The IRHUM (Isotopic Reconstruction of Human Migration) database – bioavailable strontium isotope ratios for geochemical fingerprinting in France

Strontium isotope ratios (87Sr / 86Sr) are a key geochemical tracer used in a wide range of fields including archaeology, ecology, food and forensic sciences. These applications are based on the principle that the Sr isotopic ratios of natural materials reflect the sources of strontium available during their formation. A major constraint for current studies is the lack of robust reference maps to evaluate the source of strontium isotope ratios measured in the samples. Here we provide a new data set of bioavailable Sr isotope ratios for the major geologic units of France, based on plant and soil samples (Pangaea data repository doi:10.1594/PANGAEA.819142). The IRHUM (Isotopic Reconstruction of Human Migration) database is a web platform to access, explore and map our data set. The database provides the spatial context and metadata for each sample, allowing the user to evaluate the suitability of the sample for their specific study. In addition, it allows users to upload and share their own data sets and data products, which will enhance collaboration across the different research fields. This article describes the sampling and analytical methods used to generate the data set and how to use and access the data set through the IRHUM database. Any interpretation of the isotope data set is outside the scope of this publication.

New Perspectives on the Chronostratigraphy and Magmatic Evolution of the Auckland Volcanic Field, New Zealand

<p>Understanding the eruptive history of a volcanically active region is critical in assessing the hazard and risk posed by future eruptions. In regions where surface deposits are poorly preserved, and ambiguously sourced, tephrostratigraphy is a powerful tool to assess the characteristics of past eruptions. The city of Auckland, New Zealand’s largest urban centre and home to ca. 1.4 million people, is built on top of the active Auckland Volcanic Field (AVF). The AVF is an intraplate monogenetic basaltic volcanic field, with ca. 53 eruptive centres located in an area of ca. 360 km2. Little is known however, about the evolution of the field because the numerical and relative ages of the eruptions are only loosely constrained, and therefore the precise order of many eruptions is unknown. Here I apply tephrostratigraphic and geochemical techniques to investigate the chronology and magmatic evolution of the AVF eruptions. First, I present an improved methodology for in-situ analysis of lacustrine maar cores from the AVF by employing magnetic susceptibility and X-ray density scanning on intact cores. These techniques are coupled with geochemical microanalysis of the tephra-derived glass shards to reveal details of reworking within the cores. These details not only allow assessment of the deposit relationships within cores (e.g. primary vs. reworked horizons), but also to correlate tephra horizons between cores. Through the correlation of tephra units across cores from a variety of locations across the field, an improved regional tephrostratigraphic framework for the AVF deposits has been established. Following on from this, I detail the methods developed in this study to correlate tephra horizons within the maar cores back to their eruptive source. This technique uses geochemical fingerprinting to link the glass analyses from tephra samples to whole rock compositions. Such an approach has not been previously attempted due to the complications caused by fractional crystallisation, which affects concentrations of certain key elements in whole rock analyses. My method resolves these issues by using incompatible trace elements, which are preferentially retained in melt over crystals, and therefore retain comparable concentrations and concentration ratios between these two types of sample. Because of the primitive nature of the AVF magmas, their trace element signature is largely controlled by the involvement of several distinct mantle sources. This leads to significant variability between the volcanic centres that thus can be used for individually fingerprinting, and correlating tephra to whole rocks. Nevertheless, in some cases geochemistry cannot provide an unambiguous correlation, and a multifaceted approach is required to allow the correlation of the tephra horizons to source. The other criteria used to correlate tephra deposits to their source centre include, Ar-Ar ages of the centres, modelled and calculated ages of the tephra deposits, the scale of eruption, and the deposit locations and thicknesses. The results of this research outline the methodology for assessing occurrence and characteristics of basaltic tephra horizons within lacustrine maar cores, and the methodology for correlating these horizons to their eruptive source. In doing this the relative eruption order of the AVF is accurately determined for the first time. Temporal trends suggest acceleration of eruption repose periods to 21 ka followed by deceleration to present. Although no spatial evolution is observed, coupling of some centres is seen when spatial and temporal evolution are combined. The geochemical signature of the magmas appears to evolve in a cyclic manner with time, incorporating increasing amount of a shallow source. This evolution is seen both during a single eruption sequence and throughout the lifespan of the AVF. Finally, pre-eruptive processes are assessed as part of the study of the magmatic evolution of the AVF. The effects of contamination from the crust and lithosphere through which the magma ascends are evaluated using the Re-Os isotope system. The results show there are variable inputs from crustal sources, which have previously not been identified by traditional isotope systems (e.g. Pb-Sr-Nd isotopes). Two sources of contamination are identified based on their Os systematics relating to two terranes beneath the AVF: the metasedimentary crust and the Dun Mountain Ophiolite Belt. The identification of this process suggests there is interaction of ascending melt with the crust, contrary to what previous studies have concluded. This body of research has provided a detailed reconstruction of the chronostratigraphy and magmatic evolution of the AVF to aid accurate and detailed risk assessment of the threat posed by a future eruption from the Auckland Volcanic Field.</p>

New Perspectives on the Chronostratigraphy and Magmatic Evolution of the Auckland Volcanic Field, New Zealand

<p>Understanding the eruptive history of a volcanically active region is critical in assessing the hazard and risk posed by future eruptions. In regions where surface deposits are poorly preserved, and ambiguously sourced, tephrostratigraphy is a powerful tool to assess the characteristics of past eruptions. The city of Auckland, New Zealand’s largest urban centre and home to ca. 1.4 million people, is built on top of the active Auckland Volcanic Field (AVF). The AVF is an intraplate monogenetic basaltic volcanic field, with ca. 53 eruptive centres located in an area of ca. 360 km2. Little is known however, about the evolution of the field because the numerical and relative ages of the eruptions are only loosely constrained, and therefore the precise order of many eruptions is unknown. Here I apply tephrostratigraphic and geochemical techniques to investigate the chronology and magmatic evolution of the AVF eruptions. First, I present an improved methodology for in-situ analysis of lacustrine maar cores from the AVF by employing magnetic susceptibility and X-ray density scanning on intact cores. These techniques are coupled with geochemical microanalysis of the tephra-derived glass shards to reveal details of reworking within the cores. These details not only allow assessment of the deposit relationships within cores (e.g. primary vs. reworked horizons), but also to correlate tephra horizons between cores. Through the correlation of tephra units across cores from a variety of locations across the field, an improved regional tephrostratigraphic framework for the AVF deposits has been established. Following on from this, I detail the methods developed in this study to correlate tephra horizons within the maar cores back to their eruptive source. This technique uses geochemical fingerprinting to link the glass analyses from tephra samples to whole rock compositions. Such an approach has not been previously attempted due to the complications caused by fractional crystallisation, which affects concentrations of certain key elements in whole rock analyses. My method resolves these issues by using incompatible trace elements, which are preferentially retained in melt over crystals, and therefore retain comparable concentrations and concentration ratios between these two types of sample. Because of the primitive nature of the AVF magmas, their trace element signature is largely controlled by the involvement of several distinct mantle sources. This leads to significant variability between the volcanic centres that thus can be used for individually fingerprinting, and correlating tephra to whole rocks. Nevertheless, in some cases geochemistry cannot provide an unambiguous correlation, and a multifaceted approach is required to allow the correlation of the tephra horizons to source. The other criteria used to correlate tephra deposits to their source centre include, Ar-Ar ages of the centres, modelled and calculated ages of the tephra deposits, the scale of eruption, and the deposit locations and thicknesses. The results of this research outline the methodology for assessing occurrence and characteristics of basaltic tephra horizons within lacustrine maar cores, and the methodology for correlating these horizons to their eruptive source. In doing this the relative eruption order of the AVF is accurately determined for the first time. Temporal trends suggest acceleration of eruption repose periods to 21 ka followed by deceleration to present. Although no spatial evolution is observed, coupling of some centres is seen when spatial and temporal evolution are combined. The geochemical signature of the magmas appears to evolve in a cyclic manner with time, incorporating increasing amount of a shallow source. This evolution is seen both during a single eruption sequence and throughout the lifespan of the AVF. Finally, pre-eruptive processes are assessed as part of the study of the magmatic evolution of the AVF. The effects of contamination from the crust and lithosphere through which the magma ascends are evaluated using the Re-Os isotope system. The results show there are variable inputs from crustal sources, which have previously not been identified by traditional isotope systems (e.g. Pb-Sr-Nd isotopes). Two sources of contamination are identified based on their Os systematics relating to two terranes beneath the AVF: the metasedimentary crust and the Dun Mountain Ophiolite Belt. The identification of this process suggests there is interaction of ascending melt with the crust, contrary to what previous studies have concluded. This body of research has provided a detailed reconstruction of the chronostratigraphy and magmatic evolution of the AVF to aid accurate and detailed risk assessment of the threat posed by a future eruption from the Auckland Volcanic Field.</p>

Machine Learning in Discriminating Active Volcanoes of the Hellenic Volcanic Arc

Identifying the provenance of volcanic rocks can be essential for improving geological maps in the field of geology and providing a tool for the geochemical fingerprinting of ancient artifacts like millstones and anchors in the field of geoarchaeology. This study examines a new approach to this problem by using machine learning algorithms (MLAs). In order to discriminate the four active volcanic regions of the Hellenic Volcanic Arc (HVA) in Southern Greece, MLAs were trained with geochemical data of major elements, acquired from the GEOROC database, of the volcanic rocks of the Hellenic Volcanic Arc (HVA). Ten MLAs were trained with six variations of the same dataset of volcanic rock samples originating from the HVA. The experiments revealed that the Extreme Gradient Boost model achieved the best performance, reaching 93.07% accuracy. The model developed in the framework of this research was used to implement a cloud-based application which is publicly accessible at This application can be used to predict the provenance of a volcanic rock sample, within the area of the HVA, based on its geochemical composition, easily obtained by using the X-ray fluorescence (XRF) technique.

Reconstructing the Changes in Sedimentation and Source Provenance in an East African Hydropower Reservoirs: A Case Study of Nyumba ya Mungu in Tanzania

This study aimed to reconstruct the sedimentation rates over time and identify the changing sources of sediment in a major hydropower reservoir in Tanzania, the Nyumba ya Mungu (NYM). Fallout 210Pb measurements were used to estimate age of sediment deposits and broad changes in sedimentation rates were reconstructed. Sedimentation peaks were cross referenced to geochemical profiles of allogenic and autogenic elemental constituents of the sediment column to confirm a causal link. Finally, geochemical fingerprinting of the sediment cores and potential sources were compared using a Bayesian mixing model (MixSIAR) to attribute the dominant riverine and land use sources to the reservoir together with changes through recent decades. Reservoir sedimentation generally increased from 0.1 g cm−2 yr−1 in the lower sediment column to 1.7 g cm−2 yr−1 in the most recent deposits. These results correlated to changes in allogenic and autogenic tracers. The model output pointed to one of two major tributaries, the Kikuletwa River with 60.3%, as the dominant source of sediment to the entire reservoir, while the other tributary, Ruvu River, contributed approximately 39.7%. However, downcore unmixing results indicated that the latest increases in sedimentation seem to be mainly driven by an increased contribution from the Ruvu River. Cultivated land (CU) was shown to be the main land use source of riverine sediment, accounting for 38.4% and 44.6% in Kikuletwa and Ruvu rivers respectively. This study explicitly demonstrated that the integration of sediment tracing and dating tools can be used for quantifying the dominant source of sediment infilling in East African hydropower reservoirs. The results underscore the necessity for catchment-wide management plans that target the reduction of both hillslope erosion reduction and the sediment connectivity from hillslope source areas to rivers and reservoirs, which will help to maintain and enhance food, water and energy security in Eastern Africa.

Analysis of Garnet by Laser-Induced Breakdown Spectroscopy—Two Practical Applications

Laser-induced breakdown spectroscopy (LIBS) is a simple and straightforward technique of atomic emission spectroscopy that can provide multi-element detection and quantification in any material, in-situ and in real time because all elements emit in the 200–900 nm spectral range of the LIBS optical emission. This study evaluated two practical applications of LIBS—validation of labels assigned to garnets in museum collections and discrimination of LCT (lithium-cesium-tantalum) and NYF (niobium, yttrium and fluorine) pegmatites based on garnet geochemical fingerprinting, both of which could be implemented on site in a museum or field setting with a handheld LIBS analyzer. Major element compositions were determined using electron microprobe analysis for a suite of 208 garnets from 24 countries to determine garnet type. Both commercial laboratory and handheld analyzers were then used to acquire LIBS broadband spectra that were chemometrically processed by partial least squares discriminant analysis (PLSDA) and linear support vector machine classification (SVM). High attribution success rates (>98%) were obtained using PLSDA and SVM for the handheld data suggesting that LIBS could be used in a museum setting to assign garnet type quickly and accurately. LIBS also identifies changes in garnet composition associated with increasing mineral and chemical complexity of LCT and NYF pegmatites.

Geochemical Fingerprinting pf Oil-Impacted Soil and Water Samples In Some Selected Areas in the Niger Delta

With over 50 years of oil exploration and exploitation in the Niger Delta, there has been an increasing rate of environmental degradation due to hydrocarbon pollution. This study is aimed at tracing the sources of the oil spills and the distribution of pollutants in selected communities in the Niger Delta using geo-chemical techniques. A total of sixteen samples made up of ten crude oil-impacted soil samples taken at a depth of 30 cm and six water samples (two from boreholes, two from burrow pits and two from surface water – one from a river and the other from rain harvest as control) were collected. The identification and quantification of aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) in the samples were performed with an Agilent 7890B gas chromatography flame ionisation detector (GCFID). The AHs including pristane and phytane, together with seventeen priority PAHs, were identified. The values of AHs and PAHs in the water samples ranged from 0.13 mg/l to 5.78 mg/l and 0.09 mg/l to 1.109 mg/l, respectively, while that for the soil samples ranged from 22.52 mg/kg to 929.44 mg/kg and 10.544 mg/kg to 16.879 mg/kg, respectively. Z več kot petdesetimi leti raziskovanja in pridobivanja nafte na območju delte reke Niger narašča stopnja degradacije okolja zaradi onesnaževanja z ogljikovodiki. Namen raziskave je slediti virom razlitij nafte in porazdelitev onesnaževal v izbranih skupnostih v delti reke Niger z uporabo geokemičnih pristopov. Skupno je bilo odvzetih 16 vzorcev, od tega 10 vzorcev z nafto nasičenih zemljin iz globine 30 cm ter 6 vzorcev vode, od tega dva iz vrtin, dva iz jame ter dva iz površinske vode (en vzorec iz reke in en iz deževnice). Z detektorjem plamenskega ioniziranja s plinskim kromatografom Agilent 7890B (GC-FID) je bila izvedena identifikacija in kvantifikacija alifatskih ogljikovodikov (AH) in policikličnih aromatskih ogljikovodikov (PAH). Identificirani so bili AH z vključujočim pristanom (pristane) in fitanom (phytane) skupaj s 17 PAH. Vrednosti AH in PAH v vzorcih vode se gibajo med 0.13 mg/l do 5.78 mg/l in 0.09 mg/l do 1.109 mg/l. Vrednosti AH in PAH v vzorcih zemljine se gibajo med 22.52 mg/kg do 929.44 mg/kg in 10.544 mg/kg do 16.879 mg/kg.

The medial offshore record of Plinian arc volcanism in the Eastern Aegean Sea: Implications for tephrostratigraphy, correlations, ages and volumes

&lt;p&gt;The Hellenic arc hosts several active volcanic centers, of which the Milos, Santorini-Kolumbo and Kos-Yali-Nisyros volcanic fields present particularly high threats due to recent unrest (2011-2012 and 1996-1997 at Santorini and Nisyros, respectively). These volcanic centers have repeatedly produced highly explosive eruptions (VEI 4 to 7) from ~360 ka into historic times. The marine tephra record provides information not only on the number of events, but also on their magnitudes and intensities inferred from tephra dispersal characteristics, and is thus essential to quantitatively assess future volcanic hazards and risks.&lt;/p&gt;&lt;p&gt;Here we complement earlier work on distal to ultra-distal east-Mediterranean sediment cores, which captured the largest eruptions. We present results from a grid of medial to distal sediment cores collected in 2017 during RV Poseidon cruise POS513 with core positions both comparatively close to and between the three volcanic fields, in order to record medium- to large-scale eruptions.&lt;/p&gt;&lt;p&gt;During this cruise, 47 gravity cores up to 7.4 m long, and 3 box cores of the uppermost 0.5 m sediment were recovered, which contain more than 220 primary ash layers. The compositions of glass shards from all layers were characterized by major (EMP) and trace-element (LA-ICPMS) analyses.&lt;/p&gt;&lt;p&gt;Geochemical fingerprinting supports correlations with 20 eruptions from all three volcanic fields as well as with the 39 ka Campanian ignimbrite eruption from the Campi Flegrei, Italy. Correlations with eleven eruptions from Santorini-Kolumbo (Kameni, Kolumbo 1650, Minoan, Cape Riva, Cape Tripiti, Upper Scoria 1 and 2, Middle Pumice, Cape Thera, Lower Pumice, Cape Therma 3) are established, and we newly identify two widespread tephras from eruptions on Milos (Lower and Upper Firiplaka). We have probably been able to solve some previous chronostratigraphic problems at Kos-Yali-Nisyros by correlating marine tephras with the Kos Plateau Tuff, and with the Yali 2 tephra, whereby we identify a second, less evolved facies produced by that eruption that has not yet been recognized on land. We also find tephras from four eruptions on Nisyros (Nisyros 1 to 4) including the previously established Lower (Nisyros 4) and Upper (Nisyros1) Nisyros Pumice eruptions.&lt;/p&gt;&lt;p&gt;These correlations also provide new age constraints for hitherto poorly or non-dated Aegean tephras based on sedimentation rates derived between multiple anchor points of dated terrestrial tephra ages. We deduce ages of ~22 ka and ~36 ka for Upper and Lower Firiplaka tephras from Milos (the latter overlying the Campanian ash) which are significantly younger than other eruption ages known from Milos, ~54 ka, ~62 ka, ~69 ka, and ~76 ka for the Nisyros 1 to 4 tephras, and ~52 ka for the Yali 1 tephra as well as a verified age of 33 ka for the Yali 2 tephra with its two contemporaneous facies.&lt;/p&gt;&lt;p&gt;These new tephrostratigraphic results help to improve quantifications of distribution and eruption characteristics for all these eruptions, and provide important pre-site survey data for the Santorini IODP proposal VolTecArc.&lt;/p&gt;

Petrographic and geochemical fingerprinting of flints from the type-Maastrichtian (SE Netherlands and NE Belgium): implications for flint formation and provenance

&lt;p&gt;The chalk deposits of the type-Maastrichtian, in the SE Netherlands and NE Belgium (the Li&amp;#232;ge-Limburg region), are characterized by abundant flint layers. Since prehistoric times, flints from this region have been used as raw materials for tool making. While the formation, cyclicity and lithostratigraphy of flint layers from the type-Maastrichtian have been previously studied, their stratigraphic, lateral and internal geochemical and petrological variability are still poorly constrained, posing challenges for tracing the provenance of flint tools. Therefore, in the context of the Maastrichtian Geoheritage Project, we are analysing &lt;em&gt;in-situ&lt;/em&gt; flint samples macroscopically, microscopically and with micro-X-ray fluorescence (&amp;#181;XRF). The flint samples were collected from a 50-m-thick interval from the Upper Cretaceous Gulpen Formation at the former ENCI quarry (NL) and the Hallembaye quarry (BE). In contrast to averaged outcomes of bulk or portable X-ray fluorescence techniques commonly used for provenance studies of flints in geoarchaeology, the use of &amp;#181;XRF has the advantage of offering insights into the internal variability and heterogeneity of flints, by displaying relative distributions of major and trace elements within flint samples. Our preliminary results show that flint nodules from the Gulpen Formation can be subdivided based on composition. Flint layers in the middle part of this formation (Vijlen Member) show a high contribution of micrite, in addition to silica, and display a heterogeneous distribution of elements such as Ca, S, K, Fe, Rb and Sr, while flint layers from the overlying Lixhe 1-3 members consist predominantly of silica and have a more homogeneous distribution of chemical elements. Both types of flint layers contain biogenic inclusions, such as fragments of sponge spicules, echinoids, shells and benthic/planktic foraminifera, and other minerals, including iron sulphides and glauconite, but with a different abundance. The observed heterogeneity and variability within the flint nodules might not only be useful for tracing the provenance of flint tools, but could also provide insights into the complex formation of flints.&lt;/p&gt;