This study has specifically developed and applied new methodologies and successfully captured very high‐resolution palaeoenvironmental and palaeoclimatic data over a period ≤55 years in the Mid‐Devonian Orcadian Basin, Scotland. Analysis of 110 successive discrete laminae (55 varve sets) in a lacustrine sequence has produced the most detailed archive of environmental and climatic change through time ever from ancient sediments. Geological and geochemical data sets have captured intra‐annual (seasonal) variation in palaeoclimate and palaeoenvironment as well as short‐term cyclical change. Varve compositions (carbonate/clastic pairs) indicate a climate with substantial intra‐annual variation in rainfall. Cycles with an average periodicity of 12 years which have previously been attributed to sunspot solar forcing also show a shift in compositional dominance from allochthonous clastic material to authochthnonous carbonate precipitate over 12 years. This indicates that climatic wetness also varied cyclically. The abundance of specific biomarker compounds – particularly β,β‐carotane but also squalane and pristine/phytane coupled with elemental data (C/S) indicate that lake waters were hypersaline. Changes in the abundance and ratios of these salinity dependant proxies show that salinity varied seasonally as well as cyclically. Stable isotope data (δ13Ccarb / δ18Ocarb) show that temperature and primary productivity also varied on a seasonal and cyclical scale, while δ13Corg and the n‐alkane skew confirm that the organic carbon present was sourced predominantly from within‐lake algal sources at all timescales observed. The rate of carbon burial (MARcarbon) also exhibits cyclical variation. An antithetic relationship between δ18O–derived palaeotemperatures and a carbon burial efficiency parameter (forganic) at cycle scale shows that the fraction of organic carbon buried decreased as temperature increased.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558654 |
| Date | January 2012 |
| Creators | Wilson, Abby Othman |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=186678 |
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