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

Lead Research Organisation: University of St Andrews
Department Name: Earth and Environmental Sciences


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).

Planned Impact

The main impact of the proposed research will be on marine and climate change scientists (see Academic Beneficiaries), on professional archaeologists and engineers working in the marine sector, and on conservation bodies concerned with the impact of increasing development of of marine renewables on archaeology. The outcomes of this research are tools that can assist these groups with the geochonology that complements the high resolution geophysical imagery and existing geochronological tools available. Techniques that target sediments, such as luminescence dating, are particularly useful for dating landforms, and for constraining the time of deposition and the rates of sedimentation. Advantages over radiocarbon dating are that OSL can be applied to different grain-sizes of quartz and feldspar, and is not reliant on organic matter. The benefits of OSL dating for the marine sector are clearly not understood or recognised, but its exploitation on a range of problems could add significant information to sea level research, evaluation of bed stability in engineering marine structures, and in dating a variety of aspects about an archaeological site. In offering and delivering workshops to these groups, we can advise on how these techniques can be applied to understand the marine record more fully, and help to develop strategies that enable rapid evaluation of marine renewable sites. This is a two-way process, and we envisage that industry will inform us of their requirements for rapid assessment of marine archaeological and renewables sites.

Our other area of impact is with outreach, involving academics, students, and early career researchers who go directly into schools to work with school pupils and teachers to promote science knowledge. It also involves work in science centres and festivals, and through National Science Week activities. Our schools outreach programme is injnovative and has broad and wide ranging impact. We have already secured funding from NERC to develop GeoBus, and matching funds from industry are also being secured also. GeoBus is an Earth science-focussed mobile teaching laboratory whose fundamental aim is to improve pupils' understanding of Earth Science and to provide resources and support to teachers whose main subject may not be geology. Earth science builds on all the pure sciences, and NERC science can be incorporated into the secondary school chemistry, physics, biology, geology, and geography curricula. The Earth System Science teaching packages and training support that GeoBus brings to a large number of science teachers, and providing equipment and materials are elements that council regions can not necessarily afford. A new development is the recent commitment of geologists at Maersk Oil Ltd to join GeoBus and visit schools with academics. This offers the opportunity to provide an exciting and interactive learning experience for a large number of schools based on NERC and industry science outcomes, and can only improve the linkage between NERC, industry, HEIs and schools and career development for school pupils.


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Description The research project had the following aims: to investigate whether sea loch sedimentary archives (from Loch Sunart) could be analysed using optically stimulated luminescence and whether the amount of bleaching that sea loch sediments undergo could be quantified.
Samples analysed included sedimentary core archived at the National Oceanographic Centre at Southampton, as well as shallow sedimentary gravity cores and suspended sediments collected as part of this project. A research cruise was undertaken with a boat and staff from SAMS Dunstaffnage.
Optically stimulated luminescence dating of sedimentary core material has been successful, though results are yet to be submitted for publication. The analysis of suspended sediment was technically more challenging, due to large amounts of organic matter present in the filtration. Though the sample seet is extensive, the actual OSL analyses are limited because of the challenge of separating the mineral and organic signals.
Exploitation Route The results, once published, will be on interest to a wide range of researchers in the luminescence community.
Sectors Environment