Volcanic Ash Layers Research Articles

Integrating the Holocene tephrostratigraphy for East Asia using a high-resolution cryptotephra study from Lake Suigetsu (SG14 core), central Japan

Tephra (volcanic ash) layers have the potential to synchronise disparate palaeoenvironmental archives on regional to hemispheric scales. Highly productive arc regions, like those in East Asia, offer a considerable number of widespread isochrons, but before records can be confidently correlated using these layers, a refined and integrated framework of these eruptive events is required. Here we present the first high-resolution Holocene cryptotephra study in East Asia, using the Lake Suigetsu sedimentary archive in central Japan. The Holocene tephrostratigraphy has been extended from four to twenty ash layers using cryptotephra extraction techniques, which integrates the deposits from explosive eruptions from North Korea/China, South Korea and along the Japanese arc. This Lake Suigetsu tephrostratigraphy is now the most comprehensive record of East Asian volcanism, and the linchpin site for correlating sequences across this region. Major element glass geochemical compositions are presented for the tephra layers in the sequence, which have been compared to proximal datasets to correlate them to their volcanic source and specific eruptions. This study has significantly extended the ash dispersal of many key Holocene marker layers, and has identified the first distal occurrence of isochrons from Ulleungdo and Changbaishan volcanoes. Utilising the high-precision Lake Suigetsu chronology, we are able to provide constrained eruption ages for the tephra layers, which can be transferred into other site-specific age models containing these markers. This new framework indicates that several isochrons stratigraphically bracket abrupt climate intervals in Japan, and could be used to precisely assess the regional and hemispheric synchronicity of these events.

Tephrostratigraphy of Grotta del Cavallo, Southern Italy: Insights on the chronology of Middle to Upper Palaeolithic transition in the Mediterranean

The Grotta del Cavallo contains one of the most important stratification of Mousterian, Uluzzian and Final Epigravettian tecnocomplexes; its chronology is of paramount importance for understanding the timing of the transition between Middle and Upper Palaeolithic in the Mediterranean region as well as the demise of the Neanderthal and the dispersal of the first anatomically modern humans through Europe. Within the stratigraphy of the cave three different volcanic ash layers occur (layer G, Fa and C-II). They are located in the middle section of the Mousterian (layer G), in between the Mousterian and Uluzzian layers (layer Fa) and on top of the Uluzzian horizons (layer C-II). The three tephra layers were chemically fingerprinted and correlated to well-known and precisely dated widespread Late Pleistocene tephra markers. Specifically, layer G, Fa and C-II were correlated to the X-6 (108.7 ± 0.9 ka), Y-6 (45.5 ± 1.0 ka) and Campanian Ignimbrite (39.85 ± 0.14 ka), respectively. These findings provide robust chronological points allowing to conclude that: (i) the Mousterian occupation of the cave took place after the fall of the sea level following the MIS 5e high-stand; (ii) the Mousterian-Uluzzian boundary can be dated to 45.5 ± 1.0 ka and climatostratigraphically firmly placed at the transition between the Greenland Interstadial 12 (GI12)-Greenland Stadial 12 (GS12); (iii) the Uluzzian lasted for at least five millennial spanning the GS12-GI9 period and ended at beginning of the Heinrich Event 4.

Geochemistry and origin of Carboniferous (Mississippian; Viséan) bentonites in the Namur-Dinant Basin, Belgium: evidence for a Variscan volcanic source

1. Introduction Several clay-rich horizons interbedded with Mississippian (Visean) limestones in the Namur-Dinant Basin (NDB), Belgium, are interpreted to be diagenetically altered volcanic ash layers based on their lateral continuity, clay mineralogy and heavy mineral assemblages (e.g. Thorez & Pirlet, 1979; Delcambre, 1989, 1996). Whilst several aspects of these clay horizons have been studied in detail, their original (unaltered) volcanic composition and the location(s) of the source volcanoes are not well constrained. The whole-rock geochemistry of altered volcanic rocks such as bentonites and tonsteins has been employed in several other studies to gain information about the composition of the original (unaltered) ash layers and ultimately the magma from which they were derived (e.g. Spears & Kanaris-Sotiriou, 1979; Merriman & Roberts, 1990; Huff et al., 1993; Christidis et al., 1995). The major elements, which are routinely used to classify fresh or slightly altered volcanic rocks, are of limited use when classifying extensively altered volcanic rocks because several elements, including K and Na, are known to be mobile during weathering and diagenesis (Winchester & Floyd, 1977; Floyd & Winchester, 1978; Zielinski, 1982; Christidis, 1998). Instead, the classification of altered volcanic rocks relies on trace elements including Ti, the high-field-strength elements (HFSE) Hf, Nb, Ta, Zr and the rare-earth elements, which are generally considered to be immobile during most u

131. 火山ガラスの組成からみた大阪層群ピンク,アズキ火山灰層の起源

131. 火山ガラスの組成からみた大阪層群ピンク,アズキ火山灰層の起源

Sustained effects of volcanic ash on biofilm stoichiometry, enzyme activity and community composition in North- Patagonia streams

Volcanic eruptions are extreme perturbations that affect ecosystems. These events can also produce persistent effects in the environment for several years after the eruption, with increased concentrations of suspended particles and the introduction of elements in the water column. On 4th June 2011, the Puyehue-Cordón Caulle Volcanic Complex (40.59°S-72.11°W, 2200m.a.s.l.) erupted explosively in southern Chile. The area affected by the volcano was devastated; a thick layer of volcanic ash (up to 30cm) was deposited in areas 50 km east of the volcano towards Argentina. The aim of the present study was to evaluate the effect of volcanic ash deposits on stream ecosystems four years after the eruption, comparing biofilm stoichiometry, alkaline phosphatase activity, and primary producer's assemblage in streams which were severely affected by the volcano with unaffected streams. We confirmed in the laboratory that ash deposited in the catchment of affected streams still leach phosphorus (P) into the water four years after eruption. Results indicate that affected streams still receive volcanic particles and that these particles release P, thus stream water exhibits high P concentration. Biofilm P content was higher and the C:P ratio lower in affected streams compared to unaffected streams. As a consequence of less P in unaffected streams, the alkaline phosphatase activity was higher compared to affected streams. Cyanobacteria increased their abundances (99.9% of total algal biovolume) in the affected streams suggesting that the increase in P may positively affect this group. On the contrary, unaffected streams contained a diatom dominant biofilm. In this way, local heterogeneity was created between sub-catchments located within 30 km of each other. These types of events should be seen as opportunities to gather valuable ecological information about how severe disturbances, like volcanic eruptions, shape landscapes and lotic systems for several years after the event.

New Zealand supereruption provides time marker for the Last Glacial Maximum in Antarctica

Multiple, independent time markers are essential to correlate sediment and ice cores from the terrestrial, marine and glacial realms. These records constrain global paleoclimate reconstructions and inform future climate change scenarios. In the Northern Hemisphere, sub-visible layers of volcanic ash (cryptotephra) are valuable time markers due to their widespread dispersal and unique geochemical fingerprints. However, cryptotephra are not as widely identified in the Southern Hemisphere, leaving a gap in the climate record, particularly during the Last Glacial Maximum (LGM). Here we report the first identification of New Zealand volcanic ash in Antarctic ice. The Oruanui supereruption from Taupo volcano (25,580 ± 258 cal. a BP) provides a key time marker for the LGM in the New Zealand sector of the SW Pacific. This finding provides a high-precision chronological link to mid-latitude terrestrial and marine sites, and sheds light on the long-distance transport of tephra in the Southern Hemisphere. As occurred after identification of the Alaskan White River Ash in northern Europe, recognition of ash from the Oruanui eruption in Antarctica dramatically increases the reach and value of tephrochronology, providing links among climate records in widely different geographic areas and depositional environments.

REUSE OF BURIAL SITES DURING THE LATE HOLOCENE: EVIDENCE FROM MULTIPLE HUMAN BURIALS AT THE RÍO BOTE 1 ROCKSHELTER, UPPER SANTA CRUZ RIVER BASIN (SOUTHERN PATAGONIA, ARGENTINA)

The first systematic research on the funerary record at the Río Bote 1 (RB1) rockshelter, located next to the Bote River, a tributary of the Santa Cruz River in southern Patagonia, has revealed at least three human burial events dating to the very early Late Holocene and one dating to the middle Late Holocene. The RB1 site appears to have been used for both subsistence and inhumation activities. All of the burials uncovered postdate the deposition of a prominent volcanic ash layer. Technological information indicates that RB1 was used by groups that were also using spaces to the west and south. Mortuary evidence indicates connections with groups living in areas extending from the Última Esperanza region to the Pali Aike volcanic field, at least at the beginning of the Late Holocene. The selection of the same place for multiple burials may explain why so few human burials are known in southern Patagonia from the beginning of the Late Holocene and earlier periods, as it is possible that sites like RB1 are yet to be discovered.

P-39 約1.3Maに噴出した中部九州起源の広域火山灰層,敷戸-イエローIテフラとその頃のテクトニクスの変化(5.地域間層序対比と年代層序スケール,口頭およびポスター発表,一般講演)

P-39 約1.3Maに噴出した中部九州起源の広域火山灰層,敷戸-イエローIテフラとその頃のテクトニクスの変化(5.地域間層序対比と年代層序スケール,口頭およびポスター発表,一般講演)

New chronological constraints for Middle Palaeolithic (MIS 6/5-3) cave sequences in Eastern Transylvania, Romania

The Middle to Upper Palaeolithic transition is one of the crucial periods of change in the prehistory of Europe due to the full emergence, continent-wide, of modern human lithic technologies, and detrimental of Neanderthal survival. Knowledge about the transition is growing, however, the evidence for cultural and technological developments for the Middle Palaeolithic in the Carpathian – Lower Danube Basin is still rather sparse. Here we discuss latest findings arising from a chronological investigation of Middle Palaeolithic assemblages within the Varghis karst, Eastern Transylvania, Romania. Combining our first chronological results with information from previous excavations, we can distinguish two main stages of habitation (albeit Middle Palaeolithic lithics and faunal remains appear scattered throughout the investigated profile) within the Abri 122 rock shelter. In order to augment the typological cultural considerations, we applied direct radiocarbon dating on bones and charcoal from within the occupation layers. Radiocarbon dating of bones suggests that the Middle Palaeolithic sequence is older than the upper dating limit of the method, whereas direct luminescence ages on the lowermost productive horizon and immediately above it indicate surprisingly old ages of ca. 106–141 ka (OSL – optically stimulated) or 99–174 ka (IRSL – infrared stimulated). Multiple-protocol dating of charcoal found within the two habitation layers produced ages >38 14C ka BP, also suggesting that the lowermost lithic-rich horizon pertains to the Middle Palaeolithic industries. Overall, the recovered lithics, currently forming one of the most significant collections for Romania, are fully consistent with two main habitation phases connected to Middle Palaeolithic cultural affinities. The occurrence of a volcanic ash layer within Ursului Cave and originating from the Ciomadul volcanic complex (Carpathians) is first reported here. Recently dated to ∼ ≥ 43 (−50) ka, it might represent an important marker horizon, providing that it is identified within other Palaeolithic cave assemblages.

Icelandic grasslands as long-term C sinks under elevated organic N inputs

About 10% of the anthropogenic CO2 emissions have been absorbed by northern terrestrial ecosystems during the past decades. It has been hypothesized that part of this increasing carbon (C) sink is caused by the alleviation of nitrogen (N) limitation by increasing anthropogenic N inputs. However, little is known about this N-dependent C sink. Here, we studied the effect of chronic seabird-derived N inputs (47–67 kg N ha−1 year−1) on the net soil organic C (SOC) storage rate of unmanaged Icelandic grasslands on the volcanic Vestmannaeyjar archipelago by using a stock change approach in combination with soil dating. We studied both early developmental (young) soils that had been receiving increased N inputs over a decadal timescale since an eruption in 1963, and well-developed soils, that had been receiving N inputs over a millennial timescale. For the latter, however, the effects on both decadal (topsoil; 40 years) and millennial (total soil profile; 1600 years) SOC storage could be studied, as the age of topsoil and the total soil profile could be determined from volcanic ash layers deposited in 1973 and 395 AD. We found that enhanced N availability—either from accumulation over time, or seabird derived—increased the net SOC storage rate. Under low N inputs, early developmental soils were weak decadal C sinks (0.018 ton SOC ha−1 year−1), but this increased quickly under ca. 30 years of elevated N inputs to 0.29 ton SOC ha−1 year−1, thereby equalling the decadal SOC storage rate of the unfertilized well-developed soils. Furthermore, for the well-developed soils, chronically elevated N inputs not only stimulated the decadal SOC storage rate in the topsoil, but also the total millennial SOC storage was consistently higher. Hence, our study suggests that Icelandic grasslands, if not disturbed, can remain C sinks for many centuries under current climatic conditions and that chronically elevated N inputs can induce a permanent strengthening of this sink.

Multimethod Approach to the Study of Recent Volcanic Ashes from Tengger Volcanic Complex, Eastern Java, Indonesia

Volcanic ash is a volcanic product with a wide distribution that can be used as a geological marker. In volcanic regions such as Indonesia, the identification of the sources of volcanic ash and tuff layers from different volcanoes or eruptive events is a challenging task. In this study, samples of volcanic ash from the 2010 eruption of Bromo—a relatively young and active tuff cone volcano within the Sandsea caldera in the Tengger volcanic complex in East Java, Indonesia—along with two older tuff layers from the same caldera (Widodaren tuff: 1.8 kyr and Segarawedi tuff: 33 kyr) were subjected to magnetic measurements, geochemical analyses, and petrographic analyses. The aim is to attempt to use magnetic characters as a fingerprint for volcanic ash and tuff layers. The results show that the samples had variations in grain size and magnetic domain as indicated by the hysteresis parameters. These magnetic characters correlated with the results of geochemical and petrographic analyses, suggesting that magnetic properties may potentially be used as fingerprints to identify volcanic ashes and tuff layers.

新潟地域の板山-Nym火山灰層,氷見層群のYT3火山灰層および東海層群の佐布里火山灰層の対比 : 中央日本における鮮新世の広域火山灰層の検出

新潟地域の板山-Nym火山灰層,氷見層群のYT3火山灰層および東海層群の佐布里火山灰層の対比 : 中央日本における鮮新世の広域火山灰層の検出

アカホヤ, イモゴ, オンヂの対比ならびに噴出源について : アカホヤの土壌肥料科学的研究(第2報)

アカホヤ, イモゴ, オンヂの対比ならびに噴出源について : アカホヤの土壌肥料科学的研究(第2報)

Thermal Conductivity and the Unfrozen Water Contents of Volcanic Ash Deposits in Cold Climate Conditions: A Review

AbstractLayers of volcanic ash and Andosol soils derived from the ash may play an important role in preserving snow and ice as well as in the development of permafrost conditions in (a) the immediate vicinity of volcanoes at high elevations or at high latitudes and (b) land areas that are often distant from volcanic activity and are either prone to permafrost or covered by snow and ice, but have been affected by subaerial ash deposition. The special properties of volcanic ash are critically reviewed, particularly in relation to recent research in Kamchatka in the Far East of Russia. Of special importance are the thermal properties, the unfrozen water contents of ash layers, and the rate of volcanic glass weathering.Weathering of volcanic glass results in the development of amorphous clay minerals (e.g. allophane, opal, palagonite), but occurs at a much slower rate under cold compared to warm climate conditions. Existing data reveal (1) a strong correlation between the thermal conductivity, the water/ice content, and the mineralogy of the weathered part of the volcanic ash, (2) that an increase in the amounts of amorphous clay minerals (allophane, palagonite) increases the proportion of unfrozen water and decreases the thermal conductivity, and (3) that amorphous silica does not alter to halloysite or other clay minerals, even in the Early Pleistocene age (Kamchatka) volcanic ashes or in the Miocene and Pliocene deposits of Antarctica due to the cold temperatures. The significance of these findings are discussed in relation to past climate reconstruction and the influence of volcanic ash on permafrost aggradation and degradation, snow and ice ablation, and the development of glaciers.

Advancing tephrochronology as a global dating tool: Applications in volcanology, archaeology, and palaeoclimatic research

Abstract Layers of far-travelled volcanic ash (tephra) from explosive volcanic eruptions provide stratigraphic and numerical dating horizons in sedimentary and volcanic sequences. Such tephra layers may be dispersed over tens to thousands of kilometres from source, reaching far beyond individual volcanic regions. Tephrochronology is consequently a truly global dating tool, with applications increasingly widespread across a range of Quaternary and geoscience disciplines. This special issue of the International Focus Group on Tephrochronology and Volcanism (INTAV) showcases some of the many recent advances in tephrochronology, from methodological developments to diverse applications across volcanological, archaeological, and palaeoclimatological research.

New time constraint on the initiation of Yanshan movement from Jurassic growth strata in the Daqingshan area, Inner Mongolia

In recent years, based on the accumulation of new data of plate tectonics and isotopic ages, Yanshan movement has been reinterpreted as regional intraplate orogenesis responding to multi-directional convergent tectonic system that extended across the East Asia, which is a much larger region than originally thought. However, the timing of Yanshanian onset remains debated, mainly including the Middle Jurassic and Late Jurassic-Early Cretaceous. The correct answer to this key scientific problem will contribute to better understand the coupling relationship between Jurassic plate tectonics in East Asia and intraplate deformation. The Daqingshan range is located in the eastern segment of the Yinshan belt, and mainly consists of the southern Daqingshan fold-and-thrust system (DFTS) and the northern Shiguai basin. In this article, the authors examined the western part of DFTS that is characterized by a series of E-trending, N-directed thrusts with a displacement no more than 10 km. The complete Jurassic sequences are well preserved in the Shiguai basin, including upwards the Lower Jurassic Wudanggou Formation, the Middle Jurassic Zhaogou and Changhangou formations, and the Upper Jurassic Daqingshan Formation. Note the contact between the Wudanggou and Zhaogou Formations is conformable and both of them are coal-bearing. 40Ar-39Ar dating of synkinematic minerals with two ages of 193.7±3.9 and 121.6±1.6 Ma indicate the Daqingshan range possibly underwent two phases of compressional events. Unfortunately, this conclusion is challenged by the discovery of syndepositional normal faults cutting the Early Jurassic-Archean unconformity and by the occurrence of Hohhot metamorphic core complex. Based on cross-cutting relationship, a Late Jurassic-Early Cretaceous age has been assigned to the thrust belt. However, growth strata preserved in the deformation front drew a very different conclusion. Growth strata record much syndepositional tectonic information and have been widely used in the study of orogenic belt. In the study area, the Early-Middle Jurassic synrift coal-bearing sequences are generally involved into shortening deformation in the southern Shiguai basin, resulting in the depocenter of Middle Jurassic Changhangou Formation (J2c) migrating markedly northwards. Along the deformation front, J2c commonly crops out ahead of overturned anticlines and exhibits typical syntectonic depositional wedge with bedding dips gradually shallowing upwards and each single horizon thinning or tapering towards fold crest. These features indicate J2c is typical growth strata, and the contact between it and synrift sediments preserved in the overturned forelimbs is called progressive unconformity, demonstrating the synchronicity of folding and sedimentation. This kind of growth geometry implies limb rotation is the main folding mechanism. Because contractional fault-related folding theories invoking limb rotation only include certain classes of detachment folds and the Lower Jurassic Wudanggou Formation mainly consist of incompetent materials, folding deformation is considered to be controlled by the movement of basal bedding-parallel detachment fault. Moreover, an increasing uplift rate can be delineated by the transition of growth geometries from onlap and overlap to offlap upsections. Fortunately, several 10-cm-thick volcanic ash layers have been found in the upper J2c, and the uppermost one has been sampled (SG0436-5) for LA-ICP-MS zircon U-Pb dating. The dating experiment that was conducted in the LA-ICPMS Laboratory of Nanjing Normal University, obtained 43 concordia ages with a weighted average age of 163.72±1.0 Ma. Given that the latest reported zircon U-Pb age of the upper Xiahuayuan coal-bearing sediments (be well correlated with the Zhaogou Formation) is 171±1.0 Ma, the initial activity of DFTS should occur in the Middle Jurassic (~170 Ma). Therefore, these discoveries provide convincing constraint on the initiation of Yanshanian deformation and have significant implications for understanding its coupling relationship with the Jurassic plate tectonics in East Asia.

Precise age for the Permian–Triassic boundary in South China from high-precision U-Pb geochronology and Bayesian age–depth modeling

Abstract. This study is based on zircon U-Pb ages of 12 volcanic ash layers and volcanogenic sandstones from two deep water sections with conformable and continuous formational Permian–Triassic boundaries (PTBs) in the Nanpanjiang Basin (South China). Our dates of single, thermally annealed and chemically abraded zircons bracket the PTB in Dongpan and Penglaitan and provide the basis for a first proof-of-concept study utilizing a Bayesian chronology model comparing the three sections of Dongpan, Penglaitan and the Global Stratotype Section and Point (GSSP) at Meishan. Our Bayesian modeling demonstrates that the formational boundaries in Dongpan (251.939 ± 0.030 Ma), Penglaitan (251.984 ± 0.031 Ma) and Meishan (251.956 ± 0.035 Ma) are synchronous within analytical uncertainty of ∼ 40 ka. It also provides quantitative evidence that the ages of the paleontologically defined boundaries, based on conodont unitary association zones in Meishan and on macrofaunas in Dongpan, are identical and coincide with the age of the formational boundaries. The age model also confirms the extreme condensation around the PTB in Meishan, which distorts the projection of any stratigraphic points or intervals onto other more expanded sections by means of Bayesian age–depth models. Dongpan and Penglaitan possess significantly higher sediment accumulation rates and thus offer a greater potential for high-resolution studies of environmental proxies and correlations around the PTB than Meishan. This study highlights the power of high-resolution radio-isotopic ages that allow a robust intercalibration of patterns of biotic changes and fluctuating environmental proxies and will help recognizing their global, regional or local significance.

南海トラフODP Site 808の火山灰層の自生粘土鉱物とその酸素同位体比から推定した生成条件

南海トラフODP Site 808の火山灰層の自生粘土鉱物とその酸素同位体比から推定した生成条件

Late Holocene environmental changes recorded in the deposits of paleolake of the Shkotovskoe Plateau, Sikhote-Alin Mountains, Russian Far East

New data have been obtained on the landscape evolution within basalt plateau under conditions of climatic fluctuations in the Late Holocene. The reconstructions were based on the studies of the lacustrine-swamp sequence of the Larchenkovo swamp in the central part of the Shkotovskoe Plateau. The swamp appeared in place of a paleolake, the latter having passed through several stages in its evolution. Within the considered period the lake had the greatest area and depth about 4.48–3.9cal.ka BP, under conditions of warming and increased rainfall. At the final stage, there were alternating intervals of the lake deepening and shallowing, against the background of general waterlogging and paludification. In the upper part of the peat sequence there is a volcanic ash layer B-Tm attributed to the Baitoushan volcano eruption in AD 969. The studies permitted to identify stages in the environmental evolution and to determine the critical points in their development; to analyze the natural landscape-forming factors and the rate of the biotic component transformation; and to make certain inferences about the geosystem stability in the past. The contribution of global and regional paleoclimatic events has been estimated. The intervals of warming were typically marked by increasing proportion of broadleaf species in the forests, while coolings featured a higher share of Korean pine and dark coniferous, particularly spruce. The expansion of dark coniferous forests occurred under conditions close to recent ones at about 2.63cal.ka BP, while the coniferous-broadleaf forests retreated towards the plateau margins. Role broadleaf/Korean pine forests increased at the Medieval Climate Anomaly, while the Korean pine and spruce proportion grew at the Little Ice Age. The changes in the last 230–240years could be related both to the natural processes, such as windfalls, and to forest felling. Larch forest persisted around the lake over the entire considered period and most probably is a relict of the last ice age.

Immobile and mobile elements during the transition of volcanic ash to bentonite – An example from the early Palaeozoic sedimentary section of the Baltic Basin

In order to check the immobility and mobility of elements during conversion of acidic volcanic glass to bentonites in normal marine environments, we studied the composition of three altered volcanic ash layers from the Palaeozoic of the Baltoscandian Region, correlated through different facies. Regular changes in element concentrations in accordance with loss and gain of material during the transformation of volcanic ash indicate that Al, Nb, Ti, Zr, Sn, Pt, Ta, Hf and Th were generally immobile and can be used for the interpretation of source magma and correlation of ash layers. Cd behaves similarly with immobile elements and this can be explained with preservation only of the immobile portion of Cd that is fixed in phenocrysts. In bentonites in shales during the formation of kaolinite, the data indicate small-scale mobility of Al and Cd. In lime muds where K-feldspar forms from volcanic ash, Ta, Hf and Th reveal some small scale mobility. These slightly mobile elements must be used with caution for interpretation of thin ash layers with thicknesses of <1cm. Sc, V, Ga, Y and Rare Earth Elements widely used for the interpretation of bentonites have noticeable mobility and can thus be used only semi-quantitatively or qualitatively in the bulk bentonite.