Review of Palaeobotany and Palynology最新文献

The Holocene evolution of vegetation and environment in the Kleine Nete valley in the coversand region of northeastern Belgium is studied through sedimentological, palynological and macrobotanical analysis of a radiocarbon dated peat sequence. Peat formation started at the beginning of the Holocene in mesotrophic fen conditions. After a period of fast peat growth, the accumulation slowed down and the peat surface became dry in the Middle Holocene.

The palynological results are compared with other pollen data from the region, in order to establish a regional pollen biozonation for the Early and Middle Holocene in the Nete Basin. This shows that pine has long been a characteristic element in the Nete Basin. Pine forest expanded immediately after the 11.4 cold event, which is earlier than in the western Scheldt Basin. Pine and birch grew along the valley, possibly also within the peatland. Peaks of microcharcoal, herbs and/or coarse sediment in the peat reflect temporary local forest disturbances in the Early Holocene. Some may reflect small-scale controlled fires induced by hunter-gatherers, although a natural cause seems much more plausible given the dominance of fire-associated pines and increased drought. Pine remained important throughout the Early Holocene. This long-lasting predominance of pine in the Nete Basin, compared to elsewhere in the Scheldt Basin, is likely related to the poor sandy subsoil in the region, which hinders more nutrient-demanding broadleaf trees to overtake.

Palynological investigations were carried out on Upper Cretaceous sediments from the three onshore sections, Tah, Amma Fatma and Oum Dbaa of the Tarfaya-Laayoune-Boujdour-Dakhla Basin, southwestern Morocco. 64 samples were collected for this palynological study, which yielded a very rich, diverse and well-preserved palynological content, including sporomorphs, prasinophytes, acritarchs, foraminiferal test linings and colonial fresh-water algae, dominated by dinoflagellate cysts comprising 141 species. The dinoflagellate cyst stratigraphic marker events used for the biostratigraphic interpretations include the first and last occurrences of stratigraphic marker species. The dinoflagellate cyst biostratigraphy allowed to assign the Amma Fatma section to the lower Turonian and the Tah section to the upper Campanian. The Oum Dbaa section is revised in detail and re-assigned to the upper Campanian–lowermost Maastrichtian. Analyses of the relative abundances of marine palynomorphs (mainly dinoflagellate cysts), as well as those of the palynofacies (amorphous organic matter, phytoclasts and palynomorphs) indicate two depositional settings alternating between a proximal inner shelf under suboxic-anoxic conditions and an outer neritic environment under dysoxic-anoxic conditions.

Echinochara is a poorly known charophyte genus of the extinct family Clavatoraceae that thrived in the Middle Jurassic–Early Cretaceous of North America, Europe, and North Africa. It represents the most ancient and plesiomorphic genus of this family. However, the fossil record of Echinochara is discontinuous, showing several gaps, one of them especially significant in evolutionary terms between the Kimmeridgian and the early Barremian. The new species Echinochara pontis sp. nov., described here from the late Berriasian of the Maestrat Basin (NE Spain), bridges, in part, this gap, shedding light on the evolution of the genus during the earliest Cretaceous. The fructification (utricle) has bilateral symmetry, formed by two superimposed series of bract cells that abaxially cover the gyrogonite. The inner series has three long cells that are born by a short basal cell and reach the oospore apex. The outer series shows a central fan of bract cells, composed of a small basal cell, triangular in shape, that bears three long cells growing upwards, which are in turn flanked by two long bract cells on each side. The central basal cell and these two lateral cells are directly attached to the base of the utricle. The thallus is corticated with cells twisting at an angle of 30°. The utricle of Echinochara pontis displays a combination of features present in Echinochara peckii (Bathonian?–Kimmeridgian) and Echinochara lazarii (Barremian–early Aptian). For instance, the bilateral symmetry of the utricle and the morphology of the inner bract-cell series allow comparison with E. lazarii, whilst the morphology of the outer bract-cell series is closer to E. peckii. Moreover, the thallus of the new species shows cortical cells with a twisting angle intermediate between that of Echinochara peckii (40°–45°) and Echinochara lazarii (not twisted). The unique combination of morphological characters in the utricle of Echinochara pontis fits well with its intermediate chronostratigraphic position between the two former species. Echinochara pontis formed monospecific meadows in brackish settings. A preference for brackish settings is also observed for Echinochara peckii and in the older populations of Echinochara lazarii, suggesting that this habitat is probably a basal character in the evolution of the genus Echinochara.

The Eocene–Oligocene Transition (EOT) marks the onset of a major phase of global cooling with significant consequences to the vegetation worldwide. Here, we present palynological analyses from a site in southern São Paulo basin, southeastern Brazil (23.67°S; 46.58°W). An Oligocene age was constrained by the abundance of Dacrydiumites florinii and Podocarpidites spp., alongside the presence of taxa such as Cicatrocosisporites dorogensis and Polypodiisporites usmensis. Autochthonous elements including Paleoazolla, Corsinipollenites spp., Monoporopollenites annulatus, and Zygnemataceae algae spores are indicative of a low-energy freshwater depositional environment. In addition, we performed a comparison of Eocene and Oligocene temperature and precipitation estimates from records in southeastern Brazil using the weighted Mutual Climate Range approach. Results support global trends with a cooling of ca. 3–4 °C from the Eocene to the Oligocene accompanied by slightly drier regional conditions. Oligocene environmental changes drove a vegetation turnover by local extinction of warm-tropical taxa or a significant retreat of species unable to stand comparatively colder and drier climates under lower CO_2atm concentrations. Our data are consistent with previous estimates and verify the impact of global cooling on the vegetation of mid-low latitudes of the Southern Hemisphere.

The present study reports and describes a new foliicolous fossil-species of Asterina Lév. (Asterinaceae: Asterinales: Dothideomycetes) namely, A. siwalika sp. nov., on a compressed leaf assigned to modern Calophyllum L. (Calophyllaceae) recovered from the Siwalik sediments (early Miocene to Pliocene: Chunabati Formation) of Darjeeling, Eastern Himalaya. This epifoliar Siwalik fungal species is characterized by a dark brown, sub-dense mycelial mat; septate, branched, superficial, oppositely arranged hyphae with one to two-celled, alternate to oppositely arranged appressoria; flattened, circular, non-ostiolate thyriothecia, scutellum with radially arranged isodiametric to cylindrical cells; and bi-celled, one-septate, conglobate to ellipsoidal, striated ascospores. Here, we reconstruct for the first time a possible sexual life cycle of A. siwalika. The in-situ occurrence of Asterina on Calophyllum leaf cuticles suggests a warm and humid tropical climate and a possible host-parasitic relationship that might have existed in the ancient forest of the Darjeeling sub-Himalaya region during the time of deposition. The conclusion is supported by published qualitative and quantitative climatic data using plant megafossils recovered from the same fossil locality.

The Late Oligocene is the time of the flourishing of typical warm temperate Turgay vegetation in Kazakhstan and adjacent areas. The Aschudasty flora described here originates from the Oshagandy Formation which correlates with the early part of the Chattian. The palaeobotanical analysis reveals 38 plant taxa, identified by macro- and microfloral remains related to Lycopodiophyta (1), Pteridophyta (3), Gymnospermae (7), Gnetophyta (1), Magnoliophyta (25) and plantae incerta sedis (1). Macrofossils include mainly Cupressaceae (Metasequoia, Taxodium and Glyptostrobus), Betulaceae (Alnus, Corylus) and Ulmus, as well as large number of monocots and aquatic ferns. The palynospectrum is dominated by pollen of the genus Picea (about 30%) and Alnus (about 40%), with noticeable amounts of pollen from other birch genera (about 7% in total). Plant functional type (PFT) and Coexistence Approach were used for palaeoenviromental reconstructions. Vegetation reconstruction shown that the microflora has a very temperate aspect reflecting a mixed deciduous conifer forest with a diverse, mainly deciduous shrub layer. The macroflora also reflects deciduous forest vegetation with conifers and possibly a very minor evergreen component. The climatic analysis shows a seasonal temperate climate. The pollen data reflect the zonal regional vegetation, the macroflora most probably reflects the lakeside wetland vegetation which may have experienced a warmer microclimate, compared to the upland realm. In whole significant climatic changes was not documented since Early Oligocene Rupelian time.

Confocal scanning laser microscopy (CSLM) is becoming a powerful tool for palynological studies. CSLM allows palynomorph image sectioning, internal and surface structures visualization, and 3D reconstruction at a higher resolution than standard light microscopy without extra processing. CSLM images are suitable for several image analysis techniques that could help improve the accuracy and reproducibility of taxa identification. Here, using the palm subtribe Mauritiinae (Arecaceae: Calamoideae: Lepidocaryeae) as a model group, we identify modern and fossil pollen grains using CSLM images coupled with ImageJ/Fiji 1.54f plugins and machine learning statistical analyses. Modern taxa pollen grains including Lepidocaryum tenue Mart., Mauritia flexuosa L.f., Mauritiella armata (Mart.) Burret and Mauritiella aculeata (Kunth) Burret were obtained from Smithsonian Tropical Research Institute (STRI) pollen collection or herbarium exsiccates. Fossil pollen of Grimsdalea magnaclavata Germeraad et al. 1968, and Mauritiidites franciscoi (van der Hammen) van der Hammen & Garcia de Mutis 1966, both from Miocene, and Mauritia pollen type from Holocene were obtained from STRI collection. We measured nine shape and exine quantitative parameters, and one qualitative parameter (pollen aperture). Pollen volume was the most important variable (28.270 mean decrease accuracy), followed by pollen aperture (15.003), Skewness (13.466), and spine density (10.246). The machine learning analysis, which included CART and Random Forests, correctly identified both fossil and extant grains. CSLM and the quantitative analysis of morphological traits are a new frontier in palynological studies.

Fossil spores provide important insights into the evolutionary history of ferns, including their morphological changes and adaptations over time. The morphology and ultrastructure of trilete spores with cicatricose sculpture composed of sets of parallel or near-parallel ribs (muri) have been studied. Observations on the spores were performed using light microscopy, scanning electron microscopy, and transmission electron microscopy. The cicatricose spores were extracted from a single sporangium-bearing structure collected from Casal do Borracho mesofossil flora near Torres Vedras (Lusitanian Basin, western Portugal) from sediments belonging to the Almargem Formation, considered to be of late Barremian or early Aptian age (and possible younger than that). The sporangium-bearing structure of a schizaealean fern and in situ cicatricose spores are compared with the family Anemiaceae. On the basis of spore size and shape, laesura length, with about 20 proximal narrow ribs, oriented perpendicular to the spore sides, and three sets of distal ribs forming V-shaped patterns, the cicatricose spores in the present study are clearly assigned to the fossil-taxon Cicatricosisporites venustus. The spore ultrastructure includes a homogeneous exospore of a blechnoid type with a slight difference in the thickness in the proximal, distal, and equatorial regions. The morphology and ultrastructure of the studied spores are corresponded to Anemia type.

Bauhinia s.l. widely distributed across tropical and subtropical regions and has a complex taxonomic history and divided into two main clades: the Bauhinia clade and the Phanera clade. The fossil records of Bauhinia s.l. are predominantly found in Asia, but they were reported worldwide. In this study, we describe two leaf fossil taxa of Bauhinia s.l. and one legume fossil taxon from western Yunnan, China. The results of the morphological and phylogenetic analysis indicate that the newly identified species Bauhinia tengchongensis sp. nov. is a part of the Phanera clade. The phylogenetic analysis suggests that the divergence between the two clades likely occurred before the late Oligocene. The fossil distribution and phylogenetic data suggest that South China may have been an early diversity centers for Bauhinia s.l. Given the distribution of extant Bauhinia s.l. members and the warmer climate during the Late Pliocene in Tengchong, we propose that the cooling period following the Pliocene in western Yunnan may have driven the migration of some thermophilic Bauhinia s.l. species towards Eastern and Southern China.

Pinus L. is a genus of coniferous trees, belonging to the class Pinopsida and the family Pinaceae of the division Gymnosperms (naked-seeded plants). Being anemophilous (wind pollinated), Pinus produces huge quantities of pollen grains, which often completely overwhelm the other pollen taxa in the palynological assemblages. This, coupled with its efficient transport by wind (due to its excellent buoyancy) and good preservation potential in the sediments, makes it abundant in the pollen assemblages. This over-representation of Pinus pollen creates an ambiguity in both the modern and fossil pollen records. Moreover, the over-representation of Pinus pollen often hampers in the understanding of modern pollen–vegetation relationship, as well as in the interpretation of fossil pollen records, for the reconstruction of past vegetation dynamics and contemporary climate (change). In the present article, the bountiful abundance of Pinus pollen in the palynological assemblages is assessed, and the implications of its over-representation in reconstructing the fossil pollen records and interpreting the past climatic changes are reviewed from the Indian Himalayas.