ESCADARIAS DE TERRAÇOS MARINHOS EM PORTUGAL CENTROOCIDENTAL – RELEVÂNCIA COMO INDICADORES DE SOERGUIMENTO CRUSTAL STAIRCASES OF WAVE-CUT PLATFORMS IN WESTERN CENTRAL PORTUGAL – RELEVANCE AS INDICATORS OF CRUSTAL UPLIFT

This study addresses the coastal terrace staircases of western central Portugal (Cape Mondego to Cape Espichel). Below the culminant marine unit that records the last episode of aggradation before the ongoing stage of incision, several terrace levels ar identified. The following methodology was used: a) production of geomorphological maps, combining analysis of detailed MDT’s and aerial photos, with field surveys calibrated with GPS; b) stratigraphic and sedimentological study of the sedimentary deposits associated with the marine platforms; c) luminescence dating. On each terrace staircase, the number of platforms and their elevations are different, indicating differential uplift. Quartz OSL provided age estimates up ca. 150 kyr and post-IR IRSL on K-feldspar up to ca. 700 kyr for the marine terraces under study. Using the culminant platform as reference and assuming that it is ca. 3.6 Ma old, uplift rates were estimated as ranging spatially from 0.071 m/ky to 0.019 m/ky. The ongoing luminescence dating will provide uplift rates estimated for the lower and middle marineterraces, clarifying if an acceleration of the crustal uplift is going on

Violet stimulated luminescence dating of quartz from Luochuan (Chinese loess plateau): Agreement with independent chronology up to ∼600 ka

Luminescence dating at the Luochuan loess type (China) section is at present limited to ∼0.1 Ma using quartz blue light stimulated luminescence (BLSL), but can be extended back in time to ∼0.5 Ma by resorting to the more developmental post-infrared infrared stimulated luminescence (post-IR IRSL) and thermally transferred OSL (TT-OSL) signals. Since both the latter are associated with systematic uncertainties due to the potential (a)-thermal instability of these signals, a search continues for alternative, and demonstrably stable luminescence signals that can cover the entire Quaternary timescale. Here we explore the violet stimulated luminescence (VSL) signal at the Luochuan section, which provides a continuous archive of homogenous sediment with favourable luminescence characteristics and a solid independent age framework. By testing several VSL protocols and their associated performance, we demonstrate that the Multi-Aliquot Additive-Dose (MAAD) protocol produces a VSL chronology at Luochuan which is in agreement with independent ages up to ∼0.6 Ma. For a more representative environmental dose rate of ∼2 Gy/ka (∼35% lower than at Luochuan), the documented range of MAAD-VSL sensitivity (200-1800 Gy) would correspond to the ability to date sediment up to ∼1 Ma back in time, offering a remarkable advance over existing methods.</p

Towards an improvement of optically stimulated luminescence (OSL) age uncertainties:Modelling OSL ages with systematic errors, stratigraphic constraints and radiocarbon ages using the R package BayLum

International audienceAbstract. Statistical analysis has become increasingly important in optically stimulated luminescence (OSL) dating since it has become possible to measure signals at the single-grain scale. The accuracy of large chronological datasets can benefit from the inclusion, in chronological modelling, of stratigraphic constraints and shared systematic errors. Recently, a number of Bayesian models have been developed for OSL age calculation; the R package “BayLum” presented herein allows different models of this type to be implemented, particularly for samples in stratigraphic order which share systematic errors. We first show how to introduce stratigraphic constraints in BayLum; then, we focus on the construction, based on measurement uncertainties, of dose covariance matrices to account for systematic errors specific to OSL dating. The nature (systematic versus random) of errors affecting OSL ages is discussed, based – as an example – on the dose rate determination procedure at the IRAMAT-CRP2A laboratory (Bordeaux). The effects of the stratigraphic constraints and dose covariance matrices are illustrated on example datasets. In particular, the benefit of combining the modelling of systematic errors with independent ages, unaffected by these errors, is demonstrated. Finally, we discuss other common ways of estimating dose rates and how they may be taken into account in the covariance matrix by other potential users and laboratories. Test datasets are provided as a Supplement to the reader, together with an R markdown tutorial allowing the reproduction of all calculations and figures presented in this study

Combining dating techniques in paleo-earthquake chronologies: the example of El Saltador (Alhama de Murcia fault)

Presentamos la cronología de paleoterremotos establecida para la rama sur de la Falla de Alhama de Murcia (Béticas Orientales) a partir del estudio paelosismológico de la localidad de el Saltador (Lorca). Mostramos la aplicación combinada de cuatro métodos de datación; luminiscencia en cuarzo y feldespato (OSL en cuarzo y pIRIRSL), datación de series de Uranio en carbonatos pedogénicos, y radiocarbono. Para acotar la edad de los paleoterremotos con la mejor definición posible, se han integrado las edades de las capas que definen temporalmente los paleosismos en un modelo deposicional. Para ello se usó el programa OxCal (versión 4.2), que realiza un tratamiento estadístico bayesiano de las funciones de probabilidad de las edades de materiales afectados según un orden estratigráfico conocido y calcula la recurrencia media y la recurrencia particular entre eventos sucesivos. La secuencia de materiales aluviales muestra el registro de ocho eventos paleosísmicos ocurridos desde hace 54,3 ± 9,1 ka. El tiempo de recurrencia medio varía entre 3,5- y 5,3 ka , localizándose el último evento entre el s. XIII y el s. XVIII.We present a chronology of paleo-earthquakes established at El Saltador (Lorca), a paleoseismical site in the southern branch of the Alhama de Murcia Fault (Eastern Betics). Because of the difficulties in dating the affected sediments using a single dating approach, we combined four types of methods; Two of them based on the luminescence of quartz and feldspar (Quartz-OSL and pIR-IRSL), U-series on pedogenic carbonates and radiocarbon dating. To obtain the best possible accuracy for the age of each paleoearthquake, we integrated the age of the layers that constrain the seismic events into a depositional model. To this end, we relied on the OxCal program (version 4.2), which performs a Bayesian statistical treatment of the probability functions of the ages assigned to a sequence of layers of known stratigraphical order, at the time that it provides the average recurrence and the single recurrence between successive events. The sequence of alluvial deposits analyzed shows the record of eigth paleoseismic events occurred since 54,3 ± 9.1 ka. The average recurrence intervals ranges between 3,5- and 5,3 ka with the last event taking place between the XIII and XVII centuries.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Ciencia e Innovación (MICINN)Generalitat de Catalunyapu

Mid-late quaternary fluvial archives near the margin of the MIS 12 glaciation in Southern East Anglia, UK: amalgamation of multi-disciplinary and citizen-science data sources

This paper presents an updated geological reconstruction of the Quaternary evolution of the River Thames at its downstream extremities, close to the North Sea coast, based on new data from multi-disciplinary and citizen-science sources. In this area, the interaction of the Thames with the MIS 12 (Anglian) glaciation is an important part of the Quaternary archive. The Anglian ice sheet, which reached parts of north and east London, was responsible for diverting the Thames southwards into its present course, although the footprint of the maximum ice sheet(s) does not reach the North Sea coast south of Hollesley, Suffolk. Further south, the coastal zone hosts pre-Anglian and early Anglian river-terrace deposits of the pre-diversion Thames system, superimposed upon which are products of later post-Anglian rivers, of both Middle and Late Pleistocene age. On the peninsula between the Stour and Blackwater–Colne estuaries, the lowest and most recent terrace of the pre-diversion Thames includes evidence directly pertaining to the glacial disruption event, for which geochronological data are reported here for the first time. The first post-diversion terrace of the Thames also reaches this peninsula, the river having essentially re-joined its original valley before crossing the alignment of the modern coastline. This terrace passes beneath Clacton-on-Sea, where it includes the type locality of the Clactonian Palaeolithic Industry. The area of interest to this paper, in NE Essex and southern Suffolk, includes a number of interglacial and Palaeolithic sites, the data from which assist in constraining the chronostratigraphy of the sequence. In some cases, there has been uncertainty as to whether these sites represent pre-Anglian environments and hominin occupations, part of the palaeo-Thames sequence, or whether they are the product of later post-Anglian streams, formed after the Thames had migrated southwards. This paper compiles evidence from a wide range of recent sources, including developer-funded archaeological appraisal and citizen-science activities, to explore and update the evidence from sites at Ipswich, Upper Dovercourt and Thorpe-le-Soken, as well as a number of localities associated with the Clacton Channel Deposits (host to the type-Clactonian), amongst others. The resulting new data are placed within the wider context of the Quaternary fluvial archives in southern Britain, with a discussion of how disparate sources of information, including the work of citizen scientists, have contributed