Extending sea loch sedimentary records: OSL dating of shallow marine systems

我们对陆地表面的地质认识很大程度上是由于年代测定技术的应用，这些技术限制了陆地表面如何随着时间的推移而演变。海湖（峡湾）的独特之处在于它们有效地捕获沉积物，因此捕捉到陆地和海洋（陆地-海洋系统）的相互作用，以及这些相互作用如何随着气候波动而随时间变化。该项目将证明发光测年技术可以用于测定古代海湖沉积物的年代，并且该技术可以作为14C（或其他用于海洋沉积物的技术）的补充工具。发光测年技术比放射性碳测年技术有优势，因为它的年龄范围比放射性碳测年（5万年）更长（石英的年龄范围从几十年到20万年以上），而且它几乎可以应用于所有的沉积物。这使我们能够延长海湖的年代学，那里的有机物保存得很差，那里保存的沉积物年龄超过5万年。这两个方面都使陆地-海洋相互作用得以记录、确定年代和调查。过去~ 20ka陆地系统对冰川消融的响应率是一个活跃的研究领域，发光测年有可能提供在14C有机质很少的时期内陆地表面响应的海湖年表。由于发光测年也反映了沉积物的运输历史，因此可以使用这种技术解决额外的沉积信息。我们的项目包括三个部分：首先，我们将比较从苏纳特湖收集的沉积物岩心中收集的放射性碳年表与作为该项目一部分开发的新发光年表。我们将把发光年代学扩展到记录过去20 ka冰川消融的沉积物，以证明这种技术有可能用于测定放射性碳限制以外的沉积物的年代。我们研究的第二部分将涉及一些影响发光测年的基本特性的实验，即沉积物敏感性和运输过程中的漂白。这些实验将在从苏纳特湖收集的现代沉积物上进行。研究的最后一部分涉及沉积物的环境辐射剂量率，这是发光测年所需要测量的。我们将探讨海湖环境中不同的沉积物岩性和水含量如何影响铀的不平衡，以及需要进行哪些调整来纠正这些随时间对剂量率的影响。随着海洋数据集在数量和分辨率上的增长，我们需要建立海岸线周围沉积物档案的年表，以了解海岸变化的速度，并推进我们对晚第四纪期间因海平面变化而淹没的丰富考古记录的理解。此外，随着海洋可再生能源产业的发展，需要沉积物测年技术来确定淹没考古遗址的年代，并限制近海砂系统的移动速度。测年是了解变化速率的必要条件，OSL测年的优点是可以广泛应用于几乎所有的沉积物和环境，不依赖于有机物的可用性，并且有可能测定200-400 ka（石英）或100万年（长石）的沉积物。

Much of our geological understanding of the land surface is due to the application of dating techniques that constrain how the land surface has evolved through time. Sea lochs (fiords) are unique in that they trap sediments efficiently and therefore capture the interactions of land and sea (the land-ocean system), and how those interactions change through time due to climatic fluctuations. This project will demonstrate that luminescence dating techniques can be applied to date ancient sea loch sediments, and that the technique can be a complementary tool to 14C (or other techniques applied to marine sediments). Luminescence dating techniques have advantages over radiocarbon dating, because the age range is longer (from decades to greater than 200,000 years for quartz) than radiocarbon (50,000 years) and it can be applied to almost all sediments. This permits us to extend the sea loch chronology where organic matter is poorly preserved, and where preserved, sediments that are older than 50,000 years in age. Both of these aspects permit land-ocean interactions to be recorded, dated and investigated. The response rates of the land system to deglacation over the last ~ 20 ka is an active area of research, and luminescence dating has the potential to provide a sea loch chronology of the land surface response over that tme period when little orgnic matter is available for 14C. Since luminescence dating also reflects the sediment's transport history, there is additional sedimentary information that can be resolved using this technique. Our project comprises of 3 parts: we will first compare a published radiocarbon chronology from sediment cores collected in Loch Sunart to a new luminescence chronology developed as part of this project. We will extend the luminescence chronology to sediments recording deglacation over the last 20 ka, to demonstrate that this technqiue has the potential to be used to date sediments beyond the limits of radiocarbon. The second part of our research will involve some fundamental experiments on characterisitics that affect luminescnece dating, namely sediment sensitivity and bleaching during transport. These experiments will be conducted on modern sediments collected from Loch Sunart. The final part of the research involves the environmental radiation dose rate of sediments which is required measurement for luminecence dating. We will explore how uranium disequilibium is affected by different sediment lithologies and water contents in sea loch environments, and what adjustments are required to correct for these influences on dose rate over time. As marine datasets grow in number and resolution, we need to build chronologies of the sediment archive accumulating around our coastline in order to understand rates of coastal change, and to advance our understanding of the rich archaeological record that has been drowned by changing sea levels during the Late Quaternary. In addition, with the marine renewables industries growth sediment dating techniques are required to date drowned archaeological sites, and constrain the rates of movement of offshore sand systems. Dating is an imperative for understanding rates of change and OSL dating has the advantage of being widely applied to almost all sediments and environmments, is not reliant on the availability of organic matter, and has the potential to date sediments as old as 200-400 ka (quartz) or a million years (feldspar).