XRF Core Scanning Research Articles

Diatom-based estimation of sea surface salinity in the south Baltic Sea and Kattegat

A new diatom-based sea surface salinity (SSS) estimation has been applied to a collection of 27 taxa in 48 present-day sediment and surface water samples recovered in the Baltic Sea and Kattegat. The sediment core 303610-12 (2005) from the Eastern Gotland was chosen for study of Holocene sequence, ranging the last 8160 yrs BP. The Artificial Neuronal Network (ANN) method allows the estimation of spring SSS (March-April) values ranging between 7.04 ‰ and 8.25 ‰ at an averaged Root Mean Squared Error (RMSE) of 0.49 ‰. The rather low amplitude of salinity change might be caused by mixing of fresh water with upper surface layer of the Baltic Sea due to high precipitation and riverine input. The estimates of spring SSS from core 303610-12 were compared with independent geochemical proxies for salinity (K, Ti and S) derived from XRF Core Scanner record. Conspicuous correlation between salinity and sulphur records and reverse-correlation to K and Ti demonstrates that the ANN method combined with quantitative and qualitative analyses of diatoms provides a useful tool for palaeosalinity reconstructions in the Holocene sediments of the Baltic Sea

Bighorn Basin Coring Project (BBCP): a continental perspective on early Paleogene hyperthermals

Abstract. During the summer of 2011, the Bighorn Basin Coring Project (BBCP) recovered over 900 m of overlapping core from 3 different sites in late Paleocene to early Eocene fluvial deposits of northwestern Wyoming. BBCP cores are being used to develop high-resolution proxy records of the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2) hyperthermal events. These events are short-term, large magnitude global warming events associated with extreme perturbations to the earth's carbon cycle. Although the PETM and ETM2 occurred ~55–52 million years ago, they are analogous in many ways to modern anthropogenic changes to the carbon cycle. By applying various sedimentological, geochemical, and palynological methods to the cores, we hope to better understand what caused these events, study the biogeochemical and ecological feedbacks that operated during them, and reveal precisely how they impacted continental environments. Core recovery was >98% in all holes and most drilling was carried out without fluid additives, showing that continuous coring of continental smectitic deposits like these can be achieved with minimal risk of contamination to molecular biomarkers. Cores were processed in the Bremen Core Repository where the science team convened for 17 days to carry out data collection and sampling protocols similar to IODP projects. Initial results show that the weathered horizon extends to as much as ~30 m below the surface and variations in magnetic susceptibility within the cores record an interplay between grain size and pedogenesis. Previous investigations of outcrops near the BBCP drill sites allow detailed evaluation of the effects of weathering on common proxy methods. Studies of lithofacies, organic geochemistry, stable isotope geochemistry, calibrated XRF core scanning, paleomagnetics, and palynology are underway and will represent the highest resolution and most integrated proxy records of the PETM from a continental setting yet known. An extensive outreach program is in place to capitalize on the educational value associated with the Bighorn Basin's unusually complete record of Phanerozoic earth history.

Combining sedimentological, trace metal (Mn, Mo) and molecular evidence for reconstructing past water-column redox conditions: The example of meromictic Lake Cadagno (Swiss Alps)

Here, we present sedimentological, trace metal, and molecular evidence for tracking bottom water redox-state conditions during the past 12,500years in nowadays sulfidic and meromictic Lake Cadagno (Switzerland). A 10.5m long sediment core from the lake covering the Holocene period was investigated for concentration variations of the trace metals Mn and Mo (XRF core scanning and ICP-MS measurements), and for the presence of anoxygenic phototrophic sulfur bacteria (carotenoid pigment analysis and 16S rDNA real time PCR). Our trace metal analysis documents an oxic-intermediate-sulfidic redox-transition period beginning shortly after the lake formation ∼12.5kyr ago. The oxic period is characterized by low sedimentary Mn and Mo concentrations, as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria. Enhanced accumulation/preservation of Mn (up to 5.6wt%) in the sediments indicates an intermediate, Mn-enriched oxygenation state with fluctuating redox conditions during a ∼2300-year long transition interval between ∼12.1 and 9.8kyr BP. We propose that the high Mn concentrations are the result of enhanced Mn2+ leaching from the sediments during reducing conditions and subsequent rapid precipitation of Mn-(oxyhydr)oxide minerals during episodic and short-term water-column mixing events mainly due to flood-induced underflows. At 9800±130calyr BP, a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of Mo in the sediments (up to 490ppm), accompanied by an abrupt drop in Mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column. Persistently high Mo concentrations >80ppm provide evidence that sulfidic conditions prevailed thereafter until modern times, without any lasting hypolimnetic ventilation and reoxygenation. Hence, Lake Cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over ∼12kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment, possibly depicting analogous conditions in an ancient ocean. Our study underscores the value of combining sedimentological, geochemical, and microbiological approaches to characterize paleo-environmental and -redox conditions in lacustrine and marine settings.

Tracing bottom water oxygenation with sedimentary Mn/Fe ratios in Lake Zurich, Switzerland

Redox dynamics of manganese (Mn) were studied in the sediment of Lake Zurich using precise sediment core age models, monthly long-term oxygen (O2) monitoring data of the water column (1936–2010) and high-resolution XRF core scanning. The age models were based on bi-annual lamination and calcite precipitation cycles. If present, Mn exhibits distinct maxima, which coincide with the annual maximum deep-water O2 concentrations in spring according to the monitoring data. In contrast, the iron (Fe) signal is mainly the result of calcite dilution, as indicated by a strong negative correlation between Fe and calcium (Ca) XRF data. The Mn/Fe ratio in the core from the maximum lake depth (ZH10-15, 137m) revealed a moderate correlation with O2 measurements in the lake bottom water confirming the successful application of the Mn/Fe ratio to semi-quantitatively reconstruct bottom water oxygenation in the lake. Mostly low ratios were observed between 1895 and the mid-1960s as a result of eutrophication. However, geochemical focusing and sedimentological factors can reduce the applicability of the Mn/Fe ratio in reconstructing O2 concentrations in the bottom water of lakes.

Magnetic signatures of Heinrich-like detrital layers in the Quaternary of the North Atlantic

Magnetic parameters are useful for distinguishing North Atlantic Heinrich-like detrital layers from background sediments. Here we compare magnetic properties with XRF scanning data back to 700ka and 1.3Ma at IODP Sites U1302–U1303 and U1308, respectively. Multi-domain magnetite, with grain sizes >20µm, is characteristic of both Ca- and Si-rich detrital layers, as defined by XRF core scanning, confirming the contribution of ice rafting. Reflectance spectra and magnetic parameters distinguish Ca- and Si-rich IRD layers due the presence of high coercivity hematite in Si-rich layers. Heinrich layer 6 (H6) at Site U1302–U1303 is unlike other detrital layers, being marked by a 45-cm thick homogeneous cream-colored clay layer underlain by a thin (5-cm) graded coarse-sand. Comparison of Site U1302/03 and Site U1308 detrital layers implies a dominant Laurentide source for both Ca- and Si-rich detrital layers. At Site U1308, low benthic δ13C values during stadials are in-step with magnetic grain-size coarsening associated with Si-rich detrital layers back to 1.3Ma, indicating a link between deep-sea ventilation and ice rafting. The surface-sediment tan-colored oxic layer (~2m thick at Site U1308) yields magnetic hysteresis ratios that are offset from the single-domain to multi-domain (SD–MD) magnetite mixing-line in hysteresis-ratio diagrams. This offset is attributed to maghemite grain-coatings, that form on magnetite in surface sediment, and undergo dissolution as they pass through the oxic/anoxic boundary.

Destructive and non-destructive density determination: method comparison and evaluation from the Laguna Potrok Aike sedimentary record

Density measurements play a central role in the characterization of sediment profiles. When working with long records (>100 m), such as those routinely obtained within the frame of the International Continental Scientific Drilling Program, several methods can be used, all of them varying in resolution, time-cost efficiency and source of errors within the measurements. This paper compares two relatively new non-destructive densitometric methods, CT-Scanning and the coherent/incoherent ratio from an Itrax XRF core Scanner, to data acquired from a Multi-sensor core logger Gamma Ray Attenuation Porosity Evaluator (MSCL Grape) and discrete measurements of dry bulk density, wet bulk density and water content. Quality assessment of density measurements is performed at low and high resolution along the Laguna Potrok Aike (LPA) composite sequence. Giving its resolution (0.4 mm in our study), its high signal to noise ratio, we conclude that CT-Scan provides a precise, fast and cost-efficient way to determine density variation of long sedimentary record. Although more noisy that the CT-Scan measurements, coherent/incoherent ratio from the XRF core scanner also provides a high-resolution, reliable continuous measure of density variability of the sediment profile. The MSCL Grape density measurements provide actual density data and have the significant advantage to be completely non-destructive since the acquisition is performed on full cores prior to opening. However, the quality MSCL Grape density measurements can potentially be reduced by the presence of voids within the sediment core tubes and the dry and bulk density measurements suffers from sampling challenges and are time-consuming.

Sedimentary earthquake records in the İzmit Gulf, Sea of Marmara, Turkey

Sedimentary earthquake records of the last 2400a, including that of the devastating 17 August 1999 İzmit earthquake (Mw=7.4), were studied in cores from the 210m-deep central Karamürsel Basin of the İzmit Gulf in the eastern Sea of Marmara, using laser grain-size, physical properties, stable O and C isotopes and XRF Core Scanner analyses, and dated by radionuclide and radiocarbon methods. The earthquake records are represented by turbidite–homogenite mass-flow units (THU) that commonly contain a basal coarse layer, a middle laminated silt layer and an overlying homogeneous mud layer. The coarse basal part has a sharp and sometimes scoured lower boundary, and includes multiple coarse (sand/silt) layers or laminae showing normal size grading. Multiple coarse layers and occasional bi-directional cross-bedding suggest deposition from a bed-load during water column oscillations, or seiche effect. The grain-size characteristics of the overlaying laminated silt and the homogeneous mud units indicate deposition from weak oscillating currents and homogeneous suspension, respectively. High Mn value just below the base of THUs suggests diagenetic enrichment at oxic/anoxic redox boundary before the mass-flow event. Sharp decrease in Mn with very low values within the THUs suggests transient redox conditions following the mass-flow. Variable geochemical compositions of the basal coarse layers indicate different sediment sources for different THUs. Eight sedimentary earthquake records observed in the last 2400a in the İzmit Gulf can be confidently correlated with the historical earthquakes of 1999, 1509AD (Ms=7.2), 1296AD (I=VII), 865AD (I=VIII), 740AD (I=VIII), 268AD (I=VIII), 358AD (I=IX), and 427 BC. This gives an earthquake recurrence time of ca. 300a, with the interval between consecutive events ranging from 90 to 695a.

Lake Bourget regional erosion patterns reconstruction reveals Holocene NW European Alps soil evolution and paleohydrology

Two well-dated ca Holocene-long sedimentary sequences from deepest parts of Lake Bourget provide new insights onto the evolution of erosion patterns at a regional scale in NW European Alps. The combination of high resolution geochemistry – XRF core scanning, calibrated by 150 punctual measurements – and isotope geochemistry (ɛNd) of the terrigenous fraction permitted the reconstruction not only of the intensity, but also the type (physical erosion vs. chemical weathering) and the location (Prealpine massifs vs. High Crystalline massifs) of dominant erosion processes. Those data point the persistency of weak erosion fluxes from 9600 to 5500 cal. BP due both to a dry climate and the growing sheltering effect of soils that rapidly progressed between 9600 and 8000 cal. BP. Soils then reached a steady state before being destabilised around 4400 cal. BP, probably in response to human impact. The human impact then reached a sufficient intensity to change erosion patterns at a regional scale, but did not result in a significant increase of the regional terrigenous flux. The following enhancement of erosion processes occurred around 2700 cal. BP. It was first paced by changing climatic conditions, but probably reinforced by human impact during Late Iron Age – Antiquity period. Over the long-term trend, the Lake Bourget record pinpoints an evolution of paleohydrological conditions in the Alps dominated by dry conditions from 9500 to 4400 cal. BP and a subsequent drift toward wetter conditions that culminated during the so-called Little Ice Age (ca 1350–1900 AD). In such a context the current dry conditions in European Alps appear out-of-trend. At high resolution, 17 periods of enhanced hydrological activity highlight the rapid climatic changes that are typical of the Holocene.

A geochemical record of flooding on the upper River Severn, UK, during the last 3750 years

Projected future changes in climate call for more definite information on the magnitude–frequency relationships of major floods than can be obtained from short instrumental or historical records alone. Floodplains represent a sedimentary archive of unrecorded flood events, which can potentially be used to extend existing flood records by centuries or millennia. In this study a c. 3750-year flood record was produced using ln(Zr/Rb) profiles from two 4-m-deep cores through floodplain silts at the Roundabout in the upper Severn catchment, UK. Sediment geochemical profiles were obtained using high resolution (500μm) XRF core scanning. Ages were assigned to the flood record using 14C dating and contaminant Pb profiles. Comparison of sediment ln(Zr/Rb) with sediment grain size showed that ln(Zr/Rb) increases with increasing grain size and indicates that it can be used as a grain size proxy at this site. Within the ln(Zr/Rb) flood record, two floods that occurred at c. 235 and c. 10cal. BC were probably the largest that have occurred at the site during the past 3750years while the historical flood of A.D. 1795 appears to be the largest since c. AD 200. The record shows that, during the past c. 3750years, multicentennial periods characterized by the occurrence of high magnitude floods (return periods>c. 30years) have alternated with periods of similar length without such floods. These periods correspond to large-scale variations in hydroclimate recorded in the North Atlantic region. However, the incidence of the highest magnitude floods appears to be unaffected by changes in catchment land use. This study provides information about flood magnitude–frequency relationships and their controls at a local level that could be used to help catchment managers in assessing future flood risk at a time of rapidly changing climate.

The influence of siliciclastic input on Chaetoceros abundance in an early Pliocene segment of the ANDRILL AND-1B drill core

In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing- McMurdo Ice Shelf) project recovered a 1285m sediment core from beneath the Ross Ice Shelf near Ross Island, Antarctica. Contained within the upper ~600m of this core are sediments recording 38 glacial/interglacial cycles of Early Pliocene to Pleistocene time, including 13 discrete diatomite units (DU). The thickest of these, DU XI, is ~76m thick, has been assigned an Early Pliocene age (5–3Ma), and represents several extended periods of uninterrupted sediment accumulation. A combination of geochemical and biological data was used to examine the role of changes in sediment source areas on diatom community composition. Peak-area count-ratios from the data collected with the XRF core scanner include K:Fe and Ti:K. K is lower and Ti higher in the volcanic series sampled. K:Fe is an indicator of the source area of fine-grained sediment delivered to the site by terrestrial and marine sedimentary processes (glacial, fluvial, eolian, gravitational, marine currents), while Ti:K is primarily associated with Ross Sea volcanic sources. A comparison of these two elemental ratios shows an anti-correlation, indicating changes in source rocks with time. Furthermore, relative abundance of the diatom genus, Chaetoceros, varies in the same sense and magnitude as K:Fe, suggesting that climatically-driven changes in sediment source regions are related to variations in abundance. It is suggested that increases in TAM-sourced sediment at the ANDRILL AND-1B site caused increased nutrient levels in the water column, leading to blooms of this genus, which is consistent with current known ecological preferences.

Multiple early Eocene benthic foraminiferal assemblage and δ13C fluctuations at DSDP Site 401 (Bay of Biscay — NE Atlantic)

Abstract Within the last decade, several early Eocene hyperthermals have been detected globally. These transient warming events have mainly been characterized geochemically – using stable isotopes, carbonate content measurements or XRF core scanning – yet detailed micropaleontological records are sparse, limiting our understanding of the driving forces behind hyperthermals and of the contemporaneous paleoceanography. Here, detailed geochemical and quantitative benthic foraminiferal records are presented from lower Eocene pelagic sediments of Deep Sea Drilling Project Site 401 (Bay of Biscay, northeast Atlantic). In calcareous nannofossil zone NP11, several clay-enriched levels correspond to negative δ13C and δ18O bulk-rock excursions with amplitudes of up to ~ 0.75‰, suggesting that significant injections of 12C-enriched greenhouse gasses and small temperature rises took place. Coeval with several of these hyperthermal events, the benthic foraminiferal record reveals increased relative abundances of oligotrophic taxa (e.g. Nuttallides umbonifera) and a reduction in the abundance of buliminid species followed by an increase of opportunistic taxa (e.g. Globocassidulina subglobosa and Gyroidinoides spp.). These short-lived faunal perturbations are thought to be caused by reduced seasonality of productivity resulting in a decreased Corg flux to the seafloor. Moreover, the sedimentological record suggests that an enhanced influx of terrigenous material occurred during these events. Additionally, the most intense δ13C decline (here called level δ) gives rise to a small, yet pronounced long-term shift in the benthic foraminiferal composition at this site, possibly due to the reappraisal of upwelling and the intensification of bottom water currents. These observations imply that environmental changes during (smaller) hyperthermal events are also reflected in the composition of deep-sea benthic communities on both short (

Variations of the Nile suspended discharges during the last 1.75 Myr

Planktonic foraminiferal oxygen isotopes, carbonate and organic carbon contents, as well as XRF core scanning Ti, V and Ba intensities have been analyzed on sediments of a Mediterranean marine core (Core MD90-964) to reconstruct changes in the Nile discharges during the last 1.75 Ma. Chronology of Core MD90-964 is established by correlating the planktonic foraminiferal δ 18O record to the Mediterranean Globigerinoides ruber δ 18O stack. A total number of 42 dark layers are observed under visual observation, among which 21 of them are identified as sapropels by organic carbon contents (> 1 wt.%). It is observed that oxidation of sapropels is very active during 1000 and 240 kyr, indicating that the local climate is much colder and dryer during this interval. Our results provide new evidences that oxidation of organic material play a major role in determining the organic carbon contents in sapropels. Carbonate contents and normalized titanium and vanadium contents in bulk sediments are suggested to reflect mostly changes in the Nile discharge. It is found that variation of the African monsoon intensities can strongly affect changes in the Nile suspended discharge via both runoff and drainage precipitation. Elevated Nile discharges are generally observed during African monsoon maxima (deposition of sapropelic layers). Our results suggest that oscillations in the Nile suspended discharges are more the result of river transport capability than that of erosion potential in source areas. It is also observed that cyclicity of the variation of the Nile suspended discharge is generally paced by a 78-kyr cycle, the physical meaning of which remains hitherto unclear. It is probably a bundling of 2–3 obliquity cycles, as a result of nonlinear responses of Atlantic SST to orbital forcing.

2010 international workshop on XRF core scanning

2010 international workshop on XRF core scanning

Quantitative climate reconstruction linking meteorological, limnological and XRF core scanner datasets: the Lake Sanabria case study, NW Spain

Monthly limnological monitoring in Lake Sanabria (Spain) since 1986 provided a unique opportunity to test relationships among climate, hydrology and lake dynamics and how they are recorded in the lake sediments. Four datasets were employed: (1) meteorological (monthly maximum and minimum air temperature and total precipitation), (2) limnological (Secchi disk, water temperature, conductivity, pH, dissolved oxygen, nitrate, silicon, total and reactive phosphorus, and total chlorophylls and chlorophyll a), (3) hydrological (Tera River water input and output), and (4) XRF core scanner measurements carried out in short cores. Linear models between the different dataset variables allowed us to characterize the climate signal transmission from one to the other and cross-correlation analyses permitted us to identify the different response times (if any) between them. Principal Component Analyses (PCA) of the limnological and geochemical datasets allowed us to identify the main processes that link lake dynamics, primarily nutrient supply and organic productivity, with some sedimentological processes, e.g. organic matter and phosphorus accumulation. Sediment chronology was established by gamma spectrometry (210Pb). Water input to Lake Sanabria is controlled mostly by the Tera River input and is linked directly to precipitation. Response of the Lake Sanabria water budget to climate oscillations is immediate, as the strongest correlation between these two datasets occurs with no lag time. PCA of the limnological dataset indicated that most of the variance is related to nutrient input, and comparison with the Tera River water discharge shows that nutrient input was controlled mainly by oscillations in the hydrological balance. The lag time between the hydrological and limnological datasets is 1 month. The PCA of the XRF core scanner dataset showed that the principal process that controls the chemical composition of the Lake Sanabria sediments is related to sediment and nutrient delivery from the Tera River and organic productivity. Comparison of the nutrient input reconstructed using the limnological dataset and the XRF core scanner data indicated that the sediments act as a low-pass filter, smoothing the climate signal. It was, however, possible to establish the link between these datasets, and obtain a quantitative reconstruction of precipitation for the 1959–2005 AD period that captures the regional variability. This quantitative precipitation reconstruction suggests it is possible to obtain accurate climate reconstructions using non-laminated sediments.

Late-Holocene sea-surface conditions offshore Newfoundland based on dinoflagellate cysts

Dinoflagellate cysts and XRF core scanning data from two marine sediment cores from embayments north (Bonavista Bay) and south (Placentia Bay) of Newfoundland show significant changes in ocean and atmospheric conditions of the SW Labrador Sea region during the last 5700 years. Fresh and cold conditions, probably accompanied by seasonal sea ice, prevailed both north and south of Newfoundland from c. 5.7 to 4.0 cal. kyr BP. This may be linked to intensified Labrador Current export of cold meltwater and/or sea ice from the Arctic, presumably related to warmer conditions in the northernmost latitudes and the prevalence of strong (north)westerly winds. After c. 4.0 cal. kyr BP, sea-surface conditions warmed up and sea ice decreased northeast of Newfoundland, but conditions were still cold south of Newfoundland. This suggests a decrease in Arctic meltwater export and westerly wind strength. After 2.9—2.5 cal. kyr BP, only minor changes in sea-surface conditions affected the study sites. Sea-surface temperatures increased and sea ice decreased at both sites, which may be related to a more meridional atmospheric circulation pattern associated with the general Northern Hemisphere neoglacial cooling. In Placentia Bay the warmest part of the record corresponds to the Roman Warm Period, while the warmest part of the records in Bonavista Bay notably corresponds to the Dark Ages.

Tempo and scale of late Paleocene and early Eocene carbon isotope cycles: Implications for the origin of hyperthermals

The upper Paleocene and lower Eocene are marked by several prominent (> 1‰) carbon isotope (δ 13C) excursions (CIE) that coincide with transient global warmings, or thermal maxima, including the Paleocene–Eocene Thermal Maximum (PETM). The CIE, which are recorded mainly in marine sedimentary sequences, have also been identified in continental sequences, occurred episodically, and yet appear to be paced or triggered by orbital forcing. To constrain the timing and scale of the CIE relative to long-term baseline variability, we have constructed a 4.52 million year (myr) long, high-resolution (~ 3 kyr) bulk sediment carbon isotope record spanning the lower Eocene to upper Paleocene (C25r–C24n) from a pelagic sediment section recovered at ODP Site 1262 in the southeast Atlantic. This section, which was orbitally-tuned utilizing high-resolution core log physical property and geochemical records, is the most stratigraphically complete upper Paleocene to lower Eocene sequence recovered to date. Time-series analysis of the carbon isotope record along with a high-resolution Fe intensity record obtained by XRF core scanner reveal cyclicity with variance concentrated primarily in the precession (21 kyr) and eccentricity bands (100 and 400-kyr) throughout the upper Paleocene–lower Eocene. In general, minima in δ 13C correspond with peaks in Fe (i.e., carbonate dissolution), both of which appear to be in phase with maxima in eccentricity. This covariance is consistent with excess oceanic uptake of isotopically depleted carbon resulting in lower carbonate saturation during periods of high eccentricity. This relationship includes all late Paleocene and early Eocene CIE confirming pacing by orbital forcing. The lone exception is the PETM, which appears to be out of phase with the 400-kyr cycle, though possibly in phase with the 100-kyr cycle, reinforcing the notion that a mechanism other than orbital forcing and/or an additional source of carbon is required to account for the occurrence and unusual scale of this event.

Climate variability over the last two millennia in the North American Monsoon region, recorded in laminated lake sediments from Laguna de Juanacatlán, Mexico

High-resolution titanium (Ti) data obtained using an ITRAX XRF core scanner from a laminated sediment core from the Laguna de Juanacatlán, western central Mexico yield a unique high-resolution record of runoff (precipitation) change for the last 2000 years. In the absence of reliable, long-term meteorological records, comparison of the Ti data with information from the rich Spanish colonial period archives and the post-Independence period, confirms that Ti is a proxy for runoff. This interpretation is supported by comparison with other high-resolution archives from the surrounding region, primarily tree rings and other lake sediment sequences. The Juanacatlán Ti record is therefore a proxy for summer, monsoonal rainfall. The record provides new evidence from the Pacific margin of tropical North America of the occurrence of dry conditions through much of the Classic period ( c. AD 300—900), and wetter conditions during the later Medieval period ( c. AD 1200—1350). The period commonly known as the ‘Little Ice Age’ (LIA) shows considerable variability, with dry conditions in the early part ( c. AD 1400—1600) and wetter conditions, punctuated by multiyear droughts through the eighteenth century. A notable feature of the record is the apparent decoupling of lacustrine sedimentation from the climate since the mid-twentieth century, possibly resulting from anthropogenic disturbance. Preliminary interpretations of the Ti record indicate that patterns are consistent with changes in monsoon strength associated with ENSO and solar forcing over the last two millennia.

Geochemical provenance analysis of fine-grained sediment revealing Late Miocene to recent Paleo-Environmental changes in the Western Ross Sea, Antarctica

Bulk chemical fine-grained sediment compositions from southern Victoria Land glacimarine sediments provide significant constraints on the reconstruction of sediment provenance models in the McMurdo Sound during Late Cenozoic time. High-resolution (∼1ka) geochemical data were obtained with a non-destructive AVAATECH XRF Core Scanner (XRF-CS) on the 1285m long ANDRILL McMurdo Ice Shelf Project (MIS) sediment core AND-1B. This data set is complemented by high-precision chemical analyses (XRF and ICP-OES) on discrete samples.Statistical analyses reveal three geochemical facies which are interpreted to represent the following sources for the sediments recovered in the AND-1B core: 1) local McMurdo Volcanic Group (MVG) rocks, 2) Transantarctic Mountain rocks west of Ross Island (W TAM), and 3) Transantarctic Mountain rocks from more southerly areas (S TAM). Data indicate in combination with other sediment facies analyses (McKay et al., 2009) and provenance scenarios (Talarico and Sandroni, 2009) that diamictites at the drill site are largely dominated by local sources (MVG) and are interpreted to indicate cold polar conditions with dry-based ice. MVG is interpreted to indicate cold polar condition with dry-based ice. A mixture of MVG and W TAM is interpreted to represent polar conditions and the S TAM facies is interpreted to represent open-marine conditions.Down-core variations in geochemical facies in the AND-1B core are interpreted to represent five major paleoclimate phases over the past 14Ma. Cold polar conditions with major MVG influence occur below 1045mbsf and above 120mbsf. A section of warmer climate conditions with extensive peaks of S TAM influence characterizes the rest of the core, which is interrupted by a section from 525 to 855mbsf of alternating influences of MVG and W TAM.

Calibration of XRF core scanners for quantitative geochemical logging of sediment cores: Theory and application

On-line analysis of split sediment cores by XRF core scanners has become increasingly popular in the past decade, because it allows nondestructive extraction of near-continuous records of element intensities from sediment cores with a minimum of analytical effort. A disadvantage of XRF core scanning relative to conventional geochemical analysis is the problematic conversion of core-scanner output to element concentrations. The main reason for this long-standing problem is the poorly constrained measurement geometry, attributable to inhomogeneity of the specimens (e.g. variable water content and grain-size distribution), irregularities of the split core surface, and in some setups, spatial variations in thickness of an adhesive pore-water film which forms directly below a protective foil covering the core surface. We propose a log-ratio calibration model for XRF core scanners, derived from a combination of XRF-spectrometry theory, principles of compositional data analysis, and empirical evidence. The log-ratio calibration model provides accurate and precise predictions of sediment composition (element concentrations) from XRF core-scanner output with a limited number of parameters, namely 2( D − 1), where D equals the number of chemical elements whose concentrations are to be estimated. The model can accommodate the inherent non-linearity of the relation between (relative) intensities and concentrations, which is apparent from the fact that it provides unbiased estimates. An immediate corollary of our results is that log-ratios of element intensities, which are related to log-ratios of element abundances by a simple linear transformation, provide the most easily interpretable signals of relative changes in chemical composition. Consistent use of log-ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies. The relative standard deviation (precision) of predicted element concentrations in core GeoB7920 is less than 2%. Stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens. Improved control over input errors and development of robust goodness-of-fit statistics allows XRF core scanning to be developed into a rigorous quantitative measurement technology. The log-ratio calibration equation derived in this study may be adapted to inter-laboratory and inter-instrument calibration as well.

The Cenomanian Turonian of the Wunstorf section (North Germany): global stratigraphic reference section and new orbital time scale for Oceanic Anoxic Event 2

The Cenomanian–Turonian Boundary Event (CTBE) is reflected by one of the most extreme carbon cycle perturbations in Earth's history and is characterized by the widespread occurrence of sediments indicating oxygen deficiency in oceanic waters (Oceanic Anoxic Event 2 = OAE 2). At Wunstorf (northern Germany) the CTBE is represented by a 26.5 m thick sedimentary succession consisting of rhythmically bedded laminated black shales, dark organic-rich marls and marly limestones yielding abundant micro- and macrofossils, making the locality particularly well suited to serve as an international standard reference section for the CTBE. In 2006 a newly drilled continuous core recovered 76 m of middle Cenomanian to middle Turonian sediments. A high-resolution carbonate δ13C curve derived from core samples resolves all known features of the positive δ13C anomaly of OAE 2 with high accuracy. Throughout the middle Cenomanian – middle Turonian succession, the δ13C curve shows numerous small-scaled positive excursions, which appear to be cyclic. High-resolution borehole geophysics and XRF core scanning were performed to generate two time series of gamma-ray data and Ti concentrations for the CTBE black shale succession. Hierarchical bundling of sedimentary cycles as well as spectral analysis and Gaussian filtering of dominant frequencies reveal cycle frequency ratios characteristic for short eccentricity modulated precession (100 kyr, 21 kyr). This new orbital time scale provides a time estimate of 430–445 kyr for the duration of OAE 2 and refines the existing orbital age models developed at localities in the English Chalk, the Western Interior Basin and the Tarfaya Basin. Based on the new age model and high-resolution carbon isotope correlation, our data allow for the first time a precise basin-wide reconstruction of the palaeoceanographic modifications within the European shelf sea during OAE 2.