cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3453644.v1
title: Observation of centimetre-scale argon diffusion in alkali feldspars: implications for <sup>40</sup>Ar/<sup>39</sup>Ar thermochronology

description: New data from a gem-quality feldspar from Itrongay, Madagascar, record naturally occurring <sup>40</sup>Ar/<sup>39</sup>Ar age profiles which can be numerically modelled by invoking a single diffusion mechanism and show that microtexturally simple crystals are capable of recording complex thermal histories. We present the longest directly measured, naturally produced <sup>40</sup>Ar*-closure profiles from a single, homogeneous orthoclase feldspar. These data appear to confirm the assumption that laboratory derived diffusion parameters are valid in nature and over geological timescales. Diffusion domains are defined by crystal faces and ancient cracks, thus in gem-quality feldspars the diffusion domain size equates to the physical grain size. The data also illustrate the potential of large, gem-quality feldspars to record detailed thermal histories over tens of millions of years and such samples should be considered for future studies on the slow cooling of continental crust.
DOI: 10.6084/m9.figshare.3453638
title: U–Pb detrital zircon ages of Upper Jurassic continental successions: implications for the provenance and absolute age of the Jurassic–Cretaceous boundary in the Neuquén Basin

description: New U–Pb detrital zircon ages are presented for the Tordillo Formation. The ages indicate that the most important source region of sediment supply was the Jurassic Andean arc (peaks at <em>c.</em> 144, 153 and 178 Ma), although two secondary sources were defined at <em>c.</em> 218 and 275 Ma. Temporal variation in the provenance indicates that at the beginning of the sedimentation, Carboniferous to Lower Jurassic magmatic rocks and Lower Palaeozoic metamorphic rocks were the most important sources. Towards the top, the data suggest that the Andean arc becomes the main source region. The comparison between provenance patterns of the Tordillo Formation and of the Avilé Member (Agrio Formation) showed some differences. In the former, the arc region played a considerable role as a source region, but this is not identified in the latter. The results permit a statistically robust estimation of the maximum deposition age for the Tordillo Formation at <em>c.</em> 144 Ma. This younger age represents a discrepancy of at least 7 Ma from the absolute age of the Kimmeridgian and Tithonian boundary (from the chronostratigraphic timescale accepted by the International Commission of Stratigraphy, IUGS), and has strong implications for the absolute age of the Jurassic–Cretaceous boundary.
DOI: 10.6084/m9.figshare.3453638.v1
title: U–Pb detrital zircon ages of Upper Jurassic continental successions: implications for the provenance and absolute age of the Jurassic–Cretaceous boundary in the Neuquén Basin

description: New U–Pb detrital zircon ages are presented for the Tordillo Formation. The ages indicate that the most important source region of sediment supply was the Jurassic Andean arc (peaks at <em>c.</em> 144, 153 and 178 Ma), although two secondary sources were defined at <em>c.</em> 218 and 275 Ma. Temporal variation in the provenance indicates that at the beginning of the sedimentation, Carboniferous to Lower Jurassic magmatic rocks and Lower Palaeozoic metamorphic rocks were the most important sources. Towards the top, the data suggest that the Andean arc becomes the main source region. The comparison between provenance patterns of the Tordillo Formation and of the Avilé Member (Agrio Formation) showed some differences. In the former, the arc region played a considerable role as a source region, but this is not identified in the latter. The results permit a statistically robust estimation of the maximum deposition age for the Tordillo Formation at <em>c.</em> 144 Ma. This younger age represents a discrepancy of at least 7 Ma from the absolute age of the Kimmeridgian and Tithonian boundary (from the chronostratigraphic timescale accepted by the International Commission of Stratigraphy, IUGS), and has strong implications for the absolute age of the Jurassic–Cretaceous boundary.
DOI: 10.6084/m9.figshare.3453626
title: Holocene tephra from Iceland and Alaska in SE Greenland Shelf Sediments

description: The record of Icelandic volcanic events in Holocene marine sediments off SE Greenland provides evidence for the frequency and timing of atmospheric tephra plume dispersal from Iceland towards Greenland. Geochemistry of tephra abundance peaks from two SE Greenland shelf cores: MD99-2322 and JM96-1215-2GC are compared with core MD99-2269, north Iceland shelf, to evaluate the dispersal direction of Icelandic eruptions. Glass shard counts (106–1000 µm) in MD99-2322 revealed 16 distinct cryptotephra peaks. Geochemical analyses of eight cryptotephra peaks in MD99-2322 and two in JM96-1215 indicate sources in the volcanic systems of Iceland and Alaska. A tephra layer matching in geochemistry and stratigraphy to the <em>c.</em> 3600 BP eruption of the Aniakchak Volcano in the Aleutian Islands was identified in JM96-1215/2GC. The Settlement Tephra (AD 871±2) and Hekla B (H-B) were identified in MD99-2322. A new marker horizon, Katla EG-6.73, was found in both SE Greenland cores. Three basaltic peaks between 9.9 and 10.4 cal kyr BP, exhibit major-element geochemistry indistinguishable from the <em>c.</em> 10.2 kyr Saksunarvatn tephra. These layers represent 3 out of≥seven westward and northward-dispersed Grímsvötn layers found on the SE Greenland shelf and the north Iceland shelf between 9.9 and 10.4 cal kyr BP.
DOI: 10.6084/m9.figshare.3453626.v1
title: Holocene tephra from Iceland and Alaska in SE Greenland Shelf Sediments

description: The record of Icelandic volcanic events in Holocene marine sediments off SE Greenland provides evidence for the frequency and timing of atmospheric tephra plume dispersal from Iceland towards Greenland. Geochemistry of tephra abundance peaks from two SE Greenland shelf cores: MD99-2322 and JM96-1215-2GC are compared with core MD99-2269, north Iceland shelf, to evaluate the dispersal direction of Icelandic eruptions. Glass shard counts (106–1000 µm) in MD99-2322 revealed 16 distinct cryptotephra peaks. Geochemical analyses of eight cryptotephra peaks in MD99-2322 and two in JM96-1215 indicate sources in the volcanic systems of Iceland and Alaska. A tephra layer matching in geochemistry and stratigraphy to the <em>c.</em> 3600 BP eruption of the Aniakchak Volcano in the Aleutian Islands was identified in JM96-1215/2GC. The Settlement Tephra (AD 871±2) and Hekla B (H-B) were identified in MD99-2322. A new marker horizon, Katla EG-6.73, was found in both SE Greenland cores. Three basaltic peaks between 9.9 and 10.4 cal kyr BP, exhibit major-element geochemistry indistinguishable from the <em>c.</em> 10.2 kyr Saksunarvatn tephra. These layers represent 3 out of≥seven westward and northward-dispersed Grímsvötn layers found on the SE Greenland shelf and the north Iceland shelf between 9.9 and 10.4 cal kyr BP.
DOI: 10.6084/m9.figshare.3453620
title: The ‘rgr’ package for the R Open Source statistical computing and graphics environment - a tool to support geochemical data interpretation

description: The development of interactive computer graphics to support applied geochemistry over the last 40 years at the Geological Survey of Canada (GSC) is briefly discussed. The loss of an interactive computing environment, IDEAS, in 1995 based on a DEC VAX computer largely negated nine years of work, though the experience gained was invaluable. The availability of the commercial S-PLUS package in a Windows PC environment led to the redevelopment of most of the functionality of IDEAS in the S language for statistical analysis and graphics. In 2006 a request from a sister federal government department for the S-PLUS software led to the decision to translate the S functions into R, an Open-Source implementation of the S language, and therefore free to the user. Since that time all development has been in R, resulting in the 2007 release to the public of a package of tools, ‘rgr’, to assist applied geochemists in interpreting their data. Subsequently, ‘rgr’ has been updated and extended. The move to Open Source R and the release of the ‘rgr’ package on the Comprehensive R Archival Network (CRAN) has made these tools, and their documentation, available for Windows, Unix and Mac computing environments. The paper outlines the features of ‘rgr’ and illustrates key graphic and tabular displays. Its functionality is reviewed in the context of earlier GSC interactive graphics packages.
DOI: 10.6084/m9.figshare.3453617
title: Predicting Archaean volcanogenic massive sulphide deposit potential from lithogeochemistry: application to the Abitibi Greenstone Belt

description: Archaean greenstone belts are prime exploration targets for volcanogenic massive sulphide deposits and the use of lithogeochemistry plays an important role in detecting and mapping hydrothermal alteration zones and in recognizing the massive sulphide potential of volcanic assemblages. This study reviews the state of existing lithogeochemical databases and the use of new geochemical analyses for the identification of alteration associated with massive sulphide deposits. This paper also provides a new methodology for the prediction of missing values in geochemical compositions. Through the application of statistical methods, combined sets of lithogeochemical data can be used to create predictive maps of prospective massive sulphide successions. Predictive maps are created through the use of multivariate statistical methods, lithogeochemical alteration indices and normative minerals from which areas of multi-element enrichment and depletion are defined. These indices, when combined in an exploration programme, are potentially useful for massive sulphide discovery. Additionally, the use of rare earth elements can be used to characterize differences in the various supracrustal assemblages and provide a better regional understanding of potential metal endowment.
DOI: 10.6084/m9.figshare.3453614
title: Dynamics of late Cenozoic aeolian deposition along the South African coast: a record of evolving climate and ecosystems

description: Dune systems along the South African coast are sensitive barometers of fluctuations in palaeoenvironments, as archived in their orientation, geometry, internal architecture, composition, granulometry, diagenesis, palaeontology and archaeological content. Presently, the pronounced climatic/oceanographic gradients around the southern African coastline, including the west coast Mediterranean climate type, with cold upwelling to progressively warmer in terms of climate and sea temperatures eastwards, are mirrored by variations in these parameters. Here, we review and contribute new information concerning their fluctuations from the Miocene to the present to track changes in the bio-, hydro- and geospheres through time. West coast dunes take the form of dune plumes, which have an orientation since the Miocene that mirrors the southerlies of the South Atlantic Anticyclone (SAA), muted during the warm Pliocene, as reflected by intense bioturbation. Shoreline-parallel, vertically aggraded dune cordons dominate along the southern and eastern coasts, formed by (winter) polar westerlies since the Miocene. The contrasting dunefield morphologies relate to seasonality of wind strength and precipitation. Subtropical east coast dunes are profoundly weathered – on the shelf, glacial-period dunes indicate different atmospheric circulations. The long-term stability of the warm Agulhas Current contrasts with variability in the Benguela. The aeolianites host a rich human and faunal archive, including human ichnofossils.
DOI: 10.6084/m9.figshare.3453617.v1
title: Predicting Archaean volcanogenic massive sulphide deposit potential from lithogeochemistry: application to the Abitibi Greenstone Belt

description: Archaean greenstone belts are prime exploration targets for volcanogenic massive sulphide deposits and the use of lithogeochemistry plays an important role in detecting and mapping hydrothermal alteration zones and in recognizing the massive sulphide potential of volcanic assemblages. This study reviews the state of existing lithogeochemical databases and the use of new geochemical analyses for the identification of alteration associated with massive sulphide deposits. This paper also provides a new methodology for the prediction of missing values in geochemical compositions. Through the application of statistical methods, combined sets of lithogeochemical data can be used to create predictive maps of prospective massive sulphide successions. Predictive maps are created through the use of multivariate statistical methods, lithogeochemical alteration indices and normative minerals from which areas of multi-element enrichment and depletion are defined. These indices, when combined in an exploration programme, are potentially useful for massive sulphide discovery. Additionally, the use of rare earth elements can be used to characterize differences in the various supracrustal assemblages and provide a better regional understanding of potential metal endowment.
DOI: 10.6084/m9.figshare.3453614.v1
title: Dynamics of late Cenozoic aeolian deposition along the South African coast: a record of evolving climate and ecosystems

description: Dune systems along the South African coast are sensitive barometers of fluctuations in palaeoenvironments, as archived in their orientation, geometry, internal architecture, composition, granulometry, diagenesis, palaeontology and archaeological content. Presently, the pronounced climatic/oceanographic gradients around the southern African coastline, including the west coast Mediterranean climate type, with cold upwelling to progressively warmer in terms of climate and sea temperatures eastwards, are mirrored by variations in these parameters. Here, we review and contribute new information concerning their fluctuations from the Miocene to the present to track changes in the bio-, hydro- and geospheres through time. West coast dunes take the form of dune plumes, which have an orientation since the Miocene that mirrors the southerlies of the South Atlantic Anticyclone (SAA), muted during the warm Pliocene, as reflected by intense bioturbation. Shoreline-parallel, vertically aggraded dune cordons dominate along the southern and eastern coasts, formed by (winter) polar westerlies since the Miocene. The contrasting dunefield morphologies relate to seasonality of wind strength and precipitation. Subtropical east coast dunes are profoundly weathered – on the shelf, glacial-period dunes indicate different atmospheric circulations. The long-term stability of the warm Agulhas Current contrasts with variability in the Benguela. The aeolianites host a rich human and faunal archive, including human ichnofossils.
DOI: 10.6084/m9.figshare.3453611
title: Chapter 20 Multi-stage collapse events in the South Soufrière Hills, Montserrat as recorded in marine sediment cores

description: We present new evidence for sector collapses of the South Soufrière Hills (SSH) edifice, Montserrat during the mid-Pleistocene. High-resolution geophysical data provide evidence for sector collapse, producing an approximately 1 km<sup>3</sup> submarine collapse deposit to the south of SSH. Sedimentological and geochemical analyses of submarine deposits sampled by sediment cores suggest that they were formed by large multi-stage flank failures of the subaerial SSH edifice into the sea. This work identifies two distinct geochemical suites within the SSH succession on the basis of trace-element and Pb-isotope compositions. Volcaniclastic turbidites in the cores preserve these chemically heterogeneous rock suites. However, the subaerial chemostratigraphy is reversed within the submarine sediment cores. Sedimentological analysis suggests that the edifice failures produced high-concentration turbidites and that the collapses occurred in multiple stages, with an interval of at least 2 ka between the first and second failure. Detailed field and petrographical observations, coupled with SEM image analysis, shows that the SSH volcanic products preserve a complex record of magmatic activity. This activity consisted of episodic explosive eruptions of andesitic pumice, probably triggered by mafic magmatic pulses and followed by eruptions of poorly vesiculated basaltic scoria, and basaltic lava flows.
DOI: 10.6084/m9.figshare.3453611.v1
title: Chapter 20 Multi-stage collapse events in the South Soufrière Hills, Montserrat as recorded in marine sediment cores

description: We present new evidence for sector collapses of the South Soufrière Hills (SSH) edifice, Montserrat during the mid-Pleistocene. High-resolution geophysical data provide evidence for sector collapse, producing an approximately 1 km<sup>3</sup> submarine collapse deposit to the south of SSH. Sedimentological and geochemical analyses of submarine deposits sampled by sediment cores suggest that they were formed by large multi-stage flank failures of the subaerial SSH edifice into the sea. This work identifies two distinct geochemical suites within the SSH succession on the basis of trace-element and Pb-isotope compositions. Volcaniclastic turbidites in the cores preserve these chemically heterogeneous rock suites. However, the subaerial chemostratigraphy is reversed within the submarine sediment cores. Sedimentological analysis suggests that the edifice failures produced high-concentration turbidites and that the collapses occurred in multiple stages, with an interval of at least 2 ka between the first and second failure. Detailed field and petrographical observations, coupled with SEM image analysis, shows that the SSH volcanic products preserve a complex record of magmatic activity. This activity consisted of episodic explosive eruptions of andesitic pumice, probably triggered by mafic magmatic pulses and followed by eruptions of poorly vesiculated basaltic scoria, and basaltic lava flows.
DOI: 10.6084/m9.figshare.3453608
title: Sedimentological thickness variations within Silurian mudstone-dominated turbidite deposits and the effects on cleavage fanning (Anglo-Brabant Deformation Belt, Belgium)

description: The effect of vertical changes in lithology on cleavage refraction and cleavage fanning is relatively well understood. In contrast, the control that lateral changes in bed thickness and related multilayer characteristics have on cleavage fanning has not been widely documented. Mudstone-dominated Wenlock-age turbidites of the Anglo-Brabant Deformation Belt, Belgium, exhibit pronounced lateral thickness changes, which we attribute to intraslope flow ponding during foreland basin development. The mudstone-dominated nature of the turbidites is considered to reflect a particularly fine-grained source area, rather than a distal origin. Formation boundaries and lateral changes in lithofacies unit thickness are reflected in the amount of cleavage fanning. The degree of convergent cleavage fanning increases with an increase in thickness of the less competent units and with a decrease in thickness and number of the more competent units. As such, a detailed analysis of changes in cleavage–bedding angle aids in the distinction of different lithostratigraphic units of similar appearance, the location of their boundaries and identification of subtle lateral sedimentological changes. The utilization of cleavage and bedding data to recognize and describe vertical and lateral changes in a semi-quantitative way allows the linkage of subtle changes in multilayer rheology to finite strain trajectories.
DOI: 10.6084/m9.figshare.3453608.v1
title: Sedimentological thickness variations within Silurian mudstone-dominated turbidite deposits and the effects on cleavage fanning (Anglo-Brabant Deformation Belt, Belgium)

description: The effect of vertical changes in lithology on cleavage refraction and cleavage fanning is relatively well understood. In contrast, the control that lateral changes in bed thickness and related multilayer characteristics have on cleavage fanning has not been widely documented. Mudstone-dominated Wenlock-age turbidites of the Anglo-Brabant Deformation Belt, Belgium, exhibit pronounced lateral thickness changes, which we attribute to intraslope flow ponding during foreland basin development. The mudstone-dominated nature of the turbidites is considered to reflect a particularly fine-grained source area, rather than a distal origin. Formation boundaries and lateral changes in lithofacies unit thickness are reflected in the amount of cleavage fanning. The degree of convergent cleavage fanning increases with an increase in thickness of the less competent units and with a decrease in thickness and number of the more competent units. As such, a detailed analysis of changes in cleavage–bedding angle aids in the distinction of different lithostratigraphic units of similar appearance, the location of their boundaries and identification of subtle lateral sedimentological changes. The utilization of cleavage and bedding data to recognize and describe vertical and lateral changes in a semi-quantitative way allows the linkage of subtle changes in multilayer rheology to finite strain trajectories.
DOI: 10.6084/m9.figshare.3453602
title: Use and calibration of portable X-Ray fluorescence analysers: application to lithogeochemical exploration for komatiite-hosted nickel sulphide deposits

description: Portable X-Ray Fluorescence (pXRF) analysers allow on-site geochemical analysis of rock powders and drill core. The main advantages of pXRF analysis over conventional laboratory analysis are the speed of data collection and the low cost of the analyses, permitting the collection of extensive, spatially representative datasets. However, these factors only become useful if the quality of the data meets the requirements needed for the purposes of the study. Here, we evaluate the possible use of portable XRF to determine element concentrations and ratios used in exploration for komatiite-hosted nickel sulphides. A portable XRF analyser was used to measure a series of chalcophile and lithophile element concentrations (Si, S, K, Ca, Ti, Cr, Fe, Ni, Cu, Zn, As, Sr, and Zr) of 75 samples from three komatiite units associated with nickel sulphide ores in the Yilgarn Craton, Western Australia. Crucial steps in the study were the development of a strict calibration process as well as numerous data quality checks. The 670 analyses collected in this study were compared with conventional laboratory XRF data on discriminant diagrams commonly utilized in exploration for komatiite-hosted nickel sulphides (Cr vs Ni and Ni/Ti vs Ni/Cr). After comparing the results obtained with pXRF during this study with the laboratory values, we can conclude that portable XRF analyses can be used for rapid assessment of the nickel sulphide prospectivity of komatiites provided that strict control protocols are followed.