An early Eocene Sphagnum bog at Schöningen, northern Germany

International Journal of Coal Geology 159 (2016) 57–70

Contents lists available at ScienceDirect

International Journal of Coal Geology journal homepage: www.elsevier.com/locate/ijcoalgeo

An early Eocene Sphagnum bog at Schöningen, northern Germany Walter Riegel a,b, Volker Wilde a,⁎ a b

Senckenberg Forschungsinstitut und Naturmuseum Frankfurt am Main, Senckenberganlage 25, 60325 Frankfurt am Main, Germany Georg-August-Universität Göttingen, Geowissenschaftliches Zentrum, Geobiologie, Goldschmidtstr. 3, 37077 Göttingen, Germany

a r t i c l e

i n f o

Article history: Received 10 December 2015 Received in revised form 21 March 2016 Accepted 24 March 2016 Available online 8 April 2016 Keywords: Lignite Palynology Ombrogenous peat Restionad bog Palaeoclimate Palaeoecology

a b s t r a c t A thin local seam in the early Eocene lignite succession of the opencast mine Schöningen-Südfeld (Lower Saxony, northern Germany) revealed pollen and spore assemblages of low diversity. They are characterized by an abundance of Sphagnum-type spores, especially Tripunctisporis, and fern and lycopod spores together with the common occurrence of pollen of Ericaceae, Restionaceae and Droseraceae. Well-preserved fragments of Sphagnum leaves are common and loricae of Habrotrocha-like bdelloid rotifers have been recorded occasionally. We reconstruct an ombrogenous domed peat bog maintained by prolific growth of Sphagnum in association with a rich fern cover, oligotrophic and acidophilic plants as well as insectivorous plants indicating severe nutrient deficiency. This resembles in many respects an Eocene equivalent of a Quaternary high latitude Sphagnum bog. In view of the significant amount of Restionaceae pollen, however, it appears more similar to Southern Hemisphere restionad bogs. The total lack of a waterlogged layer in the highly permeable substrate strongly argues in favour of a purely rain-fed ombrogenous peat bog. The required high precipitation in combination with frequent wildfires as evidenced by the abundance of charcoal, however, suggests a highly stressed hydrological cycle under an alternating wet/dry climate close to the alleged Early Eocene Climatic Optimum (EECO). © 2016 Elsevier B.V. All rights reserved.

1. Introduction Peat mosses of the genus Sphagnum are outstanding in their ability to store water (up to 20–30 times their dry weight; Yoshikawa et al., 2004) and in generating an acid environment (between pH 3 and 5; Naucke, 1980) within themselves and in their surroundings thus literally creating their own environment (Gerken, 1983). Today the genus Sphagnum comprises ca. 300 species and has an almost worldwide distribution (Michaelis, 2011), but especially dominates in high-latitude peat mires of the Northern Hemisphere. The species are widely considered to be preadapted to oligotrophic habitats and attained their present significance and distribution in response to the late Neogene climatic deterioration and to the repeated glacial advance and retreat during the Pleistocene (Greb et al., 2006; Shaw et al., 2010b). However, according to molecular data sphagnoid mosses have a long phylogenetic history indicating that the lineage separated early from the other bryophyte classes (Shaw and Renzaglia, 2004; Shaw et al., 2010a). This is well supported by leaf remains of so-called Protosphagnales ranging back into the Lower Carboniferous (Hübers and Kerp, 2012; Hübers et al., 2013). They are especially known from the Permian of Russia (e.g., Neuburg, 1958, 1960; Ignatov, 1990) and characterized by a midrib, which is missing in leaves of modern Sphagnum.

⁎ Corresponding author. E-mail addresses: [email protected] (W. Riegel), [email protected] (V. Wilde).

http://dx.doi.org/10.1016/j.coal.2016.03.021 0166-5162/© 2016 Elsevier B.V. All rights reserved.

However, in spite of the importance and widespread occurrence of peat mosses today (e.g., Clymo and Hayward, 1982; Greb et al., 2006) and the resistance of their leaves to decay (Kroken et al., 1996) leaf remains of sphagnoid mosses have rarely been described from the fossil record and are extremely rare in the Mesozoic. Sphagnophyllites (Pant and Basu, 1978) was described as representing sphagnoid leaves from the Triassic of India. The earliest leaf that was assigned to the genus Sphagnum itself has been figured from the Lower Jurassic of Germany (Reissinger, 1950). Another leaf fragment most probably also belonging to the genus was recovered from Upper Cretaceous coals of Greenland (Arnold, 1932), and “Sphagnum ‘leaf’ tissue” was mentioned from the Upper Cretaceous of Wyoming (Wilson and Webster, 1946). For the Cenozoic, Boulter (1994, Fig. 11.9.8) figured a Sphagnum leaf which was recovered together with “Stereisporites” and fern remains from Paleocene marine clastic sequences of the Forties Field, North Sea, to where they are supposed to have been transported from coastal mires by surface drift or turbidity currents. The only other Paleogene remains of Sphagnum leaves figured are from the Baltic Amber (Frahm, 2009). Furthermore, Sphagnum leaf remains were mentioned for the Paleogene of the Canadian Arctic (Kuc, 1973a). Leaf remains from Miocene and Pliocene coals or peat of Germany, China and the Canadian Arctic (Kuc, 1973b; Lu and Zhang, 1989; Ovenden, 1993; Schneider, 2012) bridge the gap to the Quaternary record. In contrast to the few remains of leaves a diversity of Sphagnum-type spores has been recorded from the Triassic upwards (Krutzsch, 1963; Döring et al., 1966; Schulz, 1970). Sphagnum peat today is an important sink for organic carbon especially in humid areas of the Northern Hemisphere (e.g., Clymo and

58

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Hayward, 1982), but Sphagnum has rarely been identified as a peat/coalforming element before the Quarternary. A Sphagnum coal has been described as a “new genetic type of coal” from the Pliocene of China (Lu and Zhang, 1989), and Sphagnum peat of a similar age has been recovered from Ellesmere Island (Canadian Arctic; Ovenden, 1993). Based on the occurrence of spores Sphagnum was suggested as an element of the coal-forming vegetation in the Miocene of Germany (Thomson, 1952; Minnigerode and Klein-Reesink, 1984). This has recently been confirmed by some leaf remains from the Miocene of Lusatia, Germany (Schneider, 2012). Sphagnum-type spores have frequently been observed in the Paleogene of North America and the Arctic and sometimes also been used to suggest peat mosses as common elements of a swamp vegetation (e.g., Sweet and Cameron, 1991; Nichols, 1995; Daly et al., 2011). This paper presents an early Eocene record of Sphagnum leaves together with a great number of Sphagnum-type spores. They occur together with pollen and spores of other putative peat-swamp elements in a locally developed lignite at Schöningen, northern Germany (Riegel et al., 2012). This is regarded as strong evidence for a Sphagnum peat origin of the respective lignite. 2. Geological situation Migration of Upper Permian (Zechstein) salt in the subsurface of northern Germany resulted in the formation of numerous salt domes

and ridges rising along ancient structural sutures (Baldschuhn et al., 1996). One of them is the prominent NW–SE trending Helmstedt– Stassfurt salt wall which is accompanied by two parallel rim synclines. In the Helmstedt–Schöningen mining district they accommodated up to more than 400 m of alternating terrestrial and marine sediments of late Paleocene to early Oligocene age including several lignite seams of economic importance (Look, 1984; Riegel et al., 2012). The lignite mine Schöningen Südfeld which will finally be closed in October 2016 still exposes a c. 150 m thick section of the Schöningen Formation, which probably starts in the uppermost Paleocene and covers the entire early Eocene (Riegel et al., 2012). The Schöningen Formation at Schöningen includes nine almost continuous lignite seams (Fig. 1), which are separated by siliciclastic interbeds showing marine influence to varying degrees. Several minor seams, with thicknesses of less than 20 cm, have a lateral extent of up to few hundred metres, but cannot be traced across the entire open cast mine. They have been recognized during various stages of our study and are therefore not included in the numbered series of seams (Riegel et al., 2012). One of them, the object of the present study, has been designated as the “Sphagnum Seam” once the common occurrence of Sphagnum leaves and spores became clear. It is situated within the nearly 20 m thick Interbed 4, about 7 m above Seam 3, for which an early Eocene (Ypresian) age can be assumed as discussed by Riegel et al. (2012) on the basis of palynological evidence (pollen, spores and dinoflagellate cysts; Pflug,

Fig. 1. Generalized section of the Paleogene succession at Schöningen showing the stratigraphic position of the Sphagnum Seam (modified from Riegel et al., 2012).

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

59

1952, 1986; Krutzsch, 1992; Köthe, 2003; Riegel et al., 2012) and some scattered radiometric dates from glauconites (K/Ar: Ahrendt et al., 1995). Palaeogeographically the Helmstedt–Schöningen area was located at the southern edge of the Eocene North Sea (Fig. 2) near the mouth of a broad estuary (Blumenstengel and Krutzsch, 2008; Standke, 2008). There the area was exposed to sea level changes, to subsidence due to subsurface salt migration, and to varying intensities of terrestrial runoff due to changes in precipitation. 3. Material and methods The part of Interbed 4 including the Sphagnum Seam was measured and sampled by the first author in the mine in 2004 (Fig. 3) and 2006 (Fig. 4). For the purpose of palynological analysis the section shown in Fig. 4 was sampled in detail. Two samples each were taken from the underlying and overlying clastic sediments. The 12 to 15 cm thick seam was taken as a block in the field and split into about 1 cm thick slices in the laboratory. The samples were labelled SF1 to SF5 (“SF” = Sphagnumflöz, the German word for Sphagnum Seam) with individual SF3-subsamples characterized by cm designations. Coal samples were crushed to a particle size of 1 to 2 mm. All samples were treated with hot 15% H2O2 and c. 5% KOH for 1 to 2 h. The clastic samples were further treated with 20% HF for several days. HF was removed by 5 to 6 steps of decanting and diluting. All samples were finally sieved through a 10 μm-mesh sieve. Residues are stored in glycerine and permanent glycerine jelly slides were made. Quantitative palynological analysis is based on counting 300 individual grains of pollen and spores from at least two slides. In addition to pollen and spores charcoal particles larger than c. 10 μm but otherwise independent of their size were counted and normalized to 100 pollen and spores, in order to obtain at least a semiquantitative measure of the abundance of charcoal. To further concentrate pollen and spores for a better yield in scanning electron microscope (SEM) preparations, two representative samples from the seam (SF3, 3–4 cm and 5–6 cm) were briefly treated once more with hot diluted H2O2 and KOH. Residues of these samples were air-dried on a piece of photographic film fixed to a SEM-stub. They have been studied together with some isolated leaf fragments in a JEOL JSM-6490LV.

Fig. 3. Outcrop section from 2006 showing the sedimentological context of the Sphagnum Seam.

Individual leaf fragments of Sphagnum were picked from uncovered spreads of residue at 100× magnification and transferred and embedded in glycerine jelly on permanent microscope slides. Palynomorphs

Fig. 2. Early Eocene palaeogeography of Northwestern Europe showing the position of the mining district of Helmstedt–Schöningen (modified from Ziegler, 1990).

60

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Fig. 4. Photograph of the Sphagnum Seam outcrop (section from 2004) showing position of samples SF1 to SF5 with SF3 representing a set of cm-thick subsamples from the Sphagnum Seam (“SF” = Sphagnumflöz, the German word for Sphagnum Seam).

and leaf fragments were studied under a LEITZ Metallux 3 microscope equipped for interference contrast and photographed with a LEICA DFC 490 digital camera connected to the LEICA software LAS and further processed by commercial software such as Adobe Photoshop, CorelDraw and MS Publisher. 4. Results

bedded and locally bioturbated. The coarsening-upward trend is accompanied by a decrease in dinoflagellate cyst abundance and diversity indicating a concomitant reduction in marine influence. The upper c. 4 m thick coarsening-upward sequence grades into a rather homogeneous cross-bedded fine sand, which is finely rooted and bleached near the top and overlain by the 15 cm thick Sphagnum Seam. The Sphagnum Seam terminates a coarsening- and shallowing-upward sequence. It is overlain by a few metres of intensely bioturbated fine sand and mostly parallel-bedded dark silty clay followed by c. 7 m of “Spurensand”, a massive sandy unit, in which bedding is completely destroyed by bioturbation (Riegel et al., 2012). In the 2004 section (Figs. 4 and 5) the Sphagnum Seam is also up to 15 cm thick and rests on white bleached sand, which is penetrated by very fine root traces near the top. A thin layer, about 1 to 3 cm thick, of almost black sand separates the white sand from the Sphagnum Seam proper. The seam appears compact but internally thin-bedded at c. 1 cm thick intervals. The matrix-dominated coal lithotype includes a noticeable proportion of finely dispersed charcoal, which appears to be concentrated on bedding planes. The top of the seam is slightly irregular due to minor erosion before deposition of the overlying clastics causing the thickness of the seam to vary between 12 and 15 cm. The seam is overlain by beige to reddish-brown fine sand and silt with some clay laminae and locally recognizable irregular crossbedding. The reddish-brown colour and the slight solidification in the lower part of this layer are presumably due to secondary siderite impregnation. In this small outcrop, the top layer, of which only 100 cm is exposed, consists of a very fine alternation of light-coloured silt to fine sand with dark clay laminae. Sand/clay couplets may vary in thickness from 7 mm to less than 0.5 mm. The bed is dissected by up to 20 cm deep channels which are filled with exactly the same type of sediment. Bimodal cross-bedding and channelling are indicative of tidal sedimentation, although direct evidence of marine conditions has not been found.

4.1. Sedimentary framework

4.2. Quantitative palynology (Fig. 5)

Fig. 3 shows the stratigraphic relation of the Sphagnum Seam to Seam 3 in the section from 2006. The nearly 7 m thick interval consists of two coarsening- and shallowing-upward sequences, each of which begins with dark silty clay and silt grading into light-coloured silt to fine sand, which is in part parallel bedded, in part small-scale cross-

Among the spores those assignable to Sphagnum are most frequent. They are dominated by Tripunctisporis (Krutzsch in Döring et al., 1966) Herngreen et al., 1986, which was initially introduced by Döring et al. (1966) as a subformgenus of Stereisporites Thomson and Pflug, 1953. However, the genus name Stereisporites is invalid since S. stereoides,

Fig. 5. Selected palynology of the Sphagnum Seam (section from 2004).

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

which was selected as the type by Thomson and Pflug (1953), had previously been used as type of Sphagnumsporites Raatz, 1937. Therefore, we follow Potonié (1970), who recommended raising Tripunctisporis to generic rank, which was later formally validated by Herngreen et al. (1986) when selecting T. maastrichtiensis, the type species of the former subgenus Tripunctisporis (see Döring et al., 1966), as the type.

61

Tripunctisporis is characterized by a distinct cingulum of variable width and a circular to rounded triangular thickening at the distal pole, c. 10 μm in diameter, with three deep small pits in radial position (Fig. 6.7–6.13). Tripunctisporis makes up between 75% and 95% of all specimens assignable to Sphagnum within the Sphagnum Seam proper. The remainder corresponds to either Distancorisporis (Krutzsch in

Fig. 6. Sphagnum remains: Fig. 6.1 and 6.2: Slightly charred fragments of Sphagnum leaves showing chlorophyll cells (dark) and hyaline cells (light) with spiral thickenings and pores (TML). Fig. 6.1 from sample SF3, 3–4 cm and Fig. 6.2 from sample SF3, 11–12 cm. Fig. 6.3: Fragment of Sphagnum shoot, not charred (TML). Sample SF3, 3–4 cm. Fig. 6.4–6.6: SEM images of Sphagnum leaves. Sample SF3, 4–5 cm. Fig. 6.7: Distal view of Tripunctisporis with diagnostic structure (SEM). Sample SF3, 5–6 cm. Fig. 6.8: Proximal view of Tripunctisporis showing trilete mark and “ghost” of distal structure (SEM). Sample SF3, 5–6 cm. Fig. 6.9: Complete tetrad of Tripunctisporis (SEM). Sample SF3, 11–12 cm. Fig. 6.10–6.13: Series of foci from distal (Fig. 6.10) to proximal (Fig. 6.13) of Tripunctisporis (TML), scale on Fig. 6.10. Sample SF3, 3–4 cm. Fig. 6.14–6.17: Series of foci from distal (Fig. 6.14) to proximal (Fig. 6.17) of Distancorisporis (TML), scale on Fig. 6.17. Sample SF3, 3–4 cm.

62

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Döring et al., 1966) Srivastava, 1972, with a simple triradiate distal thickening, or to Sphagnumsporites without distal thickening and only a thin cingulum. Sphagnum-type spores are common but not frequent below the seam and rare to absent above. Within the seam their frequency rises

from 14% of the total sporomorph assemblages at the base and top of the seam to as high as 38% in the middle. It should be noted that the proportion of Tripunctisporis versus other Sphagnum-type spores is highest in the middle of the Sphagnum Seam and decreases significantly outside the seam.

Fig. 7. Pteridophyte spores: Fig. 7.1–7.3: Foveotriletes crassifovearis Krutzsch, 1962. Fig. 7.1 and 7.2 from sample SF3, 2–3 cm and Fig. 7.3 from sample SF3, 5–6 cm. Fig. 7.4–7.6: cf. Corrugatisporites corruvallatus (Krutzsch, 1967a) Nagy, 1985 sensu Stuchlik et al. (2001), pl. 20, Fig. 1-2. Fig. 7.4 and 7.5 from sample SF3, 2–3 cm and Fig. 7.6 from sample SF3, 5–6 cm. Fig. 7.7–7.9: Trilites multivallatus (Pflug in Thomson and Pflug, 1953) Krutzsch, 1959 sensu Nickel (1996). Fig. 7.7 and 7.8 from sample SF5, 11–12 cm and Fig. 7.9 from sample SF3, 5–6 cm. Fig. 7.10–7.12: Goczanisporis baculatus Krutzsch, 1967b). All from sample SF3, 11–12 cm. Fig. 7.13: Cicatricososporites pseudodorogensis (Potonié, 1951); Thomson and Pflug, 1953. Sample SF3, 11–12 cm. Fig. 7.14: Leiotriletes cf. microadriennis Krutzsch, 1959. Sample SF3, 11–12 cm. Fig. 7.15: Toroisporis longitorus Krutzsch, 1959. Sample SF3, 5–6 cm. Fig. 7.16: Camarozonosporites cf. eocaenicus Krutzsch and Vanhoorne, 1977. Sample SF3, 11–12 cm.

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Trilete spores with variable foveolate to verrucate ornamentation which are closely associated with Tripunctisporis. (Fig. 7.1–7.9) comprise three forms suggesting different species, which, however, in fact are linked by transitions making the delineation of species and even generic assignment rather difficult. Therefore, they are grouped as trilete foveolate/verrucate spores in the pollen diagram (Fig. 5). One of these forms (Fig. 7.1–7.3) is characterized by a relatively even surface, pitted with small foveae of less than 1 μm in diameter, and compares favourably with Foveotriletes verrucatoides Krutzsch, 1962. However, the most abundant among this group are forms (Fig. 7.4–7.6) with a highly netted rugulate to reticulate sculpture of low ridges surmounted by rounded knobs and surrounding irregularly shaped luminae of 2 to 4 μm diameter, which are pitted by minute pits similar to those in the formerly described type. They may best be compared to Corrugatisporites corruvallatus (Krutzsch, 1967a) Nagy, 1985 sensu Stuchlik et al. (2001). The third type is densely and prominently verrucate and the flaring bases of the verrucae appear to surround irregular luminae (Fig. 7.7– 7.9). This type is closely comparable to Trilites multivallatus (Thomson and Pflug, 1953) Krutzsch, 1959, as figured by Nickel (1996) from middle Oligocene deposits of the northern part of the Upper Rhine Graben (Germany). Smooth trilete Leiotriletes-type spores (e.g., Leiotriletes microadriennis Krutzsch, 1959; Fig. 7.14) are common although not abundant and similar to spores of recent and fossil Lygodium (Schizaeaceae; Zhang et al., 1990, Gandolfo et al., 2000, personal observation of in situ spores from the middle Eocene of Eckfeld, Eifel, Germany, by V.W.), a genus of climbing ferns today widely distributed in tropical and subtropical areas. Larger specimens of smooth trilete spores of c. 50 μm in diameter with distinct tori have been assigned to Toroisporis longitorus Krutzsch, 1959. Goczanisporis baculatus Krutzsch, 1967b (Fig. 7.10–7.12), a trilete spore of unknown biological affinity with a characteristic densely baculate sculpture, is present but infrequent throughout most of the Sphagnum Seam. The species is slightly more common at the top (sample SF 3, 11–12 cm), but missing above and below the seam. It is similarly restricted in occurrence throughout other seams at Schöningen. In the Sphagnum Seam, monolete polypodiaceous spores, such as e.g., Laevigatosporites hardtii (Potonié and Venitz, 1934) Thomson and Pflug, 1953, are exceptionally rare never reaching more than 0.3% of the total assemblage. Similarly, Cicatricososporites pseudodorogensis (Potonié, 1951) Thomson and Pflug 1953, has been recorded only with rare specimens at the top of the seam (sample SF 3, 11–12 cm). Lycopods are represented by rare specimens of Camarozonosporites cf. eocaenicus Krutzsch and Vanhoorne, 1977 (Fig. 7.16). Bisaccate pollen of Pinuspollenites Raatz, 1937 sensu Stuchlik et al. (2002) (Fig. 8.14) is rare in the Sphagnum Seam (averaging 2.3%), but more than three times more abundant than in any other major lignite seam at Schöningen such as Main Seam, Seam 1 and Seam 2. Significantly, there is no change in abundance of bisaccates between the seam and accompanying sediments. Inaperturate pollen, generally attributed to the Taxodiaceae which have recently been included in the Cupressaceae s.l. (Inaperturopollenites verrupapillatus Trevisan, 1967 sensu Stuchlik et al. (2002); Fig. 8.15), plays a subordinate role within the seam, but rises significantly in frequency immediately above the seam. Similar sharp increases of inaperturates have often been observed in clastic interbeds immediately above lignite seams in other sections at Schöningen. Pollen of Restionaceae, such as Milfordia incerta (Thomson and Pflug, 1953) Krutzsch, 1961 (Fig. 8.1–8.2) is common albeit not frequent within, but missing outside the Sphagnum Seam. In contrast, palm pollen which may be assigned to Monocolpopollenites tranquillus (Potonié, 1934) Thomson and Pflug, 1953, is rare within the seam but quite common outside. Triporate pollen taxa, particularly those with an affinity to Myricaceae and Betulaceae are equally dominant as Tripunctisporis.

63

Being most abundant in the middle of the seam and rare outside their distribution closely parallels that of the Sphagnum-type spores. They have been summarized in the “Triporopollenites robustus/rhenanus group” in the diagram (Fig. 5), since it is difficult to consistently assign them to a distinct species. Less frequent, but similar in distribution are triporate pollen of juglandaceous affinity such as species of Plicatopollis, Platycaryapollenites and Momipites. An inverse distribution is exhibited by Pompeckijoidaepollenites subhercynicus (Krutzsch, 1954) Krutzsch in Góczán et al., 1967. Tricolpopollenites liblarensis (Thomson in Potonié, 1951) Thomson and Pflug, 1953, is dominant in the clastic sediments immediately underlying the seam and relatively rare within, while Tricolporopollenites cingulum (Potonié, 1931a) Thomson and Pflug, 1953, is frequent within and highly dominant above the seam. Within the seam there is a marked inverse relationship between T. cingulum and triporate taxa. Very striking is the inverse frequency of T. liblarensis and T. cingulum, which has often been observed at Helmstedt (Lenz, 2005) and Schöningen (personal observation W.R.). This inverse relationship is rather consistent though either taxon is likely to include pollen from more than one parent plant. Ericaceae pollen tetrads such as Ericipites ericius (Potonié, 1931b) Potonié, 1960 (Fig. 8.13) and E. callidus (Potonié, 1931b) Krutzsch, 1970, are a common but not frequent element of the assemblages within the Sphagnum Seam and represent plants generally growing on nutrient-poor and acidic soils. Even rare specimens of Droseridites echinosporus (Potonié, 1934) Krutzsch, 1961 (Droseraceae or Nepenthaceae, see discussion below) have been observed (Fig. 8.11–8.12), but do not appear in the percentage calculation. 4.3. Non-pollen/spore palynofacies The most noteworthy structured components in the palynological residues are vegetative remains of Sphagnum (Fig. 6.1–6.6). Wellpreserved fragments of leaves clearly assignable to Sphagnum commonly occur within the seam, especially in its central part. They are medium- to dark-brown and clearly exhibit the typical anatomy of Sphagnum leaves consisting of a network of the originally photosynthetic cells (now dark brown in transmitted light) enclosing the large thinwalled hyaline cells complete with diagnostic spiral thickenings and pores (Fig. 6.1, 6.2, 6.4 and 6.5). SEM micrographs show that the hollow strands of the originally photosynthetic cells (Fig. 6.6) are largely enclosed by the hyaline cells (Fig. 6.4). In addition to the remains of leaves, the palynological residues of some seam samples commonly include fragments of shoots of Sphagnum (Fig. 6.3). The highly compressed peripheral stem cells are relatively large and very thin-walled. The central strands are formed by a bundle of elongated smaller cells. In contrast to the remains of leaves, which appear slightly charred, the shoot remains of Sphagnum are light-coloured and show no indication of any degree of charring, suggesting that they have been preserved within the waterlogged part (catotelm) of the peat section. Relatively long strands (up to 1 mm in length) of vascular tissues with sieve plates and fibres (Fig. 9.3) are rather common in a few samples of the Sphagnum Seam. They are flexible and transparent and appear to consist of lipid-rich material, since they exhibit yellowish fluorescence under blue light irradiation and have resisted regular palynological preparation. They are considered here to represent primary vascular tissue of herbaceous angiosperms, which is preserved due to lipid impregnation. Scalariform tracheids are also commonly represented in the residues, however, almost exclusively as highly charred fragments (Fig. 9.2). Since they are generally considered to be indicative of primary vascular bundles of ferns (Collinson et al., 2007), their occurrence conforms well to the abundance of fern spores. Charcoal fragments are a major constituent in palynological residues of all seam samples (Fig. 10). As indicated above, fragments of Sphagnum leaves also appear

64

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Fig. 8. Angiosperm and gymnosperm pollen: Fig. 8.1 and 8.2: Milfordia incerta (Thomson and Pflug, 1953) Krutzsch, 1961. Sample SF3, 2–3 cm. Fig. 8.3 and 8.4: Juglandaceous triporate pollen grain with typical juglandaceous microsculpture. Sample SF3, 5–6 cm. Fig. 8.5 and 8.6: Triporopollenites robustus (Mürriger and Pflug, 1951) Thomson and Pflug, 1953. Sample SF3, 5–6 cm. Fig. 8.7 and 8.8: specimen characteristic of the Tricolporopollenites cingulum group. Sample SF3, 5–6 cm. Fig. 8.9 and 8.10: Tricolporopollenites cf. microreticulatus Thomson and Pflug, 1953. Sample SF3, 5–6 cm. Fig. 8.11 and 8.12: Droseridites echinosporus (Potonié, 1934) Krutzsch, 1961. Sample SF3, 11–12 cm. Fig. 8.13: Ericipites ericius (Potonié, 1931b) Potonié, 1960. Sample SF3, 11–12 cm. Fig. 8.14: Pinuspollenites sp. sensu Stuchlik et al. (2002). Sample SF3, 2–3 cm. Fig. 8.15: Inaperturopollenites verrupapillatus Trevisan, 1967. Sample SF3, 5–6 cm.

slightly charred. Even a few specimens of Tripunctisporis are clearly darkened and therefore probably thermally altered. Of particular interest is the unique although rare occurrence of tests (Fig. 9.1) that show close resemblance to the loricae of the extant bdelloid rotifer Habrotrocha (al. Callidinia) angusticollis as described and figured in Van Geel (1978) from Holocene peat bogs of Germany

and The Netherlands where they are commonly associated with Sphagnum peat (personal communication Van Geel, 2014). Rather abundant but restricted in occurrence to a few samples (f.i. in sample SF3, 6-7 cm) are tubes of c. 15 μm in diameter (Fig. 9.4–9.6). A few specimens have one flaring end (Fig. 9.4) similar to putative conidiophores of parasitic fungi (Type 96A of Van Geel, 1978) as known from

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

65

Fig. 9. Fig. 9.1: Habrotrocha cf. angusticollis (Rotifera). Sample SF3, 3–4 cm. Fig. 9.2: Highly charred scalariform tracheid. Sample SF3, 11–12 cm. Fig. 9.3: Uncharred fragment of vascular strand with vessel and sieve plate. Sample SF3, 3–4 cm. Fig. 9.4–9.6: Fragments of tubes of putative fungal origin with possible base of conidiophore (Fig. 9.4) and closed terminal portions (Fig. 9.5 and 9.6). All from sample SF3, 6–7 cm. Fig. 9.7: Globose-polygonal body similar to spores of extant Tilletia sphagni (Fungi inc. sed.). Sample SF3, 3–4 cm.

Sphagnum bogs (Van Geel, 1978) and sediments of dystrophic lakes (Fiłoc and Kupryjanowicz, 2015). Others are closed at one end with a rounded top probably representing a terminal portion (Fig. 9.5 and 9.6). The great number of fragments that are open-ended on both sides, however, indicates that such tubes originally reached considerable length. The biological affinity of the latter two is unknown, but a fungal origin appears most likely. Non-pollen palynomorphs also comprise some specimens of globose-polygonal bodies quite similar to spores of extant Tilletia sphagni Nawaschin (Fig. 9.7), a fungal parasite

of unknown systematic affinity on Sphagnum (e.g., Bauch, 1938, Van Geel, 1978, Fiłoc and Kupryjanowicz, 2015). 5. Discussion The discussion of our results mainly aims at the reconstruction of the composition of the flora and the structure of the vegetation forming the Sphagnum Seam. This has to take a number of factors into consideration, e.g., the preservation potential of certain plant parts, the dispersal

Fig. 10. Abundance of Tripunctisporis vs. charcoal particles (section from 2004). Please note different scales: Scale for Tripunctisporis is the percentage of total sporomorph assemblage, and scale for charcoal is the number of charcoal particles per 100 counted sporomorphs.

66

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

potential especially in the case of pollen and spores, their taphonomic mode and their relation to modern plants. Soft plant tissues (e.g., mosses, leaf parenchyma, flowers), embedded in situ in peat, are readily amalgamated with humic matrix beyond recognition in lignites, unless they are slightly charred, hence the poor fossil record of Sphagnum leaves. The dispersal potential of pollen and spores, on the other hand, is highly variable and depends on pollen production, pollination mechanism (entomo- vs. anemophily) and growth habit of their parent plant. In general, most of the pollen record is of local or regional origin (e.g., Moore et al., 1991; Matthias et al., 2015). Although anemophilous tree pollen may be transported over some distance, it is generally accepted that about 95% of all tree pollen settles down within 1 km of its source (Traverse, 1988; Moore et al., 1991). A more local origin is generally suggested for pteridophyte spores (Cousens, 1988; Peck et al., 1990) and entomophilous pollen (e.g., Straka, 1975; Faegri et al., 1989), even if they may sometimes be transported over greater distances (e.g., Bhattacharya et al., 1999). As discussed by Moore et al. (1991) the pollen record of ombrogenous peat is mainly of local origin with some influx through the air from the surrounding vegetation. Therefore, most fern spores and pollen of low-growing herbs are incorporated in peats very close to their parent plants and may be used for the recognition of a peatland habitat. The reconstruction of a Sphagnum peat bog for our seam strongly relies on the common occurrence of fragments of Sphagnum leaves in combination with the frequency of Sphagnum-type spores (Tripunctisporis). In view of the rarity of remains of Sphagnum leaves in pre-Quaternary coals (and sediments) their common occurrence in the Sphagnum Seam at Schöningen is highly significant and already suggests that Sphagnum was the main peat-forming plant. This is true even if their preservation may have been enhanced by partial charring during short-lived wildfires, evidence of which is shown by the frequency of charcoal particles in the palynological residues. Besides, the abundance of Sphagnum-type spores and their almost perfect normal (Gaussian) distribution around the middle of the seam are strong arguments for in situ growth of Sphagnum. The exceptional preservation of complete tetrads of Tripunctisporis (Fig. 6.9) provides further support for an autochthonous origin of the Sphagnum spores. The numerous species of modern peat mosses (Sphagnum spp.) are closely adapted to the broader peatland realm where they often occur restricted within a mosaic of subenvironments and ecological niches (e.g., Müller, 1965; Clymo and Hayward, 1982; Rydin et al., 2006). A similar ecological mosaic can be assumed to have existed in ancient peat bogs, where it is difficult to recognize, since identification of different modern Sphagnum species on the basis of spores alone is not possible (Schulz, 1970; personal communication, A. Hölzer, 2010). The great predominance of Tripunctisporis, however, suggests a rather homogeneous population and a close affinity of the corresponding Sphagnum species to the specific conditions represented by the Sphagnum Seam. Rather intriguing is the discovery of several specimens of tests very similar to the loricae of the rotifer Habrotrocha angusticollis, which in modern peat bogs uses Sphagnum as its preferred habitat. This is compelling support for our interpretation of a Sphagnum bog. To our knowledge, the only pre-Quaternary record of loricae of habrotrochid rotifers has been reported from the exceptional preservation as inclusion in late Paleogene Dominican amber (Waggoner and Poinar, 1993). Their preservation in the early Eocene at Schöningen, therefore, is rather startling and may be due to the highly acidic and aseptic primary conditions during peat formation. Other non-pollen palynomorphs strongly supporting a Sphagnum bog origin for the Sphagnum Seam are fungal spores similar to those of the extant Sphagnum-parasite Tilletia sphagni and putative conidiophores which are frequently found in association with Sphagnum (Van Geel, 1978; Fiłoc and Kupryjanowicz, 2015). Foveotriletes verrucatoides and Corrugatisporites corruvallatus are key fern spore species for the Sphagnum Seam, which have rarely been observed at other localities at Schöningen except for assemblages rich in

Tripunctisporis (personal observation, W. R.). Both show close resemblance to spores of the extant genus Botrychium as figured by, e.g., Zhang et al. (1990) and Large and Braggins (1991). Today Botrychium is a genus of low-growing eusporangiate ferns with a nearly worldwide distribution, preferring open habitats (Tryon and Tryon, 1982). When immersed within the surrounding herbaceous vegetation its spore dispersal pattern is mostly local or even “sharply curtailed” (Peck et al., 1990). Goczanisporis bacupilosus is rare in numbers but has repeatedly been found as tetrads. It is strictly associated with Tripunctisporis and the parent plant must equally be considered an indigenous Sphagnum peat bog element. However, in spite of a likely fern origin there is no modern counterpart, with which it can be compared, despite the very distinctive morphology. Smooth-walled trilete spores (e.g., Leiotriletes microadriennis; Fig. 7.14) are common and may be compared with spores of the schizaeaceous fern Lygodium. Most living Lygodium species are climbing ferns (Tryon and Tryon, 1982), a habit that has also been discussed for early Cenozoic Lygodium (Collinson, 2002) and fits poorly with our reconstruction of a Sphagnum peat bog. However, since modern Lygodium prefers well-lit sites, such as forest margins, gallery forests, shrubby savannahs and occasionally forms tangled growth in brushy clearings (Tryon and Tryon, 1982), it may be considered to have occupied the margin of the Sphagnum peat bog or even shrubby patches on its surface. Monolete spores of Polypodiaceae (Laevigatosportes hardtii), which are frequent in association with Sphagnum-type spores in charcoalrich horizons of the lower seams at Schöningen (Main Seam, Seam 1, Seam 2; Riegel et al., 2012), are nearly absent in the Sphagnum Seam. This is rather unusual and significantly adds to the uniqueness of the Sphagnum Seam. Sporadic specimens of Cicatricososporites pseudodorogensis near the top of the seam are clearly assignable to Schizaea (see figures in Zhang et al., 1990). In addition, spores of Lycopodiaceae (Camarozonosporites cf. eocaenicus) have occasionally been observed. Herbaceous angiosperms which preferably grow in open, wet environments and on nutrient deficient peat bogs are represented by Milfordia and Droseridites. Milfordia (Milfordia incerta; Fig. 8.1–8.2) is generally accepted as pollen of Restionaceae (Hochuli, 1979). Today, Restionaceae are almost exclusively restricted to a highly disjunct and endemic distribution in the Southern Hemisphere, where they preferably grow in lowlands on wet and nutrient-poor soils (Cronquist, 1981; Campbell, 1983) and “favor seasonally wet habitats which dry out each year” (Heywood, 1993: 283). They were widespread in the early Paleogene of the Northern Hemisphere prior to the expansion of grasses, sedges and rushes in marsh environments (Hochuli, 1979), except for North America. To our knowledge, the only North American record of Milfordia (M. incerta, M. minima) is from the Jackson group, upper Eocene of the Gulf coast (Frederiksen, 1977) and an association of Sphagnum with Milfordia has not been recorded there, thus far, although Sphagnum spores are well known from the Paleogene of North America. Although Droseridites is rare in numbers and its distribution in all Cenozoic lignites is limited any record serves as a very distinctive environmental signal. It has originally been assigned to Droseraceae, but later reassigned to Nepenthes by Krutzsch (1985) without presenting evidence. Takahashi and Sohma (1982) distinguish Nepenthaceae pollen as inaperturate from the proximally porate pollen of Droseraceae. However, recognition of presence or absence of a pore appears to be rather ambiguous in pollen tetrads, which are otherwise very similar. Since most species of Nepenthes today live in tropical rain forests, while Droseraceae live mostly in temperate to tropical peatlands worldwide, an affinity to Droseraceae appears much more likely for the occurrence of Droseridites in the Sphagnum Seam. In either case, the occurrence of insectivorous plants indicates that nutrient deficiency was rather severe during formation of the Sphagnum Seam.

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Ericaceae, represented by Ericipites ericius and E. callidus, are a shrubby element preferentially inhabiting nutrient poor soils and are common associates within peatlands or in fringes around them. Possible modern equivalents for the parent plants of Ericipites tetrads as found in the Spagnum Seam are species of Erica or Rhododendron (see figures in Tianqing, 2010; Sarwar and Takahashi, 2014). Since Ericipites is a common constituent in all Eocene lignite seams in the Helmstedt/ Schöningen district, but rare in associated sediments (Pflug, 1952; Lenz, 2005), it can be regarded as a reliable indicator of mire conditions. From its ubiquitous occurrence and abundance triporate pollen is generally considered to be anemophilous and an important component of the regional Paleogene pollen rain (Pflug, 1952; Lenz, 2005; Lenz and Riegel, 2001). Triporates of the Triporopollenites robustus/rhenanus complex are considered to be derived from Betulaceae or Myricaceae (Thomson and Pflug, 1953; Stuchlik et al., 2009) which both are close associates of modern peat bogs. Abundance of these triporates and the parallel frequencies with Tripunctisporis suggest close areal proximity of their parent plants to the Sphagnum peat bog, forming either part of an ecologic series, or an integral part of the bog environment. On the basis of their distribution a similar ecological role may be implied for the parent plants of juglandaceous pollen, such as e.g., Momipites or Platycaryapollenites. On the other hand, Pompeckjoidaepollenite subhercynicus may be assumed to have been introduced from an outside or marginal source to the Sphagnum peat bog on the basis of its inverse frequency distribution. It is often abundant in association with characteristic ecological successions around marine/terrestrial transitions at Helmstedt and Schöningen (Lenz, 2005; Lenz and Riegel, 2001; Riegel et al., 2012). But marine influence cannot be inferred from the relatively low frequency around the Sphagnum Seam despite the apparent nearshore position. The small tricolpate and tricolporate pollen (Tricolpopollenites liblarensis respectively Tricolporopollenites cingulum) often reach peak abundances in Eocene lignites and are likewise considered as one of the most important elements of the regional pollen rain in the Eocene (Pflug, 1952; Lenz, 2005; Lenz and Riegel, 2001). Each of the two rather broad fossil species is thought to include more than one parent taxon, but T. cingulum is generally attributed to castaneoid Fagaceae (e.g., Lithocarpus, see figures in Crepet and Daghlian, 1980; Miyoshi, 1981) and considered to be derived from Paleogene mire forests (Pflug, 1952; Lenz, 2005). Botanical affinities of Tricolpopollenites liblarensis are more ambiguous (Fagaceae?) but it is likewise considered to be anemophilous (Pflug, 1952; Lenz, 2005), however, derived from a different, probably more open vegetation since it commonly alternates in its dominance of assemblages with Tricolporopollenites cingulum. This is indicated in the Sphagnum Seam section (Fig. 5) by its dominance below and great reduction within and above the seam. Of all potentially anemophilous pollen bisaccates are best adapted to transport by wind and known to be most widely spread over great distances (e.g., Erdtman, 1954; Chaloner and Muir, 1968). Therefore, the extreme rarity of bisaccates in most Eocene assemblages appears rather puzzling. Thus, even the slight increase of bisaccate pollen in the Sphagnum Seam over this very low general Eocene background may be considered significant and attributed to the lack of a closed canopy in the dominantly herbaceous vegetation. A mostly herbaceous origin for the Sphagnum Seam is strongly supported by the fact that only tiny roots have been observed at the base. Eocene analogues of a modern Sphagnum bog have not been described, thus far. Assemblages somewhat similar to those of the Sphagnum Seam also occur in other seams at Schöningen (Main Seam, Seam 1, Seam 2; Hammer-Schiemann, 1998, unpublished doctoral thesis; Inglis et al., 2015). They differ, however, in some important aspects. Although Sphagnum-type spores are also dominant, they are more variable and equally represented by Tripunctisporis, Distancorisporis, and Sphagnumsporites. Besides, they lack elements considered as important environmental indicators in the Sphagnum Seam. For instance,

67

Droseridites as well as Cicatricososporites are absent, while Foveotriletes type spores and fragments of Sphagnum leaves are extremely rare (personal observation, W.R.). Instead, there is an increase in freshwater phytoplankton (e.g., Tetraporina, Schizophacus) indicating a gradual rise of the water table in Seam 1 ahead of a marine transgression in the overlying interbed (Inglis et al., 2015). Furthermore, the frequent occurrence of charred tracheids with bordered pits, entirely missing in the Sphagnum Seam, indicates a considerable proportion of woody elements. Nevertheless, Sphagnum was an important part of the coal-forming vegetation in Seam 1 as confirmed by geochemical evidence (Inglis et al., 2015) and possibly represented by more than one species. Nichols and Traverse (1971) mention a somewhat similar CorylusSphagnum assemblage from lignites of the Wilcox Group (late Paleocene/early Eocene) in East Texas (they use “Corylus” as a working term for triporate pollen that includes Triporopollenites robustus as the prominent species). Sphagnum-type spores make up only 10% of the assemblage. Besides, this assemblage is reported to occur in fluvial facies lignites and is absent in deltaic and coastal environments. But the Corylus-Sphagnum assemblage of Nichols and Traverse (1971) suggests that at least variants of this type of association had an intercontinental distribution during the Eocene. In search for a modern equivalent the occurrence of Restionaceae precludes direct comparison of the Eocene peat bog at Schöningen with modern Northern Hemisphere Sphagnum peat bogs despite considerable similarities. However, closer comparison is possible with raised bogs, which have been described from New Zealand and SAustralia (e.g., Campbell, 1964, 1975, 1983; Dodson and Wilson, 1975; Clarkson et al., 2004). These are mainly formed by the roots of certain Restionaceae in association with peat mosses, and the accompanying vegetation includes Droseraceae, some ferns and Lycopodiaceae. Accordingly, It has been shown that most of the spores of Sphagnum and pollen of Restionaceae remain on the surface of such a restionad bog (Martin, 1999). In any case, ombrogenous Sphagnum peat bogs from subtropical to tropical mid-palaeolatitudes are unusual or have not been described as such, thus far. Climate reconstructions as inferred from marine isotope records (Zachos et al., 2001, 2008) generally agree that the peak of the Paleogene greenhouse climate is reached in the so-called Early Eocene Climatic Optimum (EECO). Based on charcoal abundance Robson et al. (2015) even suggest that the lower part of the Schöningen Formation including the Sphagnum Seam falls within the warmest period including the hyperthermal events of the Paleocene-Eocene Thermal Maximum (PETM) and the Early Eocene Climatic Optimum (EECO). Although important tropical elements are missing, the presence of palm pollen in and around the Sphagnum Seam suggests a subtropical to tropical climate. In our earlier interpretations we opted for an alternating wet/dry climate for the early Eocene followed by a perhumid climate in the middle Eocene (Riegel et al., 1999, 2012), which is supported by the abundance of charcoal in the early Eocene lignites and their near total absence in the middle Eocene. The juxtaposition of abundant Sphagnum-type spores (Tripunctisporis) and charcoal particles in the Sphagnum Seam (Fig. 10) demonstrates quite convincingly that wildfires commonly occurred during the peat bog development under the alternating wet/ dry early Eocene climate, possibly even restraining peat growth to some extent. Fig. 10 shows that in the middle of the seam Sphagnumtype spores are most abundant and Sphagnum growth probably most prolific when wildfires and charcoal are at a low. Interestingly, a similar scenario of herbaceous swamps with Restionaceae and some ferns, here especially Gleicheniaceae, controlled by a natural fire regime under a seasonally-dry climate has been envisaged for some Oligocene to Miocene coals of the Latrobe Valley Depression of southeastern Australia (Blackburn and Sluiter, 1994). Climate is an essential factor controlling the hydrological cycle. Under the early Paleogene greenhouse climate, especially during hyperthermals, the hydrological cycle intensified considerably

68

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

(Krishnan et al., 2014) and differed fundamentally from that of modern temperate Sphagnum peat bogs. Thus, increased rates of evapotranspiration and high insolation probably caused frequent lowering of the water table followed by drought at the surface, which became more susceptible to ignition and short-lived wildfires as indicated by the abundance of charcoal. In its sedimentological context (Fig. 3) the Sphagnum Seam occurs at the top of a stacked coarsening-upward sequence of low-angle crossbedded sands. Continuous upward shallowing and decreasing marine influence is indicated by a decrease of dinoflagellate cysts and bioturbation and finally by rooting at the very top, which was emergent at the onset of peat bog formation. Peat growth was terminated by drowning under a freshwater cover which was tidally influenced as indicated by bimodal cross-bedding and channelling in the overlying sediments. From the narrow mine exposure it is difficult to assign this deltaic type of succession to a specific depositional site within the broader estuarine setting. Approximate stratigraphic equivalents have been interpreted as bayhead delta deposits on the basis of rather general litholog records (Osman et al., 2013). However, a delta plain of limited areal extent and duration which provided the surface and substrate for the peat bog formation in the present case appears to be of a more local scale and hardly qualifies for a bayhead delta of the larger estuary. The formation of the Sphagnum Seam represents only a rather brief singular episode within the ca. 5 million years estimated for the Schöningen Formation. Assuming Sphagnum-peat growth of 1 cm in 10 to 20 years (Gerken, 1983) and a relatively high compaction rate from rather porous Sphagnum peat to lignite of 1:10 a duration of 1200 to 2400 years is calculated for the existence of the peat bog in the Schöningen Formation. 6. Summary and conclusions Quantitative palynological analysis of a thin local seam (section 2004, Fig. 5) in the early Eocene lignite succession exposed in the opencast mine Schöningen (Lower Saxony, northern Germany) revealed pollen and spore assemblages of rather low diversity. They are characterized by an abundance of Sphagnum-type spores, especially Tripunctisporis, and fern and lycopod spores together with the common occurrence of pollen of oligotrophic and acidophilic plants such as Ericaceae (Ericipites ericius, E. callidus), Restionaceae (Milfordia incerta) and Droseraceae (Droseridites echinosporus). The frequency and diversity of trilete spores of the foveolate/verrucate type indicating a rich fern cover appears unique to an Eocene peat bog. Most noteworthy is the frequency of well-preserved fragments of Sphagnum leaves and the occasional occurrence of loricae of Habrotrocha-like bdelloid rotifers and spores similar to those of Tilletia sphagni. From the distribution of palynomorphs and their known or alleged biological affinity and by comparison with likely modern equivalents we reconstruct an ombrogenous domed peat bog maintained by prolific growth of Sphagnum in association with a variety of ferns (e.g., Botrychium, Lygodium), lycopods, Restionaceae, some Ericaceae and Droseraceae. The occurrence of insectivorous plants indicates severe nutrient deficiency in the Sphagnum peat bog. The bog is bordered by an ecotonal rim of shrubs or low trees (Betulaceae, Myricaceae, Juglandaceae, some Ericaceae and possibly some palms) succeeded by more distant mire forests including Fagaceae, Taxodiaceae and palms. In many respects this resembles an Eocene equivalent of a Quaternary high latitude Sphagnum bog, except for the absence of Cyperaceae and the presence of palms. In view of the significant proportion of Restionaceae pollen (Milfordia), however, it appears more akin to southern hemisphere restionad bogs, again except for the absence of Cyperaceae, which made their major advance later in the Oligocene. The total lack of a waterlogged layer in the highly permeable substrate strongly argues in favour of purely rain-fed ombrogenous maintenance of peat bog formation. The required high precipitation in combination with frequent wildfires as indicated by the abundance of

charcoal, however, suggests a highly stressed hydrological cycle under an alternating wet/dry climate close to the alleged Early Eocene Climatic Optimum (EECO). Acknowledgements The management and staff of the mine Schöningen Südfeld of the “Helmstedter Revier” of MIBRAG (formerly BKB, Braunschweigische Kohle-Bergwerke) is greatfully acknowledged for generously granting access to the mine and for logistic support of field work. Lab facilities and office space were provided to W. Riegel by the Geobiology Division (Prof. J. Reitner) of the Geoscience Center, University of Göttingen. Thanks are due to the thorough reviewer and last but not least to Prof. Alan Lord (London/Frankfurt am Main) as native speaker for cross-checking the language. References Ahrendt, H., Köthe, A., Lietzow, A., Marheine, D., Ritzkowski, S., 1995. Lithostratigraphie, Biostratigraphie und radiometrische Datierung des Unter-Eozäns von Helmstedt (SE-Niedersachsen). Z. Dtsch. Geol. Ges. 146, 450–457. Arnold, C.A., 1932. Microfossils from Greenland coal. Pap. Mich. Acad. Sci. Arts Lett. 15, 51–61. Baldschuhn, R., Binot, F., Fleig, S., Kockel, F., 1996. Geotektonischer Atlas von NordwestDeutschland und dem deutschen Nordsee-Sektor. Geol. Jahrb. 153, 1–88 (3 CD). Bauch, R., 1938. Über die systematische Stellung von Tilletia Sphagni Nawaschin. Ber. Deut. Bot. Ges. 56, 73–85. Bhattacharya, A., Mondal, S., Mandal, S., 1999. Entomophilous pollen incidence with reference to atmospheric dispersal. Aerobiologia 15, 311–315. Blackburn, D.T., Sluiter, I.R.K., 1994. The Oligo-Miocene coal floras of southeastern Australia. In: Hill, R.S. (Ed.), History of the Australian Vegetation: Cretaceous to Recent. Cambridge University Press, Cambridge, pp. 328–367. Blumenstengel, H., Krutzsch, W., 2008. Tertiär. In: Bachmann, G.H., Ehling, B.-C., Eichner, R., Schwab, M. (Eds.), Geologie von Sachsen-Anhalt. E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, pp. 267–292. Boulter, M., 1994. An approach to a standard terminology for palynodebris. In: Traverse, A. (Ed.), Sedimentation of Organic Particles. Cambridge University Press, Cambridge, pp. 199–216. Campbell, E.O., 1964. The restiad peat bogs at Motumaoho and Moanatuatua. Trans. R. Soc. N. Z. 2 (16), 219–227. Campbell, E.O., 1975. Peat deposits of Northern New Zealand as based on identification of plant fragments in the peat. Proc. NZ Ecol. Soc. 22, 57–60. Campbell, E.O., 1983. Mires of Australasia. In: Gore, A.J.P. (Ed.), Mires: Swamp, Bog, Fen and MoorEcosystems of the World 4B. Elsevier Scientific Publishing Company, Amsterdam, Oxford, New York, pp. 153–180. Chaloner, W.G., Muir, M., 1968. Spores and spore floras. In: Murchison, D.G., Westoll, T.S. (Eds.), Coal and coal-bearing strata. Oliver & Boyd, Edinburgh, London, pp. 127–146. Clarkson, B.R., Schipper, L.A., Lehmann, A., 2004. Vegetation and peat characteristics in the development of lowland restiad peat bogs, North Island, New Zealand. Wetlands 24, 133–151. Clymo, R.S., Hayward, P.M., 1982. The ecology of Sphagnum. In: Smith, A.J.E. (Ed.), Bryophyte Ecology. Chapman and Hall, London and New York, pp. 229–289. Collinson, M.E., 2002. The ecology of Cenozoic ferns. Rev. Palaeobot. Palynol. 119, 51–68. Collinson, M.E., Steart, D.C., Scott, A.C., Glasspool, I.J., Hooker, J.J., 2007. Episodic fire, runoff and deposition at the Paleocene–Eocene boundary. J. Geol. Soc. Lond. 164, 87–97. Cousens, M.I., 1988. Reproductive strategies of pteridophytes. In: Doust, J.L., Doust, L.L. (Eds.), Plant Reproductive Ecology. Patterns and Strategies. Oxford University Press, Oxford, pp. 307–328. Crepet, W.L., Daghlian, C.P., 1980. Castaneoid inflorescences from the Middle Eocene of Tennessee and the diagnostic value of pollen (at the subfamily level) in the Fagaceae. Am. J. Bot. 67, 739–757. Cronquist, A., 1981. An Integrated System of Classification of Flowering Plants. Columbia University Press, New York, Oxford. Daly, R.J., Jolley, D.W., Spicer, R.A., 2011. The role of angiosperms in Paleocene arctic ecosystems: a palynological study from the Alaskan North Slope. Palaeogeogr. Palaeoclimatol. Palaeoecol. 30, 374–382. Dodson, J.R., Wilson, I.B., 1975. Past and present vegetation of Marshes Swamp in southeastern South Australia. Aust. J. Bot. 23, 123–150. Döring, H., Krutzsch, W., Schulz, E., Timmermann, E., 1966. Über einige neue Subformgenera der Sporengattung Stereisporites Th. & Pf. aus dem Mesozoikum und dem Tertiär. Geol. Beih. 55, 72–83. Erdtman, G., 1954. An Introduction to Pollen Analysis. Chronica Botanica, Waltham Mass. Faegri, K., Kaland, P.E., Krzywinski, K., 1989. Textbook of Pollen Analysis. fourth ed. John Wiley & Sons, Chichester, New York, Brisbane, Toronto, Singapore. Fiłoc, M., Kupryjanowicz, M., 2015. Non-pollen palynomorphs characteristic for the dystrophic stage of humic lakes in the Wigry National Park, NE Poland. Stud. Quaternaria 32, 31–41. Frahm, J.-P., 2009. The first record of a Sphagnum from the Tertiary in Baltic Amber and other new records of mosses from Baltic and Dominican amber. Cryptogam. Bryol. 30, 259–263.

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70 Frederiksen, N.O., 1977. Affinities of Late Eocene spores and pollen grains from southeastern North America. United States Geological Survey, Open-file Report 77-691, pp. 1–26. Gandolfo, M.A., Nixon, K.C., Crepet, W.L., 2000. Monocotyledons: a review of their Early Cretaceous record. In: Wilson, K., Morrison, D. (Eds.), Proceedings of the Second International Conference on Comparative Biology of the Monocotyledons. CSIRO, Sydney, pp. 44–52. Gerken, B., 1983. Moore und Sümpfe, bedrohte Reste der Urlandschaft. Verlag Rombach, Freiburg. Góczán, F., Groot, J.J., Krutzsch, W., Pacltová, B., 1967. Die Gattungen des „Stemma Normapolles Pflug 1953b“ (Angiospermae). Neubeschreibungen und Revision europäischer Formen (Oberkreide bis Eozän). Paläontol. Abh. B 2, 429–539. Greb, S.F., DiMichele, W.A., Gastaldo, R.A., 2006. Evolution and importance of wetlands in earth history. In: Greb, S.F., DiMichele, W.A. (Eds.), Wetlands through time. Geological Society of America Special Paper 399, pp. 1–40. Herngreen, G.F.W., Felder, W.M., Kedves, M., Meessen, J.P.M.T., 1986. Micropaleontology of the Maastrichtian in borehole Bunde, The Netherlands. Rev. Palaeobot. Palynol. 48, 1–70. Heywood, V.H. (Ed.), 1993. Flowering Plants of the World, Updated ed. Oxford University Press, New York. Hochuli, P.A., 1979. Ursprung und Verbreitung der Restionaceen. Vierteljahrsschrift Naturforschenden Ges. Zürich 124, 109–130. Hübers, M., Kerp, H., 2012. Oldest known mosses discovered in Mississippian (late Visean) strata of Germany. Geology 40, 755–758. Hübers, M., Kerp, H., Schneider, W., Gaitzsch, B., 2013. Dispersed plant mesofossils from the Middle Mississippian of eastern Germany: bryophytes, pteridophytes and gymnosperms. Rev. Palaeobot. Palynol. 193, 38–56. Ignatov, M.S., 1990. Upper Permian mosses from the Russian Platform. Palaeontogr. B 217 (4-6), 147–189. Inglis, G.N., Collinson, M.E., Riegel, W., Wilde, V., Robson, B.E., Lenz, O.K., Pancost, R.D., 2015. Ecological and biogeochemical change in an early Paleogene peat-forming environment: linking biomarkers and palynology. Palaeogeogr. Palaeoclimatol. Palaeoecol. 438, 245–255. Köthe, A., 2003. Dinozysten-Zonierung im Tertiär Norddeutschlands. Rev. Paléobiol. 22, 895–923. Krishnan, S., Pagani, M., Huber, M., Sluijs, A., 2014. High latitude hydrological changes during the Eocene Thermal Maximum 2. Earth Planet. Sci. Lett. 404 (0), 167–177. Kroken, S.B., Graham, L.E., Cook, M.E., 1996. Occurrence and evolutionary significance of resistant cell walls in charophytes and bryophytes. Am. J. Bot. 83, 1241–1254. Krutzsch, W., 1954. Bemerkungen zur Benennung und Klassifikation fossiler (insbesondere tertiärer) Pollen und Sporen. Geologie 3, 258–311. Krutzsch, W., 1959. Mikropaläontologische (sporenpaläontologische) Untersuchungen in der Braunkohle des Geiseltales. Geol. Beih. 21 (22), 1–425. Krutzsch, W., 1961. Beitrag zur Sporenpaläontologie der präoberoligozänen kontinentalen und marinen Tertiärablagerungen Brandenburgs. Ber. Geol. Ges. 4, 290–341. Krutzsch, W., 1962. Atlas der mittel- und jungtertiären dispersen Sporen- und Pollen sowie Mikroplanktonformen des nördlichen Mitteleuropas. Lieferung I. Laevigate und toriate trilete Sporenformen. – 1-108. VEB Deutscher Verlag der Wissenschaften, Berlin. Krutzsch, W., 1963. Atlas der mittel- und jungtertiären dispersen Sporen- und Pollen sowie Mikroplanktonformen des nördlichen Mitteleuropas. Lieferung III. Sphagnaceoide und selaginellaceoide Sporenformen. VEB Deutscher Verlag der Wissenschaften, Berlin. Krutzsch, W., 1967a. Atlas der mittel- und jungtertiären dispersen Sporen- und Pollensowie der Mikroplanktonformen des nördlichen Mitteleuropas. Lieferung IV und V. Weitere azonotrilete (apiculate, murornate), zonotrilete, monolete und alete Sporenformen sowie Nachträge zu den Lieferungen I-III. VEB Gustav Fischer Verlag, Jena. Krutzsch, W., 1967b. Lotschisporis und Goczanisporis, zwei neue Sporengattungen aus dem Maastricht und dem tieferen Alttertiär Mitteleuropas. Monatsberichte Dtsch. Akad. Wiss. Berlin 9, 933–939. Krutzsch, W., 1970. Zur Kenntnis fossiler disperser Tetradenpollen. Paläontol. Abh. B 3 (3/ 4), 399–433. Krutzsch, W., 1985. Über Nepenthes-Pollen (alias „Droseridites“ p.p.) im europäischen Tertiär. Gleditschia 13, 89–93. Krutzsch, W., 1992. Paläobotanische Gliederung des Alttertiärs (Mitteleozän bis Oberoligozän) in Mitteldeutschland und das Problem der Verknüpfung mariner und kontinentaler Gliederungen (klassische Biostratigraphien – paläobotanischökologische Klimastratigraphie – Evolutionsstratigraphie der Vertebraten). Neues Jahrb. Geol. Palaontol. Abh. 186, 137–253. Krutzsch, W., Vanhoorne, R., 1977. Die Pollenflora von Epinois und Loksbergen in Belgien. Palaeontogr. B 163, 1–110. Kuc, M., 1973a. Plant macrofossils in Tertiary coal and amber from northern Lake Hazen, Ellesmere Island, N.W.T. Geol. Surv. Can. Pap. 73-1 (Part B), 143. Kuc, M., 1973b. Fossil flora of the Beaufort Formation, Meighen Island, NWT — Canada. Can.-Pol. Res. Inst. Biol. Earth Sci. A 1, 1–44. Large, M.F., Braggins, J.E., 1991. Spore Atlas of New Zealand Ferns and Fern Allies. SRI Publishing, Wellington. Lenz, O.K., 2005. Palynologie und Paläoökologie eines Küstenmoores aus dem mittleren Eozän Mitteleuropas – Die Wulfersdorfer Flözgruppe aus dem Tagebau Helmstedt, Niedersachsen. Palaeontogr. B 271, 1–157. Lenz, O.K., Riegel, W., 2001. Isopollen maps as a tool for the reconstruction of a coastal swamp from the Middle Eocene at Helmstedt (Northern Germany). Facies 45, 177–194.

69

Look, E.-R., 1984. Geologie und Bergbau im Braunschweiger Land (Nördliches Harzvorland, Asse, Elm-Lappwald, Peine-Salzgitter, Allertal). Dokumentation zur Geologischen Wanderkarte 1: 100 000. Bericht der Naturhistorischen Gesellschaft Hannover 127, 1-467. Lu, Jie, Zhang, Xiuyi, 1989. Characteristics of Sphagnum coal considered as a new genetic type of coal. Int. J. Coal Geol. 11, 191–203. Martin, A.R.H., 1999. Pollen analysis of Digger's Creek Bog, Kosciuszko National Park: vegetation history and tree-line change. Aust. J. Bot. 47, 725–744. Matthias, I., Semmler, M.S.S., Giesecke, T., 2015. Pollen diversity captures landscape structure and diversity. J. Ecol. 103, 880–890. Michaelis, D., 2011. Die Sphagnum-Arten der Welt. Bibl. Bot. 160, 1–403. Minnigerode, C., Klein-Reesink, J., 1984. Das Dörentruper Braunkohleflöz als Zeuge eines fossilen Moores. Petrographische und palynologische Untersuchungen zur Flözgenese. Geol. Paläont. Westfalen 2, 1–68. Miyoshi, N., 1981. Pollen morphology of Castanopsis, Pasania and Castanea (Fagaceae). Hikobia Suppl. 1, 381–385. Moore, P.D., Webb, J.A., Collinson, M.E., 1991. Pollen Analysis. second ed. Blackwell Scientific Publications, Oxford. Müller, K., 1965. Zur Flora und Vegetation der Hochmoore des nordwestdeutschen Flachlandes. Schriften Naturwiss. Ver. Schleswig-Holstein 36, 30–77. Mürriger, F., Pflug, H., 1951. Über die Altersstellung der Braunkohle von Burghasungen, Bezirk Kassel, auf Grund pollenanalytischer Untersuchungen und Vergleiche mit anderen Braunkohlenvorkommen. Notizblatt Hessischen Landesamtes Bodenforschung Wiesbaden VI Folge 2, 87–97. Nagy, E., 1985. Sporomorphs of the Neogene in Hungary. Geol. Hung. Ser. Palaeontol. 47, 1–471. Naucke, W., 1980. Chemie von Moor und Torf. In: Göttlich, K. (Ed.), Moor- und Torfkunde. 2. vollständig überarbeitete und erweiterte Auflage. Schweizerbart‘sche Verlagsbuchhandlung, Stuttgart, pp. 173–195. Neuburg, M.F., 1958. Permian true mosses of Angaraland. J. Palaeontol. Soc. India 3, 22–29. Neuburg, M.F., 1960. Leafy mosses from the Permian of Angaraland. Academioa Nauk SSSR Tr. Geologicheskij Inst. 9, 1–108 (in Russian). Nichols, D.J., 1995. The role of palynology in paleoecological analyses of Tertiary coals. Int. J. Coal Geol. 28, 139–159. Nichols, D.J., Traverse, A., 1971. Palynology, petrology, and depositional environments of some Early Tertiary lignites in Texas. Geosci. Man 3, 37–48. Nickel, B., 1996. Palynofazies und Palynostratigraphie der Pechelbronn Schichten im nördlichen Oberrheintalgraben. Palaeontogr. B 240, 1–151. Osman, A., Pollok, L., Brandes, C., Winsemann, J., 2013. Sequence stratigraphy of a Paleogene coal bearing rim syncline: interplay of salt dynamics and sea level changes, Schöningen, Germany. Basin Res. 25, 675–708. Ovenden, L., 1993. Late Tertiary mosses of Ellesmere Island. Rev. Palaeobot. Palynol. 79, 121–131. Pant, D.D., Basu, N., 1978. On two structurally preserved bryophytes from the Triassic of Nidpur, India. Palaeobotanist 25 (for 1976), 340–349. Peck, J.N., Peck, C.R., Farrar, D.R., 1990. Influence of life history attributes on formation of local and distant fern populations. Am. Fern J. 80, 126–142. Pflug, H., 1952. Palynologie und Stratigraphie der eozänen Braunkohle von Helmstedt. Paläontol. Z. 26, 112–137. Pflug, H.D., 1986. Palyno-Stratigraphie des Eozän/Oligozän im Raum von Helmstedt, in Nordhessen und im südlichen Anschlußbereich. In: Tobien, H. (Ed.), Nordwestdeutschland im TertiärBeiträge zur Regionalen Geologie der Erde 18. Gebrüder Borntraeger, Berlin, Stuttgart, pp. 567–582. Potonié, R., 1931a. Pollenformen der miozänen Braunkohle. Sitzungsberichte Ges. Naturforschender Freunde Berlin 1931, 24. Potonié, R., 1931b. Zur Mikroskopie der Braunkohlen. Tertiäre Blütenstaubformen Braunkohle 30, 325–333. Potonié, R., 1934. Zur Mikrobotanik des eocänen Humodils des Geiseltales. Arb. Inst. Paläobotanik Petrographie Brennsteine 4, 25–125. Potonié, R., 1951. Revision stratigraphisch wichtiger Sporomorphen des mitteleuropäischen Tertiärs. Palaeontogr. B 91, 131–151. Potonié, R., 1960. Synopsis der Gattungen der Sporae dispersae III. Teil: Nachträge Sporites, Fortsetzung Pollenites mit Generalregister zu Teil I-III. Beih. Geol. Jahrb. 39, 1–189. Potonié, R., 1970. Synopsis der Gattungen der Sporae dispersae. V. Teil. Nachträge zu allen Gruppen (Turmae). Beih. Geol. Jahrb. 87, 1–172. Potonié, R., Venitz, H., 1934. Zur Mikrobotanik des miocänen Humodils der niederrheinischen Bucht. Arb. Inst. Paläobotanik Petrographie Brennsteine 5, 5–54. Raatz, G.V., 1937. Mikrobotanisch-stratigraphische Untersuchung der Braunkohle des Muskauer Bogens. Abh. Preußischen Geol. Landesanst. Neue Folge 183, 1–48. Reissinger, A., 1950. Die “Pollenanalyse” ausgedehnt auf alle Sedimentgesteine der geologischen Vergangenheit. Palaeontogr. B 90 (4-6), 99–126. Riegel, W., Bode, T., Hammer, J., Hammer-Schiemann, G., Lenz, O., Wilde, V., 1999. The paleoecology of the Lower and Middle Eocene at Helmstedt, Northern Germany — a study in contrasts. Acta Palaeobotanica Suppl. 2, 349–358. Riegel, W., Wilde, V., Lenz, O.K., 2012. The Early Eocene of Schöningen (N-Germany) — an interim report. Aust. J. Earth Sci. 105, 88–109. Robson, B.E., Collinson, M.E., Riegel, W., Wilde, V., Scott, A.C., Pancost, R.D., 2015. Early Paleogene wildfires in peat-forming environments at Schöningen, Germany. Palaeogeogr. Palaeoclimatol. Palaeoecol. 437, 53–62. Rydin, H., Gunnarsson, U., Sundberg, S., 2006. The role of Sphagnum in peatland development and persistence. In: Wieder, R.K., Vitt, D.H. (Eds.), Boreal Peatland EcosystemsEcological Studies 188. Springer, Berlin, pp. 47–65. Sarwar, A.K.M.G., Takahashi, H., 2014. Pollen morphology of Erica L. and related genera and its taxonomic significance. Grana 58, 221–223.

70

W. Riegel, V. Wilde / International Journal of Coal Geology 159 (2016) 57–70

Schneider, W., 2012. Das Schwingmoor von Piskowitz. In: Museum der Westlausitz (Ed.), Klimawandel im Tertiär. Tropenparadies Lausitz?Museum der Westlausitz, Kamenz, pp. 178–213. Schulz, E., 1970. Die Sporen der Gattung Stereisporites Thomson & Pflug, 1953 aus dem älteren Mesophytikum des Germanischen Beckens. Paläontol. Abh. 3 (3/4), 683–709. Shaw, A.J., Renzaglia, K., 2004. Phylogeny and diversification of bryophytes. Am. J. Bot. 91, 1557–1581. Shaw, A.J., Cox, C.J., Buck, W.R., Devos, N., Buchanan, A.M., Cave, L., Seppelt, R., Shaw, B., Larraín, J., Andrus, R., Greilhuber, J., Temsch, E.M., 2010a. Newly resolved relationships in an early land plant lineage: Bryophyta class Sphagnopsida (peat mosses). Am. J. Bot. 97, 1511–1531 ([Shaw et al. 2010a]). Shaw, A.J., Devos, N., Cox, C.J., Boles, S.B., Shaw, B., Buchanan, A.M., Cave, L., Seppelt, R., 2010b. Peatmoss (Sphagnum) diversification associated with Miocene Northern Hemisphere climatic cooling? Mol. Phylogenet. Evol. 55, 1139–1145 ([Shaw et al. 2010b]). Srivastava, S.K., 1972. Some spores and pollen from the Paleocene Oak Hill Member of the Naheola Formation, Alabama (U.S.A.). Rev. Palaeobot. Palynol. 14, 217–285. Standke, G., 2008. Paläogeografie des älteren Tertiärs (Paleozän bis Untermiozän) im mitteldeutschen Raum. Z. Dtsch. Ges. Geowiss. 159, 81–103. Straka, H., 1975. Pollen- und Sporenkunde. Eine Einführung in die Palynologie. Gustav Fischer Verlag, Stuttgart. Stuchlik, L., Ziembińska-Tworzydło, M., Kohlman-Adamska, A., Grabowska, I., Ważyńska, H., Słodkowska, B., Sadowska, A., 2001. Atlas of pollen and spores of the Polish Neogene. Volume 1 — Spores. W. Szafer Institute of Botany, Polish Akademy of Sciences, Kraków. Stuchlik, L., Ziembińska-Tworzydło, M., Kohlman-Adamska, A., Grabowska, I., Ważyńska, H., Sadowska, A., 2002. Atlas of pollen and spores of the Polish Neogene. Volume 2 — Gymnosperms. W. Szafer Institute of Botany, Polish Akademy of Sciences, Kraków. Stuchlik, L., Ziembińska-Tworzydło, M., Kohlman-Adamska, A., Grabowska, I., Słodkowska, B., Ważyńska, H., Sadowska, A., 2009. Atlas of pollen and spores of the Polish Neogene. Volume 3 — Angiosperms (1). W. Szafer Institute of Botany, Polish Akademy of Sciences, Kraków. Sweet, A.R., Cameron, A.R., 1991. Palynofacies, coal petrographic facies and depositional environments: Amphitheatre Formation (Eocene to Oligocene) and Ravenscrag Formation (Maastrichtian to Paleocene). Int. J. Coal Geol. 19, 121–144.

Takahashi, H., Sohma, K., 1982. Pollen morphology of the Droseraceae and its related taxa. Science Reports of the Tohoku University, 4th Series. Biology 38, 81–156. Thomson, P.W., 1952. Die Sukzession der Pflanzenvereine und Moortypen im Hauptflöz der Rheinischen Braunkohle mit einer Übersicht über die Vegetationsentwicklung im Tertiär Mitteleuropas. Ber. Geobotanische Forschungsinstitut Rübel Zürich 1951, 81–87. Thomson, P.W., Pflug, H., 1953. Pollen und Sporen des mitteleuropäischen Tertiärs. Gesamtübersicht über die stratigraphisch und paläontologisch wichtigen Formen. Palaeontogr. B 94, 1–138. Tianqing, Li, 2010. Pollen flora of Chinese Woody Plants. Science Press, Beijing. Traverse, A., 1988. Paleopalynology. Unwin Hyman Ltd., Boston. Trevisan, L., 1967. Pollini fossili del Miocene superiore nei Tripoli del Gabro (Toscana). Palaeontographia Ital. 62, 1–78. Tryon, R.M., Tryon, A.F., 1982. Ferns and Allied Plants With Special Reference to Tropical America. Springer-Verlag, New York, Heidelberg, Berlin. Van Geel, B., 1978. A palaeoecological study of Holocene peat bog sections in Germany and the Netherlands, based on the analysis of pollen spores and macro- and microscopic remains of fungi, algi, cormophytes and animals. Rev. Palaeobot. Palynol. 25, 1–120. Waggoner, B.M., Poinar, G.O., 1993. Fossil habrotrochid rotifers in Dominican amber. Experientia 49, 354–357. Wilson, L.R., Webster, R.M., 1946. Plant microfossils from a Fort Union coal of Montana. Am. J. Bot. 33, 271–278. Yoshikawa, K., Overduin, P.P., Harden, J.W., 2004. Moisture content measurements of moss (Sphagnum spp.) using commercial sensors. Permafr. Periglac. Process. 15, 309–318. Zachos, J., Pagani, M., Sloan, L., Thomas, E., Billups, K., 2001. Trends, rhythms and aberrations in global climate 65 Ma to Present. Science 292, 686–693. Zachos, J.C., Dickens, G.R., Zeebe, R.E., 2008. An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics. Nature 451, 279–283. Zhang, Yulong, Xi, Yizhen, Zhang, Jintan, Gao, Guizhen, Du, Naigin, Sun, Xiangjun, Kong, Zhaochen, 1990. Spore Morphology of Chinese Pteridophytes. Science Press, Beijing. Ziegler, P.A., 1990. Geological Atlas of Western and Central Europe. Shell Internationale Petroleum Maatschappij B.V, The Hague.