How to cite:O'Connell, M., Molloy, K., and Jennings, E.: Long-term human impact and environmental change in mid-western Ireland, with particular reference to Céide Fields -an overview, E&G Quaternary Sci. J., 69, 1-32, https://doi.org/10.5194/egqsj-69-1-2020, 2020. Abstract:This paper presents new palaeoecological data from north County Mayo (Co. Mayo), western Ireland, and reviews published data with a view to achieving a better understanding of the timing and nature of early farming in the region, its impact on the natural environment, and the factors, including climate change, that influenced mid-and late-Holocene vegetation dynamics and farming in the region. A long pollen profile from Glenulra, a deep basin situated within Céide Fields, and short profiles from blanket peat that overlies the prehistoric stone-wall field system provide unambiguous evidence for substantial farming, including widespread woodland clearance, in the early British and Irish Neolithic (beginning ca. 3800 BCE). This was followed by a distinct lull that lasted several centuries until farming activity resumed again, at first modestly (at ca. 2700 BCE) and then more markedly from 2350 BCE, i.e. at the Neolithic-Chalcolithic transition. It is argued on the basis of this and other palaeoecological evidence, including pollen analytical investigations at nearby Garrynagran, that, contrary to recent suggestions, there is no reason to doubt the widely held view that the stone-wall field system -unique in a western European Neolithic context -is correctly ascribable to the earlier part of the British and Irish Neolithic. The history of pine growing in bog contexts (mainly blanket bog) in the region is considered in the light of 14 C dates derived from pine timbers, and the results of dendrochronological investigations at Garrynagran that have enabled two floating pine chronologies to be constructed, are presented. The climatic implications of these data are discussed within local and wider regional contexts. Kurzfassung: Diese Studie präsentiert neue paläoökologische Daten aus dem nördlichen Co. Mayo (Grafschaft Mayo), Westirland, und überprüft bereits veröffentlichte Daten in Hinblick auf ein besseres Verständnis der Zeitstellung und des Typus früher Landwirtschaft in der Region, deren Auswirkungen auf die natürliche Umwelt, und auf Faktoren, einschließlich des Klimawandels, die die mittelbis spätholozäne Vegetationsdynamik und Landwirtschaft der Region beeinflusst haben. Ein langes Pollenprofil aus Glenulra, einem tiefen Becken im Bereich der Céide Fields, und kurze Profile aus Torfen, die das prähistorische System aus Steinmauern flächenhaft überlagern, liefern eindeutige Published by Copernicus Publications on behalf of the Deutsche Quartärvereinigung (DEUQUA) e.V. 2 M. O'Connell et al.: Holocene environmental change in western Ireland Beweise für umfangreiche Landwirtschaft, einschließlich ausgedehnter Rodung von Waldgebieten, im frühen Britischen und Irischen Neolithikum (beginnend ca. 3800 BC). Daran schloss eine ausgeprägte Flaute der l...

The Thunder Bay Amethyst Mine exploits a vein system in which the main zoned sequence consists of chalcedony, colorless quartz, and three to four stages of amethyst. The main sequence surrounds fragments of a brecciated earlier sequence containing chalcedony, colorless quartz, and prasiolite, which appears to be thermally bleached amethyst. The vein system occupies a fault in Archean granodiorite and is associated with a narrow zone of chloritic and hematite alteration overprinted by weak argillic alteration. Fragments of Proterozoic (1339 Ma) Sibley Group rocks occur in the vein system, indicating the former presence of a shallow cover during deposition of quartz and limiting the maximum age of the deposit. These downfallen fragments and the abundance of vugs indicate near-surface formation of the deposit.Main-stage fluid-inclusion homogenization temperatures are in the range from 91.2 to 40.9 °C (mean 68.4 °C) in amethyst, whereas in colorless quartz homogenization temperatures range from 146.5 to 114.7 °C (mean 132.1 °C). Eutectic temperatures fall in three ranges with means of −50.9, −48.7, and −43.9 °C, which are related to paragenetic position and indicate an NaCl–CaCl2–H2O system, with possible additional components in later inclusions. Salinities in amethyst-hosted inclusions decrease in the growth direction from 22.9 to 15.3 equiv.wt% NaCl.Trace sulfide and other mineral inclusions indicate a trend of decreasing Eh and pH from an initially rather oxidized (sulfate stable) to a reduced (sulfide stable) condition during deposition. Sulfur isotopic composition in pyrite and chalcopyrite ranges from δ34S = −0.4 to −1.4‰ and is similar to values obtained from lead–zinc–barite in other vein deposits surrounding the Sibley depositional basin. Oxygen isotopes in quartz range from δ18O = +12.7 to +17.1‰, corresponding to δ18O(H2O) = −2.1 to −12.8‰ using fluid-inclusion temperatures. Fresh quartz monzonite wall rock (δ18O = +11.82‰) and altered quartz monzonite (δ18O = +11.01‰) do not seem to have undergone significant isotopic exchange with the hydrothermal solution, and the trend of isotopic change does not account for the trend of δ18O(H2O) determined in quartz. Rather, mixing of local meteoric water with a basinal brine appears to explain the observed trend.The amethyst deposits are believed to have been formed by basinal brines expelled from Sibley Group sediments. The brines dissolved silica by alteration processes accompanying their passage through granitic basement rocks in basin marginal faults. Amethyst was deposited on mixing with meteoric water. The temperature interval for amethyst formation appears to be restricted to less than ~90 °C. Temperatures causing thermal bleaching of amethyst are as low as 145 °C, and possibly 115 °C, as indicated by these results. This low range of temperature is not in agreement with bench-type experiments indicating bleaching at hundreds of degrees Celsius.

Palaeoecological investigations, involving pollen analysis, dendrochronology, and radiocarbon dating of bog-pine, provide the basis for reconstruction of vegetation dynamics, landscape development, and human impact in two contrasting parts of lowland northern Connemara, western Ireland, namely Ballydoo and Derryeighter in the east, and Renvyle/Letterfrack/Cleggan at the Atlantic coast some 40 km to the west. The history of Scots pine (Pinus sylvestris) is traced in detail. Standout features include the dominant role the tree played from the early Holocene onwards and especially at Ballydoo, its ability to grow on peat surfaces (so-called pine flush) over the course of several millennia during the mid-Holocene (centred on c. 5 ka), and its demise in a three-step fashion to become regionally extinct at c. 2.3 ka. The factors influencing these developments, including climate change, are discussed. Another natural phenomenon, namely the spread of blanket bog, is shown to be an on-going process since the early mid-Holocene, with accelerated spread taking place during the Neolithic and Bronze Age. The course of human impact, as reflected in pollen records and in archaeological field monuments, including megaliths and prehistoric stone walls, is reconstructed in detail.

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