The Tertiary and Quaternary vegetation history of Ireland
Ireland’s diverse and rugged scenery is the product of both long-term landscape evolution and repeated and very extensive glaciation during the last 2.6Myr (Quaternary). Despite complete and highly erosive ice cover (e.g. during the LGM) biogenic deposits have survived (Coxon and McCarron 2009). This talk will outline the biostratigraphic evidence that allows us to gain an insight into both Neogene and Pleistocene landscape evolution and into Ireland’s vegetation history.
The search for Ireland’s Palaeogene and Neogene (e.g. Mitchell 1980) has led to the discovery of a number of remarkable sites many of which are located on Carboniferous limestone. Some of these deposits provide irrefutable evidence of Tertiary surfaces, e.g. the gorge and cave infills at Pollnahallia in County Galway and the associated (immediately) subsurface Pliocene lignites whilst others, especially landforms and cave sediments, remain enigmatic. Furthermore the identification of a Neogene surface overlying weathered granite in Connemara (Coxon 2001; Coxon and McCarron 2009) opened up the possibility of finding further datable palaeosurfaces on rocks other than limestone in Ireland.
The majority of Irish Pleistocene temperate stage deposits are believed to be related to one stratotype sequence (the Gortian). The latter are characterised by a Holsteinian (MIS 11) style vegetation succession but attempts at dating suggest the deposits may be younger and may indicate the repetition of Holsteinian style vegetation succession in more than one interglacial.
This talk will examine the nature of Irish Pleistocene biogenic deposits, their gemorphological setting and accommodation space and their floristic assemblages. A possible complete sequence of last interglacial (MIS 5e) age at Knocknacran will also be presented along with organic sediments believed to date to MIS 5 that lie on a raised rock platform around Ireland’s coast.
Coxon, P. 2001. Understanding Irish landscape evolution: Pollen assemblages from Neogene and Pleistocene palaeosurfaces in western Ireland. Proceedings of the Royal Irish Academy, 101B (1–2), 85–97
Coxon, P. and McCarron, S.G. 2009. Cenozoic: Tertiary and Quaternary (until 11,700 years before 2000) in, editor(s) Charles H. Holland & Ian S. Sanders, The Geology of Ireland (2nd Edition), Edinburgh, Dunedin Academic Press, 2009, pp355 – 396.
Coxon, P., McCarron,S. and Mitchell, F. (eds) 2017. Advances in Irish Quaternary Studies. Atlantis Press. Paris. 316pp. DOI 10.2991/978-94-6239-219-9
Mitchell, G.F. 1980 The search for Tertiary Ireland. Journal of Earth Sciences Royal Dublin Society, 3, 13–33.
Professor Peter Coxon
Department of Geography, Trinity College Dublin, Dublin, Ireland
Palynology from the perspective of a pollination biologist
Pollination is the process of release, transfer and deposition of the male microgametophyte, the pollen, from anther to stigma in seed plants. This process has influenced the evolution of pollen grains – their structure, chemical composition, how they are stored and released, temporal and spatial patterns of dispersal, and longevity. The study of pollen contributes to several scientific disciplines including biostratigraphy, taxonomy, melissopalynology, archaeological palynology and even forensics, linking the accused to a victim and a place, and methods can be shared across disciplines. For pollination biologists, the study of pollen can help us to understand plant evolution, breeding systems and gene flow, as well as pollinator behaviour, foraging, diet and response to landscape. The quantity and quality of pollen production can influence both the reproductive success of plants, and, as the primary source of protein for many pollinating insects, the fitness of these animals. In this talk, I will use examples from my own work on bee health, invasive plants, and crop pollination, to illustrate how palynology contributes to contemporary pollination biology.
Professor Jane Stout
Botany Department, Trinity College Dublin, Ireland
The evolution of grasses and grasslands
Poaceae (grasses) is arguably among the most important plant families on Earth today, dominating vegetation in several ecosystems together estimated to cover nearly half of the terrestrial surface. These ecosystem, which include savannas, woodlands, and grasslands are of immense importance both ecologically and economically; they influence global climate and biogeochemical cycles, and provide habitat and food for billions of animals, including humans. Yet, grasses are thought to have evolved only in the Late Cretaceous, and to have remained relatively rare until the mid-late Cenozoic. Investigation into the evolutionary history of grasses and grass-dominated habitats was long inhibited by the scarce and often ambiguous fossil record of grass macrofossils and pollen, forcing paleontologists to rely on indirect evidence, in particular the occurrence of fossil mammals reminiscent of modern grassland dwellers. In recent years, plant silica (phytoliths) has emerged as an alternative means of tracking grass-and grassland evolution. Unlike pollen and most macrofossils, grass phytoliths are diagnostic of ecologically distinct grass subclades; in addition, phytoliths occur in facies that do not typically preserve plant fossils, such as those reflecting well-oxidized floodplain environments.
Combined with other paleontological and geochemical evidence, phytolith data collected on several continents (e.g., North and South America, Asia, Africa) have started to uncover the Cretaceous taxonomic radiation and early ecology of the grass clade, and the complex assembly of the grassland biome during the Cenozoic. Existing data indicate that crown-group grasses had undergone diversification by the end of the Cretaceous and were present on several Gondwanan continents; in addition, they may have formed a substantial part of some plant communities in India. Open-habitat grasses started diversifying at least by the late Eocene, long before their rise to dominance in the Oligocene or Miocene, with the exact timing varying among continents and regions. Similarly, C4 grasses diversified well before their late Miocene-Pliocene ecological expansion at low-mid latitudes. The decoupling between taxonomic radiation and increase in abundance points to different causal factors for these events. Comparison between faunal and plant silica-based floral data also shows that presumed grazers did not evolve in tight coevolution with grasslands. Thus, in North America and Eurasia, grass-dominated vegetation preceded grazer types by several million years; in South America grazer-like morphology originated independently of grasslands, in non-analog palm shrublands. These results suggest that region-by-region studies integrating multiple lines of evidence are required to test what factors contributed to the unrivaled success of the grass clade.
Professor Caroline Stromberg
University of Washington, Seattle, USA.