 3.81

d 13Corg 23.38 25.02 26.72 26.06 26.70 26.98 26.90 24.54 24.80 24.50 23.39 23.76 24.07 24.10 25.00 25.05 24.95 25.02 23.77 24.18 24.60 24.56 23.81 24.14 24.22 24.72 25.24 24.81 23.89 23.71 23.86 24.24 24.38 23.98 24.26 24.83 25.46 25.15 25.32 25.01 24.96 25.67 20.78 20.94 21.01 23.17 23.23 24.46 24.60 24.62 24.69 24.53 24.68

Metres 19.75 19.05 18.95 18.85 18.75 18.65 18.65 17.45 16.95 15.95 14.20 14.00 13.80 13.70 13.60 13.60 13.50 13.50 13.30 13.00 12.70 12.20 11.70 11.20 10.70 10.30 9.80 9.30 8.90 8.80 8.80 8.70 8.60 8.50 8.20 8.00 7.60 7.40 7.40 7.30 7.20 7.10 7.05 6.90 6.90 6.20 6.20 5.00 5.00 3.40 3.40 2.80 1.70

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Table 1 (continued) Sample

Lithology

wt.%Corg

GV04-03 GV04-02 GV04-01

Carb/mudst Carb/mudst Lignite

3.62 4.06 88.16

d 13Corg 23.99 24.05 24.34

Metres 1.00 0.50 0.00

Metre levels refer to the composite section scale. Clayst=claystone, Carb sh=carbonaceous shale, Mudst=mudstone, Siltsn=siltstone.

notation relative to the international V-PDB standard (Table 1).

5. Results 5.1. Taphonomic controls on the pollen floras Different depositional environments yield different collections of pollen and spores that may affect the interpretation of time series data (Farley, 1989, 1990; Wing and Harrington, 2001). Work from the Bighorn Basin in Wyoming shows that the biggest difference mediated by taphonomic factors is between swamp deposits (including wet soils, reduced floodplains, and swamps) and channel fill deposits that tend to have more taxa within-samples and different relative proportions of taxa than in swamps (Wing and Harrington, 2001; Harrington, 2001b). To tease apart taphonomic effects from actual composition change throughout our section, we coded the pollen samples into either carbonaceous sediments (including carbonaceous shales, lignites and coals) or clastic sediments (including claystones, siltstones, sandstones) and applied DCA onto the relative abundance and presence– absence matrices (Fig. 4A and B). The results show that axis 1 median sample scores are significantly different for relative abundance data (U 28, 18 = 0.450, p = 0.001; Fig. 4A). The differences on axis 2 are not statistically significant. Median axis 1 sample scores are not significantly different for presence–absence data (U 28, 18 = 217, p = 0.450; Fig. 4B). The only significant difference between clastic and carbonaceous samples on the presence–absence matrix is the distribution of samples on axis 2 (D 28, 18 = 0.456, p = 0.01). These results caution that clastic and carbonaceous samples require separate analysis for documenting changes in composition.

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erate a difference of only two taxa. Hence, depositional environments do not strongly influence sample diversity. 5.2. First and last occurrences There are no apparent last occurrences in the studied section. Previous work on pollen floras across the P/E boundary in the Bighorn Basin failed to identify any taxa that become regionally extinct that could be correlated directly with the boundary (Wing and Harrington, 2001). First occurrences from the sporomorph record in the Farmers Butte section show the arrival of Intratriporopollenites instructus (Tilia-type pollen; most similar to the linden, sterculia or cotton tree families) and Platycarya spp. (walnut, wing nut, pecan family) below the AB lignite at 18.65 m in the upper borangeQ or lowermost bcarbonaceousQ zones. However, the barren interval between 13.65– 18.65 m unfortunately precludes an accurate placement for the first occurrence of these taxa in the

Fig. 4. Detrended correspondence analysis (DCA) of all productive samples from the Farmers Butte section coded by clastic (claystones, siltstones, very fine sandstones) and lignite (including carbonaceous shales) categories. (A) DCA ordination on relative abundance sporomorph data. (B) DCA ordination on presence– absence sporomorph data. In both ordinations, axis one sample scores are plotted against axis two sample scores.

Rarefaction of the pollen data (Fig. 5) show that samples have the same number of expected taxa if 181 grains are counted in either clastic or carbonaceous samples (n = 16 taxa). The same pattern is observed if 301 grains are counted in each sample (n = 18 taxa). There are no significant differences in distribution between either carbonaceous sediments or clastic sediments, and no detectable trends in within-sample diversity over time. If samples are binned into clastic and carbonaceous categories, there is a small difference between them in the number of expected taxa if 8600 grains are counted from each set of environments (Fig. 6). Lignites should yield 46 taxa (s = 0.07) and clastic samples should yield 48 taxa (s = 0.72). However this difference is only 5% and not significant considering the number of specimens needed to gen-

Fig. 5. Rarefied sample taxonomic richness at 181 counted grains for all productive samples from the Farmers Butte section coded by clastic (claystones, siltstones, very fine sandstones) and lignite (including carbonaceous shales) categories. Open diamonds indicate clastic samples and black squares indicate lignites. All samples are plotted against the composite metre scale.

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Fig. 6. Rarefied among-sample taxonomic richness for all binned samples coded by clastic (claystones, siltstones, very fine sandstones) and lignite (including carbonaceous shales) categories from the Farmers Butte section. One standard deviation error bars are also plotted around the mean values.

Farmers Butte section. Both Platycarya and Tilia-type pollen mark the Early Eocene in the U.S. western interior basins (Tschudy, 1976; Pocknall, 1987; Wing and Harrington, 2001) but data show currently that they are not present from within the PETM in the U.S. western interior (Wing et al., 2003). On the basis of biostratigraphy, the Farmers Butte section certainly brackets the P/E boundary and may also contain the important PETM interval. 5.3. Composition change The floral list compiled from the Farmers Butte locale (Appendix 1) indicates that the composition of the Fort Union and Golden Valley formations in the Williston Basin is very similar to that reported in the neighbouring Powder River Basin c200 miles to the southwest (Tschudy, 1976; Pocknall, 1987; Pocknall and Nichols, 1996). The pollen flora is well represented by families that are today mostly associated with eastern North America and eastern Asia such as Juglandaceae (pecans, walnut), Ulmaceae (elms), Taxodiaceae (bald cypress, sequoias), Nyssaceae (gum tree), and Cercidiphyllaceae (katsura tree). Detrended correspondence analysis shows changes in the composition of the pollen floras throughout the Farmers Butte section (Fig. 7). Composition change is best expressed in the presence–absence data rather than

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in the relative abundance ordination, although both metrics show that the only change in the section occurs between the Fort Union and Golden Valley formations; there are no changes in composition or co-occurrence patterns within the Golden Valley Formation. However, samples from 0 to 7 m in the relative abundance ordination are significantly different from those between 7.01–20 m in both the carbonaceous (U 9, 9 = 80, P b 0.0001) and clastic samples (U 11, 17 = 149, P = 0.009). These differences are expressed both in the median values and distribution of sample scores on axis 1. But this is not a sharp contact; samples from clastic samples show a bdriftingQ trend in composition to greater loadings on DCA axis 1 into the bgray zoneQ (Fig. 7A). In contrast, presence–absence data show a sharp change in sample scores at c7 m in both carbonaceous and clastic samples (Fig. 7B). The changes are again statistically significant (carbonaceous: U 9, 9 = 78, P = 0.0003, clastics: U 11, 17 = 183, P b 0.0001) but there is no associated bdriftQ in co-occurrence patterns into the bgray zoneQ (Fig. 7B). Neither changes in relative abundance nor co-occurrence patterns are correlated with the arrival of Eocene taxa because all changes in sample compositions occur significantly below the barren borange zoneQ and the AB lignite sample containing pollen of Platycarya spp. and Tilia-type pollen. Both of these Eocene taxa first occur approximately 6 m above the changes in assemblage composition using either assessments of the presence– absence or relative abundance components of the assemblages. Several taxa increase in relative abundance at c7 m and include Laevigatosporites haardtii (51% more abundant, U 20, 27 = 456, P b 0.0001) which is a probable fern (Appendix 1) together with Pistillipollenites mcgregorii (79% more abundant, U 20, 27 = 373, P = 0.023), and Rousea crassimurina (95% more abundant, U 20, 27 = 376, P = 0.005). The modern systematic affinities for the last two pollen types are unknown (Appendix 1). Both P. mcgregorii and R. crassimurina are common in lignites in the Powder River Basin (Pocknall and Nichols, 1996). Other taxa appear to show relative abundance increases, such as the fern Deltoidospora spp. and the reed Dyadonipites reticulatus (?Sparganiaceae) although these are not statistically significant. Several taxa also appear to decline in relative abundance and these include tripo-

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Fig. 7. Results from bulk d 13Corg analysis and detrended correspondence analysis (DCA) on pollen floral data plotted against stratigraphic depth and major lithofacies type on the composite measured scale for the Farmers Butte section. The first occurrence of Platycarya spp. and Intratriporopollenites instructus are noted on the left side of the relative abundance DCA. (A) DCA ordination on relative abundance data showing axis one sample scores. (B) DCA ordination on presence–absence data showing axis one sample scores. In both ordinations, lignites (black squares) are plotted separately from clastic sediments (open diamonds). (C) Bulk d 13Corg analysis drafted from data in Table 1. The informal colour zones of Hickey (1977) are noted on the right side, GZ=gray zone, OZ=orange zone, and CZ=carbonaceous zone. AB=Alamo Bluff lignite, and HL=Harnisch lignite.

rate pollen belonging to Betulaceae/Myricaceae (birch/sweet gales) and Nyssa spp (gum tree). There are no obvious, or statistically significant, changes in the abundance of any other pollen taxa throughout the section, including Alnipollenites spp. (alder), Caryapollenites spp. (hickories), Eucommia sp., Momipites spp (walnut family) and Ulmipollenites spp. (elms) which all have notable relative abundance changes across the P/E boundary in the Bighorn, Powder River and Wind River basins (Tschudy, 1976; Nichols and Ott, 1978; Pocknall, 1987; Harrington, 2001b, Wing and Harrington, 2001). Hence, only about seven taxa are responsible for influencing the changes in DCA sample scores in the relative abundance ordination. 5.4. Bulk-organic carbon isotopes Stable isotopic analyses performed on bulk-organic carbon samples generated a d 13Corg curve with a baseline value ( 24.4x) that is representative of C3 vegetation (Fig. 7C). Superimposed upon this bulk d 13Corg baseline are two conspicuous excursions, a

positive one within the lower part of the section just below the gradational Fort Union–Golden Valley formational contact and a negative one within the AB lignite at the top of the Bear Den member. The magnitude (c 3.6x) of the positive shift culminates in a bulk d 13Corg maximum of approximately 21x. This large positive d 13Corg increase occurs in a systematic fashion over a 1-m thick interval (6– 7 m) within the Harnisch lignite zone of the upper Sentinel Butte member (Fort Union Formation), and is defined by three contiguous samples (Fig. 7C). Duplicate analyses of these three Harnisch lignite bulk samples reproduced the conspicuous d 13Corg increase with only a minor degree of isotopic offset (~0.1x) indicating that this is a robust signal and that intra-sample d 13Corg variation is relatively minor compared to inter-sample differences. The gradual increase in d 13Corg is followed by a sharp decrease near the top of the Harnisch lignite (c 7 m). The magnitude (c 4.5x) of this decrease returns bulk d 13Corg ratios ( 25.7x) back to baseline values. The intervening interval (7–14 m) brackets both the Fort Union/Golden Valley formational contact and

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the lower bgray zoneQ of the Bear Den member and is characterized by background d 13Corg values with small c. 1x oscillations. The bulk d 13Corg record is less well-resolved further up-section through the borange zoneQ (14–17.5 m above base of section) of the Bear Den member because organic carbon content is generally low and poorly preserved within this interval-only three bulk d 13Corg values (c. 25x) are reported (Fig. 7C). A negative shift of c2.4x occurs in the bulk d 13Corg record just above the borange zoneQ within the bcarbonaceous zoneQ of the Bear Den member (Fig. 7C). This negative shift coincides with the AB lignite at 18 m, and yields the lowest bulk d 13Corg value ( 26.9x) of the entire study section. The rapidity, or nature, of this d 13Corg decrease is unclear owing to the lack of data from within the underlying borange zoneQ. The uppermost bulk d 13Corg value ( 23.5x) is recorded from within the Camels Butte member at 19 m, and is nearly 3.5x higher than those measured from the underlying AB lignite.

6. Discussion 6.1. Bulk d 13Corg chemostratigraphy The presence of the CIE signature in both marine and terrestrial materials reflects rapid exchange of CO2 derived from methane oxidation between the oceanic and atmospheric reservoirs, with this isotopically light CO2 being incorporated into the terrestrial organic carbon pool via land–plant photosynthesis (Koch et al., 1992, 1995). Similar d 13C excursions have proven useful for global correlation and provide chemostratigraphic frameworks for the study of other bCIE-likeQ perturbations that have occurred at various times in the Phanerozoic (e.g., Jahren et al., 2001; Padden et al., 2001; Arens and Jahren, 2002; Hesselbo et al., 2000; 2002). Thus, one would expect the organic matter of C3 vegetation to record a d 13C shift correlative with the CIE (e.g., Arens et al., 2000). However, several PETM studies have yielded bulk d 13Corg data to the contrary, suggesting that diagenesis may have altered the d 13C signals of bulk organic carbon (Koch et al., 2003; Wing et al., 2003). The rich vertebrate faunas and isotope records preserved in the expanded PETM sequences of the

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Bighorn Basin (Wyoming, USA) qualify these sections as a reference with which to compare other terrestrial PETM records in North America (e.g., Gingerich, 1989, 2003; Koch et al., 1992, 1995, 2003; Clyde and Gingerich, 1998; Fricke et al., 1999; Bowen et al., 2001). Of particular interest is the bulk d 13Corg record generated for a well-documented PETM section from Polecat Bench (Magioncalda et al., 2004) near Powell in the Bighorn Basin, Wyoming. The Polecat Bench d 13Corg record indicates that the base of the CIE is marked by a c 3.5x negative shift in the isotopic composition of terrestrial vegetation, resulting in an initial minimum value of 28x. This record also shows that the ensuing CIE recovery is delimited by a contiguous series of bulk d 13Corg ratios that fall below 26x (Magioncalda et al., 2004). Thus, the Polecat Bench bulk d 13Corg record provides a chemostratigraphic benchmark useful for gauging the quality and completeness of other terrestrial bulk d 13Corg records spanning the P/E boundary. Comparison of our Farmers Butte bulk d 13Corg record to that of Polecat Bench reveals a number of inconsistencies. In particular, a positive shift (c 3.5x), like the one recorded through the Harnisch lignite positioned just below the Fort Union–Golden Valley contact, is not present in the Polecat Bench d 13Corg stratigraphy. Hence, we suspect that this anomalous feature may reflect a local preservational bias in our section. This interpretation warrants consideration because the systematic d 13Corg increase tracks a general lithostratigraphic trend of increasing carbonisation; the Harnisch lignite grades up-section from carbonaceous siltstone (5 wt.% Corg) to subbituminous coal (53 wt.% Corg). Thus it is likely that progressive decarboxylation may have preferentially removed the more labile components of fossil plants (lipids, lignin) that are 12C-enriched relative to the whole plant, potentially imparting an overall higher bulk d 13Corg composition to the residual coal (e.g., Friedrich and Ju¨ntgen, 1973; Arthur et al., 1983; Stott et al., 1996). Perhaps thermogenic methane evolved from the Harnisch lignite was enriched in 12 C because the weaker binding energies of 12C–12C bonds in organic molecules are the first to chemically break during the early stages of thermocatalytic alteration (e.g., Sackett, 1968; Stahl, 1974). Isotope effects caused by coalification is not the only tenable explanation for the Harnisch lignite d 13Corg maximum,

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especially since some experimental studies have concluded that coalification has only a minor affect on the d 13C composition of preserved plant tissues (Colombo et al., 1968; DeNiro and Hastorf, 1985). We also note that similar d 13Corg increases have been recorded in other terrestrial PETM sections just below the base of the CIE (Sinha et al., 1995; Stott et al., 1996; Collinson et al., 2003). The exact processes that gave rise to the positive d 13Corg ratio ( 21x) recorded from the Harnisch lignite remain unclear, but this d 13Corg value is anomalous relative to most other coals (Deines, 1980; Smith et al., 1982) and we therefore provisionally attribute it to diagenesis. The negative (2.4x) shift registered by the carbonaceous shale from within the AB lignite at the top of the Bear Den member (c 18 m) is a more interesting feature of the Farmers Butte bulk d 13Corg record. The AB lignite d 13Corg minimum ( 26.9 x) approaches CIE d 13Corg minima reported for terrestrial PETM records from the Paris Basin, France (Stott et al., 1996) and Cobham lignite, southern England (Collinson et al., 2003), which are 27.0x and 27.5x, respectively. In contrast, the amplitude and minimum value of the AB lignite d 13Corg decrease are not as great as those reported for the PETM section from Polecat Bench (Magioncalda et al., 2004), though this low bulk d 13Corg ratio would qualify as a bCIE valueQ (b 26x). If one were to equate increased organic carbon content with enhanced preservation, then it could be argued that the negative d 13Corg shift associated with the AB lignite represents another preservational artefact (e.g., Arens and Jahren, 2002). However, such a negative correlation is not present between our wt.% organic carbon and bulk d 13Corg values (r s = 0.03, P = 0.846), suggesting that increased organic content does not systematically decrease bulk d 13Corg values. Omission of the Harnisch lignite bulk d 13Corg values from this regression does not significantly alter the correlation coefficient (r s = 0.31, P = 0.03). It is also important to note that two organic carbon samples, one at the base and one at the top of the PETM, from Powder River Basin (north-east Wyoming) have d 13Corg values of 24.6x and 29.4x, respectively (Wing et al., 2003). Thus, comparison of the Farmers Butte d 13Corg record to other PETM sections from around the U.S. western interior suggests that absolute d 13Corg values may not be a reliable criterion for detecting the

CIE, and that this isotopic shift is best delineated by a consistent decrease to more negative d 13Corg values over a series of contiguous, high-resolution samples (Koch et al., 2003; Magioncalda et al., 2004). One possibility is that the AB lignite d 13Corg decrease represents a condensed PETM record. Unlike the thick (c. 40 m) stratigraphic sequences preserved in the more westerly basins proximal to the Laramide uplift (e.g. the Bighorn Basin), the fine-grained sediments of the Bear Den member reflect slow deposition in a distal basin that is tectonically less active. Hence, a brief period of non-deposition could have omitted the base of the CIE at Farmers Butte. It is also possible that the base of the CIE is obscured by poor preservation within the borange zoneQ lying directly beneath the bcarbonaceous zoneQ and AB lignite. Thus, the borange zoneQ of the upper Bear Den member may be correlative with the prominent, well-developed palaeosols that typify the PETM intervals in both the Bighorn and Powder River basins (e.g., Wing et al., 2003). An added complication is that, although bulk d 13Corg ratios brecoverQ to higher background values ( 23.4x) within the overlying Camels Butte member, this isotopic increase is recorded within fluvial sandstone, raising the possibility that the uppermost part of the CIE has been truncated. We therefore suggest that a condensed record of the PETM is present within the Farmers Butte section, perhaps beginning within the borange zoneQ of the upper Bear Den member (where organic matter is scarce) and ranging up-section through the AB lignite. 6.2. The vegetation record Placing the PETM in the upper part of the Bear Den member, around the AB lignite, would indicate that climate change had no significant effect on vegetation because there are no changes in the co-occurrence patterns of taxa at this level. This is a feature of every other North American latest Palaeocene–earliest Eocene vegetation record (Wing and Harrington, 2001; Harrington et al., 2004). There is very little organic matter preserved within the borange zoneQ of the upper Bear Den member and so the PETM could be present here. An interval of depleted organic matter would be consistent with the PETM because other North American PETM sections, such as those in the Bighorn (Wing, 1998; Harrington, 2001b; Wing and Harring-

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ton, 2001) and Powder River basins (Wing et al., 2003), have enhanced development of red palaeosols depleted in organic matter. In addition, the reconstructed climate from the lower Bear Den member, where there is a demonstrable shift in vegetation type composition, is not above background values from the U.S. western interior at this time: Hickey (1977) estimates mean annual temperature at c15 8C based on leaf morphology and taxonomic composition. By comparison, mean annual temperature in the latest Palaeocene and earliest Eocene of the Bighorn Basin is c16–17 8C based on both leaf morphology and d 13O from hematite (Bao et al., 1999; Wing et al., 2000). If estimates of c4–6 8C warming are correct for the U.S. western interior during the PETM (Fricke et al., 1999; Fricke and Wing, 2004), the Bear Den flora should reflect this by showing a mean annual temperature of N 19 8C. Hickey (1977) noted nothing unusual about the Bear Den member except that marsh communities are prevalent in the upper part. This is consistent with the general deposition of the bcarbonaceous zoneQ and development of the laterally extensive AB lignite. The change in general lithology and depositional environments from the Sentinel Butte member of the Fort Union Formation into the Bear Den member of the Golden Valley Formation essentially marks a regional change in sedimentation style to more active depositional environments, prone to disturbance. Hence subtle changes in the composition of the pollen and spore floras probably reflect the general change in environments that may be long-lasting, permanent, but independent from the PETM. The relative abundance of some pollen taxa associated with swamps and wet environments increase, but others such as Juglandaceae do not. The change in relative abundance of key range-through families such as Eucommiaceae, Juglandaceae and Ulmaceae is a clear marker for the PETM (Harrington, 2001a,b; Wing and Harrington, 2001; Harrington et al., 2004) and the absence of change in the lower Bear Den member of these families further argues for placement of the PETM elsewhere in the Farmers Butte section.

7. Conclusions The Farmers Butte section in North Dakota (46.928 N, 103.118 W) demonstrates palynological and geo-

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chemical changes during an important interval of global change at c 55 Ma. In common with other U.S. western interior basins, only two pollen taxa unequivocally indicate the transition into the Early Eocene, Platycarya spp. and Intratriporopollenites instructus (Tilia-type pollen). These Early Eocene taxa first appear at Farmers Butte immediately below the AB lignite, which is a regionally important unit separating the Bear Den and Camels Butte members of the Golden Valley Formation. Hickey (1977) previously placed the P/E boundary at the AB lignite and the pollen data agree with this assignment. Bulk d 13Corg values decrease to their most negative values ( 26.9x) within the thin carbonaceous shale of the AB lignite. Hence, in answer to our first question posed in this investigation, we believe that a PETM record is exposed in the Golden Valley Formation of North Dakota. The collective evidence suggests that the upper portion (borange zoneQ) of the Bear Den member and the AB lignite of the Golden Valley Formation likely represents a condensed version of the PETM. In answer to our second question, the vegetation record shows a pronounced response to local environmental changes and evidence for a transition from the Palaeocene into the Eocene. However, productive palynological samples above and below the AB lignite show no floral change in terms of either taxa relative abundance or co-occurrence shifts which are two patterns indicative of the P/E boundary in the U.S. western interior. There are probably insufficient samples in the Early Eocene to thoroughly test for significant changes in vegetation that other studies have detected. Except for the first occurrences of Platycarya spp. and Intratriporopollenites instructus just below the AB lignite, the only floral changes documented from our study occur at the Harnisch lignite and bgray zoneQ contact between the Fort Union–Golden Valley formations. The sporomorph changes in the Harnisch lignite and bgray zoneQ are related to local environmental conditions that are dominated firstly by swamps and then by fluvial environments. Palynological changes in the lower Bear Den member probably do not represent the PETM because 1) the palaeo-temperature estimates within the Bear Den member approximate background U.S. western interior levels for the latest Palaeocene– earliest Eocene and, 2) not all taxa identified from previous studies change in abundance (e.g., Caryapol-

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lenites spp., Ulmipollenites spp., Pandaniidites typicus and Eucommia). Only those taxa related to marsh or wet conditions (e.g. reeds, ferns and Pistillipollenites mcgregorii) change in relative abundance. The Harnisch lignite is also marked by a positive increase in bulk d 13Corg values. Hence, the palynological data are still consistent with other plant-bearing P/E boundary sections because the vegetation does not show massive community change across the PETM.

Acknowledgements The authors thank Lee Clayton (Wisconsin Geological Survey) for discussions that initiated this endeavour, and Ed Murphy (North Dakota Geological Survey) for logistical assistance. We are also grateful to Scott Wing for fieldwork assistance and providing funding for GJH. We are indebted to John Valley (Univ. of Wisconsin–Madison) for the use of his stable isotope lab, Mike Spicuzza (Univ. of Wisconsin–Madison) for assistance with these analyses, and Reuben and Angie Treiber for land access. Cindy Stiles (Soil Sciences, Univ. of Wisconsin–Madison) provided many fruitful discussions. Sincere thanks also go to Leo Hickey for allowing us to review his unpublished maps and sections from his pioneering work on the Golden Valley Formation. Constructive reviews from two anonymous reviewers helped improve this paper. This research is supported by NSF award 0120727 (Scott Wing) and a Sylvester-Bradley award from the Palaeontological Association (GJH), and student grants-in-aid courtesy of the Geological Society of America and Evolving Earth Society (ERC). This is ETE contribution number 105.

Appendix A Palynofloral list of taxa found in the Fort Union Formation (Sentinel Butte member) and Golden Valley Formation at the Farmers Butte section, Stark County, North Dakota, USA. SPORES: Mosses: ?Sphagnaceae: Stereisporites stereoides (Potonie´ and Venitz, 1934) Thomson and Pflug, 1953.

Unknown: Zlivosporis novamexicanum (Anderson, 1960) Leffingwell 1971. Ferns: Gleicheniaceae: Gleicheniidites sp. cf. G. triangulus (Stanley, 1965) Nichols and Brown, 1992. Osmundaceae: Baculatisporites primarius (Wolff, 1934) Thomson and Pflug, 1953. Polypodiaceae: Polypodium-type. Schizaeaceae: Cicatricosisporites sp. 1; Cicatricosisporites dorogensis Potonie´ and Gelletich, 1933. Incertae sedis: Deltoidospora spp.; Laevigatosporites haardtii (Potonie´ and Venitz, 1934) Thomson and Pflug, 1953; Microfoveolatosporis pseudodentatus Krutzsch, 1959. Gymnosperm pollen Pinaceae: Bisaccates group (cf. Pinus, Picea). Taxodiaceae: [Cupressacites hiatipites (Wodehouse, 1933) Krutzsch, 1971; Sequoiapollenites sp. included together] Incertae sedis: Cycadopites spp.; Cycadopites scabratus Stanley 1965; Monocolpopollenites tranquillus (Potonie´, 1934) Nichols et al., 1973. Angiosperm pollen Monocotyledons ?Araceae, Pandanaceae: Pandaniidites typicus (Norton and Hall, 1969) Farabee and Canright, 1986. ?Liliaceae: Liliacidites crassiterminatus Pocknall and Nichols, 1996. Palmae, Cycadales: Arecipites spp. Arecipites sp. cf A. texuiexinous Leffingwell, 1971 Sparganiaceae: Dyadonapites reticulatus Tschudy, 1973; Sparganiaceaepollenites sp. cf. Sparganium globites (Wilson and Webster, 1946) Nichols and Brown, 1992. Unknown: Liliacidites sp.

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Dicotyledons ?Aceraceae: Striatopollis sp. Pocknall and Nichols, 1996. ?Anacardiaceae: Aesculiidites circumstriatus (Fairchild in Stover et al., 1966) Elsik, 1968; Rhoipites spp. ?Anacardiacease/Leguminosae/Sapindaceae/Simaroubaceae: Ailanthipites berryi Wodehouse, 1933. Betulaceae: Alnipollenites spp. Buxaceae: Erdtmanipollis cretaceus (Stanley, 1965) Norton and Hall, 1969. ?Caprifoliaceae/Anacardiaceae: Caprifoliipites spp.; Caprifoliipites paleocenicusPocknall and Nichols, 1996. Cercidiphyllaceae: Cercidiphyllites sp. ?Ericaceae: Ericipites spp. Eucommiaceae: Eucommia? leopoldae Frederiksen, 1983. ?Fagaceae: Siltaria hanleyi Pocknall and Nichols, 1996. ?Hamamelidaceae: Periporopollenites sp. (Liquidamber-type) Juglandaceae: Caryapollenites spp.; Momipites spp.; Platycaryapollenites anticyclus Krutzsch and Vanhoorne, 1977; Platycarya platycaryoides (Roche, 1969) Frederiksen and Christopher, 1978; Platycaryapollenites ? swasticoidus (Elsik, 1974) Frederiksen and Christopher, 1978; Platycarya spp.; Plicatopollis spp.; Polyatriopollenites vermontensis (Traverse, 1955) Frederiksen, 1980. ?Loranthaceae: Cranwellia striata (Couper, 1953) Srivastava, 1966. Malvaceae, Euphorbiaceae, Tiliaceae: Malvasipollis spp. Myricaceae, Betulaceae: Paraalnipollenites confusus (Zaklinskaya, 1963) Hills and Wallace, 1969; Triatriopollenites spp.; Triporopollenites spp. ?Nyssaceae: Nyssapollenites explanata (Anderson, 1960) Pocknall and Nichols, 1996; Nyssa kruschii (Potonie´, 1931) Frederiksen, 1980; Nyssapollenites spp. ?Salicaceae/Oleaceae: Rousea linguiflumenaPocknall and Nichols, 1996. ?Sapindaceae: Talisiipites pulvifluminus Pocknall and Nichols, 1996.

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?Sapindaceae/Myrtaceae: Insulapollenites rugulatus Leffingwell, 1970. Symplocaceae: Symplocos ? thalmannii (Anderson, 1960) Frederiksen, 1980. Tiliaceae/Sterculiaceae/Bombaceae: Intratriporopollenites instructus (Potonie´ and Venitz, 1934) Thomson and Pflug, 1953; Tilia vescipites Wodehouse, 1933. Ulmaceae: Ulmipollenites spp. Unknown: Cupuliferoidaepollenites liblarensis (Potonie´ et al., 1950) Potonie´, 1960; Echitricolpites supraechinatusPocknall and Nichols, 1996; Favitricolpites baculoferus (Thomson and Pflug, 1953) Srivastava, 1972; Fraxinoipollenites variabilis (Stanley, 1965) Nichols and Brown, 1992; Fraxinoipollenites spp.; Intratriporopollenites sp. cf. Tilia tetraforaminipites (Wodehouse, 1933) Pocknall and Nichols, 1996; Jarzenipollenites trinus (Stanley, 1965) Kedves, 1980; Periporopollenites (Chenopod type); Pistillipollenites mcgregorii Rouse, 1962; ?Retitrescolpites sp.; Rousea crassimurina Pocknall and Nichols, 1996; Rousea spp., Siltaria spp.; Tricolpites hians Stanley, 1965; Tricolpites sp. cf. Tricolpites hians; Tricolporites spp. INCERTAE SEDIS Aquilapollenites spinulosus Funkhouser, 1961; Trudopollis sp.

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