Hiroaki Ishiga

Development of a largely anoxic stratified ocean and its temporary massive mixing at the Permian/Triassic boundary supported by the sulfur isotopic record

Systematic sulfur isotope data for whole-rock sulfides have been obtained from the chert-dominated, continuous, pelagic sedimentary sequences spanning the Permian/Triassic (P/Tr) boundary at Tenjinmaru in the Chichibu Terrane and at Sasayama in the Tanba Terrane in Japan. The P/Tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed Cretaceous/Tertiary (K/T) boundary claystone. The observed data clearly demonstrate a significant bimodalism. The 34S/32S ratios with respect to CDT are generally low throughout the Middle Permian (ca.−39 to −25%0) and show a remarkable increase beginning in the lower Upper Permian and persisting into the Lower Triassic (ca.−20 to −2%0), with a temporary and drastic negative shift, down to roughly the same isotopic level as in the Middle Permian, just at the suspected P/Tr boundary (ca.−41 to −23%0). Interestingly, the mode of isotopic excursion across the P/Tr boundary is in striking contrast to that across the K/T boundary which was recently described at Kawaruppu in Hokkado, Japan. The apparent extent of fractionation, with respect to contemporaneous seawater sulfate, in the high 34S/32S group lies within the range of −25 ± 10%0, which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction, and that in the low 34S/32S group mostly exceeds this range, giving the values typically in the range of −45 ± 10%0, which is similar to what is generally observed in the present-day oceanic sediments. The present data would provide strong evidence for the development of a largely stagnant, anoxic, stratified ocean, which presumably began to form in the lower Upper Permian and persisted into the Lower Triassic, and for a brief episode of its temporary massive mixing just at the suspected P/Tr boundary. Such an oceanic oxic-anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal Triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal Permian mass extinction.

GEOCHEMISTRY OF PERMIAN-TRIASSIC SHALES IN THE SALT RANGE, PAKISTAN : IMPLICATIONS FOR PROVENANCE AND TECTONISM AT THE GONDWANA MARGIN

Abstract Upper Permian and Lower Triassic (Griesbachian, Dienerian, Smithian and Spathian) shales in the Salt Range, Pakistan, were deposited at the margin of Gondwana during a time of active rifting. XRF and INAA major element, trace element and rare earth element (REE) analyses of shales exhibit progressive change in chemistry from Upper Permian to Spathian. SiO 2 /Al 2 O 3 decreases upsection, and K 2 O/Na 2 O increases, together with an increase in the Chemical Index of Alteration (CIA). HFS elements are enriched relative to PAAS at the base of the sequence, but are progressively depleted upward. Most compatible elements are depleted throughout, relative to PAAS. Sc, however, is relatively enriched, producing a general decline in Th/Sc upward. With the exception of a single sample at the base of the sequence, ∑REE shows little variation from Upper Permian to Smithian, ranging from 159 to 146, but increases to 206 in the Spathian. Chondrite-normalised La N /Yb N also increases upsection, from ∼9.0 to 12.8. Eu/Eu* values are 0.48–0.54 in the Upper Permian–Dienerian sequence, but anomalies become smaller (0.53–0.65) and more similar to PAAS (0.66) in the Smithian and Spathian. Such values are typical of continentally derived sediments, but the slight decrease upward suggests a small influx of more mafic material. This, and decreasing Th/Sc, contrasts with increasing La N /Yb N and ∑REE, which imply an increasingly felsic source. These anomalies may be resolved by modeling potential sources using the REE and Th/Sc. The modeling suggests that the Permian–Dienerian sediments could have been derived from a source of Upper Proterozoic crust (UPC), Phanerozoic granite (PG) and amphibolite (AMP) in ratios around 60:38:2. In the Smithian and Spathian, proportions change to 76:20:4 and 68:28:4, respectively. Although the increase in the AMP component is small, when combined with increase in UPC at the expense of PG, it is sufficient to approximate the changes in Th/Sc and Eu/Eu*. La N /Yb N ratios in the Permian–Dienerian may be influenced by concentrations of HREE-enriched garnet and zircon. CIA indices and A–CN–K relations show that source weathering conditions oscillated between non-steady state (Permian, Dienerian, Smithian) and steady state (Griesbachian, Spathian), indicative of episodic uplift at the Gondwana margin. CIA ratios in the Spathian are greatest in the Spathian, indicative of more intense weathering at that time. However, A–CN–K relations, ∑REE contents and the modeled UPC:PG:AMP mix in the Spathian could also have been produced by recycling of Smithian sediments.

High productivity in the earliest Triassic ocean: black shales, Southwest Japan

Abstract Bedded cherts containing the Permian/Triassic (P/T) boundary exposed in the Tanba and Chichibu Belts, Southwest Japan, contain interbedded organic-rich black shales. The organic carbon concentration of black shales before thermal maturation was evaluated to be about 3% (average), considering their maturity levels. Kerogens do not contain any debris of higher-plant origins, but are mostly composed of structureless amorphous kerogen. Black shales comprise organic matter derived mainly from plankton with additional organic matter derived from bacterial activity, showing that the high primary production took place intermittently in the earliest Triassic. A stratified ocean with a well-developed oxygen-minimum layer rich in nutrients was intermittently disturbed due to tectonically and/or climatically induced active ocean current systems in the earliest Triassic, resulting in upwelling, causing remarkably high primary production, to form organic-rich black shales.

Lithology and structure of the Wandilla terrane, Gladstone‐Yeppoon district, central Queensland, and an overview of the Palaeozoic subduction complex of the New England Fold Belt

The Wandilla terrane consists of, from west to east, the Doonside Formation and the Wandilla Formation. The Doonside Formation is dominated by chert and mudstone. Conodonts from a single locality (Devils Bend) indicate an age in the interval Late Silurian to Middle Devonian. The Wandilla Formation consists of mudstone with greywacke, tuff, chert and greenstone. The greywacke is dominated by volcanic detritus with sparse but persistent ooliths that suggest contemporaneity with Early Carboniferous strata of the Yarrol shelf to the west. The Wandilla terrane is structurally complex with two main deformation events. The first deformation (D1) formed widespread lenticular melange during offscraping at the toe of a subduction complex. The second deformation (D2) formed a moderately to shallowly east‐dipping cleavage that typically dips less steeply than the north‐northwest‐trending D1 structures, and contains a down‐dip elongation lineation. D2 structures were produced by the Late Permian to Triassic Hunter‐Bow...

Vertical distribution of arsenic in ganges delta sediments in Deuli Village, Bangladesh

Abstract Major and trace elements, including total arsenic (T-As), 1 M HCl-extractable arsenic (Ex-As), total organic carbon (TOC), total nitrogen (TN), and total sulfur (TS), in sediment columns collected in 2000 through 5 boring operations to a depth of 15 m in Deuli Village, Bangladesh were analyzed to reveal the source of arsenic contamination in groundwater. This area mainly consists of sandy, clayey, and peaty layers, and the chemical composition changes considerably with the sediment properties. The concentrations of T-As (20 to 111 mg kg−1) in the samples of peat and peaty clay sediments from a depth of 7 to 10 m were significantly higher than the concentrations in the samples of clayey sediments (4 to 18 mg kg−1) or sandy sediments (3 to 7 mg kg−1), and the concentrations of the other elements were also high in the samples of peaty sediments. T-As concentration shows a significant correlation with the contents of both TS and TOC (p < 0.05). These results suggest that arsenic is retained in the sediments in the form of sulfide or is combined with organic matter. On the other hand, the extraction rate (Ex-As / T-As) changed depending on the Toe content in the sediments, in spite of the high correlation between the concentrations of T-As and Ex-As. This indicates that arsenic speciation was different in the samples of peaty sediments from the sandy and clayey sediments with a relatively low TOC content. The peat layer, in which arsenic is concentrated as a pool, may be the key layer to elucidate the mechanism of solubilization of arsenic in the sediments by groundwater.

Geochemical evaluation of present-day Tuul River sediments, Ulaanbaatar basin, Mongolia

The Tuul River flows through the Ulaanbaatar basin of Mongolia and is the main source of water for the capital city, Ulaanbaatar. The Tuul catchment can be divided into three parts around Ulaanbaatar (upper, middle, and lower), according to the extent of urbanization. Sixteen surface water and groundwater samples were collected to evaluate present-day water quality and 34 stream sediment samples taken to examine their geochemical composition in relation to provenance and to assess the impact of urban activity on heavy metal accumulation. Groundwater quality in the upper and central water sources was adequate, but high concentrations of NO3− were found in the lower water source. Heavy metal concentrations in the sediments are evaluated by comparison with average upper continental crust (UCC) values, coupled with ecological risk assessment by reference to sediment quality guidelines (SQG). The results show average abundances of potentially toxic metals such as As, Pb, Zn, Cu, Ni, Cr, and V are higher in the middle part (within the city) than in the upper and lower parts. However, all three parts show depletion in some chalcophile and high field strength elements (Cu, Ni, Cr, Sr, Nb, Zr, Th, Sc) relative to UCC, indicating that the river sediments were derived from a highly felsic crustal source. The assessment using SQG shows As and Cr are present in levels that cause adverse aquatic biological effects. Although concentrations of Pb, Zn, Cu, and Ni are generally below their respective threshold effect levels, in the middle reaches, values increase and border on the probable effect level. This suggests significant anthropogenic contamination in the urban areas, increasing values above a naturally low regional background.

Influence of soil type and properties on distribution and changes in arsenic contents of different paddy soils in Bangladesh

Abstract Analysis of background As contents in soils is important for determining whether a soil is polluted or not. The total As contents of 66 archived surface soil (Ap horizon) samples (22 for 1967 and 44 for 1995) were determined using the RIX 2000 XRF system to analyze the distribution and changes in the As contents in the different physiographic units during the period 1967–1995 in Bangladesh. Arsenic distribution showed lower mean As contents of <6.22 mg kg−1 in the soils of the Old Himalayan Piedmont Plain (OHP), TIsta Floodplain (TF), and Barind Tract (BT) in the northwestern region. Mean As contents in the soils of the Northern and Eastern Piedmont Plains (NEP) and those of the Brahmaputra Floodplain (BF), Madhupur Tract (MT), Meghna River and Estuarine Floodplain (MF), and Chittagong Coastal Plain (CCP) in the central and the southeastern regions ranged between 6.22 and 8.70 mg kg−1. The soils in the Ganges Floodplain (GF) in the southwestern region and those of the Surma-Kushiyara Floodplain (SKF) in the northeastern region showed the higher mean As contents of <8.70 mg kg−1. The mean As contents of 5.35, 7.85, and 9.52 mg kg−1 were observed in the highland, medium lowland, and the lowland parts of the landscapes, respectively, in this study. An undifferenciated histosol also showed an As content of 12.3 mg kg-I in 1995 in Bangladesh. Results of this study suggested that soil properties (clay, total Fe content, ECEC, total Al and total C contents, pH, total S and total phosphorus contents) are important factors affecting natural background soil-As contents. The baseline soil-As contents should be defined appropriately based on the magnitude of the observed natural variations in the As contents among the different soils. This therefore suggested that site-specific As contents should be used as baseline levels for proper assessment of the potential As contamination in the soils of Bangladesh. Over a 27 year period, the As contents increased in the soils of Atwari (10%) and Jagdal (5%) in OHP; Pirgacha (8%) in TF; Belabo (25%) in BT; Ghior from Faridpur (19%) in GF; Kalma (12%) in MT; Tippera (9%) and Gumti (6%) in MY; Phagu (35%) in SKF and Harta series (12%) for peat soils. Also, the As contents decreased in the Kaunia series (13%) in TF; Dhamrai (20%) in BF; Sidhirganj (3%) in MF; Manu (14%) in NEP and all the soils of GF (4 to 40% decrease with a mean of 15%) except for the Ghior series from Faridpur. The increase or decrease of the As contents in the different soils was possibly due to local differences in the parent materials and biogeochemical activities. However, the mean As content in the surface soils remained almost unchanged (decreased by 4.82%) during the period between 1967 and 1995 in Bangladesh.

Elemental composition of sediments in Lake Jinzai, Japan: Assessment of sources and pollution

Bottom sediments from Lake Jinzai in southwest Japan were analyzed to determine their chemical compositions and to assess the potential for ecological harm by comparison with sediment quality guidelines. The pollution status of lake sediments was evaluated by employing contamination factor (CF), pollution load index (PLI), and geoaccumulation index (Igeo), focusing on a suite of elements in lakebed and core sediments. Elevated concentrations of As, Pb, Zn, Cu, TOC, N, and P were present in several layers of the upper core and other surface sediments. The elevated metal concentrations are likely related to the fine-grained nature of the sediments, reducing bottom conditions produced by abundant organic matter, and possibly minor non-point anthropogenic sources. Moreover, correlations between the concentrations of trace metals and organic carbon, nitrogen, phosphorus, and iron, suggest that these elements play a role in controlling abundances. Calculated CF, PLI, and Igeo indicate that the sediments are strongly polluted with respect to As, moderately to strongly polluted with Zn, and moderately polluted with Pb and Cu. Metal concentrations exceed the New York State Department of Environmental Conservation (NYSDEC) lowest effect level and the Canadian Council of Ministers of the Environment (CCME) interim sediment quality guidelines that indicate moderate impact on aquatic organisms in the study area.

Distribution and changes in heavy metal contents of paddy soils in different physiographic units of Bangladesh

Abstract The distribution and changes in the background levels of V, Cr, Mo, Ni, Cu, Zn, Pb, U, and As were assessed using 66 archived surface (Ap horizon) soil samples (22 for 1967 and 44 for 1995) analyzed by RIX 2000 x-ray fluorescence spectrometry to determine whether a soil was polluted or not during the period 1967–1995 in Bangladesh. Distribution of the mean V content showed lower values (<15.6 mg kg−1) in the soils of the Old Himalayan Piedmont Plain (OHP), Barind Tract (BT), and Madhupur Tract (MT), values ranging between 115.6 and 169.0 mg kg−1 (mean ± SD / 2) in the Tista Floodplain (TF), Brahmaputra Floodplain (BF), Meghna River and Estuarine Floodplain (MF), Northern and Eastern Piedmont Plains (NEP), and Chittagong Coastal Plain (CCP), and higher values (>169.0 mg kg−1) in the Ganges Floodplain (GF) and Surma-Kushiyara Floodplain (SKF). The mean Cr contents were lower (<84.7 mg kg−1) in OHP, TF, BT, and MT, ranged between 84.7 and 107.1 mg kg−1 in GF, BF, MF, NEP, and CCP, and a higher content (>107.1 mg kg−1) was recorded in SKF. The mean Mo contents ranged between 2.01 and 2.11 mg kg−1 in all the physiographic units except for a lower content (<2.01 mg kg−1) in TF and a higher content (>2.11 mg kg−1) in the MT unit. The mean Ni contents were lower (<39.5 mg kg−1) in OHP, TF, and BT, ranged between 39.5 and 62.3 mg kg−1 in GF, BF, MF, MT, NEP, and CCP and a higher content (>62.3 mg kg−1) was recorded in SKF. The mean Cu contents were lower (<23.4 mg kg−1) in OHP, TF, BT, MT, and NEP, ranged between 23.4 and 39.8 mg kg−1 in MF, SKF, and CCP, and a higher content (>39.8 mg kg−1) was recorded in GF and BF. The mean Zn contents were lower (<60.3 mg kg−1) in OHP, BT, MT, and NEP, ranged between 60.3 and 90.9 mg kg−1 in TF, MF, and CCP, and a higher content (>90.9 mg kg−1) was recorded in GF, BF, and SKF. The mean Pb contents were lower (<21.7 mg kg−1) in TF, BT, and NEP, and ranged between 21.7 and 25.3 mg kg−1 in the other physiographic units. The mean U content was lower (<3.47 mg kg−1) in NEP and an almost uniform distribution between 3.47 and 5.29 mg kg−1 was observed in the other physiographic units except for a higher content (>5.29 mg kg−1) in TF. The mean As contents were lower (<6.2 mg kg−1) in OHP, TF, and BT, ranged between 6.2 to 8.7 mg kg−1 in BF, MT, MF, NEP, and CCP, and a higher content (>8.7 mg kg−1) was recorded in the GF and SKF soils. The contents of V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As in the peat soil were 222.2, 111.1, 2.11, 63.4, 57.4, 108.8, 25.4, 5.28, and 12.3 mg kg−1, respectively. However, the distribution of the V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As contents was in the range of 43.3–275.0, 61.0–176.0, 1.90–2.21, 14.0–134.0, 8.7–65.7, 27.8–138.0, 14.3–31.0, 2.23–5.93, and 3.9–14.0 mg kg−1, with mean values of 142.3, 95.9, 2.06, 51.0, 31.6, 75.6, 23.5, 4.38, and 7.5 mg kg−1, respectively, in 1995. The heavy metal contents of the surface soils were, generally, higher on the lower slopes than in the middle or upper parts of the landscapes. A wide variation in the changes of heavy metal contents was observed among the soils of different physiographic units in Bangladesh. Changes in the V, Cr, Mo, Ni, Cu, Zn, Pb, V, and As contents showed higher increases up to 33.1, 25.0, 15.38, 28.5, 35.5, 24.9, 19.0, 22.10, and 34.6% and higher decreases down to 24.3, 13.1, 2.56, 36.4, 51.0, 21.5, 12.3, 18.98, and 40.0% respectively, with mean values remaining almost unchanged (−1.87 to +6.81%) except for a decrease of 17.1% Cu during the period 1967–1995. Results of this study suggested that the soil properties (clay, total Fe and Al contents, ECEC, total C content, pH, total Sand P contents) are important factors regulating the natural background levels of heavy metals in the soils of Bangladesh.

Groundwater Quality in Different Climatic Zones of Sri Lanka: Focus on the Occurrence of Fluoride

The chemical and physical parameters of groundwater in some areas of dry and wet zones of Sri Lanka are described. Hydrochemical data from 114 water samples are used to evaluate water quality and to identify the processes that control fluoride levels in water. The results indicate that fluoride levels of groundwater in the dry zone are very high (< 8.0 mg/L) compared to those of the wet zone (< 0.8 mg/L). The measured nutrients (NO3- < 15 mg/L, PO43− < 5 mg/L) concentrations and chemical oxygen demand (< 18 mg/L) in both regions inferred that higher fluoride levels reported in the groundwater are not from anthropogenic sources. The pH-Eh stability diagrams show that nitrate, phosphate and iron does not co-exist with fluoride under prevailing redox condition. Physical parameters further show that fluoride values increase in slightly alkaline in pH (7.5-8.2), relatively low EC (1.0-2.5 mS/m) and highly oxidized water (50-200 mV). Groundwater movements of shallow regolith aquifers in the country are mainly controlled on joint and fault system in the partially weathered basement. This study observed that their variation in the dry and wet zones is a major parameter for the control fluoride levels in water. Thus less fractured rocks in the dry zone water discharge areas show higher values and may be due to lesser mixing of water with non-fluoride sources. Conversely, highly fractured rocks are predominant in the wet zone and hence mixing of fluoride poor and rich waters in both recharge and discharge regions in the zone results in low fluoride levels. 2