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Nachiketa Das ¹, Angus B. Mackenzie ²

Affiliations
1 Ministry of Science and Technology, New Delhi 110016, IN
2 Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 OQU, GB

Abstract

Fission track study on thin sections of whole rocks and separated minerals from different sedimentary facies of the lacustrine Orcadian basin, northeast Scotland has shown variations in uranium distribution in different facies which can be correlated with the prevailing redox conditions during deposition. Uranium in sandstones is associated exclusively with detrital grains of apatite and zircon but not with any authigenic phase indicating oxidizing environment. In contrast, in shales and dolostones very little uranium is associated with detrital zircon and apatite, and mostly occurs either adsorbed on grain surfaces or incorporated in the crystal structure of the authigenic minerals and organic matter pointing to reducing environment.

Keywords

Uranium, Geochemistry, Orcadian, Scotland.

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Nachiketa Das ¹

Affiliations
1 Department of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ, Scotland, GB

Abstract

The carbonates occurring within the sandstones of the Middle Old Red Sandstone of the Orcadian basin (Middle Devonian) in Caithness, N.E. Scotland are of minor abundance, predominantly calcite and may be petrographically ascribed to early diagenetic origin.

Isotopic analyses (C, O, Sr) have been undertaken to elucidate the depositional mileu of these carbonates at two localities, Wick and Reay. Calcite and dolomite coexist in carbonate facies rocks and their similarity in δ¹³C_PDB (-4.57 ± 0.64 and -4.56 ± 0.53‰ respectively at Wick and -2.39 ± 0.30 and -2.00 ± 0.48 respectively at Reay) suggest a cogenetic origin at each locality. The δ¹³C values also suggest deposition from lighter, freshwater.

Mean calcite δ¹⁸O_PDB values of -7.76 ± 1.92‰ and -8.76 ± 2.23‰ for Wick and Reay samples respectively also support this contention. Dolomite δ¹⁸O_PDB values are consistently heavier which is not inconsistent with a generally cogenetic origin. The oxygen isotope data reflects a lighter pore fluid composition either because of diagenetic modification by carbonate recrystallization or a greater contribution of freshwater via river supply during sandstone deposition in an ephemerally evaporative lacustrine environment. Mean Sr^87/86 value of 0.711167 for the carbonates of Wick confinn a nonmarine origin.

Keywords

Isotope Geochemistry, O, C and Sr Isotopes, Cogenetic Calcite and Dolomite, Orcadian, Lacustrine, Freshwater.

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Nachiketa Das ¹

Affiliations
1 1332 Ooda-Akitsu, Higashi-Hiroshima-City, 739-2404, JP

Abstract

Japan, the country of high-Technology, is a clean and tidy nation that has an abundant supply of very high quality water Hiroshima, because of its geography and climate, is endowed with an abundance of fresh-water. Moreover, practically all the good waters of Hiroshima are soft, with the highest recorded hardness of 120 mg/l. Many of these waters from the springs and wells in the granitic terrains of Hiroshima are rich in Radon (Rn). The average concentrations of ²²²Rn Ci/litre of water are in the order of 80 x 10^-10 and the highest recorded concentration is at Onomichi Toraku Station (647.2 x 10^-l0) (pers commn, Prof Ken Sasaki). These Rn-rich waters are traditionally believed to be health-giving and restorative.

In Hiroshima, Prof Ken Sasaki has pioneered water-tasting as an independent branch of science. Currently esoteric, water-tasting makes use of water chemistry, presence of dissolved solutes and minerals in water, and the science of tasting by human palate. Chemical analyses and sensory tests carried out on 82 samples of well, spring, river, and commercial mineral waters showed good correlation for organic matter, total hardness, iron and bicarbonate. Multiple regression analyses using these four chemical constituents produced correlation coefficients of 0.8217 for Hiroshima (n = 47) and 0.8401 for other districts (n = 35) (Sasaki et al 1996). Fuzzy reasoning, when applied to the evaluations of palatable water, where the chemical constituents organic matter, total hardness, iron and bicarbonate formed the four input variables, and sensory test, produced a correlation coefficient of 0.8621 (Iwanaga and Sasaki, 1996).

Keywords

Hiroshima, Granitic Terrains, Soft-Water, Radon, Water-Tasting, Hygiene, Japan.

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Nachiketa Das ¹

Affiliations
1 NRI Enviro-Geo-Tech Australia, 18 Barina Road, Lane Cove, NSW 2066, AU

Abstract

Chemostratigraphy of sedimentary sequences involves the application of major- and trace-element geochemistry for the characterisation and subdivision of sedimentary sequences into geochemically distinct units and correlation of strata in sedimentary basins. Chemostratigraphic correlation is particularly applicable to sequences that have very poor biostratigraphic control or to thick. rapidly deposited sequences that cannot be subdivided further by biostratigraphic data.

In order to maximise the number of geochemical characteristics of a given sediment, it is important to determine as many elements as possible. Such characterisation now routinely involves the analytical determination of concentrations of approximately 50 elements. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) enable the rapid acquisition of major- and trace-element data for a large number of elements. Elements of simple mineralogical affinity, limited or no involvement in diagenetic activity and high concentration in refractory minerals are most suitable for chemostratigraphic correlation purposes.

Chemostratigraphic correlation is carried out on a reservoir scale as well as on a basin-wide basis for inter well correlation. The major- and trace-element data generated for chemostratigraphic correlation purposes could also be applied to studies of provenance and basin evaluation, diagenesis, reservoir characterisation and interpretation of wireline logs. In this review article, five case studies are also discussed in brief to demonstrate the applicability of chemostratigraphic correlation.

Keywords

Chemostratigraphy, Sedimentology, Geochemistry.

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