Capturing the Surface Texture and Shape of Pollen: A Comparison of Microscopy Techniques

Research on the comparative morphology of pollen grains depends crucially on the application of appropriate microscopy techniques. Information on the performance of microscopy techniques can be used to inform that choice. We compared the ability of several microscopy techniques to provide information on the shape and surface texture of three pollen types with differing morphologies. These techniques are: widefield, apotome, confocal and two-photon microscopy (reflected light techniques), and brightfield and differential interference contrast microscopy (DIC) (transmitted light techniques). We also provide a first view of pollen using super-resolution microscopy. The three pollen types used to contrast the performance of each technique are: Croton hirtus (Euphorbiaceae), Mabea occidentalis (Euphorbiaceae) and Agropyron repens (Poaceae). No single microscopy technique provided an adequate picture of both the shape and surface texture of any of the three pollen types investigated here. The wavelength of incident light, photon-collection ability of the optical technique, signal-to-noise ratio, and the thickness and light absorption characteristics of the exine profoundly affect the recovery of morphological information by a given optical microscopy technique. Reflected light techniques, particularly confocal and two-photon microscopy, best capture pollen shape but provide limited information on very fine surface texture. In contrast, transmitted light techniques, particularly differential interference contrast microscopy, can resolve very fine surface texture but provide limited information on shape. Texture comprising sculptural elements that are spaced near the diffraction limit of light (∼250 nm; NDL) presents an acute challenge to optical microscopy. Super-resolution structured illumination microscopy provides data on the NDL texture of A. repens that is more comparable to textural data from scanning electron microscopy than any other optical microscopy technique investigated here. Maximizing the recovery of morphological information from pollen grains should lead to more robust classifications, and an increase in the taxonomic precision with which ancient vegetation can be reconstructed

Mesozoic mass extinctions and angiosperm radiation: does the molecular clock tell something new?

Angiosperms evolved rapidly in the late Mesozoic. Data from the genetic-based approach called ’molecular clock’ permit an evaluation of the radiation of flowering plants through geological time and of the possible influences of Me -sozoic mass extinctions. A total of 261 divergence ages of angiosperm families are considered. The radiation of flowe -ring plants peaked in the Albian, early Campanian, and Maastrichtian. From the three late Mesozoic mass extinctions (Jurassic/Cretaceous, Cenomanian/Turonian, and Cretaceous/Palaeogene), only the Cretaceous/Palaeogene event coincided with a significant, abrupt, and long-term decline in angiosperm radiation. If their link will be further pro -ven, this means that global-scale environmental perturbation precluded from many innovations in the development of plants. This decline was, however, not unprecedented in the history of the angiosperms. The implication of data from the molecular clock for evolutionary reconstructions is limited, primarily because this approach deals with only extant lineages

Early Cretaceous angiosperm pollen from a low-latitude succession (Araripe Basin, NE Brazil)

The radiation of flowering plants during the Cretaceous represents a marked evolutionary turnover from gymnosperm- to angiosperm-dominated ecosystems within a time span of about 30 Ma. Despite the importance of this profound ecological transformation, many aspects regarding the timing, floral composition and spatial distribution of early angiosperms are poorly documented. Here, we present a record of early angiosperm pollen from the Brazilian Araripe Basin from the late Aptian to early Albian time interval. For this study, 17 samples from 5 sedimentary sections, spanning a total of not, vert, similar 150 m, have been investigated for their palynological content with particular attention on the occurrence of angiosperm pollen. Our results show a relatively high angiosperm pollen diversity of 70 different taxa, including numerous undescribed forms. Across the succession, angiosperm pollen accounts on average for 7% of the total palynoflora, with maximum abundances reaching 18%. Dominant taxa include monocolpate pollen of “magnoliid” or monocotyledon origin (e.g. Stellatopollis, Retimonocolpites, Pennipollis, Dichastopollenites, and Trisectoris) as well as pollen with eudicotyledon affinities (e.g. triaperturate forms like Rousea, Tricolpites, and Striatopollis). Judging from the existing evidence it appears that the diversity of the late Aptian–early Albian angiosperm palynoflora from the Araripe Basin has been underestimated. In addition, the composition of the total palynoflora shows congruent shifts in the abundance of hygrophilic ferns, Afropollis spp. and angiosperm pollen. The co-occurrence of moisture-loving ferns and early angiosperm pollen may support the hypothesis that early angiosperms evolved and diversified in moist and shady disturbed habitats near the palaeoequator

Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

The study of past greenhouse climate intervals in Earth history, such as the Mesozoic, is an important, relevant, and dynamic area of research for many sedimentary geologists, geochemists, palaeontologists and climate modellers. The Mesozoic sedimentary record provides key insights into the mechanics of how the Earth system works under warmer conditions, providing examples of natural climate change and perturbations to ocean chemistry, including anoxia, that are of societal relevance for understanding and contextualizing ongoing and future environmental problems. Furthermore, the deposition of widespread organic-carbon-rich sediments (“black shales”) during the Mesozoic means that this is an era of considerable economic interest. In July 2015, an international group of geoscientists attended a workshop in Ascona, Switzerland to discuss all aspects of the Mesozoic world and to celebrate the four-decade-long contributions to our understanding of this fascinating era in Earth history made by Hugh Jenkyns (University of Oxford) and Helmut Weissert (ETH Zurich). This volume of Sedimentology arose from that meeting and contains papers inspired by (and co-authored by!) Hugh and Helmi. Here a brief introduction to the volume is provided that reviews aspects of Hugh and Helmi's major achievements; contextualizes the papers of the Thematic Issue; and discusses some of the outstanding questions and areas for future research

State of the Science: Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

The study of past greenhouse climate intervals in Earth history, such as the Mesozoic, is an important, relevant, and dynamic area of research for many sedimentary geologists, geochemists, palaeontologists and climate modellers. The Mesozoic sedimentary record provides key insights into the mechanics of how the Earth system works under warmer conditions, providing examples of natural climate change and perturbations to ocean chemistry, including anoxia, that are of societal relevance for understanding and contextualizing ongoing and future environmental problems. Furthermore, the deposition of widespread organic-carbon-rich sediments (“black shales”) during the Mesozoic means that this is an era of considerable economic interest. In July 2015, an international group of geoscientists attended a workshop in Ascona, Switzerland to discuss all aspects of the Mesozoic world and to celebrate the four-decade-long contributions to our understanding of this fascinating era in Earth history made by Hugh Jenkyns (University of Oxford) and Helmut Weissert (ETH Zurich). This volume of Sedimentology arose from that meeting and contains papers inspired by (and co-authored by!) Hugh and Helmi. Here a brief introduction to the volume is provided that reviews aspects of Hugh and Helmi's major achievements; contextualizes the papers of the Thematic Issue; and discusses some of the outstanding questions and areas for future research

Absence of major vegetation and palaeoatmospheric pCO2 changes associated with oceanic anoxic event 1a (Early Aptian, SE France)

The deposition of organic-rich sediments during the late Early Aptian Oceanic Anoxic Event (OAE) 1a has been interpreted to result in a major decrease of palaeoatmospheric CO2 concentrations, accompanied by significant changes in the terrestrial flora. In order to test this hypothesis, the OAE 1a interval in the Vocontian Basin (SE France) has been studied with a combined approach including stable carbon isotopes, organic geochemistry and palynology. To estimate changes in palaeoatmospheric CO2 levels across the OAE 1a, the 13C composition of presumed algal biomarkers (low molecular weight n-alkanes, steranes) and of bulk carbonate carbon are used. Our results yield estimated Early Aptian carbon dioxide partial pressure (pCO2) values three to four times the preindustrial level and only a moderate drop across the black shale event. This moderate drop in pCO2 is supported by palynological results. The frequency patterns of climate-sensitive sporomorphs (incl. pteridophyte spores, bisaccate pollen and Classopollis spp.) display only minor fluctuations throughout the studied section and indicate relatively stable patterns of terrestrial vegetation during and after formation of the OAE 1a black shale. The occurrence of a characteristic Early Aptian carbon isotope pattern across the OAE 1a interval permits accurate chemostratigraphic correlation with the well-studied Livello Selli interval of the Cismon record (N Italy). The contemporaneous formation of individual black shale layers at both sites indicates that transient episodes of dysoxic–anoxic bottom waters prevailed over large areas in the W Tethys Ocean independent of depositional setting. Comparison of the palynological data from the two locations displays significant differences in the frequency patterns of bisaccate pollen. The contrasting pollen spectra are interpreted to reflect prominent changes in the palaeoceanographic current patterns and/or selective sorting due to sea-level rise rather than latitudinal shifts of the major floral belts