Clastic Swamps Research Articles

Stratigraphy, palaeoenvironments and palaeoecology of the Loch Humphrey Burn lagerstätte and other Mississippian palaeobotanical localities of the Kilpatrick Hills, southwest Scotland.

Background and Aims. The largely Mississippian strata of the Kilpatrick Hills, located at the western end of the Scottish Midland Valley, enclose several macrofossil floras that together contain ca 21 organ-species of permineralised plants and ca 44 organ-species of compressed plants, here estimated to represent 25 whole-plant species (Glenarbuck = nine, Loch Humphrey Burn Lower = 11, Upper = seven). The most significant locality is the internationally important volcanigenic sequence that is reputedly intercalated within the Clyde Plateau Lava Formation at Loch Humphrey Burn, where ca 30 m of reworked tuffs and other clastic sediments enclose one of the world’s most important terrestrial lagerstätten of this period. We here explore the palaeoecology and palaeoenvironments of the locality, and elucidate its controversial age.Methods. Repeated re-excavation of key exposures allowed recognition of five main depositional units, differing in thickness from 4 m to 12 m. It also permitted detailed sampling for plant macrofossils and microfossils throughout the succession. Several approaches are integrated to re-assess the taphonomy and preservation of these exceptional plant fossils.Key Results. The deposits are rich in taxonomically diverse miospores and in toto contain at least six well-developed compression floras, together with two beds yielding nodules that enclose well-researched anatomically preserved plants permineralised in calcite. Bulk geochemistry shows that the upper nodules formed by migration of Ca with subordinate Mn and Na. Some phylogenetically important plant fossils recovered in the early 20th century have been traced to their source horizons. Trends in relative proportions of macrofossil and microfossil taxa through the sequence are only moderately congruent, perhaps reflecting the likelihood that microfossils sample the regional rather than the local flora.Conclusions. The Loch Humphrey Burn sequence encompasses a wide range of depositional environments that intercalates high-energy fluvial channels (possibly developed during flash floods in a seasonally arid environment) with lower energy flood plains and a brief lacustrine interval; all yield macrofloras typically dominated by allochthonous pteridosperms. The uppermost unit represents clastic swamps dominated by (hypo)autochthonous lycopsids and ferns s.l., and is tentatively correlated with the entire—reputedly mid-Visean—exposure at nearby Glenarbuck. Other nearby localities with rooted tree-lycopsids appear to have immediately pre-dated the onset of regional volcanism. These interpretations allow revised provenancing and dating of historical collections of key plant fossils. The late Tournaisian date previously attributed on palynological evidence to the lowest unit at Loch Humphrey Burn appears increasingly improbable when our re-appraisal of the macrofloras and microfloras is placed in the context of (a) statistical comparison with other permineralised Mississippian assemblages and (b) recent stratigraphic and geochronologic studies in the region; rather, we ascribe the entire Kilpatrick Hills sequence to the mid-Visean. Stratigraphic and palaeoenvironmental interpretations of the Mississippian rocks of the Kilpatrick Hills have especially profound implications for our understanding of the physical evolution of Scotland during the Variscan orogeny and formation of Pangea.

Conifer-dominated palynofloras in the Middle Pennsylvanian strata of the De Lutte-6 borehole, The Netherlands: Implications for evolution, palaeoecology and biostratigraphy

The evolutionary history of Pennsylvanian tropical dryland/upland communities remains enigmatic. In this paper, we describe conifer-dominated palynofloras in a facies context from the early to mid-Moscovian (Middle Pennsylvanian) interval of the De Lutte-6 borehole (the Netherlands) that shed light on this issue. Our data suggest that, in the upper Bolsovian–lowermost Asturian part of the borehole succession, Florinites-producing cordaitaleans with subordinate tree-ferns, pteridosperms, calamiteans, and lycopsids, covered low-lying braidplains draining the rising Variscan Orogen, while Cordaitina/Latensina-producing cordaitaleans, walchian conifers and enigmatic pteridosperms mostly grew in hinterland regions (Assemblage I). At one relatively brief interval, a mire dominated by calamiteans and arborescent lycopsids developed within this braidplain complex (Assemblage II). In the mid-Asturian part of the borehole succession, following a switch from humid to seasonally-dry climates (indicated by paleosols), palynofloras associated with a shallow, but extensive, lake deposit imply that communities of walchian conifers, Cordaitina/Latensina-producing cordaitaleans, and engimatic pteridosperms covered low-lying drylands, but were cyclically replaced by lycopsid ‘ephemerals’ during short-term pluvial events (Assemblage III). Across tropical Pangaea, the climate-driven migration of diverse conifers from Bolsovian hinterlands to mid-Asturian basins coincides with (1) the more frequent appearance of conifer megafloral remains in the fossil record, (2) a gradual increase in the frequency of tree-ferns in clastic swamps, (3) a decline in the abundance of arborescent lycopsids in mires, and (4) a change from perhumid raised mires to humid planar mires in cratonic areas. We therefore highlight that the mid-Asturian (mid-Moscovian) interval is an under-appreciated event in the evolution of Pennsylvanian tropical vegetation, on a par with the better-known climate-driven floral changeovers that occurred in the earliest Kasimovian and Gzhelian–Asselian. Our palaeoecological findings also clarify a long-running biostratigraphic controversy by showing that conifer dominance in the De Lutte-6 borehole is completely consistent with its Bolsovian–Asturian age, and does not require the invocation of an unconformity separating an inferred Westphalian part of the succession from an inferred upper Stephanian/Permian part of the succession, as suggested by some earlier workers. This, in turn, emphases the importance of selecting isotaphonomic (isoclimatic) samples for biostratigraphic purposes.

Palaeobotany of the Pennsylvanian (mid-Bolsovian–Cantabrian; Moscovian) Warwickshire Group of the Bristol Coalfield, U.K.: Biostratigraphy and palaeoecology

The Bristol Coalfield of southwest Britain, although intensively studied in the early history of palaeobotany, has received little attention for 75years. Here we review the palaeobotany of the mid-Bolsovian to Cantabrian (Moscovian) Warwickshire Group of the Bristol Coalfield, which comprises, from base to top, the Winterbourne, Pennant Sandstone and Grovesend formations. Based on an investigation of all available adpression and sandstone-cast plant assemblages in a facies context, we develop a new system of biostratigraphical zonation and elucidate palaeoecology. Our key findings are: (1) Using the new biozonation we identify a stratigraphical gap encompassing the early to mid-Asturian, occurring between the mid- and late Bolsovian Pennant Sandstone and the late Asturian Grovesend formations. This tectonic-induced stratigraphical gap most likely relates to the Leonian Phase of the Variscan uplift and can be correlated with contemporaneous hiatuses in the South Wales and other European coalfields. (2) We recognise a diverse patchwork of plant communities as follows: Peat mires of the Bolsovian Winterbourne and Pennant Sandstone formations were dominated by lepidodendrids and ferns, but were replaced by tree-fern and fern-dominated mires in the late Asturian Grovesend Formation. Clastic swamps fringed these mires and were characterised by a diversity of pteridosperm, calamitaleans and ferns. Riparian communities associated with the coarse-grained deposits of large-scale braided fluvial systems that vertically alternate with the coals/shales, variously comprised Sigillaria, calamitaleans and cordaitaleans, with pockets of pteridosperms and calamitaleans surrounding channel abandonments. In addition, large cordaitaleans were common in drier interfluve and/or hinterland areas. Switching between stable mire communities and disturbed fluvial communities either reflects autocyclic channel switching or allocyclic alternations driven by climate change.

Viséan flora from the Moscow Coal Basin (Baltic Plate; European Russia): Local evolution in the context of global tendencies

Global-scale palaeoenvironmental perturbations during the Viséan Stage affected all regional plant communities within the Equatorial Belt. The Moscow Coal Basin, which occupies the central part of the present-day Russian Platform, provides an exceptional palaeobotanical record permitting to document the patterns of floral responses to the noted perturbations. A careful study of macroplant remains allowed to identify 28 species and to establish their stratigraphic ranges. Five types of plant communities evolved on the southern margin of the basin, namely flood-plain peat bogs with lycopods, semi-aquatic sphenopsids, mesophilic communities of river valleys with fern-like plants, lepidophytic communities of flood-plain clastic swamps, and coastal communities of lycopods. These communities developed on the western basin margin: peat bogs of freshwater lakeshores and flood-plains dominated by lycopsids and gymnosperms with Cordaites sp. leaves, flood-plain clastic swamps with lepidophytes, semi-aquatic sphenopsids, mesophilic communities of river valley and lake depression sides formed by plants with fern-like leaves, and coastal communities of lycopods. Two Viséan palaeophytogeographic units such as the Southern Moscow District and the Western Moscow District can be distinguished. Each belonged to the particular palaeo-river valley. In the local stratigraphic record, the Gryzlovia meyenii Assemblage Zone (Bobrikian–lower Tulian) and the Sublepidodendron shvetzovii Assemblage Zone (upper Tulian–Venevian) are delineated. A boundary between them correlates with vegetation changes traced through the entire Equatorial Belt. Thus, this boundary corresponds to a major floristic turnover. The Viséan climate does not provide an unambiguous explanation of the latter. Dynamics of the shorelines linked to the eustatic fluctuations was able, however, to affect the local plant communities. Specific “stigmarian limestones” were formed in regressive conditions, when plant colonized rapidly the coastal carbonate mud. The plate tectonics was a very important factor of plant migrations within Euramerican Floristic Realm. Pre-existed separation of the Hunic terranes and the Laurussian margin might have been responsible for differences between the Northern and Southern European palaeophytogeographic provinces.

Six rare Lepidostrobus species from the Pennsylvanian of the Czech Republic and their bearing on the classification of lycospores

Grouping of the common and diverse Carboniferous dispersed miospore genus Lycospora is suggested. Authors divide Carboniferous lycospores into six subgroups, based on their morphology and the knowledge of their in situ records. The stratigraphical range of the cones is from the Langsettian to the Stephanian B. Six plant specimens from the Bohemian Late Palaeozoic continental basins belong to six Lepidostrobus species. Differing morphology of fructifications and their in situ spores lead to a separation of the cones into the following species: Lepidostrobus kohoutii sp. nov. containing Lycospora uzunmehmedii spores, Lepidostrobus cf. haslingdenensis containing Lycospora uber spores, Lepidostrobus sp. A yielded spores that compare with the dispersed species Lycospora microgranulata, Lepidostrobus sp. B possessed Lycospora cf. microgranulata spores, Lepidostrobus sp. C yielded spores of the Lycospora torquifer-type, and Lepidostrobus sp. D contains Lycospora cf. subjuga spores. It means, that each cone species yielded lycospores comparable to one dispersed spore species. The palaeoecology of the plant fossils is discussed. Their environment is typified by either clastic or mixed clastic/peat substrates and standing water. Therefore, they grew in clastic swamps developed along the lake margins or shallows.

Reconstruction of Different Wetland Plant Habitats of the Pannonian Basin System (Neogene, Eastern Austria)

AbstractSedimentary and palynofacies analysis, total organic carbon content (TOC), and palynology from a densely sampled, small, lignite-bearing succession of Late Miocene age at Badersdorf, SE Austria, were compared with modern wetland ecologies. From this, six hydrologically controlled palynofacies types and six associated paleo-plant habitats in an ancient wetland system were differentiated. The associated woody and herbaceous hinterland flora also were distinguished. At least four horizons with relatively high fusinite content have been preserved, indicating occurrence of paleo-wildfires in either the wetland or the hinterland. The palynofacies types were used to determine the taphonomic bias of the associated palynomorph assemblages, which, together with a comparison with modern wetland vegetation, led to differentiation of the paleo-plant habitats. The paleo-wetland was dominated mainly by Glyptostrobus-containing vegetation, and comprised clastic swamp forests with woody angiosperms, natural levee forests, fern- and Glyptostrobus-dominated organic swamps, freshwater marshes, and wet prairies. The occurrence of more than 40 herbaceous taxa at this locality indicates that the lowland vegetation was not composed of only different closed-forest types, but also of areas with herbaceous vegetation. The more zonal vegetation of the adjacent hinterland has been interpreted as a mix of Pinaceae and woody angiosperms with patches of more herbaceous xeric layers.

Palynology and palynofacies of Miocene coal-bearing (clastic) sediments of the Hausruck area (Austria)

Two drill cores with coal-bearing sediments from the localities Lukasberg and Kalletsberg of the Hausruck area were investigated. Particular attention was paid to the clastic intercalations between and within the coal seams to complete the previous database of the coal-petrological and geochemical analyses of the coals made by Gruber and Sachsenhofer (1999) and Bechtel et al. (2003). In this work, pollen and spores, the acid-resistant organic components (palynofacies), and the total organic carbon content (TOC) of the clastic sediments have been examined in order to interpret the palaecological conditions of the different plant habitats. The TOC and structured components of the Lukasberg site displayed a recurring cyclicity between coal seams and are interpreted as frequent changes of the depositional environment: coal swamps and peat bogs, lacustrine conditions (lake or pond) and marshes or clastic swamps. It is therefore assumed that the Hausruck area, particularly at the Lukasberg locality, was subjected to periodical submersions, in which the ground-water level repeatedly flooded the coal swamps. This cyclicity is unfortunately not clearly documented at the Kalletsberg locality. In addition, the occurrence of up to 32% fusinite in the palynofacies from some samples of both sites and charred logs at the Lukasberg open cast mine indicate the presence of palaeo-wildfires within forests of the Hausruck area. The age of the sedimentary succession is late Sarmatian to the early/middle Pannonian (upper Middle Miocene to lower Upper Miocene). The frequent occurrences of pollen of Mastixia, a warmth loving plant, which during this time interval occurred sporadically and in low numbers, suggest that the Hausruck was a relict area with a particular humid and warm climate.

Palaeoecological constraints of some Lepidostrobus cones and their parent plants from the Late Palaeozoic continental basins of the Czech Republic

About 60 strobilar specimens of six Lepidostrobus species ( Lepidostrobus sternbergii, Lepidostrobus nemejcii sp. nov., Lepidostrobus thomasii sp. nov., Lepidostrobus obovatus, Lepidostrobus ronnaensis sp. nov. and Lepidostrobus stephanicus) and their microspores from the Bohemian Late Palaeozoic continental basins were studied. The stratigraphical range of cones is from the Langsettian to the Stephanian B. Microspores isolated from six species of Lepidostrobus cones belong to six dispersed spore species of the genus Lycospora. Lepidostrobus crassus was synonymised with L. sternbergii based on identical spore content and closely similar morphology of the type specimens of both species. Lepidostrobus nemejcii, L. thomasii and L. ronnaensis have been erected as new species according to the cone morphology, spore content and parent plant. Ecological constraints of all the species are discussed. Two groups of species preferring different habitats were distinguished. The first group consists of species that preferred clastic to mixed peat/clastic substrates and high water table. Their parent plants grew either in clastic swamps along the lake margins and shallows or in planar mires frequently disturbed by clastic input during floodings. This group involves most of the studied species and their parent plants. Differences between habitats of the species of this group are indicated but their precise specifications needs further investigation. The second group involves only L. ronnaensis and its parent plant Lepidodendron ophiurus ( sensu Němejc). It preferred peat substrate of planar eutrophic mires with only minor clastic disturbances. The palynological comparison with in situ lycospores from compressed and petrified Lepidostrobus cones is made.

Dicotyledonous leaf macrofossils from the latest Albian-earliest Cenomanian of the Eromanga Basin, Queensland, Australia.

Ten types of dicotyledonous angiosperm cuticle are described from bore core samples from the Early Cretaceous (latest Albian-earliest Cenomanian) of the Eromanga Basin, central Queensland. To date, these are the oldest organically preserved angiosperm macrofossils in Australia. Most of this material is found as small dispersed fragments, but two more intact lobed leaves were found. The affinities of some specimens are suggested to lie with the Chloranthaceae and Illiciales, and possibly the Platanaceae, but the rest are unknown. None of the cuticles show the paracytic stomatal arrangement which is common in extant plant families often regarded as 'primitive'. However, one of the cuticle forms exhibits a 'plastic,' variable form of subsidiary cell arrangment, which has previously been suggested as the most primitive condition. These angiosperms were a small component of an overwhelmingly gymnosperm (mostly conifer) dominated flora. They grew in clastic swamps, but may also have occured in coal swamps or sandy levees. The notably thin cuticle of some forms is consistent with an understory or deciduous habit.

Paleoecological Analysis of Two Early Pennsylvanian Mineral-Substrate Wetlands

Abstract The biomass within two Early Pennsylvanian (Langsettian [Westphalian A] equivalent) penecontemporaneous swamp communities was sampled quantitatively to obtain an estimate of the taxonomic contribution to each assemblage. Blocks of organic-rich shale were removed from a clastic parting within the Black Creek Coal, and ∼0.5-m2 siltstone quadrats were chain-sawed from a clastic swamp community directly above the Bear Creek Coal. Bedding planes were exposed, and the surface areas for each taxon per bedding surface were measured and used as proxies for biomass contribution in each locality. Biomass over a combined area of 5.47 m2 was assessed for the Black Creek Coal parting; biomass covering an area of 9.70 m2 was evaluated for the assemblage preserved above the Bear Creek coal. In addition to calculating standard diversity indices, this data set was analyzed using cluster analyses and non-metric multidimensional scaling (NMDS) to differentiate variations within the general flora. Low species diversi...

Comparative Palynology of Clastics and Lignites from the Manning Formation, Jackson Group, Upper Eocene, Grimes County, TX: ABSTRACT

ABSTRACT The 3500 lignite seam at the Gibbons Creek mine in Grimes Co., Texas was sampled for pollen and spores at 10 cm intervals. Most samples were dominated by Momipites (to 60%) from the Juglandaceae (walnut family) as is common for Jackson Group sediments. Other taxa varied systematically, with a peak of the freshwater tree Nyssa (blackgum) and Rhoipites angustus (to 17%) occurring at the base. Higher in the seam, increases (to 55%) of Cupuliferoipollenites (a chestnut-like grain) and Cyrillaceaceaepollenites? ventosus (to 7%) may indicate higher salinity. A Chryophyllum (to 25%) peak near the top of the seam suggests a return to freshwater conditions, but with perhaps a change in water depth. Core samples from an interval above the lignites, representing inner shelf clastics, were taken at at least 40 cm intervals. These samples reveal a more regional pollen flora; although minor changes occur, palynomorph spectra are for the most part homogenous. The dominant grain is again Momipites coryloides, but percentages are lower (to 35%). Cupuliferoipollenites (to 17%), Chrysophyllum (to 5%), and Rhoipites angustus (to 3%) are not less important overall, but do not peak. Palm leaf megafossils in one sample suggest a clastic swamp; in this sample palm pollen (mostly Arecipities representing the modern palmetto) reaches 73%. Another sample contains high (26%) percentages of the fern spore Lygodiumsporites adreiennis. These high percentages do not occur in the lignite samples.

Carboniferous fossil forests

Forests of Carboniferous age, first described in detail in the nineteenth century, are often illustrated in textbooks, but their ecological and evolutionary significance has been largely overlooked or, worse, misrepresented. It has often been thought that the standing fossil forests found rooted in coals represent relicts of the peat‐forming vegetation. Recent research has suggested that this is not always the case and that many of the standing trees represent an essentially non‐peat‐forming wetland (‘clastic swamp’) vegetation comprising a distinctive set of genera and species of plants. Recent investigation of several famous examples ‐ Weaklaw, Arran and Joggins as well as new examples such as Mary Lee and Table Head ‐ is throwing new light on the ecological and evolutionary significance of these fossil forests.

Development of Low-ash, Planar Peat Swamps in an Alluvial-plain Setting: the No. 5 Block Beds (Westphalian D) of Southern West Virginia

ABSTRACT Coals from the No. 5 Block coal beds (Westphalian D) of the central Appalachian basin are noted for their blocky, dull character and their low ash and low sulfur content. The beds are multiple benched, with rock partings separating benches. Individual benches have limited lateral extent and, where thick, are dominated by bright, high-ash coal at the base and dull, low-ash coal in the upper parts. The duller coals contain more exinite-group and inertinite-group macerals than the brighter coals. These coal beds are encased in sandstone units dominated by fining-upward sequences. The overall depositional setting is an alluvial-plain environment with northwest-flowing channels spaced approximately 20 km apart. The channels were flanked by clastic swamps about 7 km wide. Low-ash peat accum lated in areas of the flood plain most distant from the channels. These peat-accumulating swamps were about 8 km across. In a few instances low-frequency flood events introduced fine siliciclastic sediment into the peat swamps, depositing a thin layer of sediment on top of the peat. This sediment layer is thicker where the underlying coal is the thickest. These thick coal areas are topographically lower than surrounding coal areas. This relationship between coal thickness, parting thickness, and topography indicates that these peat swamps were planar at the time of deposition. Individual coal benches contain abundant preserved cellular tissue (telocollinite, semifusinite, and fusinite) at most locations, suggesting that robust vegetation was widespread in the swamps and that the morpholo y was planar. The high concentrations of exinite-group an inertinite-group macerals in the upper parts of benches resulted from selective decomposition and oxidation of the peat in subaerial and aquatic planar-swamp environments.

Paludal environments of the Mary Lee coal zone, Pottsville formation, Alabama: stacked clastic swamps and peat mires

The Blue Creek and Mary Lee coals in the lower part of the Mary Lee coal zone, Upper Pottsville Formation, northwestern Alabama, record deposition in peat-accumulating environments or mires. Intervening strata contain a series of stacked clastic swamps (forested wetlands which grew on a classtic sediment substrate, rather than a peat soil). These clastic swamp horizons are identified on the basis of: (1) autochthonous, erect, lycophyte and Calamites trunks; (2) mud-cast, prostrate, hypoautochthonous lycophyte and Calamites trunks; (3) compression-impression assemblages of autochthonous to hypoautochthonous pteridosperm and lycophyte foliage, branches, and reproductive structures; (4) autochthonous axes and appendages of Stigmaria, and Pinnularia; and (5) siderite nodules associated with “rooting” structures and other plant material. Sedimentological and biostratinomic features of the Mary Lee coal to Blue Creek coal interval are used as the basis for the interpretation that sediment loading and compaction of buried peat controlled the alternation between peat mires and clastic swamps, and the stacking of the clastic swamps.

An Appalachian-sourced deltaic sequence, northeastern Alabama, USA: biofacies-lithofacies relationships and interpreted community patterns

The thin sequence of Lower Pennsylvania rocks along Sand Mountain, Plateau coal field, northeastern Alabama, U.S.A., records the deposition in a deltaic coastal-plain paleoenvironment along the ancient Appalachian seaway. The section is laterally continuous, well exposed, and preserves a rich macrobiota. Identified coexisting paleodepositional environments contain distinctive biofacies. Specific paleoenvironments of deposition contain unique biofacies in this Late Carboniferous (Westphalian A) sequence. The criteria established for the recognition of these biofacies can be utilized to assist in refined interpretations of deltaic sites in Carboniferous coastal paleoenvironments. Identifiable biofacies include those preserved under a variety of forested wetland (swamp) conditions, distributary and crevasse-splay channels, coastal bays (“interdistributary” and lagoonal), barrier sands, and distal storm deposits (Fig. 1; Gastaldo et al., 1989). Vegetation in forested wetlands grew either in clastic substrates or peat substrates. The principal biofacies preserved in clastic substrate swamps were lycophyte-dominated, and can be recognized by either a predominance of canopy litter or subterranean stigmarian appendages (Gastaldo, 1986). The canopy litter that has accumulated on the forest floor was preserved under unique sedimentological conditions, and reflects the ecological gradient associated with the distribution of lycophyte genera in the swamp (Gastaldo, 1987). A monotypic assemblage of lycophytes characterized edaphically stressed sites. In sites proximal to the levee, a mixed assemblage of lycophytes, calamiteans, pteridophytes and pteridosperms is common. In the absence of compressed canopy macrodetritus, subterranean axes with helically arranged appendages (“rootlets”) crosscutting the bedding may be preserved. Macro-invertebrates are restricted to traces and trails, reflecting behavioral traits when conditions were conducive for their movement into these sites. Peat-colonizing vegetation parallels that of the clastic swamp. Deep distributary channels contain sandstone-cast and compressed aerial trunks of lycophytes and spenophytes. These occur in bedload deposits along with quartz and quartzose pebbles and cobble-size phyllite clasts. Degradation of external morphology usually precludes assignment of logs to a systematic position lower than order. In shallower, en-echelon stacked crevasse sands occur a mixture of lycophyte, calamitean and pteridosperm “woody” parts. Additionally, scoriaceous fern-like foliage may be found. Little evidence exists for macro-invertebrate communities in these unstable settings. Coastal bays preserve in situ macro-invertebrate communities, as well as allochthonous macrodetritus that was derived principally from levee vegetation. Four phases of biofacies development can be delineated (Gibson and Gastaldo, 1987). Stress-tolerant inarticulate brachiopods dominate the initial transgressive phase. Individuals are found isolated in the siltstone, commonly preserved by authigenic cementation in siderite concretions. Rarely are patches or clusters of individual encountered. Where clustering does occur it is associated with the colonization of “woody” plant parts. Transition to the molluscan-dominated phase is accompanied by the establishment of a rich ichnofauna. Continued transgression and the development of more normal salinities under lagoonal conditions are paralleled by an increase in species richness and abundance. The third biofacies phase remains molluscan dominated, but the assemblages at any particular point in time are represented by monospecific genera. Plant macrodetritus was utilized by the macro-invertebrate communities, and that which is preserved is restricted to highly fragmentary, unindentifiable remains. The fourth biofacies phase reflects the development of lagoonal conditions. This change can be recognized by macro-invertebrate body and ichnofossil fauna (Seilacher's Cruziana ichnofacies) diversification. An increase in the abundance of brachiopods and other invertebrates is considered to represent more open-marine conditions. Barrier sandstone and distal storm deposits contain disarticulated epifaunal brachiopods, bivalves, gastropods, and trilobites. These stenohaline forms are concentrated in a shell lag at the base of migrating barrier-sand bodies. The overlying sandstone is devoid of macro-invertebrate body fossils and plant macrodetritus, but is characterized by the colonization of Zoophycos traces.

Palynological Facies Fossils in Nonmarine Environments in the Paleogene of the Bighorn Basin

Palynomorphs occur as lithofacies fossils among depositional environments of the uppermost Paleocene to lowermost Eocene sediments of the central Bighorn Basin in Wyoming. Carbonaceous sediments occur within the predominantly red-bedded sequences and they contain lithofacies interpretable as deposition in ponds, crevasse splays, reduced distal floodplains, swamp margins, and clastic swamps. The palynomorph content of these lithofacies, primarily from a limited stratigraphic interval, is shown by canonical variates analysis to be made up of distinct palynologic assemblages. These assemblages differ primarily in abundance of taxa present rather than their presence or absence. The ponds are particularly distinguished by high numbers of reworked marine dinoflagellates, algal zygospores (Tetraporina), bisaccate gymnosperm pollen, and low numbers of Alnus and Taxodiaceae. The levee/crevasse splay contains high numbers of some bisaccate pollen types, pteridophyte spores, and locally high quantities of Alnus. The reduced floodplain contains abundant bisaccate pollen and pteridophyte spores, Platycaryapollenites, and Taxodiaceae. Swamp margin samples are distinguished by high numbers of Cycadopites and locally high numbers of Plicatopollis and Alnus. The swamp is dominated by pollen of Taxodiaceae and Alnus as well as high numbers of Sparganiaceaepollenites, with locally high numbers of Pistillipollenites. Pond deposits are generally more numerous and contain a richer palynoflora, however, the occurrence of the important Paleocene-Eocene boundary taxon Platycaryapollenites occurs in swamp and neighboring facies about 200 m below its first occurrence in pond facies. Thus, lithofacies distribution effects can affect the accuracy of biostratigraphic interpretations. INTRODUCTION

An Appalachian-sourced deltaic sequence, northeastern Alabama, U.S.A.: biofacies-lithofacies relationships and interpreted community patterns

The thin sequence of Lowe Pennsylvania rocks along Sand Mountain, Plateau coal field, northeastern Alabama, U.S.A., records the deposition in a deltaic coastal-plain paleoenvironment along the ancient Appalachian seaway. The section is laterally continuous, well exposed, and preserves a rich macrobiota. Identified coexisting paleodepositional environments contain distinctive biofacies. Biofacies in deltaic sites are characterized by the presence of various macrofloral assemblages. Alluvial-plain swamps, identified lithologically by homogeneous mudstone and siltstone, preserve bedded-plant litter as coalified compressions and impressions. Deep-swamp biofacies are comprised either of monotypic lycophyte canopy assemblages ( Lepidophloios) or their subterranean axial systems ( Stigmaria). Alluvial swamps and proximal levee sites contain canopy detritus of a mixed flora. This is reflected in the reduced domination of Lepidophloios, the increased importance of the lycophytes Sigillaria and Lepidodendron, and an abundance of gymnosperms, pteridosperms, pteridophytes, and Calamites. Macro-invertebrates occur almost exclusively as behavioral trackways of xiphosurid arthropods and epifauna attached to fragmentary plant parts. The peat-accumulating swamp biofacies is identified from palynological preparations. Palynofloras parallel macrofloral clastic swamp diversity and contain an abundance of palynomorphs with affinities to ferns and lyginopterid pteridosperms. Channel-form sandstone represent distributary and crevasse channel deposits in the lower part of the section, and uncomformable bedload-dominated, laterally migrating, braided-river channel deposits at the top of the sequence. Oriented sandstone cast and compressed logs (lycophytes and Calamites) occur with bedload features in distributary and braided channels. Crevasse sanstones preserve a higher proportion of calamitean axes, as well as trunks and rachises of medullosan pteridosperms. Macro-invertebrates and ichnofaunas have not been identified in these paleoenvironments. Bayfill sequences contain several in situ macro-invertebrate communities in addition to allochthonous plant detritus. This plant biofacies is characterized by calamitean and pteridospermous vegetation, that originated from levee sites. The macrofaunal biofacies is characterized by a molluscan assemblage, with community replacement relative to physical parameters of the water. The initial bayfill phase contains an inarticulate brachiopod community of Orbiculoidea and Lingula. The transition to the molluscan-dominated biofacies is signaled by infaunal colonization by Pteronites and Planolites (burrows). Biotic changes are reflected by the increasing abundance of brachiopods and other invertebrates usually considered to represent more open-marine conditions. Insights into Late Carboniferous open-marine communities can be discerned from lag accumulations of marine epifauna in storm-generated sandstones.

Confirmation of Carboniferous clastic swamp communities

Tropical lowlands dominated by arborescent lycophytes are the principal foci for our understanding of Carboniferous peat and non-peat accumulating coastal swamps1,2. Suggested palaeoeco-logical interpretations of various lycophytes and accessory vegetation have been based on transported compression assemblages3,4 and palynomorphs5,6, or in situ permineralized peats7. Where transported macrodetritus, resulting in compression assemblages, is used to reconstruct past vegetational patterns, taphonomic factors tend to bias the preserved flora8–11. Taken alone, or out of depositional context, the heterogeneity of an assemblage most probably bears little or no relationship to that of the original contributing communities. Gastaldo9 suggests that reconstructions should be based on the autecology of erect in situ plants because, with peats permineralized in situ, precise resolution in time of laterally equivalent vegetation is difficult. Here I document an erect in situ Early Pennsylvanian lycophyte swamp which provides the first confirmatory evidence for previously hypothetical ecological amplitudes.

Morphology and Paleoecology of Pennsylvanian-Age Coal-Swamp Plants

There were two major kinds of Pennsylvanian-age tropical swamps: coal swamps, represented by most coal seams, and clastic swamps, commonly associated with coal as roof shale or sandstone floras. Such environments were part of depositionally-complex lowlands that also included non-swamp habitats. In general, the Pennsylvanian-age coal and clastic swamps were dominated by non-seed (lower vascular, spore-producing) plants, and the mesic, non-swamp vegetation was characterized by seed-plant (pollen-producing) dominance. On occasion, some drier-site kinds of vegetation are preserved, providing a glimpse of other kinds of plants in the lowland regions of the tropical belt; among these are the earliest known conifers (Scott and Chaloner, 1983) in the Middle Pennsylvanian.

Transition from Clastic to Peat Sedimentation in Appalachian Basin Pennsylvanian Swamps in West Virginia and Pennsylvania: ABSTRACT

Paleobotanic, sedimentologic, and lithologic analyses of 34 core samples of underclay from the New River and Kanawha Formations of the proposed Pennsylvanian System stratotype, West Virginia, and 14 samples from strip mines in the Llewellyn Formation from the anthracite fields, Pennsylvania, indicate that more than half of the coal beds studied began forming in response to changing sedimentation and edaphic conditions that were facies independent. Peak formation was a consequence of factors that favored increased organic accumulation in swamps previously dominated by clastic deposition (clastic swamps). The underclay beds grade upward from gray mudstone that is intensely rooted, but otherwise free of plant fossils, to fissile, vitrain-rich, rooted, black shale containing bundant plant fossils, to coal. The black shale flora consists of lycopod, pteridosperm, and calamite branches and large trunks. Foliage is absent because it was destroyed by rooting and decay. The trunks are lying in situ. They are unidirectionally oriented in places, and usually associated with Stigmaria rooted hummocks. Trunk accumulations are never associated with flood-transported or lacustrine sediments. Trunks were preserved when a rising water table led to a reduced oxidation potential in the underlying mud. The change from clastic sedimentation to peat formation was rapid in most swamps, as evidenced by a transition zone only a few millimeters thick. However, evidence of longer transition stages is present for some swamps where as much as 0.5 m of black shale was deposited. Occa ionally, several cycles of underclay-black shale formation were repeated before peat accumulation began. The transitional process could have been arrested at any time before ideal peat-forming conditions were attained. The gradual transitions from clastic to organic sedimentation suggest that swamp types form a continuum between clastic and peat swamp end members. End_of_Article - Last_Page 1452------------