鄂尔多斯盆地北岔沟砂岩沉积特征及其对天然气成藏的控制作用*

北岔沟砂岩为华北地台二叠系山西组与太原组划分对比的主要标志层,在鄂尔多斯盆地呈大面积连片分布,是上古生界重要的天然气储集层。依据地面露头调查结果与勘探资料,结合前人有关古构造和岩相古地理研究成果,笔者对鄂尔多斯盆地北岔沟砂岩的沉积特征进行了详细分析。结果表明,受益于物源区大量高石英含量的粗碎屑物质在短时间内的集中供应,北岔沟砂岩在地层中位置稳定,以含砾粗粒石英砂岩为主,石英含量高达90%左右,砂体叠置紧密,单砂体之间很少见泥岩隔夹层。这些砂体分别隶属于冲积扇、砾质辫状河和辫状河三角洲沉积体系,在鄂尔多斯盆地北部高、南部次高、中南部低的古地理背景控制下,由盆地南、北边缘向中部依次推进,沉积中心区以北发育4个规模宏大的三角洲沉积主砂带,以南发育6个规模较小的主砂带。受各主砂带砂体规模、矿物组分含量及其成岩作用差异影响,各砂带的储集物性具有较大变化,其中砂体规模最大、石英含量最高、长石等易溶矿物在酸性地层水作用下溶蚀彻底的杭锦旗—榆林—子洲—清涧—永和—吉县主砂带,储集能力最好,最有利于天然气的大规模聚集成藏,是鄂尔多斯盆地北岔沟砂岩天然气进一步勘探开发的有利场所。     

化石及现生真蕨类植物的根系:形态演化及古环境意义*

根是植物的重要营养器官,对维持植物生理活动及生态系统物质循环和能量流动极为重要。真蕨类植物的根系以可预测的方式起源于枝,被称为枝生根,通常也被称为不定根。相比于对种子植物根系的广泛研究,对真蕨类植物根系的认识较为薄弱。通过广泛收集各类文献中有关真蕨类根系的信息,以及观察大量化石、现生植物标本,对若干化石及现生真蕨类植物根系的形态学特征进行了综述。在繁盛于中、晚泥盆世的早期真蕨类植物中,密集的枝生根着生于茎轴、或推测的根状茎、或主干膨大的基部上;根系的分枝罕见,若存在,则仅表现为等二歧式分枝;而在真蕨纲冠群植物中,枝生根密集或稀疏,根系呈单轴式分枝,侧根发育,可达2级甚至更多。真蕨类根系统的形态演化可采用“顶枝学说”进行解释: 真蕨类植物的根系具有一定的演化保守性,均为枝生根;早期真蕨类的原始根系可视为不分枝的或偶见二歧式分枝的顶枝束;经历顶枝束的越顶生长,侧根系统在真蕨纲冠群中演化出现。真蕨类根系的构型、形态、解剖结构、生物量分配等信息可在化石记录中得以揭示,这些信息可为探讨植物根系的演化及研究地史时期的植物—土壤系统提供重要依据。最后,简述了这方面研究的1个案例,即北京西山侏罗纪地层中的真蕨类根系化石及根系—土壤系统。     

Functional groups in a single pteridosperm species: Variability and circumscription (Pennsylvanian, Nova Scotia, Canada)

Multiple foliar specimens of the Late Pennsylvanian fossil pteridosperm [gymnosperm] Alethopteris zeilleri (Ragot) Wagner were collected from one restricted stratigraphical horizon in the Canadian Sydney Coalfield. Variability of functional-group distribution using FTIR technique was studied in compressions, adaxial versus abaxial cuticles, and in unseparated cuticles as a function of maceration time from 48 to 168 h. The results obtained document spectral variability that could be expected within specimens of one species. For example, CH₂/CH₃ and Al/ox ratios can differ by as much as 20% of the values. Moreover, the experiments performed confirm that by using a previously established maceration protocol, long maceration periods do not bias FTIR spectra in terms of oxygenation overprinting. The inference that this cuticle is robust, under the given diagenetic level, probably reflects a reassuring degree of chemical fidelity of the Pennsylvanian plant to support Carboniferous chemotaxonomic observations.     

Pennsylvanian stratigraphic reefs in Kansas,some modern comparisons and implications

Broad platformlike buildups in the Stanton Limestone in southeastern Kansas are composed primarily of lime mud and phylloid algae and are rimmed with skeletal calcarenite composed largely of echinoderm and algal debris. Bordering the buildups are large (1×30 km) channels, lined or filled with similar calcarenite, and a broader basin containing shaly skeletal calcilutite.Grain abrasion and spar cement in the rimming calcarenites indicate water agitation and suggest wave resistance of the buildups during growth. Wave resistance may have been provided by 1) stalked echinoderms, which are resilient when alive and bind sediment with their roots, and also by 2) early drusy cementation of loose sediment to a coherent mass.Comparison to modern channel-separated buildups in the Persian Gulf and the Great Barrier Reef complex brings out the relative significance of organic frameworks in these different geologic settings. Recognized organic frameworks range from absent or insignificant in the Pennsylvanian examples through locally present but insignificant in the Persian Gulf, to apparently important in maintaining the buildups in the Great Barrier Reef. All three examples, however, exhibit patterns of original hydrodynamic control over initiation and gross form of the buildups. Determining significance of organic frameworks to overall buildup growth involves examining both their positions relative to evidence of wave action and the nature of binding in contemporaneous talus produced by wave action on the buildup.

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Zusammenfassung Die ausgedehnten plattformartigen Strukturen im Stanton-Kalk des südöstlichen Kansas bestehen hauptsächlich aus Kalkschlamm und phylloiden Algen, am Rand jedoch aus Kalkareniten, die weitgehend aus Echinodermen- und Algendetritus zusammengesetzt sind. An die Strukturen grenzen breite Vertiefungen (1×30 km), die von Kalkareniten gesäumt oder gefüllt sind, und ein größeres Becken mit mergeligem skeletalem Kalklutit.Kornabrasion und Sparitzementierung der randlichen Kalkarenite sind Zeichen für Wellenbewegung und lassen auf entsprechende Festigkeit während des Wachstums schließen. Diese Festigkeit könnte zwei Ursachen haben: 1. gestielte Echinodermen, die elastisch sind, wenn sie leben, und Sediment mit ihren Wurzeln binden, 2. frühe sparitische Zementierung von Lockersedimenten.Vergleiche mit rezenten, durch ähnliche Vertiefungen getrennte Strukturen im Persischen Golf und im Great-Barrier-Riffkomplex zeigen die relative Bedeutung des organogenen Gerüstes unter verschiedenen geologischen Bedingungen. Organogenes Gerüst, soweit beobachtet, ist nicht vorhanden oder doch unbedeutend im karbonischen (Pennsylvanian) Beispiel, örtlich vorhanden, aber unwichtig im Persischen Golf, dagegen wichtig als aufbauendes Strukturelement im Great-Barrier-Riff. Gemeinsam ist den drei Beispielen die ursprüngliche Kontrolle der hydrodynamischen Verhältnisse auf den Wachstumsbeginn und die allgemeine Form dieser Strukturen. Die Bedeutung des organogenen Gerüstes für die Gesamtstruktur ergibt sich aus der Analyse ihrer Lage in bezug auf nachgewiesene Wellenbewegung und der Verfestigung gleichaltrigen Vorriffschuttes, der von den Wellen an der Struktur gebildet wurde.

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Résumé Les larges «buildups» (presque «élévations»), en plate-forme, que l'on trouve dans le calcaire de Stanton, au sud-est du Kansas (E. U. A.), sont essentiellement composés de bourbe calcaire et d'algues calcaires phylloïde. Ils sont entourés de calcarenites coquillières composées surtout de débris d'échinodermes et d'algues. En bordure de ces «buildups» se trouvent de grands passages (1×30 km) bordés ou remplis de cette même calcarenite, ainsi qu'un bassin plus vaste contenant de la calcilutite coquiilière argilifère.L'usure du grain et le spath ciment observés dans les calcarenites environnantes, indiquent l'agitation de l'eau et suggèrent une résistance des « buildups » aux vagues pendant le développement. La résistance aux vagues a pu venir soit 1) des échinodermes pelmatozoaires, élastiques lorsqu'ils sont vivants et stabilisant les sédiments avec leurs racines, soit 2) d'une précoce cimentation en druse des sédiments libres pour en faire une masse cohérente.La comparaison avec les « buildups » modernes, séparés par des passages dans le Golfe Persique et dans le Récif de la Grande Barrière, fait ressortier la signification relative des structures organiques rigides dans ces divers sites géologiques. Les structures organiques rigides reconnues comprennent d'une part, celles qui sont absentes ou insignifiantes (dans le calcaire de Stanton), celles qui sont présentes localement mais insignifiantes (dans le Golfe Persique) et d'autre part celles qui sont apparemment importantes et maintiennent les «buildups» (dans le Récif de La Grande Barrière). Cependent ces trois exemples montrent des formes de contrôle hydrodynamique originel, exercées sur l'instauration et la forme générale des « buildups ». Si l'on veut déterminer la signification de ces structures organiques rigides à propos de la constitution d'ensemble d'un «buildup», il faudra examiner, et leur position relative à l'évidence de l'action des vagues, et la nature de leur constitution en pente d'éboulis, ceux-ci étant contemporains et produits par l'action des vagues sur le «buildup».

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, Stanton, , , — , . , 1 х 30 , , , . — Great Barrier. , , ; , , , Great Barrier. .

     

Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence

Improved regional and interregional stratigraphic correlations of Pennsylvanian strata permit comparisons of vegetational changes in Euramerican coal swamps. The coal-swamp vegetation is known directly from in situ coal-ball peat deposits from more than 65 coals in the United States and Europe. Interpretations of coal-swamp floras on the basis of coal-ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology. Objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation. Morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps.Changes in composition of Pennsylvanian coal-swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate. Paleobotany and paleogeography of the Euramerican province indicate a moist tropical paleoclimate. Rainfall, runoff and evapotranspiration were the variable climatic controls in the distribution of coal-swamp vegetation, peat accumulation and coal resources. In relative terms of climatic wetness the Pennsylvanian Period is divisible into five intervals, which include two relatively drier intervals that developed during the Lower-Middle and Middle-Upper Pennsylvanian transitions. The climate during Early Pennsylvanian time was moderately wet and the median in moisture availability. Early Middle Pennsylvanian was drier, probably seasonally dry-wet; late Middle Pennsylvanian was the wettest in the Midcontinent; early Late Pennsylvanian was the driest; and late Late Pennsylvanian was probably the wettest in the Dunkard Basin. The five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation. Regional differences in basinal geology and climate were significant variables, but the synchronous control of paleoclimate was of primary importance.     

Coals of the Brazil Formation (Pennsylvanian) in Indiana: observations of correlation inconsistencies and their implications

The coals of the upper part of the Mansfield, Brazil, and the lower part of the Staunton Formations (Atokan and Desmoinesian, Pennsylvanian) in Indiana (Illinois Basin) are characteristically thin and discontinuous. As a result, problems with correlation and identification of the seams have persisted for both researchers and industry. These discrepancies affect coal exploration, mine planning, and subsequently coal-fired utilities. This study presents exploration and operational examples demonstrating some of the correlation problems associated with the coals of the Brazil Formation, and the Upper Block and Lower Block, in particular, and the surrounding upper part of the Mansfield Formation and lower part of the Staunton Formations. Based on exploration boreholes, mine scale observations, and coal quality and petrographic data, this study suggests that (1) the coal mapped as the Upper Block Coal Member of Clay County may, in fact, be the same seam as the Lower Block Coal Member of Daviess County; and (2) the Lower Block coal of Clay County is not present south of the Switz City area of central Greene County, IN.     

Further evidence supporting high diversity of cyathealean tree ferns in the Early Cretaceous of Antarctica

Two new specimens of a cyathealean fern stems collected from the Lower Cretaceous (Aptian) Cerro Negro Formation, which crops out at the South Shetland Islands, Antarctica, are described in detail. The specimens are dictyostelic stems with U-shaped meristeles without sclerenchyma sheaths and petiole bases with numerous, small, vascular strands, and a mantle of adventitious roots. The anatomy of the stems show similarities with Cibotiaceae, but given they are not well preserved, some critical features that would allow a conclusive referral to this family are lacking. Preserved in the surrounding matrix, fragmentary pinnules were found, showing sori with bivalvate indusia, and sporangia with more than 20 spores, attached to an elongate receptacle. The features observed in these fertile remains suggest cyathealean affinities, but are difficult to refer to a particular family. These findings increase the diversity of cyathealean tree ferns in the Cerro Negro Formation, supporting previously suggested warm climatic conditions for this region of Antarctica during the Aptian.     

Two new species of Mesozoic tree ferns (Osmundaceae: Osmundacaulis) in Eurasia as evidence of long-term geographic isolation

The fossil trunks and rhizomes of Osmundaceae provide important information about its evolutionary history. Due to limited records of the Mesozoic trunks and rhizomes in the Eurasia of the Northern Hemisphere, our understanding on the fossil diversity of the Osmundaceae is hindered. Two new species of the Osmundaceae trunks, Osmundacaulis asiatica sp. nov. and Osmundacaulis sinica sp. nov. representing the first discovery of the Mesozoic tree fern genus Osmundacaulis in Eurasia, are described from Wudalianchi and Qiqihar, Heilongjiang Province, Northeast China, which enriches the plant diversity of the Osmundaceae in the Eurasia, and provides vital evidence for studying the distribution, radiation and evolution of the genus during the Cretaceous. The fossil records suggest that Osmundacaulis species may have evolved from a common ancestor, which first appeared in the Australian portion of Pangaea, and then spread to ancient northern North America and ancient East Asia. Since then, they developed into different species through their own evolutionary lines. The Chinese species have a special local feature that the outer cortex is thicker than the inner cortex, in contrast with reported Osmundacaulis species having thinner outer cortex and thicker inner cortex. Long-term geographic isolation may have led to the radiation of diverse Osmundacaulis species and the appearance of region-specific features, such as the thick outer cortex and the thin inner cortex of the Chinese species. Among all reported Osmundacaulis species, the two new species found in China, O. nerii from the Jurassic of Australia and the O. lemonii from the Jurassic of the USA, have special groups of mucilage-sacs inside sclerenchyma ring of petiole base. Mucilage sacs probably originated independently among taxonomic groups, representing convergent adaptations to similar habitats, rather than indicating genetic inheritance from a common ancestor.     

中国中生代木化石研究新进展:多样性变化及古气候波动

作为植物化石的重要组成部分,木化石不仅在探究地质历史时期植物群的组成特征和植物界演化方面发挥着重要作用,而且也是反映陆地生态系统古气候变化和古生态环境重建的重要证据之一。中国中生代木化石不仅数量丰富,而且类型多样,研究成果丰硕。近年来,在四川、重庆、云南、辽西和新疆等三叠纪—白垩纪化石产地和层位陆续发现了一批木化石新材料,进一步丰富了我们对中国中生代木化石的多样性的认识,并在利用木化石揭示三叠纪至白垩纪陆相古气候特征和变化方面取得积极进展。文中重点介绍在四川盆地晚三叠世、辽西侏罗纪燕辽生物群及早白垩世热河生物群中的木化石新发现并分析其古气候指示意义,揭示上述化石所反映的气候降温事件、古气候波动及其与带毛恐龙出现的关系等。通过对中生代木化石多样性演化、时空分布模式以及木材生长轮解剖特征的研究和分析揭示侏罗纪和白垩纪的古气候整体特征,并对中国中生代木化石研究领域存在的问题和未来的研究方向提出展望。     

Diagenetic mineralization in Pennsylvanian coals from Indiana, USA: C/C and O/O implications for cleat origin and coalbed methane generation

Cleats and fractures in southwestern Indiana coal seams are often filled with authigenic kaolinite and/or calcite. Carbon- and oxygen-stable isotope ratios of kaolinite, calcite, and coalbed CO₂ were evaluated in combination with measured values and published estimates of δ¹⁸O of coalbed paleowaters that had been present at the time of mineralization. δ¹⁸O_mineral and δ¹⁸O_water values jointly constrain the paleotemperature of mineralization. The isotopic evidence and the thermal and tectonic history of this part of the Illinois Basin led to the conclusion that maximum burial and heat-sterilization of coal seams approximately 272 Ma ago was followed by advective heat redistribution and concurrent precipitation of kaolinite in cleats at a burial depth of < 1600 m at  78 ± 5 °C. Post-Paleozoic uplift, the development of a second generation of cleats, and subsequent precipitation of calcite occurred at shallower burial depth between  500 to  1300 m at a lower temperature of 43 ± 6 °C. The available paleowater in coalbeds was likely ocean water and/or tropical meteoric water with a δ¹⁸O_water  − 1.25‰ versus VSMOW. Inoculation of coalbeds with methanogenic CO₂-reducing microbes occurred at an even later time, because modern microbially influenced ¹³C-enriched coalbed CO₂ (i.e., the isotopically fractionated residue of microbial CO₂ reduction) is out of isotopic equilibrium with ¹³C-depleted calcite in cleats.     

Amino acids in fossil corals: racemization (epimerization) reactions and their implications for diagenetic models and geochronological studies

Thirty-eight fossil coral samples of known age from late Pleistocene uplifted reef terraces have been analyzed for amino acid composition and for the degree of racemization of selected amino acids. Particular attention has been given to the epimerization (racemization about the α-carbon) of isoleucine. The $\text{D}\text{L}$ ratios observed in many of these samples do not conform to the concept of increasing racemization being associated with increasing fossil age. It is shown that sixteen of the samples demonstrate concordance between their known age and the age estimated from racemization data. Racemization ages are based upon a kinetic model derived from the kinetics observed in foraminifera in marine sediments and published estimates of the temperature dependence of the isoleucine epimerization reaction. Lack of concordance for the remaining samples is explained by either of two separate diagenetic phenomena: extensive leaching of free amino acids from the fossil, or contamination by ‘young’ amino acids. Ambiguities observed in many of the results may be due to the fact that coralline organic matter can have a complex history because of variations in its source and in its relation to the mineral phase. Neither of these factors has been observed to exert such a significant effect on racemization kinetics observed in fossil foraminifera or molluscs. Fossil corals are of only modest value as specimens for amino acid geochronological studies.     

Analysis of fossil testate amoebae in Selisoo Bog,Estonia: local variability and implications for palaeoecological reconstructions in peatlands

Niinemets, E., Pensa, M. & Charman, D. J. 2010: Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands. Boreas, 10.1111/j.1502‐3885.2010.00188.x. ISSN 0300‐9483. Local variability in decadal water‐table changes on an ombrotrophic peatland was explored using testate amoebae analysis of near‐surface peats in an Estonian raised bog. The distribution of testate amoebae assemblages was studied along the gradient from hummock to hollow in the upper 30‐cm layer of peat. As expected, testate amoebae assemblages in different micro‐ecotypes from hummock to hollow, even as close as 10 m apart, are distinctly different. Past water‐table change was reconstructed by applying a transfer function based on modern samples from throughout Europe. Results show a decline in water level from the mid‐late 20th century on Selisoo bog in all profiles from the different micro‐ecotypes. However, the absolute water‐table depths and amplitudes of fluctuations vary between reconstructions from different sampling micro‐ecotypes. Cores were correlated using changes in non‐mire pollen concentrations down‐core, but it was not possible to correlate minor changes in water‐table owing to non‐contiguous sampling and variable accumulation rates. We conclude that different microtopes show the same decadal trends in relative water‐table change but that the absolute magnitude of change may be more variable locally. It is important that reconstructed palaeohydrological changes in bogs consider changes in bog micro‐ecotypes, and their variation over time, as this may alter the sensitivity of an individual record to drivers such as climate change. Comparison and compilation of data from parallel cores from different micro‐ecotypes and/or different sites are likely to provide more robust reconstructions.     

中生代主要植物化石的古气候指示意义

中生代植物群以真蕨纲、苏铁纲、银杏纲、松柏纲为主,另有苔藓类、石松纲、楔叶纲及其他种子植物等。从化石的形态和结构、埋藏特点、分布及与现生类型的对比等方面,概要地分析了中生代植物群常见分子的古气候指示意义。其中,反映温暖潮湿气候或生境的主要有苔藓类,石松纲的Lycopodites和Selaginellites属等,楔叶纲,真蕨纲的单缝孢类、早白垩世的蚌壳蕨科、海金砂科的Ruffordia属、紫萁科及可能相关的小羽片大型的Cladophlebis,银杏纲银杏目的主要类型,松柏纲杉科的Athrotaxoites、Cunninghamia、Cephalotaxopsis、Sequoia等,紫杉科的Taxus、Torreya等,苏铁杉科Ferganiella、Podozamites、Swedenborgia等以及形态属Elatocladus;反映温凉气候的主要有松柏纲的松科和银杏纲的茨康目;适应热带、亚热带气候的包括真蕨类的海金沙科、合囊蕨科、马通蕨科、双扇蕨科、桫椤科、里白科以及中国蕨科的Onychiopsis等,苏铁目和本内苏铁目的主要类型;指示偏干旱型气候的主要有石松纲的Pleuromeia和Isoetites, 真蕨纲的Weichiselia, 本内苏铁目的Otozamites、Zamites、Ptilophyllum等,松柏纲掌鳞杉科的Pseudoflenelopsis、Flenelopsis、 Hirmeriella和可能属于掌鳞杉科的Brachyphyllum和Pagiophyllum,柏科的Cupressinocladus以及买麻藤目的Ephedrites等。     

Graptolites: fossil and living

Every student of palaeontology will stumble upon the term ‘graptolite’ at some point and will wonder what these strange little fossils mean. Thought to be long extinct, the few living graptolites and their extinct relatives have been united quite recently by palaeontologists through cladistic analysis. Not that the extant graptolites were overlooked, but the connection has never been made between the fossil graptolites and their modern descendants. We now have a much better scientific basis for our interpretation and understanding of these fossils and graptolites are recognized as part of a living clade of small and inconspicuous marine organisms, the Pterobranchia. They have been around since the Cambrian Period (c. 520–510 Ma) and, thus, they may represent one of the longest‐existing groups of organisms. Not that they should be termed ‘living fossils’, but their perseverance is remarkable in its own way and may lead to the question as to how they were able to achieve this success and survive for all these eons. May they be able to show us a key to survival in the future?     

A review of some fossil plant compressions associated with Mississippian and Pennsylvanian coal deposits in the central Appalachians, Illinois Basin, and elsewhere in the United States

Fossil plant compressions and impressions are abundantly associated with coals of Mississippian and Pennsylvanian age in the central Appalachians, Illinois Basin, and elsewhere in the United States. Remains of the aerial plant parts occur most commonly in shale directly overlying coal, especially in the vicinity of contemporaneous paleochannels. Most roots and a few stumps are found preserved in situ; however, most aerial plant fossils were transported prior to burial. There is good evidence that fossil plants preserved in roof shales are mostly the same types of plants from which the coal formed. Mississippian coal floras are lower in diversity than later ones. Quantitatively important plants include only 2 lycopod genera, 1 arthrophyte genus, 1 fern genus, and 5 seed fern genera. Pennsylvanian floras, on the other hand, include abundant representatives of 5 lycopod genera, 2 arthrophyte genera, 4 fern genera, 5 seed fern genera, and 1 coniferophytic genus. The swamp floras were never in equilibrium, though change appears to have been particulary rapid near the boundary between the Mississippian and the Pennsylvanian.     

Pennsylvanian coalified rhizomorphs in Illinois: evidence for non-compressive coalification to bituminous coal rank

Irregular and discontinuous coalified objects, here termed rhizomorphs, occur above the Summum (No. 4) Coal Member (Carbondale Formation) at one locality in La Salle County, Illinois. These vitrinite structures, varying between 3 mm and 4 cm in diameter, occur in a blocky to structureless mottled claystone characterized by numerous carbonaceous streaks and small-scale slickensides. The rhizomorphs twist and bend in a tightly coiled and kinked pattern, and may extend laterally through the claystone for 40 cm or more before bifurcating or terminating. The rhizomorphs display little or no evidence of compressive distortion. They are composed of two types of material: structureless bright conchoidal collinite; and cellular woody structure. One or more vascular bundles occur as discrete steles within a groundmass of collinite gel; these are generally aligned longitudinally within the coal except where steles diverge laterally as offshoots. The rhizomorphs are believed to be a diagenetic derivative of rooting structures; this is based on their occurrence in an underclay-like sediment and on their irregular, kinked form, which differs from that of most vertical supportive plant stems. Non-compressive coalification of the plant material may have occurred through: (1) aerobic alteration of cell walls to non-compressive inertinite; (2) centripetal contraction and selective degradation of plant tissue; and (3) impregnation of more resistant stelar elements by organic gel derived from degradation of thin-walled tissue.     

Chemometric study of functional groups in different layers of Trigonocarpus grandis ovules (Pennsylvanian seed fern, Canada)

We examined four dispersed, coalified ovules, Trigonocarpus grandis, of medullosalean seed-fern affinity from the Late Pennsylvanian age Sydney Coalfield, Canada, which represent the larger type of the 7–8 cm trigonocarpalean form species. At first glance it appears that the ovules are preserved like the usual Carboniferous foliar compressions, i.e. one coalified layer with one preserved anatomical tissue, the cuticle. However, careful sample preparation uncovered at least three coalified layers, and Schulze’s oxidative maceration process, which dissolves the coalified material, revealed several tissue layers. Altogether, eight sample forms were defined: (i) coalified layer, (ii) cuticle A, (iii) cupric + vitrain, (iv) vitrain, (v) cupric, (vi) cuticle B, (vii) alkaline solution and (viii) added coal seam material. The purpose of the study was twofold: first, to systematically analyze the forms by way of Fourier transform infrared (FTIR) spectrometry to fill a gap in chemical information that exits for coalified trigonocarpalean ovules of Carboniferous seed ferns; second, to use principal component analysis to focus on groupings as a function of chemical structure (functional groups) and to assess the different fossil forms in terms of FTIR chemical parameters, based on a 8 × 49 data matrix.Results include distinction among the three coaly sample forms, coalified layer (i), cupric + vitrain (iii) and cupric (v), based mainly, but not exclusively, on differences in carbonyl content, as well as length and branching of the polymethylenic chains. Important to note is the high aliphatic content of the cuticles as a signature of the biomacromolecules cutan/cutin. In particular, new insights into the structure of the original ovule are presented, and differences in chemistry are mainly a result of the complex structure of the precursor plant organ.