Journal of the Geological Society, London, Vol. 160, 2003, pp. 643–648. Printed in Great Britain.

Response of Late Carboniferous tropical vegetation to transgressive–regressive rhythms at Joggins, Nova Scotia H . J. FA L C O N - L A N G 1,2 Department of Earth Sciences, Dalhousie University, Halifax, N.S., Canada B3H 3J5 2 Present address: Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK (e-mail: [email protected]) 1

Abstract: Fossil plant assemblages are described in their sequence stratigraphic context from the Upper Carboniferous (Langsettian) Joggins Formation of Nova Scotia to elucidate ecosystem response to transgressive–regressive rhythms. Results show that rising base level resulted in retrograding submerged coastal mires co-dominated by Lepidodendron and Lepidophloios, which were replaced by short-lived Paralycopodites communities immediately following mire drowning. Extensive brackish bays existed during early highstand, distally fringed by gymnospermous and putative progymnospermous coastal and/or upland vegetation. Late highstand bay filling generated prograding distributary wetlands dominated by flood-disturbed lycopsid–pteridosperm–sphenopsid communities, and locally by cordaite mangroves. As base level fell, welldrained alluvial plains were dominated by fire-prone cordaite and/or Sigillaria communities, which persisted until the next phase of base-level rise. This rhythmic ecosystem succession repeatedly occurred on a c. 50– 200 ka time scale, and was probably driven by glacial–interglacial climate rhythms. Keywords: Late Carboniferous, sequence stratigraphy, vegetation, global change.

Fundy, Nova Scotia, Canada (Fig. 1). This coal-bearing section was brought to international attention by Sir Charles Lyell and is particularly famous for its upright fossil trees and the earliest reptiles (Scott 1998). Strata were deposited in the rapidly subsiding, strike-slip Cumberland sub-basin of the Maritimes Basin, which drained northeastwards into the Mid-European Sea (Gibling et al. 1992; Calder 1998). Despite being positioned in an intra-continental setting, minimally hundreds of kilometres from open marine waters, brackish bay facies at Joggins attest to short-lived marine incursions during periods of elevated base level (Archer et al. 1995).

The Late Carboniferous (Westphalian) tropical vegetation biome is arguably one of the best understood terrestrial ecosystems in pre-Tertiary history (DiMichele & Phillips 1994; DiMichele et al. 2001). Fossil plant-bearing strata of this age and palaeolatitude are widespread across North America, Europe and northern Asia (Calder & Gibling 1994), and have been studied for more than two centuries (Scott 1977). To date research has mainly focused on the taxonomy, biology and phylogeny of particular plant groups, and aspects of community structure and ecology (e.g. Gastaldo 1987; Phillips & DiMichele 1992; Falcon-Lang 2000). The rock successions containing the remains of these terrestrial ecosystems are characterized by repeated marine transgressive–regressive rhythms (Collier et al. 1990), resulting from the complex interaction of climate-forced changes in sea level and sediment supply, and variations in basin subsidence rates (Leeder et al. 1998). Recent studies have emphasized the long-term persistence of Late Carboniferous tropical vegetation ecosystems through tens of these major environmental perturbations (DiMichele et al. 1996; Pfefferkorn et al. 2000); however, medium-term ecosystem change within individual transgressive– regressive rhythms remains largely unknown. This latter scale of ecosystem dynamics may be elucidated through analysis of fossil plant assemblages in their sequence stratigraphic context. In this paper, floral assemblages are described within a sequence stratigraphic framework from the classic Upper Carboniferous Joggins Formation, Nova Scotia (Davies & Gibling 2003), the results of which demonstrate more clearly than before the marked response of Late Carboniferous ecosystems to repeated transgressive–regressive rhythms on a 50–200 ka time scale.

Sedimentology and sequence stratigraphy This study focuses on the lower 600 m of the Joggins Formation in which Davies & Gibling (2003) described the following facies associations (outlined here using a slightly revised nomenclature). Grey mudstone units containing coals (10–80 cm thick) are interpreted as retrogradational poorly drained coastal plain deposits dominated by temporally persistent mires. Units bearing organic-rich limestones containing an oligohaline fauna are interpreted as basin-wide brackish open water deposits. Grey, coarsening-upward units dominated by thick channelized sandstone beds and subhorizontal heterolithic beds are interpreted as progradational poorly drained coastal plain deposits characterized by large distributary channels and interdistributary wetlands. Red units containing small channel sandstones and pedogenic carbonate nodules are interpreted as the deposits of well-drained alluvial plains characterized by anastomosed channel networks. Thin grey–green intervals within well-drained alluvial plain units containing millimetre-thick coals are interpreted as alluvial plain deposits characterized by an oscillating water table. Although Davies & Gibling (2003) included these latter units in the welldrained alluvial plain facies association, they contain a distinct flora, and are formally identified in this paper as a partially

Geological setting The 1430 m thick Upper Carboniferous (Langsettian) Joggins Formation crops out in spectacular sea-cliffs on the Bay of 643

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Boss Point Formation

Fig. 1. Location of Joggins in (a) Canada and (b) Nova Scotia. (c) Stratigraphy of the Cumberland sub-basin.

drained alluvial plain association, intermediate between welldrained alluvial plain settings and progradational poorly drained coastal plain settings. Davies & Gibling (2003) noted that Joggins Formation facies associations are organized into eight sedimentary rhythms in the studied section (Fig. 2). Rhythms 1 and 5–8 are 25–80 m thick, and consist of retrogradational poorly drained coastal plain units overlain by brackish open water units, capped by progradational poorly drained coastal plain units. Rhythms 2–4 are 70 m, 30 m and 210 m thick, respectively, and comprise a very similar succession differing only in the additional occurrence of multiple intercalated partially drained and well-drained alluvial plain units above the progradational coastal plain unit and below the retrogradational coastal plain unit of the following rhythm (progradational coastal plain deposits are suppressed in rhythm 3). Given that the section represents about half the thickness of Langsettian strata in the Cumberland sub-basin (Calder 1998), and that this stage has an approximate duration of 2–3 Ma (Menning et al. 2000), rhythms may typically represent c. 50– 200 ka duration, with the abnormally thick fourth rhythm representing c. 300–500 ka duration. Depositional rhythms are interpreted as resulting from a relatively rapid base-level rise (retrogradational coastal plain units and lower brackish open water units), followed by coastal plain progradation close to mean water table during highstand (upper brackish open water units and progradational coastal plain units) and, in rhythms 2–4 only, by alluvial plain aggradation above mean water table and/or punctuated base-level fall (partially drained and well-drained alluvial plain units), before renewed base-level rise (retrogradational coastal plain units and lower brackish open water units). It is important to emphasize that because of the high accommodation setting, parasequences bounded by flooding surfaces predominate and sequence boundaries are not observed. Consequently, it is inappropriate to apply conventional Exxon-type nomenclature to the succession: system tracts are not readily identifiable in this kind of tectonic setting (Davies & Gibling 2003).

Plant assemblages in facies association context The stratigraphic distribution of the seven major types of plant assemblages is indicated in Figure 2. The retrogradational coastal plain facies association is characterized by thick coal seams, interpreted as temporally persistent peat mire deposits. It con-

Fig. 2. Stratigraphic column of lower 600 m of Joggins Formation showing facies associations, sedimentary rhythms, base-level curve and major plant assemblages (after Davies & Gibling 2003).

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tains parautochthonous megaflora and palynoflora dominantly indicative of Lepidodendron, Lepidophloiois and Diaphrodendron (Hower et al. 2000). Other lycopsids (Sigillaria) and pteridosperms (Alethopteris, Neuropteris) are less common, and are typically restricted to a few clastic-rich intervals containing rare lycopsid charcoal, interpreted as flood- or fire-disturbed mires. Grey siltstone units, interpreted as poorly drained, clastic substrate floodbasin deposits, are dominated by allochthonous compressions of Sigillaria trunks (up to 35 cm in diameter) together with minor Alethopteris and Neuropteris. Collectively retrogradational coastal plain assemblages are referred to as Assemblage 1. The brackish open water facies association contains two major plant assemblages. The first (Assemblage 2) occurs in organic limestone beds, interbedded with coaly laminae, or immediately overlying the thick coals of the retrogradational coastal plain association, interpreted as very shallow, transgressive bay margin deposits. Megafloral compressions of lycopsid rootstocks (Stigmaria) and allochthonous decorticated lycopsid trunks are common. Palynological assemblages indicate the dominance of the lycopsid Paralycopodites (Hower et al. 2000). The second plant assemblage (Assemblage 3) occurs at higher intervals in the brackish open water units, in beds totally devoid of any rooting structures. Organic-rich siltstones and planar-bedded sandstones locally exhibiting hummocky cross-stratification and waverippled tops, interpreted as open brackish bay deposits, contain purely allochthonous, fragmentary compressions of putative progymnosperms (Pseudadiantites and Rhacopterium; Wagner 2001), pteridosperms (Alethopteris, Karinopteris and Paripteris), sphenopsids (Calamites and Asterophyllites) and cordaitaleans (Cordaites). Rare, charred pycnoxylic wood also occurs, being dominated by cordaitaleans (Dadoxylon materiarium Dawson; Falcon-Lang & Scott 2000) and other gymnosperms of indeterminate affinity (D. recentium Dawson). No palynomorphs were recovered. The progradational coastal plain facies association also contains two major plant assemblages. The first (Assemblage 4) is restricted to a single stratigraphic interval near the base of one progradational coastal plain unit (Rhythm 1), and consists of thinly bedded, undulatory, heterolithic strata, interpreted as very shallow interdistributary lagoonal deposits on the bay margin. These are dominated by abundant allochthonous cordaitalean compressions (Cordaites, Cordaicarpus). Numerous, slender (up to 12 cm diameter), upright trees with flared bases, woody trunks with narrow piths, and complex adventitious rooting systems are rooted at multiple intervals in these beds. These enigmatic trees are tentatively interpreted as cordaitaleans based on their association with an exclusively cordaitalean allochthonous assemblage. The second progradational coastal plain assemblage (Assemblage 5) occurs in channelized sandstone bodies of up to 8 m thickness locally exhibiting inclined stratification, interpreted as large distributary channel deposits, and in sheet sandstone bodies, interpreted as crevasse splay deposits. These contain abundant allochthonous metre-long lycopsid trunk compressions (Lepidodendron, Lepidopholois, Sigillaria; 35–40 cm diameter), common sphenopsids (Calamites), and locally common to rare cordaitaleans (Cordaites, Artisia). Rare, allochthonous charcoal in the same beds contains an equal mixture of indeterminate lycopsid periderm and cordaite wood (Dadoxylon materiarium). Closely spaced upright Calamites stems (up to 13 m 2 ) are commonly rooted within multiple crevasse splay complexes. Inclined to horizontal, heterolithic stratal packages, interpreted as rapidly aggrading interdistributary floodbasin deposits, contain tens of upright, sandstone-cast lycopsid trees (20–40 cm diameter, up to 2–3 m high). Although upright lycopsid trunks are

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decorticated and therefore of indeterminate genus, one calcareously permineralized individual is characteristic of Sigillaria. Facies-associated parautochthonous compressions and palynoflora indicate the predominance by Sigillaria and Lepidodendron lycopsids, with common sphenopsids (Calamites), pteridosperms (Alethopteris, Neuropteris and Sphenopteris) and cordaitaleans (Cordaites). The well-drained alluvial plain facies association is characterized by small, channelized sandstone bodies, interpreted as anastomosed river channel deposits, and associated sheet sandstone bodies interpreted as crevasse splays dissected by feeder channels. These contain allochthonous assemblages dominated by the impressions, compressions and calcareous permineralizations of cordaitaleans (Artisia, Cordaites, Cordaixylon, Dadoxylon materiarium and D. acadianum Dawson) with minor pteridosperms (Alethopteris, Eusphenopteris) and sphenopsids (Calamites, Asterophyllites), and very rare lycopsids (Sigillaria). Abundant allochthonous charcoal assemblages are dominated by cordaitalean woods (Dadoxylon materiarium and D. acadianum) with an additional wood of indeterminate gymnosperm affinity (D. recentium). Autochthonous lycopsid and calamitean stems rarely occur rooted in the channel margin deposits. Red, desiccation-cracked, mudstone units bearing carbonate nodules, interpreted as well-drained floodbasin deposits, contain parautochthonous compressions and impressions dominated by cordaitaleans (Cordaites, Cordaicarpus) with minor pteridosperms (Eusphenopteris). Parautochthonous charcoal assemblages are composed entirely of cordaitalean wood (Dadoxylon materiarium). No palynomorphs were recovered. Collectively welldrained alluvial plain assemblages are referred to as Assemblage 6. The partially drained alluvial plain association characterized by mottled grey–red mudstones interpreted as wet–dry floodbasin deposits contains allochthonous megafloral compressions dominated by lycopsids (Sigillaria, Lepidodendron) with minor pteridosperms (Alethopteris, Neuropteris, Sphenopteris), cordaitaleans (Cordaites, Cordaiocarpus), and sphenopsids (Calamites, Annularia, Asterophyllites). Intercalated 1–8 mm thick muddy coals, interpreted as extremely short-lived mires, contain tens of calcareously permineralized autochthonous lycopsid stumps (24– 131 cm basal diameter) with attached Stigmaria attributed solely to Sigillaria based on periderm anatomy (Falcon-Lang 1999). Associated parautochthonous assemblages of common megafloral compressions, abundant charcoal mesofossils, and palynoflora in the thin coals are dominantly indicative of Sigillaria with minor medullosan pteridosperms (Alethopteris, Trigonocarpus), cordaitaleans (Cordaites, Dadoxylon materiarium) and sphenopsids (Calamites, Asterophyllites). Collectively these transitional assemblages are referred to as Assemblage 7.

Ecosystem response to transgressive–regressive rhythms Analysis of facies-associated plant assemblages in the context of the Joggins Formation sedimentary rhythms provides important information concerning ecosystem response to base-level fluctuations (Fig. 3). Assemblage 1 in the thick coals of the progradational coastal plain units suggests that initial base-level rise resulted in temporally persistent mires dominated by Lepidodendron, Lepidophloiois and Diaphrodendron lycopsid forests. The known ecological tolerances of these plants suggest an undisturbed, permanently submerged mire environment (DiMichele & Phillips 1994). Assemblages in charcoal-bearing clastic partings indicate

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that rare disturbances by fires and floods resulted in short-lived successional communities of Sigillaria lycopsids and pteridosperms. Based on estimates of modern peat accumulation rates and Carboniferous coal compaction coefficients (Falcon-Lang 2000), coal bed thickness data suggest that retrograding lycopsid-dominated coastal mires kept pace with rising base level for at least several hundred years before finally being drowned. Assemblage 2 in organic-rich limestones at the base of brackish open water units, immediately overlying the retrogradational poorly drained coastal plain mire deposits, indicates that Paralycopodites, an ecotonal lycopsid (DiMichele & Phillips 1994), initially colonized very shallow clastic-starved bays for a short period following mire drowning. However, as base level continued to rise, and the bays deepened, all vegetation was eventually excluded from the local region. Allochthonous Assemblage 3 in the bay deposits is dominated by gymnosperms and progymnosperms, plants that presumably must have been colonizing distal shorelines and/or emergent uplands during highstand (see Scott et al. 1997; Falcon-Lang & Scott 2000), most probably on Lower Palaeozoic basement blocks, 10–20 km from the Joggins Formation depocentre (Gibling et al. 1992). The occurrence of progymnosperms in these deposits (flora most typical of Early Carboniferous times) is particularly interesting, perhaps suggesting that these archaic elements had continued to survive in ‘upland’ settings (Wagner 2001). Assemblage 4 at the base of the progradational coastal plain unit in Rhythm 1 suggests that, as the brackish bays began to infill by means of coastal progradation, stands of slender cordaite trees locally developed in sheltered lagoons as mangrove-like communities (see Cridland 1964). The more widespread Assemblage 5 in channelized sandstones and heterolithic beds in the progradational coastal plain units (including the classic sandstone-cast fossil forests for which Joggins is most famous), indicates that additional progradation resulted in interdistributary wetlands dominated by diverse, spatially complex vegetation. These intergrading flood-disturbed communities were variously populated by lycopsids (Sigillaria and Lepidodendron), sphenopsids or pteridosperms (Scott 1998). In five rhythms (1 and 5–8), this progradational phase is followed by renewed base-level rise and a return to the Lepidodendron–Lepidophloios-dominated mires of the retrogradational coastal plain setting. However, in rhythms 2–4 continued aggradation of the coastal plain above mean water table, possibly coupled with base-level fall, resulted in the development of well-drained alluvial plains. Assemblage 6 in these welldrained alluvial plain units indicates that this environment was colonized by low-diversity cordaite vegetation, with common pteridosperm shrubs (Alethopteris, Eusphenopteris), and a very few lycopsids (Sigillaria) and calamiteans restricted to riparian niches where the water table was closest to the surface. Charcoal abundance demonstrates that these were highly fire-prone communities, and dominance–diversity assemblage characteristics imply ecological stress (Falcon-Lang 2003). Assemblage 7 in the partially drained alluvial plain units intercalated with the welldrained alluvial plain units indicates that the fire-prone cordaite vegetation of the latter deposits was repeatedly succeeded by fire-prone Sigillaria-dominated communities, which locally formed short-lived mires, during periods of slightly elevated water table. Fig. 3. Summary palaeoecological reconstruction showing idealized ecosystem response to a trangressive–regressive rhythm. rPDF, retrogradational coastal plain; WDF, well-drained alluvial plain; TDF, partially drained alluvial plain; pPDF, progradational coastal plain; BOW, brackish open water bay.

Discussion This study has demonstrated that Late Carboniferous vegetation ecosystems repeatedly changed in response to transgressive–

L AT E C A R B O N I F E RO U S V E G E TAT I O N R E S P O N S E

regressive rhythms. Two main communities are recognized in the Joggins Formation: (1) wetland vegetation dominated by lycopsids existed during periods of rising base level (retrogradational poorly drained coastal plain units and the lower part of brackish open water units) and late highstand (progradational poorly drained coastal plain units); (2) dryland vegetation dominated by fire-prone cordaites and/or sigillarian lycopsids existed during periods of low base level (partially drained and well-drained alluvial plain units). A third, poorly defined community dominated by progymnosperms and gymnosperms is identifiable during early highstand phases (upper part of brackish open water units), and may represent upland and/or coastal vegetation distally fringing the brackish bays. Two complementary hypotheses may account for the observed ecosystem response to transgressive–regressive rhythms. First, changes in ocean proximity may have altered local humidity, with highstand periods being most humid, and lowstand periods, when Joggins became isolated within an intermontane continental interior setting, being most arid (Ziegler et al. 2002). Second, although sedimentary rhythms related to glacial–interglacial climate changes cannot be unequivocally identified at Joggins because of the high accommodation setting (Davies & Gibling 2003), it is probable that dry lowstand periods mostly correlate with glacial phases and wet highstand periods with interglacial phases (see Tandon & Gibling 1994). Either or both of these mechanisms for generating lowstand aridity and highstand humidity adequately account for vegetation change because lycopsids were drought intolerant (with the exception of Sigillaria) and would therefore be restricted to transgressive–highstand periods, whereas gymnosperms, by virtue of the innovation of the seed habit, were drought resistant, and would have had the ecological advantage in well-drained regressive–lowstand settings (DiMichele & Phillips 1994). This pattern of lowstand aridity and highstand humidity has been seen at many other Late Carboniferous palaeotropical sites in Europe and North America, with the limited palaeobotanical data demonstrating the dominance of lycopsid-dominated peat mire ecosystems during the early part of transgressive phases and late highstand phases (e.g. Hartley 1993; Tandon & Gibling 1994; Demko & Gastaldo 1996). This suggests that the rhythmic ecosystem response to transgressive–regressive phases demonstrated in the Joggins Formation may actually have been characteristic for most of the Late Carboniferous tropical world, with a few local exceptions where climatic humidity and sea level apparently fluctuated out of phase (e.g. Cecil 1990). The recognition that Late Carboniferous tropical terrestrial ecosystems repeatedly oscillated between lycopsid rainforests and cordaite drylands in response to base-level fluctuations on a 50–200 ka time scale probably driven by glacial–interglacial climate rhythms is highly significant. This is not least because it may shed some light on the current controversy concerning the extent to which tropical rainforests became fragmented by more drought-tolerant vegetation during the relatively arid Last Glacial Maximum, and whether climate change augmented speciation rate by repeatedly isolating populations (e.g. Hooghiemstra & van der Hammen 1998; Colinvaux et al. 2001). Considerable further work is therefore required to examine the impact of medium-term global change on the Late Carboniferous world, and to consider its impact on the biodiversity of this early rainforest biome. This research was funded by a Killam Fellowship held at Dalhousie University, Canada, and a NERC Fellowship (NER/I/S/2001/00738) held at the University of Bristol, UK. I thank M. Gibling for his valuable

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comments on an earlier version of this manuscript, and W. A. DiMichele for the encouraging review.

References Archer, A.W., Calder, J.H., Gibling, M.R., Naylor, R.D., Reid, D.R. & Wightman, W.G. 1995. Invertebrate trace fossils and agglutinated foraminifera as indicators of marine influences within the classic Carboniferous section at Joggins, Nova Scotia, Canada. Canadian Journal of Earth Sciences, 32, 2027–2039. Calder, J.H. 1998. The Carboniferous evolution of Nova Scotia. In: Scott, A.C. & Blundell, D.W. (eds) Lyell: The Past is the Key to the Present. Geological Society, London, Special Publications, 143, 261–302. Calder, J.H. & Gibling, M.R. 1994. The Euramerican coal province: controls on Late Palaeozoic peat accumulation. Palaeogeography, Palaeoclimatology, Palaeoecology, 106, 1–21. Cecil, C.B. 1990. Palaeoclimate control on stratigraphic repetition of chemical and siliciclastic rocks. Geology, 18, 533–536. Colinvaux, P.A., Irion, G., Rasanen, M.E., Bush, M.B. & de Mello, N. 2001. A paradigm to be discarded: geological and palaeoecological data falsify the Haffer & Prance refuge hypothesis of Amazonian speciation. Amazoniana, 16, 609–646. Collier, R.E.L., Leeder, M.R. & Maynard, J.R. 1990. Transgression and regression: a model for the influence of tectonic subsidence, deposition and eustasy, with application to Quaternary and Carboniferous examples. Geological Magazine, 127, 117–128. Cridland, A.A. 1964. Ameylon in American coal balls. Palaeontology, 7, 186–209. Davies, S.J. & Gibling, M.R. 2003. Architecture of coastal and alluvial deposits in an extensional basin: the Carboniferous Joggins Formation of eastern Canada. Sedimentology, 50, 1–25. Demko, T.M. & Gastaldo, R.A. 1996. Eustatic and autocyclic influences on deposition of the lower Pennsylvanian Mary Lee coal zone, Warrior Basin, Alabama. International Journal of Coal Geology, 31, 3–19. DiMichele, W.A. & Phillips, T.L. 1994. Palaeobotanical and palaeoecological constraints on models of peat formation in the Late Carboniferous of Euramerica. Palaeogeography, Palaeoclimatology, Palaeoecology, 106, 39–90. DiMichele, W.A., Pfefferkorn, H.W. & Phillips, T.L. 1996. Persistence of Late Carboniferous tropical vegetation during glacially-driven climatic and sealevel fluctuations. Palaeogeography, Palaeoclimatology, Palaeoecology, 125, 105–128. DiMichele, W.A., Pfefferkorn, H.W. & Gastaldo, R.A. 2001. Response of Late Carboniferous and Early Permian plant communities to climate change. Annual Review of Earth and Planetary Sciences, 29, 461–487. Falcon-Lang, H.J. 1999. Fire ecology of a Late Carboniferous floodplain, Joggins, Nova Scotia. Journal of the Geological Society, London, 156, 137–148. Falcon-Lang, H.J. 2000. Fire ecology of the Carboniferous tropical zone. Palaeogeography, Palaeoclimatology, Palaeoecology, 164, 339–355. Falcon-Lang, H.J. 2003. Late Carboniferous tropical dryland vegetation in an alluvial plain setting, Joggins, Nova Scotia, Canada. Palaios, 18, 197–211. Falcon-Lang, H.J. & Scott, A.C. 2000. Upland ecology of some Late Carboniferous cordaitalean trees from Nova Scotia and England. Palaeogeography, Palaeoclimatology, Palaeoecology, 156, 225–242. Gastaldo, R.A. 1987. Confirmation of Carboniferous clastic swamp communities. Nature, 326, 869–871. Gibling, M.R., Calder, J.H., Ryan, R., Van de Poll, H.W. & Yeo, G.M. 1992. Late Carboniferous and Early Permian drainage patterns in Atlantic Canada. Canadian Journal of Earth Sciences, 29, 338–352. Hartley, A.J. 1993. A depositional model of the mid-Westphalian A to late Westphalian B Coal Measures of South Wales. Journal of the Geological Society, London, 150, 1121–1136. Hooghiemstra, H. & van der Hammen, T. 1998. Neogene and Quaternary development of the neotropical rainforest: the forest refugia hypothesis and a literature overview. Earth-Science Reviews, 44, 147–183. Hower, J.C., Calder, J.H., Eble, C.F., Scott, A.C., Robertson, J.D. & Blanchard, L.J. 2000. Metalliferous coals of the Westphalian A Joggins Formation, Cumberland Basin, Nova Scotia, Canada: petrology, geochemistry, and palynology. International Journal of Coal Geology, 42, 185–206. Leeder, M.R., Harris, T. & Kirkby, M.J. 1998. Sediment supply and climate change: implications for basin stratigraphy. Basin Research, 10, 7–18. Menning, M., Weyer, D., Drozdzewski, G., van Ameron, H.W. & Wendt, I. 2000. A Carboniferous time-scale 2000: discussion and use of geological parameters as time indicators from Central and Western Europe. Geologisches Jahrbu¨ch, 156, 3–44. Pfefferkorn, H.W., Gastaldo, R.A. & DiMichele, W.A. 2000. Ecological stability during the Late Paleozoic cold interval. In: Gastaldo, R.A. & DiMichele, W.A. (eds) Phanerozoic Terrestrial Ecosystems. Paleontological

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Society Special Papers, 6, 63–78. Phillips, T.L. & DiMichele, W.A. 1992. Comparative ecology and life-history biology of arborescent lycopsids in Late Carboniferous swamps of Euramerica. Annals of the Missouri Botanical Garden, 79, 560–588. Scott, A.C. 1977. A review of the ecology of Carboniferous plant assemblages with new data. Palaeontology, 20, 447–473. Scott, A.C. 1998. The legacy of Charles Lyell: advances in our knowledge of coal and coal-bearing strata. In: Scott, A.C. & Blundell, D.W. (eds) Lyell: The Past is the Key to the Present. Geological Society, London, Special Publication, 143, 243–260. Scott, A.C., Galtier, J., Mapes, R.H. & Mapes, G. 1997. Palaeoecological and evolutionary significance of anatomically preserved terrestrial plants in Upper

Carboniferous marine goniatite bullions. Journal of the Geological Society, London, 154, 61–68. Tandon, S.K. & Gibling, M.R. 1994. Calcrete and coal in Late Carboniferous cyclothems of Nova Scotia, Canada: climate and sea-level changes linked. Geology, 22, 755–758. Wagner, R.H. 2001. The extrabasinal elements in Lower Pennsylvanian floras of the Maritime Provinces, Canada: description of Adiantites, Pseudoadiantites and Rhacopteridium. Revista Espan˜ola de Paleontologı´a, 16, 187–207. Ziegler, A.M., Rees, P.McA. & Naugolnykh, S.V. 2002. The Early Permian floras of Prince Edward Island, Canada: differentiating global from local effects of climate change. Canadian Journal of Earth Sciences, 39, 223–238.

Received 20 August 2002; revised typescript accepted 11 November 2002. Scientific editing by Duncan Pirrie

Response of Late Carboniferous tropical vegetation to ... - CiteSeerX

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Pensions”, Review of Economic Studies 72(3), 651-664. Boldrin, M. and A. Rustichini (2000), “Political Equilibria with Social Security”,. Review of Economic ...

Modelling the Neural Response to Speech: Stochastic ... - CiteSeerX
some support to the hypothesis that designing speech cod- .... Output power spectrum obtained from the computer simu- lation of .... Nature, 365:337–340, 1993.

River flow response to changes in vegetation cover in a South African ...
Jul 23, 2008 - ties due to frequent cloud cover and shadows from mountains. Since changes in land .... had short or discontinuous records. Daily rainfall data ...

River flow response to changes in vegetation cover in a South African ...
Jul 23, 2008 - Available on website http://www.wrc.org.za. ISSN 0378-4738 .... Spectral vegetation indices based on red and near infrared .... a cloud mask.

River flow response to changes in vegetation cover in a South African ...
Jul 23, 2008 - vegetation cover derived from satellite data (the normalised difference vegetation index, ..... A full description of the AVHRR data processing is.

River flow response to changes in vegetation cover in a South African ...
Jul 23, 2008 - Available on website http://www.wrc.org.za ... Monitoring changes in above-ground green biomass in multiple large catchments is challenging, ...

Scale Interactions of Tropical Waves and Tropical ...
One of the major challenges in TC genesis prediction is the accurate simulation of complex interactions across ... genesis prediction. (4) Accurate simulations of convective-scale processes remain challenging, but their ... In addition, we will show

Late Design Changes (ECOs) for Sequentially Optimized ... - CiteSeerX
that traceability is also the basis of critical software and hardware certification, see the ..... Clicking on the states of the FSM also show the corre- sponding ...

Late Design Changes (ECOs) for Sequentially Optimized ... - CiteSeerX
down design flow is infeasible, because it would take too long and lead to undesirably .... by some automation (e.g. by the ECO compiler of Synopsys). The rest ...

Copy of Response to HTTPS Letter
Jun 26, 2009 - on for their Gmail account. ... account. Ultimately, we feel it's important to keep in mind that HTTPS is ... Software Engineer, Security and Privacy.

The response of consumption to income - ScienceDirect
In previous work we have argued that aggregate, post-war, United States data on consumption and income are well described by a model in which a fraction of ...

of high-Andean vegetation
Data analysis. Positive or ... ness, we only included in the analysis those species that occurred in at ... were included in association tests (App. 1). The richest.

AN APPLICATION OF BASIL BERNSTEIN TO ... - CiteSeerX
national structure and policy of vocational education and training (VET) in Australia. ... of online technology on the teaching practice of teachers employed in ...