Available online at www.sciencedirect.com R Review of Palaeobotany and Palynology 126 (2003) 103^129 www.elsevier.com/locate/revpalbo The in situ Glyptostroboxylon forest of Hoegaarden (Belgium) at the Initial Eocene Thermal Maximum (55 Ma) M. Fairon-Demaret a;Ã, E. Steurbaut b, F. Damblon b, C. Dupuis c, T. Smith b, P. Gerrienne a a Universite¤ de Lie'ge, De¤partement de Ge¤ologie, Pale¤obotanique et Pale¤opalynologie, Alle¤e du 6 Aou“t, Ba“timent B18, B-4000 Lie'ge, Belgium b Institut royal des Sciences naturelles de Belgique (IRSNB), De¤partement de Pale¤ontologie, 29, rue Vautier, B-1000 Brussels, Belgium c Faculte¤ Polytechnique de Mons, Ge¤ologie Fondamentale et Applique¤e, 9, rue de Houdain, B-7000 Mons, Belgium Received 19 June 2002; accepted 6 March 2003 Abstract Hundreds of silicified standing stumps have been discovered within a lignitic horizon in the middle of the Tienen Formation near Hoegaarden in northeast Belgium. The anatomical features of the fossil stumps, as those of the numerous silicified secondary xylem remains collected since the last century from this area, demonstrate that they all belong to a single taxodiaceous taxon. The stumps bear characteristics shared by Taxodioxylon gypsaceum and Glyptostroboxylon tenerum, but affinities with the latter appear closer. They are attributed to Glyptostroboxylon sp. Calibration of the sedimentological, stratigraphical and organic carbon isotope data reveals that these taxodiaceous fossil trees developed in a swampy lowland environment most probably during the Initial Eocene Thermal Maximum at ca. 55 Ma. ß 2003 Elsevier B.V. All rights reserved. Keywords: Early Eocene; fossil wood; gymnosperm; Glyptostroboxylon; taphonomy; Belgium 1. Introduction more proximal continental settings known as the Dormaal Sands, is extremely rich in remains of The Tienen Formation, occurring throughout land mammals (Smith and Smith, 1996; Smith northern Belgium and in the east of the Mons et al., 1999; Steurbaut et al., 1999; Smith, Basin (Steurbaut, 1998), has been intensively 2000). Records of land plant macro-remains studied in recent years because of its position from the Tienen Formation are relatively rare, close to the Palaeocene/Eocene boundary (Steur- and usually consist of secondary xylem fragments baut et al., 1999, 2000, in press). Its base, in the (Stockmans and Willie're, 1934; Doutrelepont et al., 1997). Current palaeobotanical information is mostly based on palynological analyses (e.g. * Corresponding author. Fax: +32-4-366-5338. Roche in Steurbaut et al., 1999, and in Steurbaut E-mail address: [email protected] et al., in press), providing a generalised, homoge- (M. Fairon-Demaret). neous picture of the vegetation. Noticeable excep- 0034-6667 / 03 / $ ^ see front matter ß 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0034-6667(03)00062-9 PALBO 2534 15-8-03 Cyaan Magenta Geel Zwart 104 M. Fairon-Demaret et al. / Review of Palaeobotany and Palynology 126 (2003) 103^129 very complex and needs some more detail. Unit 4, made up of 0.5 m of leached whitish sands, locally includes quartzitic silcretes (‘quartzite d’Overlaar- lez-Tirlemont’ of Ledoux, 1910). Occasional root casts with unidenti¢able structure are observed perforating this thick but discontinuous white, massive sandstone layer with a bumpy upper sur- face. The embedding whitish sands are devoid of organic remains. Unit 5 consists of a 45-cm-thick layer of heterogeneous more or less lignitic depos- its, enclosing the stumps and showing demonstra- Fig. 1. Geographical location of the localities mentioned in tive compaction patterns. It includes in ascending the text, especially of the Goudberg Section (black star). order (Fig. 3): (1) 5.1a, a basal layer with dark lignite wrapping the bases of the trunks (Plate I); (2) 5.1b, small sandy lenses interstrati¢ed with lignitic layers towards the base, and with brown tions are the angiosperm leaf assemblage of Leval to grey clay towards the top; (3) 5.1c, grey^brown described by Marty (1907), which is in need of strati¢ed clay with tiny black pieces of fusain; revision in the light of modern concepts of foliar (4) 5.2, an intermediary clay layer with a more morphologies, and the seeds and fruits recently or less breccia-like texture, underlain by a white described from Dormaal (Fairon-Demaret and band progressively becoming grey^blue and dark- Smith, 2002). Here we report the discovery of er, and towards the top interstrati¢ed with small, an exceptional apparently monospeci¢c fossil for- millimetre-thick lenses of brown clay; (5) 5.3, an est at Goudberg^Hoegaarden, 3 km southwest of upper light grey to brown clayey layer capped by Tienen, in the Belgian province of Vlaams-Bra- 2^3 cm of dark brown clay with numerous root bant (Fig. 1). Hundreds of silici¢ed stumps are departures; and (6) 5.4, 17 cm of blackish silt. preserved in situ within a lignitic horizon (unit Unit 6 consists of an about 45-cm-thick layer of 5) in the middle of the Tienen Formation, in an brown sandy to silty mud with in the middle 10 area extending over more than one hectare. cm of greyish clayey silt with a black organic-rich base. It is overlain by unit 7, consisting of a 5-cm- thick layer of white clayey silt, locally ¢nely lami- 2. Geographical setting and lithological description nated. The succession is not always entirely preserved The stumps were exposed during excavations along the excavation front because of subsequent for the new High Speed Train railway track at local erosion. Units 6 and 7, next to the upper 17 Goudberg^Hoegaarden, extending parallel to the cm of unit 5 were missing in the eastern part of Lie'ge/Brussels E40 motorway (50‡47P27.4QN, the excavation, reducing the thickness of the Tie- 04‡54P06.1QE; altitude: 55 m; Institut Ge¤ogra- nen Formation by about 65 cm. phique National Map 32/7^8: coordinates x = 187, y = 164; Figs. 1 and 4). An 8-m-thick section has been exposed (Figs. 2 and 3). Its upper part, 3. Stratigraphy and age of the fossil forest down to the fossil-tree-bearing lignite, was seen in outcrop and the lower part in a series of 3-m-deep The stratigraphical interpretation of the di¡er- temporary trenches dug out at the railway track. ent units of the Goudberg Section is exclusively This composite pro¢le, known as the Goudberg based on lithofacies analysis, as the entire section Section, consists of nine distinct units, of which is devoid of stratigraphically diagnostic microfos- the lithological description is given in Fig. 2. The sils (no dino£agellate cysts and calcareous micro- middle part of the section, including units 4^7, is fossils; a few pollen, spores and freshwater algae PALBO 2534 15-8-03 Cyaan Magenta Geel Zwart M. Fairon-Demaret et al. / Review of Palaeobotany and Palynology 126 (2003) 103^129 105 Fig. 2. Lithology of the Goudberg Section with position of the silici¢ed stumps; compare with Fig. 3. PALBO 2534 15-8-03 Cyaan Magenta Geel Zwart 106 M. Fairon-Demaret et al. / Review of Palaeobotany and Palynology 126 (2003) 103^129 Fig. 3. Field picture of units 4^8 (photograph by Professor N. Vandenberghe). PALBO 2534 15-8-03 Cyaan Magenta Geel Zwart M. Fairon-Demaret et al. / Review of Palaeobotany and Palynology 126 (2003) 103^129 107 (Botryococcus sp.) were found in the top of unit In the most complete settings of northwest Bel- 8; see Fig. 2 for location of samples). It includes gium (Knokke area), the Tienen Formation is un- identi¢cation of the lithofacies characteristics, conformably overlain by the Zoute Silt Member, trends and junctions, and relies on the lithostrati- the lowermost member of the Kortrijk Clay For- graphical classi¢cation of Steurbaut (1998), taking mation (Steurbaut, 1998; Moorkens et al., 2000). into account previous studies carried out in the The latter is part of the Ypresian stratotype. The Tienen area by Rutot (1887), Van den Broeck Zoute Silt Member, through calibration known to and Rutot (1894) and Gulinck (1948). be deposited within Biochron NP 10, posterior to The glauconitic obliquely laminated sands of the well-known Apectodinium acme, is missing in unit 1 are attributed to the Hoegaarden Sands, a the Goudberg Section. Instead, a clayey unit oc- not yet o⁄cially de¢ned term for the estuarine curs (unit 8), which on the ground of its geometry sands occurring in the Hoegaarden area (Steur- and lithofacies may belong to the Kortrijk Clay baut, study in progress). These sands are sand- Formation. The overlying unit 9, of which several wiched between the Upper Thanetian Grandglise metres are locally preserved, is incorporated in the Sands and the Tienen Formation. They are a lat- Brussel Formation (Sintubin et al., 2000). eral equivalent of the fully marine (infralittoral) The lignite of the Goudberg Section in which Bois-Gilles Sand Formation, cropping out in the the fossil stumps were found does not contain any southwest of Belgium and calibrated with the biostratigraphical marker. However, its age can middle part of Biochron NP 9 (Steurbaut, 1998), be reliably inferred from organic carbon isotope dated at 55.8 Ma (Berggren et al., 1995). analysis. The isotope values measured in the The overlying interval, ranging from unit 2 to Goudberg lignite present a trend towards more unit 7, is marked by an essentially £uviatile depo- positive values from 325.7x to about 325.0x sitional regime. Units 3 and 4 represent palaeo- PeeDee Belemnite (Magioncalda, pers. commun.). sols. The white clean sands of unit 4 are due to The same isotopic trend and values are recorded intense leaching of a soil pro¢le in a well-drained, at ¢ve stratigraphically distinct places in the Mont warm, wet environment.