Journal of the Geological Society A conifer-dominated palynological assemblage from Pennsylvanian (late Moscovian) alluvial drylands in Atlantic Canada: implications for the vegetation of tropical lowlands during glacial phases Graham Dolby, Howard J. Falcon-Lang and Martin R. Gibling Journal of the Geological Society 2011; v. 168; p. 571-584 doi: 10.1144/0016-76492010-061

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Journal of the Geological Society, London, Vol. 168, 2011, pp. 571–584. doi: 10.1144/0016-76492010-061.

A conifer-dominated palynological assemblage from Pennsylvanian (late Moscovian) alluvial drylands in Atlantic Canada: implications for the vegetation of tropical lowlands during glacial phases G R A H A M D O L B Y 1, H OWA R D J. FA L C O N - L A N G 2 * & M A RT I N R . G I B L I N G 3 1 Dolby and Associates, 6719 Leaside Drive S.W., Calgary, Alberta, T3E 6H6, Canada 2 Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK 3 Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 3J5, Canada *Corresponding author (e-mail: [email protected]) Abstract: New research suggests that Pennsylvanian Coal Forests were commonly replaced by coniferdominated vegetation during seasonally dry glacial phases. Here we describe palynological assemblages from stacked sequences of the Middle Pennsylvanian (late Moscovian) Sydney Mines Formation of Nova Scotia, Canada, which lends some support to this hypothesis. One critical sample from a widespread redbed succession below the Harbour Coal is dominated by conifer pollen (55%), together with abundant representatives of cordaitaleans, other coniferopsids, and rare pteridosperms, ferns and lepidodendrids. It differs markedly from 13 other samples obtained from coals, their roof shale–limestone and associated channel bodies, which are dominated by lepidodendrids, marattialean tree-ferns, cordaitaleans and/or calamiteans. The latter beds represent coastal wetlands, and are attributed to late transgressive and highstand systems tracts, whereas the conifer-bearing sample represents a dryland alluvial plain and may be attributed to lowstand or earliest transgressive systems tracts. Three additional samples from grey shale below a sequence boundary (late highstand) and between a redbed succession and major coal seam (early to mid-transgressive deposits) contain transitional palynofloras with a high proportion of herbaceous gleicheniaceous and sphenopteroid ferns, herbaceous lycopsids, and sphenophylls interspersed with cordaitaleans and/or lepidodendrids. The dominance of conifer pollen within the dryland components of well-defined sequences, which have been linked to relative sea-level change promoted by Gondwanan glaciation, supports the view that Pennsylvanian tropical biomes responded to the beat of glacial–interglacial cycles.

during glacial phases when the tropical climate was drier and more seasonal, and sea level was low (Falcon-Lang 2003a,b, 2004). This controversial idea, that the Coal Forests ‘danced to the beat’ of climate cycles (Falcon-Lang et al. 2004), has recently gained additional support from the discovery of conifers in Middle to Late Pennsylvanian incised channels and palaeovalleys, interpreted as having grown in tropical lowlands during glacial phases (Feldman et al. 2005; DiMichele et al. 2009, 2010; Falcon-Lang et al. 2011; Falcon-Lang & DiMichele 2010). These findings challenge conventional wisdom that the Coal Forests persisted intact for millions of years (Cleal & Thomas 2005) and support a more dynamic model in which rainforests repeatedly contracted into isolated refugia during glacial phases (DiMichele et al. 2009; Falcon-Lang & DiMichele 2010). However, more palaeobotanical data within a well-constrained sequence-stratigraphic context are needed to further test this hypothesis. Here we present palynological data for the Pennsylvanian Sydney Mines Formation of Nova Scotia, Canada (Fig. 1a), which is relevant to the controversy. The data were obtained in the late 1980s by one of us (G.D.) to improve biozonation of this coal-bearing succession (Dolby 1988, 1989). Palynological sampling was undertaken in tandem with sedimentological logging and sequence-stratigraphic analysis of the Bras d’Or cliff section (Bird 1987) and tied to measured sections with centimetre-scale precision (see Gibling et al. 1992, for a complete bed-by-bed log of the section). As a result of subsequent work in cliff sections across the basin, the sequence stratigraphy of the Sydney Mines Formation is now well understood (Gibling &

Pennsylvanian tropical ‘rainforests’ are an iconic feature of the History of Life illustrated in museum dioramas worldwide (DiMichele et al. 2001, 2007). The best-known component of this vegetation is the peat-forming forests or mires, commonly referred to as the Coal Forests (Falcon-Lang et al. 2009a). These Coal Forests were dominated by tree-sized lycopsids and/or marattialean ferns, together with sphenopsids, pteridosperms and cordaitaleans (DiMichele & Phillips 1994), and at their maximum extent covered hundreds of thousands of square kilometres (Greb et al. 2003; Cleal & Thomas 2005). Similar forests existed on poorly drained mineral soils (wetlands), but differed in their dominance–diversity characteristics (DiMichele et al. 2001). Both assemblages are best known from autochthonous ‘fossil forests’, which are especially abundant and widespread during this time interval (DiMichele & Falcon-Lang 2011). For many years, scientists also have been aware of a third tropical plant community, poorly preserved in redbed successions deposited in well-drained (dryland) environments (see DiMichele et al. 2010, for a review). In contrast to the pteridophytedominated wetlands, these dryland floras were gymnospermdominated, and included cordaitaleans, pteridosperms and conifers. The palaeoclimatic significance of these dryland floras began to emerge only following the recognition that repeated climatic fluctuations, widely interpreted as glacial–interglacial cycles, had profoundly shaped Pennsylvanian tropical landscapes (Cecil 1990; Tandon & Gibling 1994; Flint et al. 1995; Bohacs & Suter 1997; Hampson et al. 1999). Some of these dryland assemblages have been interpreted as the vegetation that existed 571

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Fig. 1. Map showing the location of the study site in (a) Canada and Nova Scotia, and (b) eastern Cape Breton. Bras d’Or section is marked.

Bird 1994; Gibling & Wightman 1994; White et al. 1994; Calder et al. 1996; Batson & Gibling 2002; Gibling et al. 2004) and offers a testing ground to assess how Pennsylvanian plant communities responded to sea-level changes and, by extension, to climatic fluctuations that were probably linked to glacial– interglacial cycles (Tandon & Gibling 1994, 1997; Falcon-Lang 2004).

Sequence-stratigraphic framework The Sydney Mines Formation is a late Moscovian (Middle Pennsylvanian, late Asturian–Cantabrian) coal-bearing succession (Zodrow 1986, 1989a,b; Dolby 1988, 1989; Cleal et al. 2003) preserved in the Sydney Basin of Cape Breton, Nova Scotia, Canada (Fig. 1b). Superbly exposed in numerous nearcontinuous sea-cliff sections and known from more than 200 boreholes and wells, the sedimentology and sequence stratigraphy of this unit are known in detail (for a review see Gibling et al. 2004). Cyclic patterns of sedimentation (cyclothems or sequences) are one of the most prominent features of the formation (Gibling & Bird 1994) and have been described using sequence-stratigraphic nomenclature. In total 14 sequences, ranging from 12 to 83 m thick, have been described in the lower 410 m of the Sydney Mines Formation, and can be traced across the onshore part of the basin (Fig. 2). Although there are local variations in thickness and lithology, the major coals and the sequences that contain them extend for c. 50 km along strike (as far as outcrop extends) and the most prominent coals have also been identified in wells c. 50 km offshore to the NE. Moreover, Haites (1952) correlated the Harbour Coal with a thick coal on the western margin of Cape Breton Island so it is possible that some sequences formerly covered large areas of Atlantic Canada. The presence of agglutinated foraminifera and other brackish-water biota (Gibling & Wightman 1994), with sulphur-rich coals and glaucony (Gibling et al. 2004), implies that periodic marine transgressions were closely associated with sequence formation.

Description of systems tracts At Victoria Mines and North Sydney, seven thin and fully exposed sequences with component systems tracts have been described up to and including the Lower Bouthillier Coal. Because the outcrop belt of the Sydney Mines Formation represents a strike section and basinward areas lie below the Atlantic Ocean, sequence architecture was inferred from vertical facies changes. In these sequences, thick economic coals, overlain by limestone or dark platy shale with a brackish fauna, are assigned to the transgressive systems tract (TST) formed by the retrogradation of extensive coastal peat mires (Gibling & Kalkreuth

Fig. 2. Stratigraphy of the onshore portion of Sydney Mines Formation of Nova Scotia, Canada, showing the 14 basinwide sequences identified by Gibling et al. (2004). Global correlations after Heckel (2008).

1991; White et al. 1994). The limestones and platy shales denote the maximum flooding surface (mfs), after which the re-advance of coastal systems marks the onset of the highstand systems tract (HST). Because the limestones and shales directly overlie the coals, the coals are inferred to represent a late stage of transgression. Within the HST, stacked coarsening-upward units with channels and thin coals above these major coals formed by the coalescence of small deltas on a prograding coastal plain as relative sea level continued to rise (Calder et al. 1996; FalconLang 2006). These grey strata are overlain by mottled and redbed successions containing well-developed calcretes and vertisols, laterally equivalent at some levels to incised palaeovalleys up to 30 m deep and >7 km wide (Batson & Gibling 2002). These redbed intervals represent alluvial plains that experienced seasonally dry conditions when relative sea level was low (Gibling & Bird 1994; Tandon & Gibling 1994, 1997). In some sequences, the redbed intervals commence with one or a few prominent petrocalcic (calcrete) horizons that can be correlated across the onshore part of the basin and mark interfluve sequence boundaries and the onset of a prolonged period of lowered relative sea level. They form part of the lowstand systems tract (LST).

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Overlying red and grey vertisols also mark dryland and possibly lowstand conditions. However, they could also represent early stages of the transgressive systems tract when rising relative sea level promoted renewed flooding of the interfluves, allowing detrital sediment to accumulate under dryland conditions on top of the lowstand calcretes (Wright & Marriott 1993). In some sequences, the sequence-bounding calcretes are underlain by a few metres of red palaeosols or by channel bodies with evidence of periodic exposure and high flow-strength conditions (Fielding et al. 2009). These strata may represent the falling stage systems tract (FSST), marking the onset of relative sealevel lowering and groundwater drawdown on the coastal plain, after which further lowering and drainage incision detached the plain from its sediment supply (Batson & Gibling 2002; Gibling et al. 2004). The FSST is difficult to identify in the Sydney Mines Formation, and such attributions are tentative. Grey or red mudstone samples from strata shortly below a sequence boundary could equally be attributed to the latest stage of the HST.

Palaeoclimatic interpretation The relative sea-level changes inferred from some of the Sydney Mines Formation sequences and other cyclothemic successions across North America may represent the sedimentary expression in the equatorial zone of alternate ice build-up and melting on Gondwana (Wanless & Shepard 1936; Tandon & Gibling 1994; Gibling & Rygel 2008; Heckel 2008). If so, they must bear some correlation with glacial and interglacial events in the polar regions. As noted above, the sequences are thin and widespread, and they are not readily explained by local channel- or deltaswitching. A key observation is that sea level and climate are broadly coupled, such that lowstand deposits in some sequences contain facies laid down under seasonally dry conditions (calcretes and vertisols) whereas highstand deposits with coals and hydromorphic palaeosols are inferred to represent more humid conditions (Tandon & Gibling 1994, 1997). By analogy with late Quaternary trends in global climate (e.g. Nanson et al. 1992, 2008), this phenomenon can be reasonably explained as a consequence of glacial–interglacial cycles, but is less readily explained by autocyclicity or tectonism (Gibling & Rygel 2008). In fact, analysis of stratal packages in seismic sections (Pascucci et al. 2000) implies that the Sydney Mines Formation was deposited during a prolonged thermal sag phase of basin evolution (Calder 1998; Gibling et al. 2004, 2008) so that tectonism associated with local structures is unlikely to have been a significant factor in sequence generation. Furthermore, there are significant differences in the architecture and texture of fluvial channel sandstone bodies in lowstand and highstand systems tracts (Batson & Gibling 2002), which cannot be explained by autocyclicity but make sense in terms of climateinduced changes in sediment grade and supply. None the less, there are uncertainties associated with the interpretation of the Sydney Mines sequences in terms of glacial–interglacial cycles. One issue is that thickness of sequences changes up-section (Fig. 3). The lower sequences (numbers 1–9) have a mean thickness of c. 20 m whereas the upper sequences (numbers 10–14) have a mean thickness of c. 55 m and are dominated by red beds. Although this change in stratal thickness could reflect a change in the duration of glacial–interglacial cycles somewhat akin to the change seen at the Mid-Pleistocene Revolution from 40 to 100 ka (Maslin & Ridgwell 2005), it more probably indicates a basinward shift in facies belts, such that only the most significant transgressions extended into the Sydney Basin during the formation of the

Fig. 3. Sedimentary logs of onshore part of the Sydney Mines Formation at Bras d’Or (modified from Bird 1987, after Gibling et al. 1992, 2004) showing the sequence-stratigraphic context of the 17 palynological samples with moderate to very high yields.

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upper beds (Gibling et al. 2004). This latter hypothesis, which predicts that the thicker sequences pass basinwards into multiple minor cycles, is supported by the occurrence of cryptic transgressions in some redbed intervals (Gibling & Wightman 1994). Such an interpretation for these thicker sequences implies that they are composite units laid down under varied climatic conditions.

Bras d’Or section: context for palynology In this paper we focus on palynological samples from the Bras d’Or section (Fig. 1b), in the northwestern part of the basin. In this section (Fig. 3), sequences up to the level of the Backpit Coal are only partly exposed, and the coals are thin and shaly with no evidence of red beds or prominent calcretes. This makes the precise attribution of systems tracts problematic for this part of the section. Although almost fully exposed, the overlying interval that includes benches of the Bouthillier Coal corresponds to a redbed-dominated interval across the basin with thin and uneconomic coals (Gibling & Bird 1994), also raising some difficulties in identifying systems tracts. Although sequences in this interval are based on an alternation of widespread coals and red beds, they contain discontinuous coals and red beds that may represent channel-switching events. From the Harbour Coal to the Point Aconi Coal (the highest coal exposed onshore in the basin), the sequences contain both economic coals and thick redbed and palaeosol intervals (calcretes and vertisols), so that systems tracts can be reliably inferred. However, the thick red beds of these sequences may be the inland equivalents of several stacked sequences in more basinward settings. Based on the inferred link between systems tracts and climate in an icehouse world, we tentatively interpret the position of our palynological samples in terms of a glacial–interglacial climate framework. (This approach assumes that the palynomorphs are not reworked; see discussion below.) We are tentative because, even in Quaternary successions, it is difficult to fix the boundary between ‘interglacial’ and ‘glacial’ sedimentary accumulations because polar ice cap expansion and concomitant sea-level lowering occurred gradually. None the less, combined sedimentological and palynological analysis has met with success in documenting climatic and vegetational change in Quaternary coastal and alluvial sequences (Amorosi et al. 2008), so our approach is not without precedent. Based on the above assessment, we attribute our palynological samples to the following systems tract categories: (1) late stage of the TST, represented by basinwide coal seams and immediately underlying shale and overlying grey limestone and dark platy shale; (2) HST, represented by thin coal seams and grey mudstone beds that overlie major coal seams, with a general subdivision into an early and late stage of the HST based on proximity to an underlying major coal seam or overlying sequence boundary, respectively; (3) LST or earliest stage of TST, represented by thin grey shale interbedded with red cumulative palaeosols and calcretes; (4) early to mid-stage of TST, represented by grey mudstones that directly overlie red beds but are below major coals (Fig. 4). Palynomorphs from samples within the late TST to HST ((1) and (2)) may represent relatively warm and humid conditions when relative sea level was elevated, and may thus represent the vegetation of interglacial climate phases. Those from the LST to early TST ((3) and (4)) may represent relatively cool, dry and seasonal conditions when relative sea level was low, and may thus represent vegetation during various parts of glacial climate phases. We caution that, although systems tract terminology can be

Fig. 4. Summary diagram illustrating an idealized cyclothem and its facies associations; FSST, LST, TST, and HST indicate falling stage, lowstand, transgressive and highstand systems tracts, respectively; mfs, maximum flooding surface. Circled numbers indicate the number of palynological samples from each part of the cyclothem (modified from Falcon-Lang 2004).

applied to all the sequences in the Sydney Mines Formation, we cannot preclude the possibility that some of these rhythmic successions represent channel or delta switching or tectonic events, rather than glacial–interglacial cycles of relative sea-level change. We note also that Pennsylvanian tropical cyclothem successions, although widely attributed to Gondwanan glaciation, have yet to be correlated in any precise manner with events in nearfield Gondwanan successions (Fielding et al. 2008). However, our results provide a reliable assessment of local wetland and dryland vegetation cover during Sydney Mines Formation deposition, with the likelihood that at least some of the observed secular variation in vegetation was climatically driven.

Palynological samples In total 22 palynological samples (Bd87-1 to Bd87-22) were obtained from the coastal cliff section exposed on the eastern side of the Bras d’Or Channel (Fig. 1b) between Black Rock (46817’25’’N, 60824’47’’W) and Point Aconi (46820’11’’N, 16817’33’’W). The samples comprise (1) bituminous coal, (2) limestone with brackish fauna, (3) grey, laminated roof shale, (4) channel sandstone-fills, and (5) mottled grey–red shale. After processing (Traverse 2007), three samples were barren (n ¼ 0 palynomorphs), two gave very low yields (n , 5), four gave moderate yields (n ¼ 20–30), and the remaining 13 gave high to very high yields (n . 300). To determine the relative abundance of morphotaxa in each slide, the following two-part system was

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used. All the palynomorphs in one half of the 22 mm 3 40 mm slide were counted and the percentage abundance of each common morphotaxon was determined. The second half of the slide was then examined for any rare palynomorphs not present in the first half and one occurrence of each was added to the total. The benefit of this system is that it captures the full diversity present on each slide while minimizing over-representation of the rarest morphotaxa. Results are given in Table 1 for 17 samples (excluding barren samples and those with very low yields ,5), with palynomorphs assigned to major taxonomic groups based on information given in various compilations (Balme 1995; Dimitrova et al. 2005; Traverse 2007; Bashforth et al. 2011). Where the composition of assemblages is described in the text, the following semi-quantitative descriptors are used to emphasize frequency of specific palynomorphs: superabundant, .20%; abundant, 7.5–20%; common, 2–7.5%; rare, ,2%. However, we also give exact percentages where relevant. Each sample was assigned a sequencestratigraphic context as follows: late TST–early HST, late HST, LST–earliest TST, and early to mid-TST. In Table 2, data are condensed into each of these sequence-stratigraphic categories for ease of comparison.

Late transgressive and early highstand assemblages Most of our samples (n ¼ 13) were obtained from the late TST to HST of multiple sequences (Figs 3–5). Samples span the entire formation. Four samples were obtained from coal seams (Bd87-4, 7, 13, 17), seven from roof shale immediately above coal seams (Bd87-1, 2, 6, 11, 14, 18, and 22), one from a limestone bed above a coal (Bd87-5), and one from the topmost fine-grained part of a channel-sandstone body (Bd87-15). These facies represent the wetland deposits of long-lived coastal peat mires, clastic swamps, shallow brackish bays and interdistributary channels, respectively (Gibling & Bird 1994; Gibling & Kalkreuth 1991; White et al. 1994). Although palynoassemblages are rather variable within a single coal seam (Dimitrova et al. 2009), the coal ‘spot samples’ analysed here are comparable with those reported from profiles through the Harbour and Hub Coals (Marchioni et al. 1994; Calder et al. 1996) so it is unlikely that our sampling of thick coals has biased results. Although somewhat variable in their composition, all samples are dominated by arborescent lycopsids (n ¼ 6), cordaitaleans (n ¼ 4), ferns (n ¼ 2), or sphenopsids (n ¼ 1). Both coal and wetland clastic facies (roof shale, limestone, channel sandstone) contain broadly similar palynofloras dominated by lycopsids (42.66% and 40.55%, respectively), especially Lycospora pusilla, the spore of Lepidodendron hickii (27.69% and 30.1%, respectively). The main difference is that clastic wetland facies contain far fewer calamiteans (4.54%, compared with 25.22% in coal). In addition, clastic wetland facies are richer in sphenopteroid ferns (0.99%, compared with 0.11% in coal), gleicheniacean ferns (2.82%, compared with 0.52% in coal), and conifer and coniferlike plants (1.99%, absent in coal). Finally, one cordaitalean morphospecies, Florinites visendus/pumicosus, is much more abundant in wetland clastic facies (8.98%) than in coal (1.82%).

Late highstand assemblages Two samples were obtained from the topmost strata of the HST above the Bouthillier Coal (Bd87-7) and the Harbour Coal (Bd87-12). The first sample (Bd87-7) comprises a strongly bioturbated grey mudstone immediately above a thin unnamed coal and associated with grey coarsening-upward units below a

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calcrete and red bed. The second sample (Bd87-12) comprises a bioturbated grey to purplish mudstone above benches of the Harbour Coal and associated channel bodies (Figs 3, 4 and 6). Intervals of no exposure between this level and the overlying Hub Coal introduce some uncertainty as to its position within the sequence architecture. However, a nearby drill core (Dh88-10b) and correlation with drill logs across the basin to the east show that the sampled bed lies immediately below a thick redbed interval and indurated calcrete in the poorly exposed Sequence 11. Thus, both samples Bd87-8 and 12 were obtained from strata above coal-bearing deposits and directly below calcrete-bearing red beds, and thus probably represent topmost highstand deposits. The two samples differ from most late TST and early HST samples, and show similarities to and differences from one another. The key similarities are that samples contain relatively low abundance of lycopsid spores (23.5% and 19%, respectively, compared with a mean of 38.2% in the sample suite) and show only rare calamiteans (0.89%, compared with a mean of 10.9%). However, there the similarity ends, each sample showing a distinctive composition. Sample Bd87-8 is dominated by ferns (55.1%, the second highest proportion in the suite) comprising three unusual groups: marrattialean tree-ferns are represented by Microreticulatisporites (19.8%), a taxon that is rare in the suite (mean 0.41%), whereas sphenopteroid ferns (19.7%) and gleicheniaceous ferns (15.3%) show abundances greatly elevated above the mean for the suite (0.7% and 2.11%, respectively). In addition, the enigmatic pteridophyte, Laevigatosporites, is unusually abundant (19.8%). In contrast, Bd87-12 is distinctive in its unusually high abundance of cordaitaleans (32.4%), represented by five taxa, and the presence of peltasperms (3.22%) and medullosan pteridosperms (0.35%), occurring with their second and third highest percentages in the sample suite.

Lowstand or earliest transgressive assemblage Only one sample (Bd87-10) was obtained from within a redbed succession attributed to the LST or an earliest stage of the TST (Figs 3, 4 and 6). This sample occurs near the base of Sequence 10 in strata of late Asturian age. As illustrated in Figure 5, the sampled bed lies within a grey mudstone unit 1.5 m thick that includes a 50 mm thick coal and hydromorphic palaeosols with roots. The strata above and below comprise red, largely structureless mudstones with vertical drab mottles, slickensides, roots, desiccation cracks, and calcareous nodules. Associated with the red beds are thin, indurated calcareous horizons with locally nodular fabrics and crevasse splays of fine-grained sandstone. The red strata are interpreted as vertisol-like palaeosols and the calcareous horizons as poorly developed calcretes. As discussed by Tandon & Gibling (1997), these beds represent soil formation under strongly seasonal conditions. The palynological sample thus represents a wetland deposit intercalated within a thick succession laid down on a dryland floodplain that was periodically inundated by sand-bearing floods from nearby channels. Laterally equivalent strata at seven other sections over a 40 km transect contain a similar redbed succession with calcretes, demonstrating that a widespread seasonally dry land surface developed at this stratigraphic level. Red beds, albeit subdued, are even seen in the Glace Bay Syncline at this level (R. Naylor, pers. comm.), a tectonic sub-basin that underwent relatively greater subsidence than the rest of the Sydney Basin (Gibling et al. 2004). The rich palynological assemblage obtained from Bd87-10

87-1 Late TST

4 25.00 25.00 0.00 0.00 16.67 8.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 12.50 12.50 12.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.17 4.17 0.00 0.00 0.00 0.00 4.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Sample: Systems tract:

Metres above formation base: LYCOPSIDS Lepidodendrales Granasporites medius Lycospora orbicula Lycospora pellucida Lycospora pusilla Lycospora spp. Sigillariales Crassispora kosankei Chaloneriaceae Endosporites globiformis Endosporites zonalis Herbaceous lycopods Cirratriradites saturnii Cadiospora magna SPHENOPSIDS Calamitales Calamospora spp. Sphenophyllales Vestispora colchesterensis Vestispora fenestrata Vestispora foveata Vestispora laevigata Vestispora witneyensis Vestispora spp. Striatosporites major Striatosporites ovalis FERNS Marattialales Cyclogranisporites aureus Cyclogranisporites spp. Microreticulatisporites nobilis Microreticulatisporites sulcatus Punctatosporites granifer Punctatosporites minutus Punctatosporites oculus Punctatosporites spp. Thymospora obscura Thymospora pseudothiessenii Thymospora verrucosa Thymospora spp. Torispora securis Tedaleceae Raistrickia aculeata Raistrickia saetosa Savitrisporites majus

20 24.63 24.14 0.00 1.15 11.00 11.99 0.00 0.00 0.00 0.49 0.49 0.00 0.00 0.00 0.00 0.49 0.16 0.16 0.33 0.16 0.00 0.00 0.16 0.00 0.00 0.00 0.00 6.57 2.30 0.82 0.66 0.16 0.16 0.49 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.16 0.00 0.16 0.00

87-2 Late TST 60.5 32.14 28.57 0.00 0.00 7.14 21.43 0.00 0.00 0.00 0.00 0.00 0.00 3.57 3.57 0.00 10.71 10.71 10.71 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

87-4 Late TST 61 86.93 86.76 0.00 1.19 0.68 84.89 0.00 0.00 0.00 0.17 0.17 0.00 0.00 0.00 0.00 0.51 0.00 0.00 0.51 0.00 0.17 0.00 0.00 0.34 0.00 0.00 0.00 4.58 2.04 0.00 0.00 0.00 0.00 1.70 0.00 0.17 0.00 0.00 0.00 0.00 0.00 0.17 0.00 0.00 0.00 0.00

87-5 Late TST 61.5 34.53 31.99 0.26 0.00 2.50 26.33 2.90 2.40 2.40 0.07 0.07 0.00 0.07 0.07 0.00 0.39 0.20 0.20 0.20 0.00 0.10 0.00 0.10 0.00 0.00 0.00 0.00 8.69 0.72 0.07 0.00 0.00 0.49 0.03 0.00 0.00 0.10 0.00 0.00 0.00 0.00 0.03 0.82 0.00 0.82 0.00

87-6 Late TST

Table 1. Quantitative palynological data condensed into sub-environments

90 66.67 66.67 0.00 28.57 4.76 33.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 23.81 23.81 23.81 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.76 4.76 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.76 0.00 0.00 0.00 0.00

87-7 HST

91 23.53 23.28 0.00 0.00 0.00 23.28 0.00 0.00 0.00 0.17 0.17 0.00 0.09 0.09 0.00 0.26 0.26 0.26 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 55.09 20.09 0.09 0.00 0.00 19.83 0.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.00 0.09 0.00

87-8 Late HST 153 11.98 11.98 0.00 0.00 7.31 4.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.16 0.16 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.09 0.62 0.16 0.00 0.00 0.16 0.16 0.00 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.16 0.00 0.16 0.00

87-10 LST–early TST 181 85.75 85.33 0.00 17.63 14.10 53.60 0.00 0.28 0.28 0.14 0.14 0.00 0.00 0.00 0.00 0.28 0.28 0.28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.83 0.71 0.00 0.00 0.00 0.14 0.42 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.14 0.00 0.00 0.00 0.00

87-11 Late TST 211 18.95 17.55 2.31 0.00 10.14 5.10 0.00 0.14 0.14 1.19 1.12 0.07 0.07 0.07 0.00 22.03 1.54 1.54 20.49 0.21 0.00 0.00 0.00 0.00 20.28 0.00 0.00 21.12 16.92 0.07 0.00 0.00 0.07 16.08 0.00 0.35 0.28 0.00 0.00 0.00 0.00 0.07 0.77 0.07 0.70 0.00

87-12 Late HST 239 18.72 12.34 0.09 0.00 0.00 12.25 0.00 0.00 0.00 6.30 0.17 6.12 0.09 0.09 0.00 52.76 50.74 50.74 2.01 0.00 0.00 1.84 0.00 0.17 0.00 0.00 0.00 18.64 14.87 0.17 0.00 0.00 0.00 14.00 0.00 0.00 0.00 0.00 0.09 0.00 0.44 0.17 0.96 0.00 0.96 0.00

87-13 Late TST 240 2.74 1.19 0.14 0.00 0.49 0.56 0.00 0.00 0.00 0.91 0.14 0.77 0.63 0.63 0.00 8.14 8.14 8.14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 72.35 62.25 0.00 0.00 0.07 0.14 61.40 0.00 0.00 0.00 0.00 0.49 0.00 0.00 0.14 2.53 0.00 2.32 0.21

87-14 Late TST 265 50.00 45.83 0.00 0.00 0.00 45.83 0.00 0.00 0.00 0.00 0.00 0.00 4.17 4.17 0.00 4.17 0.00 0.00 4.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.17 33.33 33.33 4.17 0.00 0.00 4.17 20.83 0.00 0.00 0.00 0.00 4.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00

87-15 HST

312 53.13 43.75 0.00 0.00 0.00 43.75 0.00 0.00 0.00 6.25 6.25 0.00 3.13 3.13 0.00 15.63 15.63 15.63 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 28.13 25.00 0.00 0.00 0.00 0.00 18.75 0.00 0.00 0.00 0.00 6.25 0.00 0.00 0.00 3.13 0.00 3.13 0.00

87-17 Late TST

313 9.22 8.26 0.00 0.74 2.33 5.19 0.00 0.00 0.00 0.64 0.53 0.11 0.32 0.21 0.11 15.36 14.83 14.83 0.53 0.00 0.32 0.21 0.00 0.00 0.00 0.00 0.00 36.55 20.44 0.21 0.00 0.00 0.32 10.91 0.21 0.11 0.00 0.42 0.42 0.11 0.00 7.73 6.36 6.36 0.00 0.00

87-18 Late TST

366 59.04 42.57 0.00 0.00 3.61 38.96 0.00 0.00 0.00 16.47 16.47 0.00 0.00 0.00 0.00 2.01 1.61 1.61 0.40 0.00 0.00 0.00 0.00 0.00 0.40 0.00 0.00 23.29 0.80 0.00 0.00 0.00 0.40 0.00 0.00 0.00 0.00 0.00 0.00 0.40 0.00 0.00 1.20 1.20 0.00 0.00

87-20 Early TST

374.5 46.15 43.16 1.28 1.28 6.41 34.19 0.00 0.43 0.43 2.56 2.56 0.00 0.00 0.00 0.00 14.96 4.70 4.70 10.26 0.00 0.85 0.00 0.00 0.00 0.00 0.43 8.97 7.69 4.27 0.00 0.00 0.00 0.00 1.71 0.43 0.85 0.00 0.00 0.85 0.00 0.00 0.43 0.85 0.85 0.00 0.00

87-22 Late TST

576 G. DOLBY ET AL.

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.17 0.00 0.00 4.17 45.83 0.00 0.00 0.00 0.00 0.00 41.67 16.67 0.00 4.17 0.00 20.83 0.00 4.17 0.00 0.00 4.17 0.00 4.17 4.17 0.00 0.00 0.00 0.00 50.00 4.17 0.00 0.00 4.17 24 2

2.79 1.97 0.16 0.00 0.00 0.66 1.31 0.00 0.82 0.33 0.16 0.00 0.00 0.00 0.00 0.33 0.00 0.00 0.33 32.02 0.16 0.16 1.15 0.66 0.49 62.89 38.59 0.00 3.78 0.00 20.53 0.00 2.79 0.00 0.16 1.81 0.82 0.33 0.00 0.00 0.00 0.33 0.00 67.32 0.66 0.00 0.00 0.66 609 2

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.57 0.00 0.00 3.57 46.43 0.00 0.00 3.57 3.57 0.00 50.00 39.29 0.00 0.00 3.57 7.14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 53.57 0.00 0.00 0.00 0.00 28 1

0.17 0.00 0.00 0.00 0.00 0.17 2.38 0.85 0.68 0.17 0.68 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 92.02 0.00 0.00 0.00 0.00 0.00 7.98 7.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 7.98 0.00 0.00 0.00 0.00 589 3

0.76 0.00 0.36 0.00 0.03 0.36 6.12 3.85 0.46 0.00 1.81 0.26 0.03 0.00 0.23 1.42 0.00 0.00 1.42 45.03 0.07 0.07 12.64 11.52 1.12 41.94 28.80 0.10 0.00 0.36 12.67 0.00 0.03 0.00 0.00 0.00 0.03 0.07 0.07 0.00 0.00 0.00 0.00 54.74 0.23 0.23 0.00 0.00 3038 2

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 95.24 0.00 0.00 0.00 0.00 0.00 4.76 4.76 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.76 0.00 0.00 0.00 0.00 21 1

19.66 0.00 17.67 1.90 0.00 0.09 15.26 2.84 10.78 0.00 1.64 0.00 0.00 0.00 0.00 19.83 0.00 0.00 19.83 98.71 0.09 0.09 0.00 0.00 0.00 0.78 0.52 0.00 0.09 0.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.86 0.43 0.43 0.00 0.00 1160 5

0.00 0.00 0.00 0.00 0.00 0.00 0.31 0.00 0.31 0.00 0.00 0.00 0.00 0.00 0.00 12.60 0.00 12.44 0.16 25.82 0.47 0.47 0.16 0.16 0.00 16.02 3.58 0.00 0.31 0.00 12.13 0.00 54.90 0.16 45.41 9.33 0.00 2.64 0.00 0.00 0.00 0.31 2.33 74.18 0.00 0.00 0.00 0.00 643 6

0.28 0.00 0.14 0.00 0.00 0.14 0.85 0.42 0.14 0.00 0.28 0.00 0.00 0.00 0.00 0.71 0.00 0.00 0.71 88.58 0.14 0.14 1.41 0.99 0.42 9.73 5.08 0.00 0.14 0.00 4.51 0.00 0.00 0.00 0.00 0.00 0.00 0.14 0.00 0.00 0.00 0.14 0.00 11.42 0.00 0.00 0.00 0.00 709 2

1.68 0.00 0.63 0.28 0.14 0.63 1.68 0.49 0.14 0.07 0.98 0.07 0.00 0.00 0.07 1.47 0.00 0.00 1.47 63.57 0.35 0.35 3.22 2.52 0.70 32.38 15.03 0.07 2.38 0.56 14.34 0.00 0.42 0.14 0.00 0.21 0.07 0.07 0.07 0.00 0.00 0.00 0.00 36.43 0.00 0.00 0.00 0.00 1430 5

0.44 0.00 0.26 0.00 0.00 0.17 2.10 0.52 0.35 0.00 1.22 0.26 0.00 0.17 0.09 8.49 0.00 0.00 8.49 98.60 0.00 0.00 0.09 0.00 0.09 1.31 1.05 0.00 0.09 0.00 0.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.40 0.00 0.00 0.00 0.00 1143 1

1.54 0.00 0.56 0.21 0.21 0.56 5.61 0.77 2.67 0.84 1.33 0.42 0.00 0.00 0.42 5.61 0.28 0.00 5.33 88.84 0.70 0.70 0.56 0.56 0.00 4.21 0.77 0.07 0.35 0.00 3.02 0.00 0.21 0.00 0.00 0.07 0.14 0.35 0.14 0.07 0.14 0.00 0.00 6.04 5.12 0.70 4.42 0.00 1425 2

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 87.50 0.00 0.00 0.00 0.00 0.00 8.33 0.00 0.00 0.00 0.00 8.33 0.00 4.17 4.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 12.50 0.00 0.00 0.00 0.00 24 4

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.13 0.00 0.00 3.13 100.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 32 1

1.38 0.00 0.64 0.74 0.00 0.00 8.26 1.80 1.91 2.01 2.54 0.11 0.00 0.11 0.00 15.47 0.11 0.00 15.36 76.59 0.11 0.11 0.74 0.42 0.32 20.76 10.06 0.11 0.53 0.00 10.06 0.00 0.32 0.00 0.00 0.32 0.00 0.32 0.22 0.11 0.00 0.00 0.00 22.25 1.17 0.53 0.64 0.00 944 2

Subenvironments: (1a) Interglacial (late TST–HST) peat mires (coal); (1b) Interglacial (late TST/HST) clastic facies; (2) latest HST; (3) calcrete-bearing red mudstone (LST or earliest TST); (4) early to mid-TST.

Sphenopteriods Convolutispora spp. Granulatisporites granulatus Granulatisporites microgranifer Lophotriletes ibrahimii Lophotriletes microsaetosus Gleicheniaceae Triquitrites additus Triquitrites sculptilis Triquitrites spinosus Triquitrites tribullatus Other ferns Apiculatisporis spinososaetosus Angulisporites splendidus Mooreisporites inusitatus Uncertain pteridophytes Alatisporites pustulatus Colatisporites spp. Laevigatosporites spp. TOTAL PTERIDOPHYTES Medullosales Schopfipollenites ellipsoides Peltaspermales Wilsonites delicatus Wilsonites vesicatus Cordaitales Florinites florinii Florinites junior Florinites mediapudens Florinites millottii Florinites visendus/pumicosus Florinites spp. Coniferales Bisaccate pollen Illinites unicus Potonieisporites spp. Protohaploxypinus spp. Uncertain coniferopsids Cananoropollis spp. Cordaitina spp. Hamiapollenites tractiferinus Plicatipollenites spp. Saccate pollen TOTAL GYMNOSPERMS UNCERTAIN Murospora kosankei Schopfites dimorphus Sinuspores sinuatus YIELD FACIES

0.00 0.00 0.00 0.00 0.00 0.00 21.29 4.82 11.24 2.01 3.21 0.00 0.00 0.00 0.00 9.24 0.00 0.00 9.24 93.57 0.40 0.40 0.40 0.00 0.40 2.81 1.61 0.00 0.00 0.00 1.20 0.00 2.01 0.00 0.00 2.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.62 0.80 0.80 0.00 0.00 249 6

1.71 0.00 0.00 1.71 0.00 0.00 0.85 0.00 0.00 0.00 0.85 0.00 0.00 0.00 0.00 24.79 0.00 0.00 24.79 93.59 0.00 0.00 0.43 0.43 0.00 5.13 3.42 0.00 0.85 0.00 0.85 0.00 0.85 0.43 0.00 0.00 0.43 0.00 0.00 0.00 0.00 0.00 0.00 6.41 0.00 0.00 0.00 0.00 234 2

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Table 2. Quantitative palynological data for the 17 palynological samples that produced moderate to very high yields Systems tract: Number of samples: Lycopsids Lepidodendrales Sigillariales Chaloneriaceae Herbaceous lycopods Sphenopsids Calamitales Sphenophyllales Ferns Marattialales Tedaleceae Sphenopteriods Gleicheniaceae Other ferns Uncertain pteridophytes Total pteridophytes Pteridosperms Medullosales Peltaspermales Coniferopsids Cordaitales Coniferales Uncertain coniferopsids Total gymnosperms Uncertain

Late TST–HST Clastic, n ¼ 9 40.55 39.07 0.35 0.55 0.58 6.31 4.54 1.78 19.53 14.47 1.19 0.96 2.82 0.09 5.83 72.22 2.01 0.13 1.88 24.51 22.52 1.39 0.60 26.52 1.26

Late TST–HST LST or earliest TST Coal, n ¼ 4 n¼1 42.66 37.83 0.00 3.14 1.70 25.73 25.22 0.50 12.88 11.16 1.02 0.11 0.52 0.07 3.80 85.07 0.91 0.00 0.91 14.02 14.02 0.00 0.00 14.93 0.00

11.98* 11.98* 0.00 0.00 0.00 0.16* 0.16* 0.00 1.09* 0.62* 0.16 0.00 0.31 0.00 12.60† 25.82* 0.62 0.47† 0.16 73.56† 16.02 54.90† 2.64† 74.18† 0.00

Late HST n¼2

Early to mid-TST n¼1

Mean

21.24 20.41* 0.07 0.68 0.08 11.14 0.90* 10.24† 38.10† 18.50 0.43 10.67† 8.47† 0.03 10.65 81.14 1.83 0.22 1.61 16.82 16.58 0.21 0.03 18.65 0.22

59.00† 42.57 0.00 16.47† 0.00 2.01 1.61 0.40 23.29 0.80* 1.21 0.00 21.30† 0.00 9.42 93.57 0.80 0.40 0.40 4.82 2.81* 2.01 0.00 5.62 1.17

38.18 35.20 0.19 2.08 0.71 10.83 8.55 2.29 19.29 12.55 1.00 1.79 3.88 0.07 6.52 74.82 1.58 0.15 1.43 22.86 18.28 4.11 0.48 24.44 0.74

* Significantly lower than average abundance. † Significantly higher than average abundance.

Fig. 5. Sequence-stratigraphic diagram and detailed sedimentary log for a typical TST– HST unit in Sequence 14 at Point Aconi near the north end of the Bras d’Or section, showing the position of key palynological samples (modified from Falcon-Lang 2006, 2009).

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low abundance in sample Bd87-10, it none the less makes up the highest proportion in the suite (mean: 0.15%). The relative proportion of pteridophyte spores in Bd87-10 is equally unusual compared with other samples. The sample contains the lowest percentage of pteridophyte spores (25.8%, compared with a mean value of 74.8%). However, nearly half of those spores comprise one unusual morphospecies, Colatisporites sp., which is unique to this sample and makes up 12.4% of the assemblage. In addition, arborescent lycopsids show relatively low abundance (12%, compared with 38.2% in the sample suite), and include Lycospora pellucida (7.31%) and Lycospora pusilla (4.67%), the spores of Lepidophloios harcourtii and Lepidodendron hickii, respectively. Sphenopsids and ferns and are also rare, showing their lowest and second lowest abundance in the sample suite (0.16% and 1.09% respectively), the latter including representatives of the marattialean, tedalaean, and gleicheniacean ferns.

Early to mid-transgressive assemblage

Fig. 6. Sedimentary log and interpreted sequence stratigraphy for the upper Bouthillier to Harbour Coal interval (Sequence 9–12), with sequences and systems tracts, highlighting the interval (145–158 m) associated with sample Bd87-10 above the Upper Bouthillier Seam (modified from Gibling & Bird 1994). Key as in Figures 4 and 5.

(643 palynomorphs counted; Fig. 7) is overwhelmingly dominated by conifer pollen grains (55%). These include superabundant Illinites unicus (45.4%), Potoniesporites sp. (9.33%) and a few other indeterminate bisaccate grains (0.16%). To put this value in context, sample Bd87-10 contains over 10 times more conifer pollen than the next richest samples in the suite (Bd87-1 and Bd87-15 both contain only 4.17% conifer pollen grains) and is highly unusual compared with typical Moscovian palaeotropical palynofloras (e.g. Eble 2002). Other gymnosperms present include abundant cordaitaleans, represented by three species of Florinites (16%), saccate pollen (2.33%), Plicatipollenites sp. (0.31%), which is probably the pollen of a conifer-like plant, rare peltasperms (0.16%) and rare medullosan pteridosperms (0.47%). Although medullosan pre-pollen is present at

One sample was obtained from the early to mid-part of the TST (Figs 3–5). This sample (Bd87-20) is from a grey mudstone that immediately overlies a 35 m thick succession of alluvial plain red beds showing desiccation cracks and isolated calcareous nodules. Overlying beds are grey, rooted coastal plain deposits containing brackish water foraminifera (Gibling & Wightman 1994; Falcon-Lang 2006), which in turn are capped by the 1 m thick Point Aconi Coal (Falcon-Lang 2009), interpreted as part of the transgressive systems tract. The widespread red beds contain calcareous nodules, and infill and overstep a palaeovalley, suggesting formation during a sustained interval of lowered base level and seasonal climate. Thus, positioned just above the boundary of the red beds and coastal plain deposits, sample Bd87-20 represents an early to mid-transgressive deposit. The composition of Bd87-20 is somewhat similar to the seven roof (wetland) assemblages, being dominated by Lycospora pusilla (39%), the spore of Lepidodendron hickii, and containing sphenopsids in rather low numbers (2.01%). There are two key differences, however. First, Endosporites globiformis, the spore of the herbaceous lycopsid family, Chaloneriaceae, is unusually abundant (16.5%, compared with a mean of 1.26%), occurring with its highest frequency in the entire sample suite. Second, although ferns make up 23.3% of the palynoflora, closely similar to the mean for roof assemblages (23.08%), the taxonomic composition is completely different, with gleicheniaceous ferns being superabundant (21.3%). In addition, the enigmatic pteridophyte, Laevigatosporites, is unusually abundant (9.4%).

Discussion We have described palynofloras in a sequence-stratigraphic context in the late Moscovian (Middle Pennsylvanian, Asturian– Cantabrian) Sydney Mines Formation. We acknowledge that our sample suite is relatively small (17 samples with good yields), and a fuller analysis is needed to represent comprehensively such a thick and complex formation. Nevertheless, examination of mean values for each sequence-stratigraphic context (Table 2) confirms that the sample from the LST to earliest TST (Bd8710) is very different from all other samples, and that samples from the latest HST (Bd87-8, 12) and the early to mid-TST (BD87-20) are somewhat different from the remaining Coal Forest samples (late TST, HST). Analysis of palynofloral assemblages in a sequence-stratigraphic context reveals provisional

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Fig. 7. Palynoflora from sample Bd87-10 collected from calcisol-bearing red bed at 153 m in the Bras d’Or section (see Figs 3 and 6). Scale bar: 50 ìm (all specimens at same scale). Superabundant taxa, .20% of total palynomorphs; (single palynomorph in this category ¼ 45.4%), abundant taxa, 7.5–20%; common taxa, 1–7.5%; rare taxa, ,1%. (1) Illinites unicus, (2) Colatisporites sp., (3) Potonieisporites sp., (4) Florinites visendus, (5) Lycospora pusilla, (6) Lycospora pellucida, (7) Florinites florinii, (8) Punctatosporites oculus, (9) Punctatosporites granifer, (10) Florinites mediapudens, (11) Wilsonites delicates, (12) Raistrickia cf. saetosa, (13) Laevigatosporites sp., (14) Triquitrites sculptilis, (15) Microreticulatisporites sulcatus, (16) Schopfipollenites ellipsoides.

trends that may represent the response of vegetation to glacial– interglacial cycles, as follows (Fig. 8). (1) During the early to mid-TST (n ¼ 1 assemblage), lepidodendrids rapidly established as the dominant trees within a matrix of herbaceous lycopsids (Chaloneria) and gleicheniaceous ferns. This assemblage may correspond to an early phase in the melting of polar ice caps (deglaciation). (2) During late TST–HST (n ¼ 13 assemblages), spatially heterogeneous rainforests of lepidodendrids, cordaitaleans, treeferns and sphenopsids developed, a typical Coal Forest community. These assemblages may correspond to warm, wet interglacial phases. (3) During the latest HST, when base level began to stabilize (n ¼ 2 assemblages), communities dominated by herbaceous gleicheniaceous and sphenopteriod ferns and/or cordaitaleans

started to replace the Coal Forests. These assemblages may correspond to peak interglacial conditions or the earliest stages of renewed ice accumulation. (4) During the LST or earliest TST (n ¼ 1 assemblage), conifers and subdominant cordaitaleans spread into the lowlands and lepidodendrids survived in low numbers, presumably in wet areas on the alluvial plain. This assemblage may correspond to a period of ice accumulation with a relatively dry climate (glacial phase). These findings lend support to a model of dynamic Pennsylvanian tropical biomes, which responded to the beat of glacial– interglacial cycles (Falcon-Lang 2003b, 2004; Feldman et al. 2005; Stephenson et al. 2008; DiMichele et al. 2010; FalconLang & DiMichele 2010). The predictable sequence architecture and extent of the sequences in the Maritimes Basin strongly

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Fig. 8. Diagram summarizing the composition of palynofloras in their sequence-stratigraphic context, interpreted in terms of glacial–interglacial cycles. The late TST–HST category is subdivided into coal and clastic assemblages (see Table 2).

suggests that some, at least, of these rhythmic successions reflect a response of tropical landscapes to global changes in sea level and climate driven by Gondwanan glaciation.

Conifers dominated Pennsylvanian dryland alluvial tracts near lowstand The most remarkable discovery we report is the finding that conifers were locally prominent in Pennsylvanian tropical lowlands in central Pangaea during a phase of lowered relative sea level that may correspond to glacial conditions (Fig. 8). Sample Bd87-10, obtained from grey shale within a calcrete-bearing redbed succession (LST or earliest TST) contains 55% conifers and 16% cordaites. Conifer pollen (especially Potoniesporites sp.) first appears in the late Serpukhovian, remains rare in the Bashkirian and Moscovian, increases in abundance in the Kasimovian, but does not become widespread and abundant in central tropical Pangaea until the Gzhelian–Permian (Jerzykiewicz 1987; Peppers 1996, 1997; Dimitrova et al. 2009; DiMichele et al. 2010). Thus, occurrence of superabundant conifer pollen in a late Moscovian coal-bearing succession is highly unusual. Only a few conifer-dominated assemblages have previously been reported from this time interval, or older, and such palynofloras are usually interpreted as the pollen rain of upland forests amplified at times of maximum flooding (Chaloner 1958; Chaloner & Muir 1968; Scott & Chaloner 1983; Davies & McLean 1996; Stephenson et al. 2008). However, in our example, this interpretation is implausible. The most parsimonious explanation is that the sample represents the vegetation growing on widespread alluvial drylands, possibly during a glacial phase. Adopting this interpretation, the composition of sample Bd8710 provides important information about the diversity and ecology of tropical dryland tracts at times of lowstand. The superabundant conifer Illinites unicus (45.4%) and abundant Potoniesporites (9.33%) are both known from Bashkirian marine bands in the UK, perhaps reflecting an earlier upland origin for these taxa (Davies & McLean 1996; McLean 2004). They are also abundant in subtropical settings in northwestern Laurasia (Rueger 1996) and Gondwana during Moscovian times (Loboziak et al. 1997; Azcuy et al. 2002; Kneller et al. 2004; Souza 2006).

The rise of conifers in lowland tropical environments suggested by sample Bd87-10 therefore implies that a combination of climatic cooling and drying caused conifer populations to migrate to lower altitudes and latitudes. The relatively low diversity of the assemblage (21 taxa) and high dominance by a single taxon further suggests that this seasonally dry vegetation was rather ecologically stressed (Falcon-Lang 2003a). Taenate pollen grains, such as Illinites, are generally considered an arid climatic indicator in younger Permian strata (Utting 2001). It is interesting that the dominant taxon, Illinites unicus, is not associated with the walchian conifers known from the Palaeozoic megafloral record, but instead with certain Triassic conifers (Rothwell et al. 2000), further emphasizing the bizarre nature of our palynological assemblage.

Could the assemblage be reworked? In arguing that Bd87-10 represents the vegetation growing on a seasonally dry alluvial plain, we are implicitly ruling out the possibility that this sample is reworked from older strata (see Collinson et al. 1985). But could the sample be reworked? Reworked palynomorphs have been noted at multiple horizons in the Sydney Basin (Dolby 1988, 1989), although they are most abundant in braided-fluvial deposits of the underlying South Bar Formation and are less common in the Sydney Mines Formation (Gibling et al. 2004). That said, maximum reworking would be expected to occur during lowstand when the alluvial plain was being actively incised. Furthermore, the abundant occurrence of Colatisporites sp., a long-ranging taxon commonly found in Mississippian rocks (Owens et al. 2005) including those of Nova Scotia (Utting 1989), may imply a reworked origin for Bd87-10. Those arguments aside, there are excellent reasons to suppose that this critical sample is not reworked and reflects the vegetation growing on the seasonally dry alluvial plain. First, incision of coal-bearing sediments during lowstand would be expected to cannibalize a variety of palynomorphs, resulting in an assemblage that approximates the average for the formation. However, the composition of Bd87-10 is highly unusual compared with that of underlying strata or any palaeotropical Moscovian strata for that matter. Cannibalization of much older (Mississippian)

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formations would not be expected to yield superabundant conifer pollen. Furthermore, although Colatisporites could be reworked from Mississippian strata (where it is a minor constituent of Windsor–Canso assemblages; Utting 1989), it is surprising that other Mississippian taxa are not also present if that were the case. None of the 643 palynomorphs counted on this slide show any physical evidence of reworking such as mechanical damage or colour changes indicative of earlier burial alteration. In fact, the palynomorphs are unusually pristine. Thus we conclude that this assemblage is not reworked.

That said, it is important to emphasize that our study is one of only a relatively small number of papers to report Pennsylvanian palynological assemblages in a sequence-stratigraphic context (e.g. Davies & McLean 1996; Stephenson et al. 2008) and the first study to explicitly report a palynological assemblage from deposits that may represent a Pennsylvanian lowstand of relative sea level (inferred to represent a glacial phase). Thus, although our dataset is small, it significantly contributes to our understanding of Pennsylvanian vegetation in environmental and/or climatic contexts where it was either previously poorly known or entirely unknown (Falcon-Lang & DiMichele 2010).

Other ecological insights In addition to the main finding that conifers were prominent on a dryland alluvial plain in the tropical lowlands during times of low relative sea level, our data improve knowledge of other aspects of Pennsylvanian palaeoecology. For example, the occurrence of abundant spores of the herbaceous lycopsid, Chaloneria, in early to mid-TST deposits (Bd87-20), preceding the onset of widespread Coal Forests, is consistent with earlier studies. DiMichele & Phillips (1996) pointed out that spores of Chaloneria are typically most abundant in the lowermost part of Middle Pennsylvanian coal seams, implying that this herbaceous lycopsid played a role as a mire pioneer. In light of our data, it is probable that Chaloneria was tolerant of drier and more disturbed conditions than lepidodendrids, thereby allowing it to flourish prior to the onset of widespread peat formation. This characteristic perhaps explains why it was able to survive the intense glacial phase at the Middle to Late Pennsylvanian boundary, which caused the palaeotropics to dry out (Heckel 1991) and led to the extirpation of lepidodendrids in central Pangaea (DiMichele & Phillips 1994; DiMichele et al. 2009; Falcon-Lang & DiMichele 2010; Falcon-Lang et al. 2011). A further interesting aspect of our data that goes some way to resolve another enigma is the high abundance of gleicheniaceous ferns (up to 21.3%) in latest HST and early to mid-TST deposits (e.g. Bd87-8, 20) that may correspond to a transition from interglacial to glacial conditions. The spores of gleicheniaceous ferns (Triquitrites sp.) are widespread but typically rather rare in Middle Pennsylvanian assemblages. However, as Dimitrova et al. (2005) noted, no megafloral remains of this group have been found in coal-bearing strata. However, if this group of plants was centred in drier environments, and became abundant in lowlands only during time intervals between peat accumulation, their absence may simply reflect a taphonomic bias (see Falcon-Lang et al. 2009b).

Is our sample size significant? We do not disguise the fact that our interpretation of vegetation response to climate cycles is based on a relatively small number of samples. Although we have a good number of samples (n ¼ 13) from late TST–HST deposits representing ‘normal’ Coal Forest vegetation, the remaining sequence-stratigraphic contexts are represented by only one or two samples each. This sampling asymmetry is not surprising given that there is a megabias in the plant fossil record that selects against the preservation of dryland assemblages (Falcon-Lang et al. 2009b) and that fossil plants are preferentially preserved during times of rising base level (Gastaldo & Demko 2010). Thus, our sampling asymmetry probably reflects the genuine frequency of palynomorph-rich sediments rather than collector bias, although this, too, may have been a significant factor because samples were collected for biozonation, not palaeoecology (Dolby 1988, 1989).

Comparison with Quaternary rainforest response to glacial cycles In broad terms, our findings are consistent with patterns of tropical rainforest response to Quaternary glacial–interglacial cycles. In a classic study, Haffer (1969) argued that the Amazon rainforest had contracted into isolated refugia during the Last Glacial Maximum when the equatorial belt is inferred to have become cooler and drier. Although this hypothesis has been strongly criticized (Hooghiemstra & van der Hammen 1998) and new research suggests that the Amazon rainforest was much more resilient to climate fluctuations than previously thought, palynological data suggest that upland elements partly displaced lowland rainforest taxa (Colinvaux et al. 1996) during glacial maximum conditions, and that the rainforest margins contracted slightly (Mayle et al. 2000). In other parts of the tropics, however, rainforest fragmentation at glacial maximum conditions was much more marked and obvious vegetation changes are seen in palynological profiles; for example, in Africa (Prentice & Jolly 2000) and SE Asia (Heaney 1991). Survival of rainforest taxa in refugia may explain the persistence of rainforest composition through both Quaternary (Meave & Kellman 1994) and Pennsylvanian glacial–interglacial cycles (Falcon-Lang & DiMichele 2010), and may even have driven speciation (Haffer 1969).

Conclusions (1) Our analysis of 17 palynological samples from stacked sequences in the Middle Pennsylvanian Sydney Mines Formation shows that tropical vegetation changed systematically through successive systems tracts that correspond to changes in relative sea level. Because at least some of the sequences, and sea-level changes, probably represent the build-up and melting of glacial ice, some of the vegetation change may reflect glacial–interglacial cycles. (2) The most unusual sample (Bd87-10), from a grey mudstone unit within a thick succession of redbed palaeosols and calcretes, suggests that conifers were prominent locally in dryland tropical lowlands, and may have been widespread during seasonally dry glacial phases. (3) In contrast, Coal Forests flourished during periods of high relative sea level that may correspond to interglacial phases. A variety of herbaceous lycopsids, sphenophylls and ferns were abundant during late stages of transgression that may correspond to times of transition between glacial and interglacial states. (4) The findings enhance our understanding of the biome-scale ecology and climate response of Pennsylvanian tropical rainforests and encourage greater integration of palynology and sequence stratigraphy in future studies. We thank the organizers of the 2009 Lyell Symposium, J. Hilton and C. Cleal, for the opportunity to contribute to this volume. H.F.L. gratefully

P E N N S Y LVA N I A N C O N I F E R - D O M I NAT E D E C O S Y S T E M S acknowledges support from an Advanced Fellowship of the Natural Environment Research Council, UK. M.R.G. thanks the Natural Sciences and Engineering Research Council of Canada for funding that allowed the basic stratigraphic information to be collected. G.D. acknowledges the help and advice given by R. Boehner and D. McNeil (Nova Scotia Department of Natural Resources) during the course of the original palynological study. The incisive reviews of S. Oplustil and C. Fielding, and the editorial remarks of C. Cleal greatly improved this paper.

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Received 13 April 2010; revised typescript accepted 2 September 2010. Scientific editing by Christopher Cleal.