SERVICES & FACILITIES ANNUAL REPORT - FY April 2008 to March 2009

SERVICE Open University Uranium FUNDING AGREEMENT ESTABLISHED as S&F TERM Series Facility (OUUSF) block F14/G6/47 1998 3

TYPE OF SERVICE PROVIDED:The purpose of the Open University Uranium-Series Facility (OUUSF) is the application of U-series methodologies to

research in Earth and environmental sciences and science-based archaeology. Research projects are carried out, subject to approval by the NERC Isotope Geosciences Steering Committee, NIGFSC, in collaboration with NERC stakeholders in the pursuit of knowledge and understanding of the Earth system.

U-series chronology is an essential component of many projects in Earth and environmental science, oceanography, hydrology and science-based archaeology. Current OUUSF research includes projects on global climatic change through dating of authigenic deposits, human (Neanderthal) evolution, mid-ocean ridge magma evolution and volcano development, and abyssal sedimentation rates. Uranium-series determinations, e.g. 234U/238U, 230Th/232Th, 231Pa/235U 230Th/234U ratios, and U, Th Pa and Ra concentrations by isotope dilution, are performed on a dedicated TIMS MAT262-RPQ-II instrument or a Nu Instruments MC-ICPMS. Both mass spectrometers have a deceleration lens to achieve the required abundance sensitivity, and have ion counting for superior detection statistics. Th isotope ratios in samples containing less then 0.5 pg 230Th can be measured with a precision better than 1% (2m) and Ra abundances, as low as 4 fg, can be determined to 1% (2m). OUUSF uses Picotrace state-of-the-art ultra-clean chemical laboratories for sample separation and purification. The low total procedure blanks and excellent instrument sensitivity are required to analyse very low abundances in samples, such as Ra in mid-ocean ridge basalts and Th dissolved in ground-water.

OUUSF provides the equivalent of one user-year of training and analyses per annum, which represents 25% of the Open University Isotope Geochemistry Laboratory, OUIGL, capacity and corresponds to circa 150 samples. PGRS and PDRA teaching and training is the most important aspect of OUUSF activity and usually a PGRS or PDRA works under close supervision in the laboratory for a number of short periods using Standard Operating Procedures and learn to work with radioactive materials in low-blank chemistry and mass spectrometry laboratories and to carry out data reduction and evaluation protocols.

Quality Assurance is maintained through the repeated analysis of Certified Reference Materials (e.g. Appendix 3.2), Total Procedure Standards, Total Procedure Blanks, internal laboratory standards, reagents and calibrations performed by staff and users and reviewed on a weekly basis. QA efforts are equivalent to >30 samples per year. OUUSF staff has some capacity to perform analyses for collaborators.

Scientific results of collaborative research may be included in PhD thesis, published in peer-reviewed journals, presented at international conferences, or disseminated in electronic media. Results of pilot projects may be essential for NERC Research Grant proposals.

OUUSF has an extensive web-site URL: http://www2.open.ac.uk/ou-usf/

ANNUAL TARGETS AND PROGRESS TOWARDS THEMThe OUUSF Agreement provides for the equivalent of 150 analyses, equating to 25% of capacity and this has been achieved. Most data were communicated to the PI within the timeframe of the project.

SCORES AT LAST REVIEW (each out of 5) Date of Last Review:Need Uniqueness Quality of Service Quality of Science & Training Average

CAPACITY of HOST ENTITYFUNDED by S&F

Staff & Status Next Review (March)

Contract Ends

(31 March)Dr P van Calsteren, Senior Research Fellow: 48%

25%Dr L E Thomas, Project Officer: 100%Dr S Hammond, Grade 6 technician: 50% 2010 2011

FINANCIAL DETAILS: CURRENT FYTotal Resource

Allocation£k

Unit Cost £k Capital Expend £k

Income £k

Full Cash

Cost £kUnit 1 Unit 2 Unit 3

152.48 1.016FINANCIAL COMMITMENT (by year until end of current agreement) £k 2008-09: 147.98 2009-10: 152.48 2010-11: 157.00 2011-12 2012-13

STEERING COMMITTEE Independent Members Meetings per annum Other S&F OverseenNIGFSC 7, (chair Prof J Andrews) 2 NIGL, AIF, ICSF

APPLICATIONS: DISTRIBUTION OF GRADES (current FY — 2008/09)

5 4 3 2 1 R*/Pilot RejectNERC Grant projects* 1Other academic 2 1 1StudentsPilotTOTALAPPLICATIONS: DISTRIBUTION OF GRADES (per annum average previous 3 financial years —2005/2006, 2006/2007 & 2007/2008)

5 4 3 2 1 R*/Pilot RejectNERC Grant projects* 0.33 1.33 0.33Other Academic 2 0.33 0.33 0.33Students 0.33 0.33PilotTOTAL 2.67 2 0.67 0.33

PROJECTS COMPLETED (current FY – 2008/09)5 4 3 2 1 R*/Pilot

NERC Grant projects* 1Other Academic 2StudentsPilot

USER PROFILE - funding type (current FY – 2008/09)

GrandTotal

Infrastructure PAYG

Supplement to NERC Grant * Student NERC C/S Other NERC

Grant*Student NERC

C/S OtherNERC Other NERC Other

3 3

USER PROFILE - funding type (per annum average previous 3 financial years - 2005/2006, 2006/2007 & 2007/2008)

GrandTotal

Infrastructure PAYG

Supplement to NERC Grant * Student NERC C/S Other NERC

Grant*Student NERC

C/S OtherNERC Other NERC Other5 2 0.67 2.33

USER PROFILE – user type (current FY – 2008/09)Academic Centre/Survey NERC Fellows PhD Commercial

3USER PROFILE - user type (per annum average previous 3 financial years - 2005/2006, 2006/2007 & 2007/2008)

Academic Centre/Survey NERC Fellows PhD Commercial5

OUTPUT & PERFORMANCE MEASURES (current year)Publications (by science area & type) (calendar year 2008)

SBA ES MS AS TFS EO Polar Grand Total Refereed Non-Ref/ Conf Proc PhD Theses2 2

Distribution of Projects (by science areas) (FY 2008/09)SBA ES MS AS TFS EO Polar

2

OUTPUT & PERFORMANCE MEASURES (per annum average previous 3 years)Publications (by science area & type) (Calendar years 2005, 2006 &2007)

SBA ES MS AS TFS EO Polar Grand Total Refereed Non-Ref/ Conf Proc PhD Theses3.33 3.33

Distribution of Projects (by science areas) (FY 2005/2006, 2006/2007 & 2007/2008)SBA ES MS AS TFS EO Polar

3.33

Distribution of Projects by NERC strategic priority (current FY 2008/09) Climate System Biodiversity Earth System Science Sustainable Use of

Natural ResourcesNatural Hazards Environment, Pollution

& Human HealthTechnologies

1.67 1.67

*Combined Responsive Mode and Directed Programme grants

NOTE: All metrics should be presented as whole or part of whole number NOT as a %OVERVIEW & ACTIVITIES IN FINANCIAL YEAR (2008/09):This year was the first year of the fourth Agreement and 5 new projects were submitted: 2 projects attracted good 4 grades, one was allowed as a pilot study to prove that the samples were suitable for dating and two projects received 2 grades and

were not funded. There are 9 ‘live’ projects and for 3 projects the analytical work was completed.The MAT262 mass spectrometer has been performing well, with only short interruption for software and firmware

upgrades. The Nu Instruments MC-ICPMS also performed well and is now used for most U and Th measurements because increasingly, higher sensitivity and therefore smaller sample size is important as well as good precision. All Pa analyses where sensitivity is essential are performed on the Nu Instruments, equally, all Ra analysis are performed on the TIMS

A 50% contribution from NERC S&F has allowed the purchase of a gamma spectrometry system for the confident tracking of 237Np and 233Pa through our chemical separation procedure for 231Pa quantification. The instrument components have been delivered in March 2008 for installation and after a return of some parts to the factory, commissioned in July/August 2008.

After many trials we finally managed to analyse the first batch of 231Pa samples and obtain results within the range of expectations, the second batch is underway in April 2009.

At the November 2008 NIGFSC meeting there was a brief discussion regarding the challenges faced by research projects that involve U-series dating of authigenic sediments that contain significant amounts of allogenic or detrital material. NIGFSC proposed to organise a workshop that would bring together researchers with experience in this type of research both from the user community and from U-series laboratories. This workshop was organised by OUUSF and held in the Department of Earth and Environmental Sciences at the OU on Friday 20 March 2009. Key-note speaker was Dr Christa Placzek from Purdue University talking on: Challenges and rewards of U/Th dating of terrestrial carbonates. The workshop was sponsored by NERC Services & Facilities, the NERC Isotope Geochemistry Laboratory at BGS and the Department of Earth and Environmental Sciences at the OU. A more detailed report is in Appendix 9.

The OUUSF website has been kept up-to-date and has an Introduction into Uranium-series methodology, examples of Projects, lists of Publications and links to the laboratory Risk Assessments. For laboratory users at OUUSF there are also links to all Standard Operating Procedures and Training Manuals, as well as spreadsheets and compilations of our laboratory standards and blanks. The intention of this e-documentation is to comply with the spirit of ISO:9001-2000: Quality Assurance by Quality Control at a day-to-day level and by frequent evaluation of QC data.

During this year, more and more use was made of the Nu Instruments MC-ICPMS, even for routine isotope ratio determinations. The normal mode of operation is that on Sunday evening the instrument is switched on and run on a wash cycle. Monday morning is used to tune all instrument variables and this culminates in a four ‘magnet’ cycle analysis of CRM U112a (see Appendix 3.2). This allows monitoring of many performance indicators including SEM yields, hydride formation, Abundance Sensitivity and RPQ performance. Then follows analysis of the ‘bracketing’ standard, -with isotope ratios and signal intensities similar to samples- and when the bracketing standard reproducibility is within expectation, samples are introduced. The instrument is then kept running (with overnight extended wash&standard cycles) for the rest of the week, or until the reproducibility of the bracketing standard gives cause for concern.

18 Total Procedure Samples of our Young Spele rock-powder standards were analysed as unknowns, as well as 60 total procedure blanks, and numerous reagent blanks and shelf standards traceable to Certified Reference Materials to maintain high levels of Quality Control. The CRM U112a database accumulates ~40 data-sets each year. The MAT262 TIMS has been used to determine isotope ratios in both ‘bracketing’ standards and other solution standards, ensuring that our MC-ICPMS data remain compatible with TIMS.

Since 2005 there were 14 projects, including 2 pilots, active, for 3 projects the analytical work was completed in 2008. Seven projects form part of a PhD project and 4 post-graduate received intensive training at the OUUSF laboratory. Two papers involving OUUSF staff or data were published in peer-reviewed journals, 4 have been submitted.SCIENCE HIGHLIGHTS:Quaternary tufa deposition in the Naukluft Mountains, Namibia: Prof David Thomas and Heather Viles, PGRS: Abi Stone. IP/937/1106Tufa deposits have great potential as palaeo-environmental indicators particularly in semi-arid to arid regions, which contain relatively little proxy evidence in geological archives. Tufas are also potentially amenable to U-series dating and four densely-cemented banded sample suites and various other facies-types have been analysed.

The U-series dating exercise has revealed significant challenges for assigning ages to Naukluft tufa deposits. U-series secular equilibrium in a densely-cemented banded unit indicates that large, extensive complexes of tufa in the Naukluft Mountains are of considerable antiquity. Other such deposits yield ages at ~ 80 ka which suggest that some large barrage features are of at least MIS 5 age, while there is some evidence for Holocene age deposits as coatings in heavily incised channels. Many densely-cemented banded samples contain more than one allogenic component and standard ‘isochron’ mixing line protocols do not adequately correct for more than two end-members. Other densely-cemented banded samples exhibit have (230Th/234U)>1 activity ratios which cannot be the result of simple radioactive decay only but could be caused by leaching of 234U or ‘initial’ incorporation of 230Th. There is no petrographic evidence for uranium leaching in these samples, and leaching would also be indicated by (234U/238U)<1, which is not observed. It would appear that ‘unsupported’ 230Th was incorporated during tufa precipitation. This could be caused by leaching of both 230Th and to a lesser extent, 232Th from Naukluft limestone karst formations. Leached Th can be mobile at high PCO2 in alkaline groundwater and can then be incorporated during precipitation of the tufa.

Four sample suites of other facies types yielded high levels of detrital contamination, but have (230Th/234U) <1, and give finite age estimates in the range of 20-160 ka. Given the magnitude of the corrections for allogenic 230Th, micro-

morphological characteristics of these samples, the heterogeneity of cements types, and the porosity values of up to 40%, we cannot express great confidence in these data.

Various tufa deposits of the Naukluft Mountains contain similar suites of deposits in different river catchments. This suggests that the hydro-climatic model of alternations between permanent steady river flow, episodic high flow conditions and quiescence, is robust for the region and this provides a first-order indication that the observed deposits relate to region-wide moisture availability, elevated groundwater levels and climatic forcing. A manuscript and Abi’s PhD thesis will be submitted this Spring; a more extensive summary is included in the Appendix 11.1.Localisation of Quaternary slip-rates in an active rift in ~105 years: an example from central Greece constrained by 234U-230Th coral dates from uplifted palaeo-shorelines. Prof John McArthur, Gerald Roberts, PGRS: Sarah Houghton. IP/671/0900Central Greece is amongst the most rapidly extending portions of the Earth’s continental crust, with 10-15 mm/yr of north-south extension localised within a <30 km wide E-W zone associated with the Gulf of Corinth. When and how extension became localised in its present position is the subject of this study. The timescale over which strain localises into the plate boundary is known for only a few examples elsewhere, due to limitations in dating syn-rift stratigraphy.234U-230Th coral ages from Cladocora caespitosa date uplifted shoreface sediments and palaeo-shorelines from glacio-eustatic sea-level high-stands at 76 ka, possibly 100 ka, 125 ka, 175 ka, 200 ka, 216 ka, 240 ka and 340 ka. The 234U-230Th coral dates for palaeo-shorelines that formed during localisation of faulting show how Quaternary slip rates changed through time on a 105 timescale. Palaeo-shorelines were identified using features including wave-cut platforms, shoreface sediments and lithophagid-bored coastal notches or marine-sub-aerial facies transitions. Uplift rates of 0.15 mm/yr until 175 ka followed by 0.51 mm/yr from 175 ka to present, were calculated to explain the elevations of mapped and dated palaeo-shorelines using initial sea-level elevations from the global sea-level curve. Comparison of palaeo-shoreline elevations and sedimentology with the Quaternary sea-level curve show that slip-rates increased by a factor of 3.2 ± 0.2 at 175 ± 75 ka, synchronous with cessation of activity on a neighbouring normal fault at 382-112 ka. We suggest that the rapid localisation of up to 10-15 mm/yr of extension into the narrow gulf (~30 km wide) resulted from synchronous fault activity on neighbouring faults followed by localisation rather than sequential faulting, with consequences for the mechanism. This allows us to constrain the mechanisms responsible for the localisation. This project is the springboard for a NERC Standard Grant application this Summer. A more extended summary is included in Appendix 11.2.

FUTURE DEVELOPMENTS/STRATEGIC FORWARD LOOKAnalytical developments:

The Nu Instruments plasma ionisation mass spectrometer (MC-ICP-MS) now has fully developed protocols for U-series analyses where its sensitivity is essential.

TIMS is used when mass-dependent isotope fractionation and instrument drift, which are both an order of magnitude better, is a requirement for high precision (for high resolution) and when concentration or availability are not limiting factors. This includes ‘certification’ of the bracketing standards used with the Nu instruments.

The performance of the MAT262-RPQ-II instrument for U-series analysis, mainly by ion counting, is on a par with more modern Thermal Ionisation Mass Spectrometers, TIMS, and in ‘total evaporation’ mode with the ultra-fast GPIB voltmeter, still out-performs modern instruments for very small samples. For Radium the sensitivity of TIMS is easily a factor of 20 better than MC-ICP-MS, and TIMS remains the instrument of choice.

OUUSF is continuing the implementation of mass spectrometric analysis of 231Pa. Radioactive Risk Assessment, in particular regarding the 237Np precursor of the 233Pa spike, required the purchase of a dedicated gamma spectrometer, in addition to the and monitors. The gamma spectrometry system, commissioned in 2008 makes it possible to ‘track’ spiked samples through the chemical separation and spike preparation procedure. It is no more difficult that placing an FEP beaker with a dry residue, which is equivalent to a -point source, on the end-cap of the detector. Naturally, the spectrometer has to be calibrated but the GammaVision software is comprehensive and the procedures fairly straightforward. Adjustments have been made to the chemical separation procedures to improve sample recovery and this has greatly improved our confidence in the efficiency of the separation protocol and we now have data that we confidently consider to be correct.

We await receipt of the new IRMM3636 233U-236U Certified Standard enabling better precision using double spike methods for samples where this would result in improved precision. Extreme care has to be exercised to eliminate any possibility of cross contamination of double-spiked U samples with samples that are used for Pa analysis.

Strategic look forward: A new arrangement where OUUSF staff manages both the MAT262 TIMS and the Nu Instruments MC-ICPMS means

faster sample throughput and project turn-around time for the future.Incorporation of the gamma spectrometer into our routine operations is an important strategic goal, not only to improve

our performance with 231Pa analysis but also to streamline 226Ra and 229Th separation and spiked procedures.

Non-Mandatory Facility-specific OPMs: utilisation, allocation of capacity etc

OUUSF Mission Statement:

OUUSF is hosted by the Isotope Geochemistry Research Group, Earth and Environmental Sciences, The Open University.

OUUSF is providing U-series methodology through collaborative projects to researchers within the NERC remit to further the goals in NERC strategy 2007-2012: Next generation science for planet Earth, Science-based Archaeology and responsive mode (‘blue skies’) research.

OUUSF provides web-based training material and one-to-one training for post-graduates and research scientists in U-series laboratory techniques, underlying theory and data evaluation.

OUUSF pursues an ‘open door’ attitude and will share methods and protocols with collaborators and the wider scientific community.

OUUSF aims to expand and improve analytical techniques for chemical preparation in a state-of-the-art laboratory, using the latest mass spectrometric instrumentation, to support innovative collaborative projects.

NERC Isotope Geoscience Facilities Steering Committee, 2008Chair: Administration:Prof Julian E AndrewsSchool of Environmental SciencesUniversity of East AngliaNorwich, NR4 7TJTel: +44 160 359 2536 E-mail: j.andrews@uea.ac.uk mailto:j.andrews@uea.ac.uk

Béatrice Bullock-von Moos NERC Isotope Geosciences Laboratory British Geological Survey Kingsley Dunham Centre Keyworth, NG12 5GG Tel. + 44 115 936 3425 bbullock@bgs.ac.uk

Members Ex-officio:Prof SA Bowring Department of earth, Atmospheric, and Planetary Sciences MIT Building 54-1126 Cambridge, MA 02139 USA Tel: +1 0617 2530 3775 E-mail: sbowring@mit.edu

Dr Ian Millar, SecretaryNERC Isotope Geosciences Laboratory British Geological Survey Kingsley Dunham Centre Keyworth, NG12 5GG Tel: +44 115 936 3402Email: ilm@gbs.ac.uk

Prof. A Chamberlain Department of Archaeology The University of SheffieldNorthgate House, West Street SHEFFIELD S1 4ET Tel: +44 114 222 2906 E-mail: a.chamberlain@sheffield.ac.uk

Dr R Lin F KayScience and Innovation FundingNERCPolaris House, North Star AvenueSwindon, SN2 1EUTel: +44 179 341 1500E-mail: rlfk@nerc.ac.uk

Dr Sarah Davies Room E21d, Institute of Geography and Earth Sciences, Llandinam BuildingPenglais Campus, AberystwythCeredigion SY23 3DB, Wales, UKTel: +44 1970 622585E-mail: sjd@aber.ac.uk

Dr Adrian J BoyceSUERCRankine AvenueEast Kilbride, G75 0QUTel: +44 1355 270143E-mail: a.boyce@suerc.gla.ac.uk

Dr Colin Mcpherson Department of earth Sciences Durham University, Science Labs Durham, DH1 3LE Tel: +44 191 334 2283 E-mail: colin.mcpherson@durham.ac.uk

Dr Fin M StuartSUERCRankine AvenueEast Kilbride, G75 0QUTel: +44 1355 270139E-mail: f.stuart@suerc.gla.ac.uk

Dr RA Mills School of Ocean and Earth Sciences National Oceanography Centre, Southampton Southampton, SO14 3ZH Tel: +44 23 8059 2678 E-mail: ram1@noc.soton.ac.uk

Prof. Melanie J LengNERC Isotope Geosciences LaboratoryBritish Geological SurveyKingsley Dunham CentreKeyworth, NG12 5GGTel: +44 115 936 3515E-mail: mjl@nigl.nerc.ac.uk

Prof Clive M RiceCollege of Physical ScienceSchool of GeosciencesGeology & Petoleum GeologyMeston Building, King’s CollegeAberdeen, AB24 3UETel: +44 1224 273433E-mail: c.rice@abdn.ac.uk

Prof. Randy R ParrishNERC Isotope Geosciences LaboratoryBritish Geological SurveyKingsley Dunham CentreKeyworth, NG12 5GGTel: +44 115 936 3427E-mail: r.parrish@nigl.nerc.ac.uk

Prof Jim Marshall Earth and Ocean Sciences,University of Liverpool Tel:+44 1517945177E-mail: isotopes@liv.ac.uk

Dr Peter van CalsterenDepartment of Earth SciencesThe Open UniversityWalton HallMilton Keynes, MK7 6AATel: +44 1908 652889E-mail: p.v.calsteren@open.ac.uk

NIGF Steering Committee: Remit

The NERC Isotope Geosciences Facilities Steering Committee exists to:

review applications for use of:the NERC Isotope Geosciences Laboratory;the Argon Isotope Facility at the SUERC;the Isotope Community Support Facility at the SUERC; andthe Open University Uranium Series Facility

monitor outputs from these Facilities;

provide advice to the Director, Science and Innovation Funding on aspects of the operations of these Facilities.

The Director, Science and Innovation Funding, in turn, provides advice to the Science and Technology Board of Council on Services and Facilities relevant to their remit.

Terms of Reference

1. To review applications and to establish priorities for the Heads of these Facilities in the allocation of those of the Facilities’ resources funded from the Science and Innovation Funding allocation, taking into account NERC Strategy and recommendations made through the NERC peer-review mechanisms.

2. To review the scientific quality of work undertaken by users utilising these Facilities, based on reports and publications.

3. To monitor the level of user-satisfaction with the Facilities, and to analyse the user-base.

4. To give guidance to the Heads of these Facilities on improvement of the Facilities’ equipment and on their service function.

5. To advise the Director, Science and Innovation Funding on:

5.1. the level and direction of the internal R & D programme for these Facilities;

5.2. the anticipated levels of future demand and any consequential anticipated changes in resource requirements from these Facilities.

5.3. on other matters, as appropriate and reasonable.

6. To receive annually a report from the Heads of these Facilities, and comment through the Chair on them before passing them to the Director, Science and Innovation Funding.

1. Equipment Inventory

OUUSF does not own any equipment but uses instruments, facilities and infrastructure of The Open University

2. Future Developments.

2.1. In situ analysis:

MC-ICPMS can be hyphenated to the Excimer laser ablation system to measure (234U/238U) and (230Th/232Th) in situ but stalagmites with sufficient U concentration and age, are fairly rare. However, the technique also has important applications in marine climate change studies because pristine corals have sufficiently high U concentration. We are assessing a project which involves stalagmites with sufficiently high U concentration for a pilot study.

The energy of the laser at the ablation point is such that a short-lived Laser-Induced Plasma is produced and this adds another process by which mass and element fractionation takes place. The use of appropriate standards with similar matrix is essential and it is not simple to find a suitable standard that is homogeneous at the spatial resolution that is required. However, age variation patterns are much easier to resolve and this is frequently the main purpose.

At the moment of writing this report, the Excimer Laser Ablation system is out of commission. The TUI excimer laser has mal-functioned but is no longer supported by NewWave, the system manufacturer. A simple replacement with a laser by Coherent, the company who took over TUI, is not supported by NewWave but it is as yet unclear if the NewWave supported excimer will function within specification on our system, and indeed where we would find the £60K that is the first estimate for this repair.

We will be applying for a NERC Standard Research Grant in July 1st round to work with colleagues at NOC, S on suphides from Mid Ocean Ridge hydrothermal vents. It is anticipated that these will contain high enough levels of U to allow the use of laser ablation.

2.2. Protactinium

OUUSF now has methods for mass spectrometric analysis of 231Pa, the daughter of 235U with a half-life of ~35,000 y. All necessary Radioactive Risk Assessments, including the 237Np precursor of the 233Pa spike, have been completed and have been approved by the University’s Radiation Protection Adviser. The analytical method to purify protactinium from silicate rocks that was published recently (Regelous et al., 2004, Thomas et al., 2007), has been adapted for the chemical separation of protactinium from carbonate-rich samples. This adaptation requires the separation of the Ca-rich fraction from the remaining solid fraction before the solid is dissolved using HF and the subsequent thorough elimination of any fluoride.

The newly purchased gamma spectrometry system was finally commissioned in August 2008 and gamma spectrometry makes it possible to ‘track’ spiked samples through the chemical separation procedure and to track the presence of 237Np in the purified 233Pa spike, hence enabling full recovery of 237Np and avoiding the potential contamination of the ion counters on mass spectrometer. Adjustments have been made to the procedure to improve sample recovery and this has greatly improved our confidence in the efficiency of the separation protocol and we now have data that we confidently consider to be correct. The gamma spectrometer will also be used in the preparation of the new Ra spike.

The main reason for the installation of gamma spectrometry was the advice from the University Radiation Safety Advisor that we should develop the ability to not only simply track radioactivity but to identify the nuclide that is the main reason for the detected radioactivity. This goal has also been achieved to the satisfaction of the RPA (who is a consultant, external to the University).

231Pa dating can provide confirmation of ages obtained by 230Th dating. Two independent estimates of the age from the same sample would be useful for dating of speleothem carbonate and particularly in archaeological bone using the Oxford U-uptake model (Millard and Hedges, 1996), recently further developed for U-series (see Pike et al., 2002).

231Pa has found application in coral dating (Mortlock et al., 2005, Edwards et al., 1997). In open oceans, 231Pa and 230Th are removed from the water column by a process of reversible scavenging (Moran et al., 2002, Moran et al., 2005) which quickly removes 230Th to the sediment. 231Pa is less efficiently scavenged onto particles than 230Th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment. The equilibrium partition coefficients for particulate versus dissolved matter may vary with particle type and the (231Pa / 230Th) activity ratio can be of great use in paleo-oceanographic studies.

231Pa/235U is part of the project to study an Axial Volcanic Ridges AVR, in the Median Valley of the Mid-Atlantic Ridge, 700km north of the Azores (IP/929/1106: Prof R Searle, Durham). The sampling cruise took place in May/June 2008 and PvC joined the ship-board scientific party to conduct the sampling of the glass rims of the pillow basalts that will be analysed for U-series isotopes, as well as for various other geochemical techniques.

2.3. Radium

The U-series sub-system 230Th-226Ra has a half-life of 1602y which makes it highly appropriate for systems with millennial ages. Using TIMS with ion counting we can analyse <4 femtogram 226Ra routinely and this is essential because 226Ra is present at the femtogram/gram level in geological materials. The age of a sample is calculated from the 226Ra/Ba ratio in the sample relative to present day 226Ra/Ba. The uncertainty in 226Ra/Ba ages depends mostly on the assumption that 226Ra/Ba has remained constant. This is a reasonable assumption because Ra and Ba have very similar geochemical characteristics. Radium dating is one of the aims of the AVR project. TIMS 226Ra dating has not previously been applied to speleothem samples and an application in conjunction with lamina counting that would re-enforce confidence in both methods and confirm the validity of the 226Ra/Ba dating method in young authigenic carbonates in Holocene speleothems, is being developed.

2.4. Lead

The energy range of our new gamma spectrometer is such that 210Pb can be detected and we plan to exploit this dating tool with a range of 0-120y tentatively.

2.5. Authigenic minerals precipitates from groundwater.

Long-standing assumptions in U-series dating of authigenic minerals are that all accumulated 230Th is from in-situ decay of 234U and only U and no Th is transported in ground water. The concentration of trace elements in water is determined by temperature, pH, redox conditions, concentration of anionic ligands and complex ions formation. Residence time in groundwater is a function of the rate of leaching, stability of complex ions, and adsorption onto particulate matter or incorporation into authigenic minerals. The resulting U/Th in groundwater is usually > 10,000.

Contrary to expectations, recent work at The Open University has shown that Th and U have similar concentrations in oxygenated ground water in the Great Artesian Basin, Australia. Recent results from the Naukluft project confirm the existence of ‘hydrogenous’ Th in this area as well. It is likely that U and Th speciation is the determining factor for this unexpected behaviour and furthermore this makes the long-standing U-series dating assumptions questionable. Any 230Th that is not derived from in-situ decay but is transported in ground water must therefore be accounted for before meaningful ages can be calculated.

The theoretical framework for the behaviour of U and Th in ground water can now be tested due to recent advances in analytical technology. These recent advances allow the speciation of U and Th to be determined at the low concentration levels encountered in groundwater.

To assess the effects of 230Th transportability in groundwater is is necessary to:1. determine the speciation of U and Th isotopes in groundwater;2. develop a thermodynamic framework for the speciations;3. evaluate the importance of these findings for U-series dating of authigenic minerals.

OU-IGL has a High-Performance Liquid-Chromatography (HPLC) for speciation research and this instrument can be hyphenated to our MC-ICPMS.

3. Summary of Performance Information

3.1. Active projects

3.2. U112a standard data

U112a

0.0000527

0.0000528

0.0000529

0.0000530

0.0000531

0.0000532

0 5 10 15 20 25

October '08-April '09

234 U

/238 U

234U/238U=0.00005298±0.00000006

4. Publication details, numbers since 1998, IP code and Science Area.4.1. Papers published in 2006

33. Thomson, J., Green, D.R., Calsteren, P. van, Richter, T.O., Weering, T.C.E. van. (2006). Holocene sediment deposition on a NE Atlantic transect including Feni Drift quantified by radiocarbon and 230Thexcess methods. Earth and Planetary Science Letters, 242, 170-185. (IP/791/1103) ES34. Hughes, P.D., Woodward, J.C., Gibbard, P.L., Macklin, M.G., Gilmour, M.A. and Smith, G.R. (2006), The Glacial History of the Pindus Mountains, Greece, Journal of Geology 114, 413–434. (IP/754/0302) GC 35. Hughes, P.D., Gibbart, P.L.and Woodward, J.C. (2006), Middle Pleistocene glacier behaviour in the Mediterranean: sedimentological evidence from the Pindus Mountains, Greece. Journal of the Geological Society, London, 163, 857–867. (IP/754/0302) GC 36. Hughes, P.D., Woodward, J.C. and Gibbard, P.L.(2006) Late Pleistocene glaciers and climate in the Mediterranean region. Global and Planetary Change, 46, 83-98. (IP/754/0302) GC 37. Hughes, P.D., Woodward, J.C. and Gibbard, P.L. (2007) Middle Pleistocene cold stage climates in the Mediterranean: new evidence from the glacial record. Earth and Planetary Science Letters,253(1-2), 50-56. (IP/754/0302) GC 4.2. Papers published in 2007-8

38. Marshall, J.D., Weedon, G.P., Lang, B., Kiriakoulakis, K., Fisher, E.H., Crowley, S.F., Ball, J.D., Jones, R,T., Calsteren, P. van, Bedford, A., Brooks, S,J., Muscheler, R., Johnsen, S. (2007). Early Holocene climate in NW Europe - abrupt events, centennial variability, and solar influence. Geology, 35( 7), 639–642. (IP/672/0900) GC39. Asrat, A., Baker, A., Umer, M., Leng, M.J., van Calsteren, P. and Smith, C.L., 2007. A high-resolution multi-proxy stalagmite record from Mechara, Southeastern Ethiopia: Paleohydrological implications for speleothem paleoclimate reconstruction. Journal of Quaternary Science, 22, 53-63. (IP/932/1106) GC

40. Caseldine, C.J., McGarry, S.F., Baker, A., Hawkesworth, C. and Smart, P.L. 2008. Late Quaternary speleothem pollen in the British Isles. Journal of Quaternary Science, DOI: 10.1002/jqs.1121. (IP/578/0998) GC 41. Pogge von Strandmann, PAE, James, RH, Peter van Calsteren, P, Gíslason, SR and Burton, KW. (2008). Lithium, magnesium and uranium isotope behaviour in the estuarine environment of basaltic islands. Earth and Planetary Science Letters V 274, 3-4, 462-471, doi:10.1016/j.epsl.2008.07.041  42. Turner,J A, Leeder, MR, Andrews, JE and Rowe, PJ. (2008). Comment on “A comparison of 103-105 year uplift rates on the South Alkonydes Fault, central Greece: Holocene climate stability and the formation of coastal notches” by Cooper et al. (2007) Geophysical research letters 35, L19314 doi:10.1029/2008GL034854

5. Targets & Milestones instrument utilisation;

The OUUSF Agreement is for the utilisation of 25% of the U-series laboratory capacity, equivalent to approximately 150 samples per year and this target has been achieved. 18 ‘rock’ standards mainly our homogenised stalagmite YS, were analysed as Total Procedure Standards to assess the full analytical protocol. Over 60 Total Procedure Blanks, reagent blanks and shelf standards traceable to Certified Reference Materials were analysed to monitor routine performance for Quality Control purposes in the spirit of ISO:9001. On the MC-ICPMS >400 traceable standards were analysed in Sample-Standard-Standard analysis ‘bracketing’ protocols. Dozens of test solutions were devised and tested as part of the 231Pa analysis protocol developments

allocation of capacity and effort;Instrument and laboratory time for OUUSF operations were scheduled in consultation with other users and there was no friction.

throughput;The analytical workload was significantly above average, partly because activity associated with PGRS working in the lab and our usual turn-around times have not always been maintained.

response times and data delivery to customers;Analytical results have mostly been submitted to PI’s within the agreed time-frame with a few exceptions. ‘Teething trouble’ with the protactinium method and the large number of samples for which a ‘detrital’ correction is required, have resulted in delays. Communications regarding interpretations and publication are always conducted with the highest priority.

user satisfaction;In this first year of the fourth Agreement, no effort was made to formally gauge user satisfaction but informally, we learn that collaborators are happy with our performance. The only negative note is associated with the protactinium project. This has taken much longer than expected but is now finally ‘on track’. However, the nature of the spike, which is milked from a neptunium solution, is such that 6 months have to elapse between milkings and this is the inevitable period between batches.

Details of the complaints procedure are on the OUUSF website; no complaints were made.

scheduled maintenance, calibrations, planned contingency, down time due to external factors etc.;Instrument maintenance is scheduled such that impact on availability is minimal, calibrations are part of the analytical ‘continuum’ and not separately accounted. Downtime due to external factors is minimised, mainly by the use of an Uninterruptable Power Supply that keeps the mains working on all our instruments. The working relationship with our Estates Division staff is such that maintenance on the Air Handling Units, Air Conditioning Plant and any other activity, is scheduled to fit with our needs.

summary of internal R&D output;Our spreadsheets for data evaluation are constantly under review and minor improvements have been implemented. Especially the Naukluft Project required efforts for the modelling of allogenic Th, if only to ascertain that the (230Th/234U)>1 cannot be due to mixing with a detrital component but has to be caused by hydrogenous Th.

The Pa spreadsheet-based model to evaluate Pa isotope ratio data is still in a quite simple form and expanding rapidly.

6. Finance Details are included in the account filed by The Open University: Finance Division.

7. Service Management

Dr Peter van Calsteren is Principal Investigator and Manager of OUUSF as Senior Research Fellow, Dr Louise Thomas is Project Officer and is OUUSF-funded through the NERC-OU Agreement. Dr Sam Hammond is Part-Time (50%) Grade 6 Technician, OUUSF-funded through the NERC-OU Agreement till 31 March 2011. Sam also has a 50% appointment running the Agilent 7500 ICPMS in EES. All OUUSF staff are employed in Department of Earth and Environmental Sciences, Faculty of Science at The Open University on its standard Terms and Conditions.

8. Outreach

We aim to better promote the U-series facility in the wider academic community through the attendance at conferences and giving talks to other universities, and we are also taking part in local ‘Outreach’ activities. We have been involved in visits to local schools and taken part in the Milton Keynes Science Festival with an interactive display about uranium in the environment. Both LET and PvC are trained as STEM Ambassadors.

9. Notes from Peter van Calsteren, convener, on the Workshop at the Open University on Allogenic Contributions in U-Series Dating, 20 March 2009

First I would like to thank all 9 speakers, in particular Christa Placzek, 24 participants, interested colleagues who could not make the workshop, my colleagues at the OU and our sponsors, for what was, in my view, a positive experience.

The main aim of the workshop was to discus methods that would allow the analysts to minimise efforts (and funds) on samples that after completion of the analytical work, fail to meet the expectation of the users, mainly because the allogenic contributions to the 230Th are too large or too poorly defined.

We heard various contributors describe laboratory sub-sampling techniques. There were no new efforts reported aimed at selective dissolution; total dissolution seems to be universally adopted. There were contributions to screening methods, either using sample luminescence, or ‘quick and easy’ laser ablation. The luminescence efforts were directed at samples where the problem turned out to be hydrogenous rather than allogenic Th. Laser ablation is hampered by the unconsolidated nature of recent lake cores.

I had hoped for criteria that would be useful for the field limnologists to inform the coring strategy, but no new insights emerged.

Interestingly, limnologists are quite sanguine about efforts to establish U-series dates and they point out that the costs of obtaining detailed pollen records dwarf the U-series analytical costs.

It would appear to me that there are no significant improvements in corrections based on mixing lines (formerly known as ‘isochrons’). single sample corrections can be based of assumed allogenic 230Th/232Th, or on assumed allogenic Th/U ratios

with also assuming secular equilibrium. It isn’t clear to me which would be preferable. the justification of assuming a 50% uncertainty on the assumed allogenic ratio seems to be arbitrary. However, I

would contend that if a 50% uncertainty assumption leads to more than doubling the analytical uncertainty-based age, the correction is too large anyway.

determination of either allogenic ratio isn’t straightforward analytically because of unconstrained leaching effects.

it is clear that allogenic corrections to account for more than a few percent detrital material can lead to calculated ages that are no longer fit for purpose. I don’t think that this should lead to a simplistic rule-of-thumb because the effects of the correction are dependant of both U content and age; I intend to attempt some modelling about this.

One clear initiative, -probably somewhat fostered by the presence of Earth-Time colleagues-, is the need for inter-comparison standards, particularly for Th. (U is probably well-enough constrained by the old NBS range, a 230Th/232Th solution without spike at ‘silicate’ ratios solution is probably not required after the recent work of Sims et al.).

I can see two types, both fairly simple ‘spiked’ mixtures of 229Th, with 230Th and 232Th. One should have a low 230Th/232Th at ‘silicate’ values the other should have a much higher ratio, at the level of a clean sample for which nobody would consider an allogenic correction, it if were a real sample.

I’ll describe one solution that we use at the OU as an easy target for your suggestions. We use a mix of our Oak Ridge 229Th spike and our Th’U’std which is a mix of NIST 3159 and our Oak Ridge 230Th spike. The 230Th/232Th is

~0.6x10-6 and the 229Th/230Th is ~25. Using our single RPQ-SEM TIMS we have acceptable intensities on both 229Th and 230Th with 232Th on a Faraday. We have a solution with ~100ng/microlitre of which we load 2 drops of 1 microlitre for TIMS. We use 1 microlitre of the TIMS solution in a 50ml centrifuge tube for ICPMS. Similarly, this gives ~200cps for 230Th and 5000cps for 229Th. This solution is used in ‘bracketing’ mode and the ratios are normalised to the TIMS values. If I were to design a second solution, I would use a much higher 230Th/232Th ratio, probably around 0.4x10-4. We have sufficient 230Th to do this. I would aim for a similar 229Th/230Th ratio ~25.

For our Total Procedure Standard in the carbonate laboratory (again, there are plenty silicate standards around, I believe) we use a ground-up stalagmite and we use this both as a consistency standard and for training purposes.

It has U ~0.07 ppm; 232Th ~1.4 ppb; (230Th/232Th) ~16; (234U/238U) ~1.09; (230Th/234U) ~0.09 and an age ~10.7ka.

I can see the need for a carbonate standard that is in secular equilibrium and would welcome offers of the ‘raw material’. At the OU we have something of a reputation for preparing fairly large quantities of standard material, as well as for distribution and evaluation of results. I’m happy to volunteer our services in this respect.

I would welcome your feedback on any of the points above, if the volume and indeed nature, of feedback would justify it, I could setup a list-server or some such system, to facilitate communication

10. Projects for which the analytical work has been completed

10.1. OUUSF #51 NIGFSC # IP/906/0506 PI prof S Metcalfe Affiliation: University of NottinghamGeography a4m Title: Climate change on glacial-interglacial timescales in the neotropics Location: Cuitzeo, Mexico Sample type: lacustrine carbonatesThis project has not resulted in any significant age information. The samples were generally rather poor in authigenic carbonate and contained far too much silicate. Limnologists are somewhat sanguine about these and similar results that from our point of view are unsatisfactory. The costs involved in efforts to use U-series methods, are considered a worthwhile gamble as good dates would be invaluable. Moreover, the U-series costs are small relative to the costs of other methods, such as the construction of a pollen stratigraphy, which are practiced on limnological cores. We are hoping to look at some samples with higher levels of carbonate from part of the core.

   OUUSF #57 NIGFSC # IP/937/1106 PI prof D Thomas Affiliation: University of Oxford OUCE NER/S/A/2005/13353 a3high 69 Location: Naukluft, Namibia Title: Multi-proxy reconstruction of Late Quaternary environments in western South Africa Sample type: tufa/calcreteSee Science Highlights, Appendix 11.1.    

OUUSF # 63 NIGFSC # IP/1025/0508 PI prof J Andrews Affiliation: University of East Anglia SES a4m4.5 16 Location: Gulf of Corinth Title: Dating late Pleistocene eustatic sea level change in Greece Sample

type: carbonate cementThis project is part of the on-going research effort by the team at UEA with determining the rate and style of crustal uplift relative to sea-level variations only part of a much wider project that also includes palaeo-climate goals.

11. Extended Science Highlights

11.1. Quaternary tufa deposition in the Naukluft Mountains, Namibia: Prof David Thomas and Heather Viles, Abi Stone, PGRS, IP/937/1106

Tufa deposits have great potential as palaeo-environmental indicators particularly in semi-arid to arid regions, which contain relatively little proxy evidence in geological archives. Tufas are also potentially amenable to U-series dating.Fluvial tufa deposits in the ephemeral headwater streams that drain the Naukluft Mountains of the Great Escarpment, Namibia are the subject of this study. The tufas are biomediated freshwater continental carbonate deposits formed in non-thermal waters.The Naukluft Mountains are part of the Great Escarpment separating the Namibian interior highlands from the coastal plain on the west coast. The flat-topped plateau rises to an elevation of 1960 m a.s.l. and is dissected by narrow valleys of the catchment streams, which drain west from the Great Escarpment into the Namib Sand Sea. The outcropping Precambrian dolomite and limestone formations of the Naukluft complex have been incised and karstified, forming steep narrow valleys and extensive underground drainage systems. Discharge of groundwater in streams and springs has resulted in tufa .

The Naukluft tufa deposits are unusual in that their evolution appears to proceed in well-defined cycles: initially in steady-state, with semi-permanent surface flow forming cascades and barrages by turbulent degassing over the breaks of slope but with limited bedload entrainment. Subsequently, when cascades have grown to a critical size, water can pool and form banded tufa units. Finally, episodic high-flow conditions capable of carrying large bedrock boulders, result in the erosion and incision of barrage and cascade features. Subsequently, bedload becomes cemented by renewed tufa precipitation as the conditions return to the steady flow state, leaving clast-supported tufa facies (Fugure 1). There is evidence of multiple such cycles in the various tufa deposits that are found at the Great Escarpment in Namibia.

Figure 1: Naukluft tufa barrage showing various evolutionary stages, including: uncemented bedload boulders in the incised channel, cemented bedload boulder bed, and 2 downstream prograding barrages with steeply forward-dipping fronts composed of ‘steady state’ tufa precipitates, Open spaces and vugs in the tufa layers are visible and these are the location of subsequent deposition of the ‘densely-cemented layered tufa’ used for most ‘U-series isochron’. Most units are separated by sub-horizontal gravel lags.

Sample types:Within the barrage there is evidence for repeated periods of growth and erosion marked by the gravel lags, and within the vugs and spaces of many barrages, densely-cemented laminated tufa can be formed. For these to form water must have flown over and through the barrage features, rather than simply along the narrow and steeply incised channels, as observed today. We refer to the laminated tufa facies as ‘banded’ and whilst banded samples are found very rarely within these catchments, we find three subtypes:

a pool-type banded facies suggested to form in low-gradient, slack-waters densely-cemented tufa-flowstone drapes, which coat the incised-channels and steep cascade fronts dense layers formed in vugs of large units of porous moss or reed

Tufa samples with the best potential for dating are densely-cemented with negligible porosity to minimise the likelihood of open-systems behaviour, and pure-cements to reduce the influence of detrital contamination. The three banded facies types meet these criteria. Samples may not always remain chemically-closed systems and fabrics with high porosity have an increased likelihood of open systems behaviour. This includes post-depositional leaching of uranium, recrystallisation and/or neomorphism and secondary calcite precipitation.

Banded units are rare within the catchments and various other facies-types were also analysed. Moss tufa facies from two fluvial barrages.A moss moss facies with an outer coating of flowstone-type drape from the front of a cascade A gravel facies type from the top of the a cascadeA reed and root facies from the front of a same barrage

U-series disequilibrium dating methods are applied to a number of selected banded samples from the large and complex barrage deposits and to other tufa samples of various facies types. The U-series dating exercise has revealed significant challenges for assigning ages to Naukluft tufa deposits. U-series secular equilibrium in a densely-cemented banded unit indicates that large, extensive complexes of tufa in the Naukluft Mountains are of considerable antiquity. Other such deposits yield ages at ~ 80 ka which suggest that some large barrage features are of at least MIS 5 age, while there is some evidence for Holocene age deposits as coatings in heavily incised channels. Many densely-cemented banded samples contain more than one allogenic component and

standard ‘isochron’ mixing line protocols do not adequately correct for more than two end-members. Other densely-cemented banded samples exhibit have (230Th/234U)>1 activity ratios which cannot be the result of simple radioactive decay only but could be caused by leaching of 234U or ‘initial’ incorporation of 230Th. There is no petrographic evidence for uranium leaching in these samples, and leaching would also be indicated by (234U/238U)<1, which is not observed. It would appear that ‘unsupported’ 230Th was incorporated during tufa precipitation. This could be caused by leaching of both 230Th and to a lesser extent, 232Th from Naukluft limestone karst formations. Leached Th can be mobile at high PCO2 in alkaline groundwater and can then be incorporated during precipitation of the tufaAll four other facies types yielded high levels of detrital contamination, but have (230Th/234U) <1, and give finite age estimates in the range of 20-160 ka. Given the magnitude of the corrections for allogenic 230Th, micromorphological characteristics of these samples, the heterogeneity of cements types, and the porosity values of up to 40%, we cannot express great confidence in these data.

Various tufa deposits of the Naukluft Mountains contain similar suites of deposits in different channel catchments. This suggests that the hydro-climatic model of alternations between permanent steady river flow, episodic high flow conditions and quiescence, is robust for the region and this provides a first-order indication that the observed deposits relate to region-wide moisture availability, elevated groundwater levels and climatic forcing.

11.2. Localisation of Quaternary slip-rates in an active rift in ~105 years: an example from central Greece constrained by 234U-230Th coral dates from uplifted palaeo-shorelines. Prof John McArthur, Gerald Roberts, PGRA Sarah Houghton: IP/671/0900

Central Greece is amongst the most rapidly extending portions of the Earth’s continental crust, with 10-15 mm/yr of north-south extension localised within a < 30 km wide E-W zone associated with the Gulf of Corinth (Fig. 1a) (Billiris et al. 1991, Davies et al. 1997, Clarke et al. 1998, Briole et al. 2000). When and how extension became localised in its present position is not well known due to lack of detailed fault-specific displacement histories with good age control. The timescale over which strain localises into the plate boundary is known for only a few examples, due to limitations in dating syn-rift stratigraphy (e.g. Cowie et al. 2005).

At the present-day, coastal uplift in the Gulf of Corinth occurs within the footwalls of high slip-rate active north-dipping normal faults. These faults have been ruptured by seven >Ms 6.0 normal faulting earthquakes since 1909, including two large normal faulting earthquakes in the eastern gulf (February 1981; Ms 6.9, 6.7) (Ambraseys and Jackson, 1990). The faults have clear geomorphic expressions and display evidence for repeated offsets in the upper Quaternary and Holocene.

Detailed mapping (Figure 1), dating and modelling of palaeo-shorelines uplifted in the footwall of the 1981 Gulf of Corinth earthquake fault (Ms 6.9-6.7), can be used to assess its slip-rate history relative to other normal faults in the area and study strain localisation. Uplifted Quaternary and Holocene palaeo-shorelines decrease in elevation towards the western tip of the fault, exhibiting larger tilt angles with age, showing that uplift is due to progressive fault slip.

Figure 1. Palaeo-shorelines, topography and active faulting on the Perachora Peninsula map with the active faults that ruptured in 1981, and locations and elevations of palaeo-shorelines. Co-seismic throws decrease from east to west.

234U-230Th coral ages from Cladocora caespitosa date uplifted shoreface sediments and palaeo-shorelines from glacio-eustatic sea-level high-stands at 76 ka, possibly 100 ka, 125 ka, 175 ka, 200 ka, 216 ka, 240 ka and 340 ka. The 234U-230Th coral dates for palaeo-shorelines that formed during localisation of faulting show how Quaternary slip rates changed through time on a 105 timescale (Figure 2). This allows us to constrain the mechanisms responsible for the localisation.

Figure 2. Mapped and modelled palaeo-shorelines along Topographic Profile 1 (Figure 1). Palaeo-shorelines were identified using features including wave-cut platforms, shoreface sediments and lithophagid-bored coastal notches or marine-sub-aerial facies transitions.

Uplift rates were calculated to explain the elevations of mapped and dated palaeo-shorelines using initial sea-level elevations from the global sea-level curve (0.15 mm/yr until 175 ka followed by 0.51 mm/yr from 175 ka to present; R2 = 0.9939). These rates were used to calculate the expected elevations of other well-known sea-level high-stands. These modelled palaeo-shoreline elevations agree well with the mapped, but un-dated palaeo-shorelines. We interpret this to mean that the modelled ages are the ages of these un-dated palaeo-shorelines. Palaeo-shorelines from 76 ka, 100 ka, 125 ka, 200 ka, 240 ka and 340 ka are expected to be preserved and we have identified those. Palaeo-shorelines from 175 ka, 216 ka, 290 ka, 316 ka and 410 ka will be drowned by subsequent sea-level rises and subjected to marine erosion; they may not be preserved. With this uplift-rate scenario, the expected 216 ka, 175 ka, 316 ka and 410 ka palaeo-shorelines occupy similar elevations to the 125 ka, 200 ka, and 340 ka palaeo-shorelines, and the expected 290 ka palaeo-shoreline elevation is the same as one of our mapped but un-dated palaeo-shorelines (see Figure 2). We used the correlations between predicted and mapped but un-dated palaeo-shorelines to infer ages to un-dated shorelines on our maps.

Since 125 ka, uplift rates varied from 0.25 mm/yr to 0.52 mm/yr over a distance of 5 km away from the fault tip. Tilting was also occurring prior to 125 ka, but uplift rates were lower because the 125 ka palaeo-shoreline is at 77% of the elevation of the 240 ka palaeo-shoreline, despite being nearly half its age. Comparison of palaeo-shoreline elevations and sedimentology with the Quaternary sea-level curve show that slip-rates increased by a factor of 3.2 ± 0.2 at 175 ± 75 ka, synchronous with cessation of activity on a neighbouring normal fault at 382-112 ka. We suggest that the rapid localisation of up to 10-15 mm/yr of extension into the narrow gulf (c. 30 km wide) resulted from synchronous fault activity on neighbouring faults followed by localisation rather than sequential faulting, with consequences for the mechanism controlling localisation of extension. Further discussion in : G. P. Roberts, S. L. Houghton, C. Underwood, I. Papanikolaou, P. A. Cowie, P. van Calsteren, T. Wigley, F. J. Cooper, J. M. McArthur. Localisation of Quaternary slip-rates in an active rift in 105 years: an example from central Greece constrained by 234U-230Th coral dates from uplifted palaeo-shorelines. Journal of Geophysiscal Research, 2009, in press.

References:

Ambraseys, N.N., Jackson, J.A., Seismicity and associated strain of central Greece between 1890 and 1988. Geophysical Journal International 101, 663-708, 1990.

Billiris, H., Paradissis, G. England, P., Featherstone, W., Parsons, B., Cross, P., Rands, P., Rayson, M., Sellers, P., Ashkenazi, V., Davison, M., Jackson J., Ambraseys, 32 N., Geodetic determination of tectonic deformation in central 956 Greece from 1900 to 1988. Nature, 350, 124-129, 1991.

Briole, P., A. Rigo, H. Lyon-Caen, J. C. Ruegg, K. Papazissi, C. Mitsakaki, A. Balodimou, G. Veis, D. Hatzfeld, A. Deschamps, Active defromation of the Corinth rift, Greece: Results from repeated Global Positioning System surveys between 1990 and 1995. Journal of Geophysical Research, 105, 25,605-25,625, 2000.

Clarke, P. J., R. R. Davies, P. C. England, B. Parsons, H. Billiris, D. Paradissis, G. Veis, P. A. Cross, P. H. Denys, V. Ashkenazi, R. Bingley, H.-G. Kahle, M.-V. Muller and P. Briole. Crustal strain in central greece from repeated GPS measurments in the interval 1989-1997. Geophysical Journal International, 135, 195-214, 1998.

Cowie, P.A., Underhill, J. R., Behn, M.D., Lin, J., Gill, C. E., Spatio-temporal evolution of strain accumulation derived from multi-scale observations of Late Jurassic rifting in the northern North Sea: A critical test of models for lithospheric extension, Earth and Planetary Science Letters, 234, 401-419, 2005.

Davies, R., England, P., Parsons, B., Billiris, H., Paradissis, D., Veis, G., Geodetic strain of Greece in the interval 1892-1992, Journal of Geophysical Research, 102, 24571-24588, 1997.