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Paleoenvironmental and paleoclimatic conditions at Thale during the late Ladinian (Middle Triassic) are assessed using both the plant megaflora and palynoflora. These two datasets are necessary because these two different types of assemblages were subjected to different taphonomic biases and together provide a more complete appraisal of Triassic conditions in the study area. The megafossil remains represent a (par)autochthonous flora with large, well-preserved leaf and shoot fragments that indicate relatively limited transport. Most fragments probably belonged to plants growing on river banks. The composition of the rich and diversified megaflora indicates lush vegetation typical of an environment without water stress and probably a high water table. On the other hand, quantitative analyses of the palynological data using different methods (morphogroups and Sporomorph EcoGroup or SEG) show a strong dominance of bisaccate pollen. River or wetland plants are well represented by trilete, laevigate spores and multicellular algae. Since the spores were normally water transported along with the sediment and the pollen grains were wind transported over long distances, but also by water, there are two possible interpretations: (1) the local flora was dominated by ferns within a larger, conifer-dominated, and possibly forested area; (2) time related, the megaflora shows a short-term signal that corresponds to a humid spell during the generally more arid period of Middle and Late Triassic, while the palynoflora shows a longer-term, regional signal.
A remarkable fossil plant assemblage from the lowermost Oligocene Haselbach horizon (Gröbers Member, Böhlen Formation) was excavated at the Vereinigtes Schleenhain opencast mine (northwestern Saxony, Germany) and is described herein. The lower unit of the Haselbach horizon represents abandoned channel deposits that contain masses of Zingiberoideophyllum liblarense leaves. Species identification of the leaves is based on morphological characters and micromorphological features of the cuticle. Other plant organs of the previously described whole plant Spirematospermum wetzleri-Zingiberoideophyllum liblarense, such as fruits, seeds, rhizomes, and rootlets, were also observed on associated bedding planes, which supports this whole-plant reconstruction. The other megafossil remains in this taphocoenosis, mostly leaves, are identified taxonomically and interpreted as being derived from a mixed softwood and hardwood riparian forest of Acer haselbachense, Apocynophyllum neriifolium, Carpinus grandis, Engelhardia orsbergensis, Populus germanica, Rosa lignitum, Taxodium dubium, and from a Nyssa-Taxodium swamp. Based on the plant taphonomy and the paleoecology of the plants, this plant assemblage was likely deposited in still water and therefore mainly parautochthonous. Vertical changes in the composition of the plant assemblage, in particular the disappearance of the Zingiberoideophyllum liblarence leaves, are attributed to changes in habitat, such as alterations in the soil substrate and/or rising water levels. Taphonomic and paleophytosociological aspects of the assemblage confirm the previously published autecological reconstruction of the Spirematospermum wetzleri-Zingiberoideophyllum liblarense whole plant as an aquatic subshrub growing in shallow standing water, most likely in monotypic dense stands or in association with the Apocynophyllum neriifolium-Microdiptera whole plant. Nomenclatural and taxonomic problems of the family assignment of Zingiberoideophyllum liblarense are discussed briefly. The presence of transverse veins, also called cross veins, suggests an assignment to Zingiberaceae and excludes it from Musaceae.
Quantitative taphonomic analyses of recent fruit and seed assemblages (carpological assemblages or carpodeposits) are essential to allow for more accurate interpretation of fossil carpodeposits. To this end, extensive taphonomic analyses were undertaken in two modern, small, fluvial catchment basins (Ca' Viettone and Valtorta-Rivara) in northwestern Italy that are characterized by different vegetation types. Quantitative data from vegetational surveys and carpodeposit analyses were compared using a standardized graphic representation (Plant Community Scenario, PCS). The contents of the carpodeposits clearly differentiate the different types of vegetation in each basin. Moreover, carpological assemblages from the same basin have a similar signature. Comparison of all samples indicates a relationship between the standing vegetation and the PCS reconstruction based on carpological analysis. The bedload carpodeposits studied seem to characterize, at least qualitatively, the vegetation of the entire basin rather than just the area adjacent to the sample site. When differences in taxonomic frequency in the standing vegetation and in the carpological assemblages are evaluated, patterns in the over- and underrepresentation of certain types of fruits and seeds become apparent. Such patterns are quantified by a bias index for diaspores of each taxon, derived from empirical observations and applicable to bedload carpodeposits. Factors biasing representation in an assemblage include disseminule size and woodiness. In addition, the mode of dispersal seems to be very important: anemochorous (wind dispersed), endozoochorous (animal dispersal via excrement), and myrmecochorous (ant dispersed) diaspores are clearly overrepresented.
Palynomorph concentrations for water-column and sediment-water interface samples are presented for two coastal deltaic systems influenced by the range of tidal regimes to assess whether any taphonomic bias exists in pollen assemblages. The localities are the microtidally influenced Mobile-Tensaw River Delta, Alabama, United States, and the meso- to macrotidally influenced Rajang River Delta, Sarawak, East Malaysia. Mobile-Tensaw Delta data represent collections over a 13-month period; Rajang River Delta data represent sampling during the 1992 dry season. Results are reported for: (1) pollen concentration in suspended sediment loads and bottom sediments of distributary channels, and (2) selected spore-and-pollen frequencies in channels influenced by meso- and macrotidal processes. An increase in pollen concentration/liter occurs in all delta distributaries at water-column depth, and a positive relationship exists between pollen concentration and suspension load. Concentrations at the sediment-water interface are highest in tidally influenced areas where Heterogenous Aggregate Organic Matter (OM) clasts (floccules) dominate palynofacies assemblages, and statistically significant for Mobile-Tensaw lower delta plain sites. Hence, microtidal influence at the interface between fresh and brackish waters affects palynomorph concentration in bottom sediment and may be a function of flocculation induced by salinity flux. In contrast, concentrations are highest in bottom sediments of Rajang River distributaries where little active sediment transport occurs and tidal range is highest, and is due to several factors including a high proportion of Heterogenous Aggregate OM clasts. Additionally, the magnitude of tidal displacement impacts palynomorph distribution in the Rajang Delta, with mangrove pollen found in alluvial plain samples, a distance of ∼120 km from distributary mouth bars. Understanding the sedimentological conditions under which coastal deltaic pollen assemblages are preserved is critical before these can be used for paleoecological reconstruction.
A recently excavated locality in the Chemnitz Petrified Forest, lower Permian in age and occurring within the Leukersdorf Formation of the Chemnitz Basin, Germany, provides evidence for an outstanding fossil assemblage buried in situ by pyroclastics. The environment is interpreted as forested lowland that sheltered a dense hygrophilous vegetation of ferns, sphenophytes, and gymnosperms, as well as a diverse fauna of reptiles, amphibians, arthropods, and gastropods. A detailed measured section of the outcrop documents the early volcanic history of the Chemnitz fossil forest, including a paleosol that shows the root systems of Psaronius tree ferns, Arthropitys calamitaleans, and Medullosa and Cordaixylon gymnosperms in the same horizon. Fifty-three trunks are still standing upright and rooted at their place of growth, providing evidence that the top of the paleosol was the land surface on which the forest grew, thereby offering insights into the original plant community structure and density. Taphonomic analysis of both the petrified and adpression-fossil assemblages enable us to reconstruct the direction, estimate the violence and extent of the volcanic events, and their effects on the entire ecosystem. A complete dataset of three-dimensional coordinates resulting from three and one-half years of continuing excavation and study permits the recognition of organ connections and results in the first reconstructions of the excavation site, the floral elements, and the plant community as a whole.
It is commonly assumed that reactions in the silicification of land plants take place at low to moderate diagenetic temperatures when the solvent for the silica (H2O) is in the liquid stability field. The early Permian forest of Chemnitz, buried by rhyolitic pyroclastic deposits ca. 290 Ma, may be an example of silicification at elevated temperatures above 100 °C by siliceous H2O vapor. Many independent observations support this theory: the presence of low-density (gaseous) inclusions in primary α-quartz, the impregnation and partial replacement of silica phases in the wood by fluorspar, the preservation of relict organic material in the form of the high-temperature mineral anthracite, and the close proximity of the fossil forest to an eruptive center, the Zeisigwald Caldera. We have designed an experimental apparatus that allows silicification to be simulated by silica-bearing H2O vapor. Water was reacted with rhyolitic obsidian at 150 °C for several days to take up silica, then passed through the parenchymatous stem tissue of Dicksonia antarctica in the form of a hot, silica-bearing steam. The reactions taking place in the organic tissue are documented. Amorphous silica gel was found deposited in vapor-treated cells, suggesting that steam can be efficient in transporting aqueous silica species and depositing them into stem tissue. These experiments cannot duplicate every detail found in the natural examples in Chemnitz, but they do underline how important it is to derive the temperature conditions at which the natural silicification reactions took place.