Late Quaternary cryptotephra detection and correlation in loess in northeastern Japan using cummingtonite geochemistry

We detected late Pleistocene cummingtonite-bearing cryptotephras in loess deposits in NE Japan and correlated them with known tephras elsewhere by using major-element compositions of the cummingtonite. This is the first time cryptotephras have been identified by analysis of a crystal phase rather than glass shards. In central NE Japan, four cummingtonite-bearing tephras, the Ichihasama pumice, the Dokusawa tephra, the Naruko–Nisaka tephra, and the Adachi–Medeshima tephra, are present in late Pleistocene loess deposits. Because the cummingtonite chemistry of each tephra is different and characteristic, it is potentially a powerful tool for detecting and identifying cryptotephras. An unidentified cummingtonite-bearing cryptotephra previously reported to be present in the late Pleistocene loess deposits at Kesennuma (Pacific coast) did not correlate with any of the known cummingtonite-bearing tephras in central NE Japan, but instead with the Numazawa–Kanayama tephra (erupted from the Numazawa caldera, southern NE Japan), although Kesennuma is well beyond the previously reported area of the distribution of the Numazawa–Kanayama tephra. Three new cummingtonite-bearing cryptotephras in the mid and late Pleistocene loess deposits (estimated to be less than 82 ka, 100–200 ka, and ca. 250 ka) on the Isawa upland were also detected.     

Tephra Fallout Models: The Effect of Different Source Shapes on Isomass Maps

Numerous tephra dispersion and sedimentation models rely on some abstraction of the volcanic plume to simplify forecasts of tephra accumulation as a function of the distance from the volcano. Here we present solutions to the commonly used advection–dispersion equation using a variety of source shapes: a point, horizontal and vertical lines, and a circular disk. These may be related to some volcanic plume structure, such as a strong plume (vertical line), umbrella cloud (circular disk), or co-ignimbrite plume (horizontal line), or can be used to build a more complex plume structure such as a series of circular disks to represent a buoyant weak plume. Basing parameters upon eruption data, we find that depositions for the horizontal source shapes are very similar but differ from the vertical line source deposition. We also compare the deposition from a series of stacked circular disk sources of increasing radius above the volcanic vent with that from a vertical line source.     

Compositions of glass in proximal tephras from eruptions in the Azores archipelago and their links with distal sites in Ireland

The Azores archipelago is one of the most active volcanic areas in the North Atlantic region, with approximately 30 eruptions during the last 600 years. The geochemical composition of associated tephra-derived glass is, however, not well characterized. This study presents major element compositions of glass shards from five major eruptives on the Azores: a trachybasaltic eruptive on the island of Faial (Capelinhos AD, 1957) and four explosive trachytic eruptives on the island of São Miguel (Fogo A c. 5600 cal yrs. BP, Sete Cidades c. AD 1440, Fogo AD 1563 and Furnas AD 1630). The major element compositions suggest that tephras from three active stratovolcanoes on São Miguel, Sete Cidades, Fogo and Furnas, can be distinguished from one another using bi-plots of FeO_tot vs. TiO₂ and FeO_tot vs. CaO. Late Holocene tephras found on Ireland have previously been attributed to eruptions occurring on Jan Mayen but possess a strong geochemical similarity to proximal tephras from the Azores, especially those from the Furnas volcano. The similarity of the proximal tephras on São Miguel, especially Furnas AD 1563 and Furnas AD 1630 and distal tephras in Ireland is demonstrated by strong similarity coefficients (>0.95) and the closeness of major element composition. The dominant wind direction over the Azores is favourable for tephra dispersal to western Europe and we suggest that at least three tephras found in Ireland were erupted from the Furnas volcano, and that trachytic tephras erupted from explosive eruptions on São Miguel have a potential to contribute to the construction of a European-wide tephrostratigraphic framework.     

Use of magnetic signatures to correlate tephra layers in Holocene loessial soil profiles from a small region, SE Iceland

Rock magnetic measurements have been applied to two adjacent loessial soil sections from a small region, SE Iceland. The soils are composed of reworked locally derived sediment (including airfall tephra) and also contain several visible discrete airfall tephra layers. The main magnetic minerals in the airfall tephras are ferrimagnetic (e.g. magnetite) with paramagnetic minerals also present. The main magnetic grain sizes in the tephras are pseudo single domain. The results show that individual tephras do not have unique magnetic signatures that can be used for identification and correlation between sedimentary sequences. However, a correlation of tephra layers was achieved through the application of statistical techniques to a comprehensive dataset of magnetic parameters. Similarity coefficients and Euclidian distance measures were used to identify the best correlation between tephra layers in the two soil profiles. The technique works well providing some tephras present within both profiles have been formally identified (e.g. Oraefajokulla ad 1362) using electron microprobe analyses. Given this initial framework, the statistical analyses of the magnetic parameters can help in the identification and correlation of unknown tephras between two soil profiles.     

鲁迅与顾琅早期地质作品新论——《中国地质略论》与《中国矿产志》知识来源考

鲁迅在日本留学期间曾于1903年在《浙江潮》发表《中国地质略论》一文,1906年与同到日本留学的顾琅合作出版《中国矿产志》(附《中国矿产全图》)一书。它们在中国地质学史上均具有开创性并产生重要影响,特别是《中国矿产志》被认为是中国第一部地质矿产著作。本文从中日地质学交流的角度,结合新发现的史料,通过文本对比分析,指出《中国地质略论》和《中国矿产志》均是吸收当时日本的一些地学著作编写而成。《中国地质略论》的地史学内容主要来源于佐藤传藏《地质学》(1898)一书,有关煤炭内容以及中国煤田分布图则来自日本海军少将肝付兼行发表在《太阳》(1903)杂志上的《东方之煤源》一文;《中国矿产志》的导言部分是在《中国地质略论》的基础上拓展而成,增补的内容则参考了矢津昌永的《清国地志》(1905)、横山又次郎的《地质学教科书》(1903)以及石川成章的《地球发达史》(1904)等著作,本言部分主要参考了日本地质调查所1902年发表的《清国及韩国主要矿产颁布图说明——附清国主要矿产地名表》;《中国矿产全图》则是顾琅依据日本《清国主要矿产分布图》绘制而成。《中国地质略论》和《中国矿产志》(附《中国矿产全图》...     

A second tephra isochron for the Younger Dryas period in northern Europe: The Abernethy Tephra

Visible and non-visible (cryptotephra) volcanic ash layers are increasingly being used to underpin the chronology and high-precision correlation of sequences dating to the last glacial–interglacial transition (LGIT). As the number of sediment records analysed for tephra content rises, and methodological developments permit the detection, extraction and chemical analysis of increasingly scantily represented glass shard concentrations, greater complexity in shard count profiles is revealed. Here we present new evidence from sites in Scotland, and review published evidence from sites elsewhere in NW Europe, that indicate complexity in the eruptive history of Katla volcano during the mid-Younger Dryas and Early Holocene. We propose evidence for a previously-overlooked tephra isochron, here named the Abernethy Tephra, which is consistently found to lie close to the Younger Dryas/Holocene transition. It has a major-element chemical composition indistinguishable from that of the Vedde Ash, which was erupted from the Katla volcano at 12,121 ± 114 cal a BP. The new data suggest that Katla may have erupted again between 11,720–11,230 cal a BP and the subsequent ash fall increases the potential to assess environmental response to Holocene warming across north and west Europe.     

Multiple approaches to date Japanese marker tephras using optical and ESR methods

The present study aimed to test reliability of luminescence and electron spin resonance (ESR) methods to date tephra. We investigated on three Japanese marker tephras, Ikeda-ko (6.4 ka), Aira-Tn (30 ka) and Aira-Iwato (45–50 ka). A systematic studies were performed using different minerals (quartz and feldspar), different grain fractions (75–250 and 250–500 μm), different luminescence and ESR signals, like optically stimulated luminescence (OSL) of quartz, infrared stimulated luminescence (IRSL) of feldspar, including recently developed least faded post infrared IRSL (pIR-IRSL), and ESR signals from paramagnetic centers Al and Ti–Li of quartz. Ages obtained using pIR-IRSL signal of plagioclase with preheat of 320 °C, 60 s and stimulation at 300 °C are consistent with the reference ages. High dose detection range (up to ∼600 Gy) and accurate age estimation enable pIR-IRSL of feldspar a promising methodology to date quaternary tephra. ESR ages from quartz are grossly correlated with the reference ages but large deviation and large associated errors are observed, possibly due to either low signal to noise ratio or heterogenous dose response of different aliquot in multiple aliquot additive dose (MAAD) approach.     

Last glacial aggradation and postglacial sediment production from the non-glacial Waipaoa and Waimata catchments, Hikurangi Margin, North Island, New Zealand

The sediment flux generated by postglacial channel incision has been calculated for the 2150 km², non-glacial, Waipaoa catchment located on the tectonically active Hikurangi Margin, eastern North Island, New Zealand. Sediment production both at a sub-catchment scale and for the Waipaoa catchment as a whole was calculated by first using the tensioned spline method within ARC MAP to create an approximation of the aggradational Waipaoa-1 surface (contemporaneous with the Last Glacial Maximum), and second using grid calculator functions in the GIS to subtract the modern day surface from the Waipaoa-1 surface. The Waipaoa-1 surface was mapped using stereo aerial photography, and global positioning technology fixed the position of individual terrace remnants in the landscape. The recent discovery of Kawakawa Tephra within Waipaoa-1 aggradation gravels in this catchment demonstrates that aggradation was coincidental with or began before the deposition of this 22 600 ¹⁴C-year-old tephra and, using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca 15 000 ¹⁴C years (ca 18 000 cal. years BP). The construction of the Waipaoa-1 terrace is considered to be synchronous and broadly correlated with aggradation elsewhere in the North Island and northern South Island, indicating that aggradation ended at the same time over a wide area. Subsequent downcutting, a manifestation of base-level lowering following a switch to postglacial incision at the end of glacial-age aggradation, points to a significant Southern Hemisphere climatic warming occurring soon after ca 15 000 ¹⁴C years (ca 18 000 cal. years BP) during the Older Dryas interval. Elevation differences between the Waipaoa-1 (c.15 ka) terrace and the level of maximum channel incision (i.e. before aggradation since the turn of the 20th century) suggest about 50% of the topographic relief within headwater reaches of the Waipaoa catchment has been formed in postglacial times. The postglacial sediment flux generated by channel incision from Waipaoa catchment is of the order of 9.5 km³, of which ~ 6.6 km³ is stored within the confines of the Poverty Bay floodplain. Thus, although the postglacial period represented a time of high terrigenous sediment generation and delivery, only ~ 30% of the sediment generated by channel incision from Waipaoa catchment probably reached the marine shelf and slope of the Hikurangi Margin during this time. The smaller adjacent Waimata catchment probably contributed an additional 2.6 km³ to the same depocentre to give a total postglacial sediment contribution to the shelf and beyond of ~ 5.5 km³. Sediment generated by postglacial channel incision represents only ~ 25% of the total sediment yield from this landscape with ~ 75% of the estimated volume of the postglacial storage offshore probably derived from hillslope erosion processes following base-level fall at times when sediment yield from these catchments exceeded storage.     

A Cartographic Analysis Using Spatial Filter Logistic Model Specifications for Implementing Mosquito Control in Kenya

Negative spatial autocorrelation (NSA), the tendency for dissimilar neighboring values to cluster on a map, may go undetected in statistical analyses of immature Anopheles gambiae s.l., a leading malaria mosquito vector in Sub-Saharan Africa. Unquantified NSA generated from an inverse variance-covariance matrix may generate misspecifications in an An. gambiae s.l. habitat model. In this research, we used an eigenfunction decomposition algorithm based on a modified geographic connectivity matrix to compute the Moran's I statistic, to uncover hidden NSA in a dataset of georeferenced An. gambiae s.l. habitat explanatory predictor variables spatiotemporally sampled in Malindi and Kisumu, Kenya. The Moran's I statistic was decomposed into orthogonal synthetic map patterns. Global tests revealed that |z_MC|s generated were less than 1.11 for the presence of latent autocorrelation. The algorithm captured NSA in the An. gambiae s.l. habitat data by quantifying all non-normal random variables, space-time heterogeneity, and distributional properties of the spatial filters.     

A geochemical method for removing the effect of tephra on lake diatom oxygen isotope records

The analysis of oxygen isotope ratios (δ¹⁸O) in biogenic silica (e.g. diatoms, sponge spicules, phytoliths) is an increasingly utilised palaeoclimatic proxy for lakes and oceans, providing an alternative to carbonate δ¹⁸O. Currently, the problems associated with the cleaning and extraction of pure diatom silica, especially from lake sediments, may compromise the precision associated with δ¹⁸O_diatom records. This is because, despite improvements in cleaning techniques, it is still difficult to remove silica-containing contaminants (e.g. tephra, silts and clays) from biogenic silica. Where it has proved difficult to remove all the silica bearing contaminants from a sample, mass balance calculations involving point counting have been used, but these are inherently inaccurate as they only consider the surface area of the contaminant, rather than volume. The new method described here assesses the volume of contamination in each sample of biogenic silica by using major and trace element geochemistry, allowing the δ¹⁸O of the contamination to be removed from the biogenic silica δ¹⁸O value by linear mass balance. In this case, diatom silica was contaminated with tephra, however the method should also be applicable to other contaminants such as silts and clays.