Volcaniclastic deposits and sedimentation processes around volcanic ocean islands: the central Azores

2021 ◽  
pp. SP520-2021-62
Author(s):  
Yu-Chun Chang ◽  
Neil C. Mitchell ◽  
Thor H. Hansteen ◽  
Julie C. Schindlbeck-Belo ◽  
Armin Freundt
Keyword(s):  
Volcanic Glass ◽  
Sedimentary Facies ◽  
Turbidity Currents ◽  
Content Type ◽  
Core Logging ◽  
Supplementary Material ◽  
Geochemical Analyses ◽  
Lithological Composition ◽  
Volcaniclastic Deposits ◽  
Ocean Islands

AbstractGeological histories of volcanic ocean islands can be revealed by the sediments shed by them. Hence there is an interest in studying cores of volcaniclastic sediments that are particularly preserved in the many flat-floored basins lying close to the Azores islands. We analyse four gravity cores collected around the central group of the islands. Three sedimentary facies (F1-F2a, F2b) are recognized based on visual core logging, particle morphometric and geochemical analyses. F1 is clay-rich hemipelagite comprising homogeneous mud with mottled structures from bioturbation. F2a and F2b are both clay-poor volcaniclastic deposits, which are carbonate-rich and carbonate-poor, respectively. More biogenic carbonate in F2a reflects the incorporation of unconsolidated calcareous material from island shelves or bioturbation. Within F2a and F2b we identify deposits emplaced by pyroclastic fallout, primary or secondary turbidity currents by combining multiple information from lithological composition, sedimentary structures, chemical composition of volcanic glass shards and morphometric characteristics of volcanic particles. Primary volcaniclastic sediments were found in all four cores, echoing activity known to have occurred up to historical times on the adjacent islands. These preliminary results suggest that greater details of geological events could be inferred for other volcanic islands by adopting a similar approach to core analysis.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5602176

The influence of volcanic supply on the composition of modern river sands: the case study of the Ofanto river, Southern Italy

2021 ◽  
pp. SP520-2021-89
Author(s):  
Mariano Tenuta ◽  
Paola Donato ◽  
Rocco Dominici ◽  
Rosanna De Rosa
Keyword(s):  
Volcanic Rocks ◽  
Pyroclastic Deposits ◽  
Content Type ◽  
Sedimentary Deposits ◽  
History Of ◽  
Supplementary Material ◽  
High Production ◽  
Volcaniclastic Deposits ◽  
Pyroclastic Fall

AbstractThe Ofanto river drains volcanic rocks from the Monte Vulture, lacustrine-fluviolacustrine deposits associated with the same volcano and sedimentary deposits of the Southern Apennines and the Bradanic foredeep sequences. Comparing the modal composition of river sands and the outcrop area of different lithologies in the different sub-basins, an over-concentration of the volcaniclastic fraction, mainly represented by loose crystals of clinopyroxene, garnet and amphibole, is shown. This has been related to the preferential erosion of pyroclastic deposits, characterized by high production of sand-sized loose minerals, together with the carbonate lability and the low sand-sized detritus production from claystones and marls. The occurrence of volcaniclastic components upstream of Monte Vulture can be explained with a contribution from the lacustrine-fluviolacustrine deposits outcropping in the upstream sector or from pyroclastic fall deposits of Monte Vulture and/or Campanian volcanoes. This research shows that the volcanic record in the fluvial sands of the Ofanto river comes from weathering and sorting processes of volcaniclastic deposits rather than of the lavas building the main edifice. Therefore, caution must be taken during paleoenvironmental and paleoclimatic reconstructions when relating the type and abundance of the volcanic component in sediments to the weathering stage and evolutionary history of the volcano.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5643959

scholarly journals Near real-time management of spectral interferences with portable XRF spectrometers: Application to Sc quantification in nickeliferous laterite ores

2021 ◽  
pp. geochem2021-015
Author(s):  
Elodie Lacroix ◽  
Jean Cauzid ◽  
Yoram Teitler ◽  
Michel Cathelineau
Keyword(s):  
Time Management ◽  
Chemical Elements ◽  
Fe Method ◽  
Portable Xrf ◽  
Experimental Conditions ◽  
Spectral Interferences ◽  
Content Type ◽  
Spectral Fitting ◽  
Supplementary Material ◽  
Geochemical Analyses

Since the development of portable XRF (pXRF) spectrometers, few studies have been conducted on the influence of spectral interferences between chemical elements. This study aims to improve the management of these interferences to obtain more reliable geochemical analyses. We specifically investigate Ca-related interferences on Sc analysis for the case of Ni-rich laterite samples using the Niton XL3t GOLDD+ pXRF analyser. Three quantification methods were tested on 59 pelletised samples using the ‘Soil’ mode. The first named ‘Manufacturer’, represents the elemental quantification directly provided by the device based on Regions of Interest (ROI) and multilinear corrections of spectral interferences configured during the spectrometer design. The second, the ‘20 Cu’ method, is based on spectral fitting using the PyMCA software. The third, the ‘18 Fe’ method, combines spectral fitting with modified experimental conditions. For each, a quantification methodology was developed, establishing (i) Ca and Sc calibration lines and (ii) Ca/Sc threshold values delimiting fields of ‘reliable’, 'to be confirmed,’ and ‘unreliable’ measurements. The ‘20 Cu’ and ‘18 Fe’ methods greatly extend the ‘reliable measurements’ field concerning the Ca/Sc ratio compared to the ‘Manufacturer’ method. The ‘18 Fe’ method was also found to provide the most negligible measurement dispersion.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5511838

Expanding the toolbox for dating basaltic lava sequences: 40Ar–39Ar dating of silicic volcanic glass from interbeds

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2019-207
Author(s):  
Simone Cogliati ◽  
Sarah C. Sherlock ◽  
Alison M. Halton ◽  
Alena Ebinghaus ◽  
Simon P. Kelley ◽  
...  
Keyword(s):  
Volcanic Glass ◽  
Depositional Environments ◽  
Basaltic Lava ◽  
Content Type ◽  
Additional Tool ◽  
Sample Data ◽  
Stratigraphic Position ◽  
Silicic Volcanic ◽  
Supplementary Material ◽  
Glass Shards

40Ar–39Ar dating of glass shards from silicic tuffs of the Ellensburg Formation (NW, USA) interbedding basaltic lavas yielded accurate, precise, reproducible plateau and isochron ages that are within error at the 2σ level. The age-spectra have flat plateaus and the inverse isochrons have atmospheric 40Ar/36Ar at the 2σ level. Ages of 12.00 ± 0.24, 11.37 ± 0.15, 10.67 ± 0.21 and 10.70 ± 0.18 Ma are consistent with the stratigraphy of four of the dated layers; the age of 10.77 ± 0.18 Ma for a fifth layer is at odds with the stratigraphy. This discrepancy arises due to the effect of glass alteration that induced K- and Ar-loss. There is no evidence of excess 40Ar or 39Ar recoil. The new ages indirectly constrain the timing of eruption of the lavas above and below the ash beds. This demonstrates that volcanic glass from interbeds can be used as an additional tool for indirectly dating basaltic lava sequences, which is independent of the lavas and complementary to other materials. Considering the numerous studies in which volcanic glass failed to provide reliable 40Ar–39Ar ages, additional and supportive constraints are still needed to assess the validity of the ages from glass shards.Supplementary material: A1 – sample location, stratigraphic position and depositional environments; A2 – electron microprobe information with calibration and sample data; A3 – Ar isotopic data of blanks and samples, data reduction software, J values, criteria for age calculation and images of age spectra and inverse isochrons are available at https://doi.org/10.6084/m9.figshare.c.5077705

scholarly journals Stable isotopes (δ13C, δ18O) and element ratios (Mg/Ca, Sr/Ca) of Jurassic belemnites, bivalves and brachiopods from the Neuquén Basin (Argentina): challenges and opportunities for palaeoenvironmental reconstructions

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-163
Author(s):  
Matthias Alberti ◽  
Horacio Parent ◽  
Alberto C. Garrido ◽  
Nils Andersen ◽  
Dieter Garbe-Schönberg ◽  
...  
Keyword(s):  
Environmental Parameters ◽  
Global Pattern ◽  
Content Type ◽  
Marginal Seas ◽  
Temperature Reconstructions ◽  
Challenges And Opportunities ◽  
Neuquen Basin ◽  
Supplementary Material ◽  
Neuquén Basin ◽  
Geochemical Analyses

Fossils from the Jurassic succession of the Neuquén Basin (Argentina) were analysed for their stable isotope (δ13C, δ18O) and elemental (Mg/Ca, Sr/Ca) composition. Mg/Ca ratios point to comparatively stable temperature conditions from the Bajocian to Early Oxfordian and during the Tithonian, but do not allow a reliable reconstruction of absolute water temperatures. Sr/Ca ratios follow the general global pattern, indicating water exchange between the basin and the open ocean. The δ18O values can be translated into water temperatures between 20 and 25°C for most of the studied intervals with possible shorter cold spells in the Late Pliensbachian, Bajocian and Late Tithonian. However, precise temperature reconstructions are complicated by bivalve shells from the northern–central part of the basin pointing to local fluctuations in the δ18O values of seawater. Potential reasons for these variations are discussed, but it seems most likely that they are caused by phases of enhanced freshwater input leading to meso- to brachyhaline conditions in the northern study areas. This paper therefore exemplifies the particular challenges for temperature reconstructions in marginal seas and highlights the opportunities of combining different geochemical proxies to disentangle the influence of different environmental parameters.Supplementary material: Detailed results of the geochemical analyses, geographical coordinates and information on biostratigraphy are available at https://doi.org/10.6084/m9.figshare.c.5173466

scholarly journals Marie Byrd Land lithospheric mantle: A review of the xenolith record

2021 ◽  
pp. M56-2020-17
Author(s):  
Monica R. Handler ◽  
Richard J. Wysoczanski ◽  
John A. Gamble
Keyword(s):  
Lithospheric Mantle ◽  
Rift System ◽  
Type I ◽  
Content Type ◽  
Partial Melt ◽  
West Antarctic ◽  
Supplementary Material ◽  
Geochemical Analyses ◽  
West Antarctic Rift System ◽  
West Antarctic Rift

AbstractThe Marie Byrd Land (MBL) lithospheric mantle xenolith record comprises over 100 samples from a range of localities spanning both major crustal terranes that comprise MBL: Ross and Amundsen provinces. Coarse granular to porphyroclastic in texture, the xenoliths are predominantly Type I spinel-bearing lherzolites to harburgites, but include rare dunite and pyroxenite examples. Garnet is absent and no hydrous phases, such as amphibole or mica, have been reported to date, although traces of apatite may be present. Characterisation of the lithospheric mantle composition and its evolution however, is hampered by patchy and uneven geochemical analyses across the xenolith suite. Nonetheless, a picture emerges of a heterogeneous lithosphere beneath both Ross and Amundsen Provinces. Previously published and new data reported here are consistent with samples ranging from variably cryptically metasomatised residua from variable (10 - 25%) degrees of partial melt extraction to refertilised compositions. Limited isotopic data point to a complex history, providing evidence for both ancient Proterozoic lithospheric mantle and preservation of Ordovician events. The Sr-Nd-Pb composition of the sampled lithospheric mantle overlaps the common low-µ isotopic endmember identified in Cenozoic magmatism from MBL and the wider West Antarctic Rift System.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5309814

scholarly journals Rapid geomorphological and sedimentological changes at a modern Alpine ice margin: lessons from the Gepatsch Glacier, Tirol, Austria

2021 ◽  
pp. jgs2021-052
Author(s):  
Daniel Paul Le Heron ◽  
Christoph Kettler ◽  
Bethan J. Davies ◽  
Lars Scharfenberg ◽  
Lukas Eder ◽  
...  
Keyword(s):  
Sedimentary Facies ◽  
Mass Wasting ◽  
Erosion And Deposition ◽  
Content Type ◽  
Glacial Sediments ◽  
Time Period ◽  
Preservation Potential ◽  
Supplementary Material ◽  
Sand And Gravel ◽  
First Time

The Gepatsch Glacier in Tirol (Austria) is a rapidly retreating valley glacier whose host valley and forefield reveal subglacial, proglacial, and reworked sediment-landform assemblages. Structures include roches moutonées develop on gneiss, compound bedrock-sediment bedforms (crag and tail structures), flutes, and small diamicton ridges. The glacial sediments and landforms are undergoing incision and terrace development by meltwater streams. Glacial geomorphological and surface geological maps maps, in concert with elevation models of difference between July 2019 and July 2020 highlight considerable changes to the forefield over a 12-month time period. Till exposed within the last 20 years has undergone substantial mass wasting and re-deposition as subaerial mass flows, or reworked into stream deposits. The lee sides of many roches moutonées completely lack subglacial sediment, and instead contain a sand and gravel deposit interpreted to result from glaciofluvial deposition. Thus, insights into the rates of erosion and deposition in a complex, proglacial setting, allow some of these processes to be quantified for the first time. Repeated monitoring of glacier forefields is expected to yield a better understanding of the preservation potential of proglacial sedimentary facies, and hence their preservation potential in Earth's sedimentary record.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5664299

Volcano-sedimentary processes at Las Derrumbadas rhyolitic twin domes, Serdán-Oriental basin, Eastern Trans-Mexican Volcanic Belt

2021 ◽  
pp. SP520-2021-144
Author(s):  
Marie-Noëlle Guilbaud ◽  
Corentin Chédeville ◽  
Ángel Nahir Molina-Guadarrama ◽  
Julio Cesar Pineda-Serrano ◽  
Claus Siebe
Keyword(s):  
Volcanic Belt ◽  
Debris Avalanche ◽  
Density Currents ◽  
Content Type ◽  
Mexican Volcanic Belt ◽  
Wide Range ◽  
Eruptive Episode ◽  
Basin Floor ◽  
Supplementary Material ◽  
Trans Mexican Volcanic Belt

AbstractThe eruption of the ∼10 km3 rhyolitic Las Derrumbadas twin domes about 2000 yrs ago has generated a wide range of volcano-sedimentary deposits in the Serdán-Oriental lacustrine basin, Trans-Mexican Volcanic Belt. Some of these deposits have been quarried, creating excellent exposures. In this paper we describe the domes and related products and interpret their mode of formation, reconstructing the main phases of the eruption as well as syn-and-post eruptive erosional processes. After an initial phreatomagmatic phase that built a tuff ring, the domes grew as an upheaved plug lifting a thick sedimentary pile from the basin floor. During uplift, the domes collapsed repeatedly to form a first-generation of hetero-lithologic hummocky debris avalanche deposits. Subsequent dome growth produced a thick talus and pyroclastic density currents. Later, the hydrothermally-altered over-steepened dome peaks fell to generate 2nd generation, mono-lithologic avalanches. Subsequently, small domes grew in the collapse scars. From the end of the main eruptive episode onwards, heavy rains remobilized parts of the dome carapaces and talus, depositing lahar aprons. Las Derrumbadas domes are still an important source of sediments in the basin, and ongoing mass-wasting processes are associated with hazards that should be assessed, given their potential impact on nearby populations.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5752296

Jurassic–Cretaceous arc magmatism along the Shyok–Bangong Suture from NW Himalaya: Formation of the peri-Gondwana basement to the Ladakh Arc

2021 ◽  
pp. jgs2021-035
Author(s):  
Wanchese M. Saktura ◽  
Solomon Buckman ◽  
Allen P. Nutman ◽  
Renjie Zhou
Keyword(s):  
Late Cretaceous ◽  
Nw Himalaya ◽  
Content Type ◽  
Magmatic Arc ◽  
Basement Rocks ◽  
Ladakh Himalaya ◽  
Accreted Terranes ◽  
Volcaniclastic Rocks ◽  
Supplementary Material ◽  
Depositional Age

The Jurassic–Cretaceous Tsoltak Formation from the eastern borderlands of Ladakh Himalaya consists of conglomerates, sandstones and shales, and is intruded by norite sills. It is the oldest sequence of continent-derived sedimentary rocks within the Shyok Suture. It also represents a rare outcrop of the basement rocks to the voluminous Late Cretaceous–Eocene Ladakh Batholith. The Shyok Formation is a younger sequence of volcaniclastic rocks that overlie the Tsoltak Formation and record the Late Cretaceous closure of the Mesotethys Ocean. The petrogenesis of these formations, ophiolite-related harzburgites and norite sill is investigated through petrography, whole-rock geochemistry and U–Pb zircon geochronology. The youngest detrital zircon grains from the Tsoltak Formation indicate Early Cretaceous maximum depositional age and distinctly Gondwanan, Lhasa microcontinent-related provenance with no Eurasian input. The Shyok Formation has Late Cretaceous maximum depositional age and displays a distinct change in provenance to igneous detritus characteristic of the Jurassic–Cretaceous magmatic arc along the southern margin of Eurasia. This is interpreted as a sign of collision of the Lhasa microcontinent and the Shyok ophiolite with Eurasia along the once continuous Shyok–Bangong Suture. The accreted terranes became the new southernmost margin of Eurasia and the basement to the Trans-Himalayan Batholith associated with the India-Eurasia convergence.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5633162

Geochemical evaluation of the in-situ regolith of Madengi hills of Dodoma, Tanzania. Implication on bedrock mapping and delineating gold mineralization target

2021 ◽  
pp. geochem2021-074
Author(s):  
Godson Godfray
Keyword(s):  
Gold Mineralization ◽  
Early Stage ◽  
Shear Zones ◽  
Soil Geochemistry ◽  
Residual Soils ◽  
Content Type ◽  
Geochemical Evaluation ◽  
Supplementary Material ◽  
Pathfinder Elements

Successful gold exploration projects depend on a piece of clear information on the association between gold, trace elements, and mineralization controlling factors. The use of soil geochemistry has been an important tool in pinpointing exploration targets during the early stage of exploration. This study aimed to establish the gold distribution, the elemental association between gold and its pathfinder elements such as Cu, Zn, Ag, Ni, Co, Mn, Fe, Cd, V, Cr, Ti, Sc, In, and Se and identify lithologies contributing to the overlying residual soils. From cluster analysis, a high similarity level of 53.93% has been shown with Ag, Cd, and Se at a distance level of 0.92. Au and Se have a similarity level of 65.87% and a distance level of 0.68, hence is proposed to be the most promising pathfinder element. PCA, FA, and the Pearson's correlation matrix of transformed data of V, Cu, Ni, Fe, Mn, Cr, and Co and a stronger correlation between Pb and U, Th, Na, K, Sn, Y, Ta and Be shows that source gold mineralization might be associated with both hornblende gneisses interlayered with quartzite, tonalite, and tonalitic orthogneiss. From the contour map and gridded map of Au and its pathfinder elements, it has been noted that their anomalies and target generated are localized in the Northern part of the area. The targets trend ESE to WNW nearly parallel to the shear zones as a controlling factor of Au mineralization emplacement.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5721965

First evidence for tooth-tooth occlusion in a ctenochasmatid pterosaur from the Early Cretaceous Jehol Biota

2021 ◽  
pp. SP521-2021-141
Author(s):  
Chang-Fu Zhou ◽  
Xinyue Wang ◽  
Jiahao Wang
Keyword(s):  
Early Cretaceous ◽  
Feeding Strategy ◽  
Three Dimensional ◽  
Tooth Wear ◽  
First Record ◽  
Jehol Biota ◽  
Content Type ◽  
Dimensional Reconstruction ◽  
Supplementary Material ◽  
Ct Data

AbstractCtenochasmatid pterosaurs flourished and diversified in the Early Cretaceous Jehol Biota. Here, a partial mandible of Forfexopterus is described based on a three-dimensional reconstruction using high-resolution X-ray Computed Tomography (CT) data. The first nine pairs of functional teeth of the rostral dentition revealed along with their replacements. The functional teeth are evenly arranged with a tooth density of 2.2 teeth/cm. The tooth crown is distinctly reduced from its base to the tip, and framed by two weak ridges, possibly as a pair of vestigial carinae. The replacement teeth are sharp and pointed, and have erupted slightly against the medial surface of the functional teeth. Surprisingly, tooth wear is observed in this specimen, the first record of tooth-tooth occlusion in ctenochasmatids. The wear facets exhibit high-angled lingual and lower-angled labial facets, implying a tooth-tooth occlusion in pterosaur clade. This discovery indicates that the Jehol ctenochasmatids possibly employed a more active feeding strategy than other filter-feeding pterosaurs (e.g. Ctenochasma, Pterodaustro, Gnathosaurus).Supplementary material at https://doi.org/10.6084/m9.figshare.c.5722060

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