Abstracts Carbonates and Evaporites Volume 15, Number 2

IDENTIFICATION OF CHINESE FRESH-WATER PEARLS USING MN 2+ ACTIVATED CATHODOLUMINESCENCE

¹Arun Banerjee and ²Dirk Habermann

¹Institute für Geowissenschaften-Edelsteinforschung, Johannes Gutenberg-Universität Mainz, D-55099 Mainz, Germany; Phone: 06131/394367; Fax: 06131/393070; [email protected]
²Institute für Experimental Physik, TU-Freiberg, 09596 Freiberg, GermanyABSTRACT: Fresh-water tissue graft-cultured pearls from China were investigated using hot cathode and cold cathode cathodoluminescence microscopes. Supplementary investigations were done using X-radiography, a Scanning Electron Microscope, an optical microscope, and an Atomic Force Microscope (AFM). The results were compared with those of natural fresh-water pearls from the Mississippi river.

Thin sections of fresh-water natural pearls from the Mississippi river could be distinguished from those of fresh-water tissue graft cultured pearls from China using a hot cathode cathodoluminescence microscope according to the distribution of Mn2+ as follows: (1) Fresh-water tissue graft cultured pearls from China contain domains of calcite, emitting orange cathodoluminescence in the central region, which are almost absent in the natural fresh-water pearls from the Mississippi river. (2) The concentration of Mn2+ in natural fresh-water pearls from the Mississippi river is marked by regular green (l = 566 nm) zones of CL from the middle up to the periphery, whereas in case of the tissue graft fresh-water pearls from China the Mn2+ concentration decreases from the middle towards the periphery of the pearl as it is revealed by the gradually diminishing of CL towards the periphery. Whole specimen of the two types of pearls mentioned above can be distinguished from one another without destroying the samples using a cold cathode cathodoluminescence microscope as follows: The intensity of CL at 566 nm emitted from the surface of natural fresh-water pearls from the Mississippi river is higher than the intensity of CL emitted from the surface of fresh-water tissue graft cultured pearls from China, due to the fact that the surface layers of the former pearls contain more Mn2+ than those of the later.

A further criterion of the Chinese tissue graft cultured pearl is the utmost smoothness of their surfaces. Moreover according to AFM observation the size of the aragonite crystals on the surface of the Chinese fresh-water tissue graft cultured pearls is much smaller than those of natural fresh-water pearls from the Mississippi river.

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METAL POLLUTION IN CARBONATE SEDIMENTS OF MAIN BASIN OF MARIUTE LAKE, ALEXANDRIA, EGYPT

¹Kamel I. El- Masry and ^1,*Gerald M. Friedman
¹Department of Geology, Brooklyn College and Graduate School of the City University of New York, Brooklyn, NY;
^*For correspondence: Northeastern Science Foundation, Inc., 15 Third Street, P.O. Box 746, Troy, NY 12181-0746; [email protected]

ABSTRACT: Lakes are ideal in defining the processes that govern the behavior of heavy metals in sediments: they are closed systems with well-known characteristics (input, outputs) and contain a memory for dynamic bottom processes (erosion, accumulation, and transportation). Lakes integrate and represent environmental conditions, in contrast with the wide variability in the water column and in open marine systems.

Lake Mariute is one of four shallow, brackish-water lakes adjoining the Mediterranean coast near Alexandria, Egypt. Eleven bottom-sediment samples were collected from different sites within Lake Mariute. Flame Atomic Absorption Spectrometry (AAS) was used to determine Co, Cu, Pb, Fe, Ni, and Zn concentrations in sediments and X-ray diffraction was used to determine carbonate-and clay-mineral percentages in analyzed samples.

The carbonate minerals observed in this study are low- magnesian calcite and aragonite. The clay minerals observed in this study - smectite and illite were-identified by their characteristic basal X- ray diffraction maxima, i. e. "peaks" or "reflections."

Low - magnesium calcite and aragonite are common carbonate minerals in modern environments and reflect the choice of most skeletal organisms in tropical seas for their hard parts. The occurrence of both low-magnesium calcite and aragonite and the absence of high-magnesium calcite indicate a slight influx of fresh, vadose or vadose- phreatic water. The diagenetic removal of magnesium from high-magnesium calcite, thereby generating low-magnesium calcite, may explain the complete absence of high-magnesium calcite in the analyzed samples.

The distribution of trace elements in the sediments, e.g., Co, Fe, Cu, and Pb is related to the carbonate mineralogy. This helps in the interpretation of the diagenetic history of the deposits, which have been studied from both mineralogical and geochemical perspectives and which suggest possible mechanisms for the various diagenetic changes. Trace-metal concentrations found at different sampling sites vary greatly from one site to another. The bottom sediments of Lake Mariute contain heavy metals in concentrations, which exceed United States Environmental Protection Agency criteria for contaminated lake water and sediments,

Radioactive dating analysis shows that two of the eleven stations have a detectable component of cesium 137 particles, indicating that some of the sediment was deposited after 1950.

*****MODE OF FORMATION AND SEDIMENTARY ASSOCIATION OF THE REEFAL SEDIMENTS, RAS ABU EL DARAG, GULF OF SUEZ, EGYPT

¹Amr A. El-Sammak, Mahmoud Kh. El-Sayed, and Mohammed A. El-Sabrouti
Department of Oceanography, Faculty of Science, University of Alexandria, Egypt
¹Corresponding author: Dr. Amr El-Sammak, United Arab Emirates University, Faulty of Science, Geology Department, Al-Ain, P.O. Box 17551, United Arab Emirates; Tel: +971375064741; Fax: +97137671291; [email protected]

ABSTRACT: The present study aims to examine the mode of formation and sedimentary association of the reefal sediments, Ras Abu el-Darag, northern Gulf of Suez. Samples were collected from different zones along a traverse section perpendicular to the coastline. Geochemical, mineralogical and petrographical studies were performed. In addition the chemistry, mineralogy, oxygen and carbon isotope analyses were been done on separate ooids from selected samples. Ras Abu el-Darag sediments consist mainly of nonskeletal components mixed with skeletal components. Low diversity of skeletal components was observed. Aragonite is the major carbonate mineral, followed by calcite (4-8 mol% MgCO₃) then Mg-calcite (> 8 mol% MgCO₃) and dolomite. Dolomite, found in Ras Abu el-Darag sediments, seems to be partially syngenetic in origin due to microbial activity and partially allochthonous derived from adjacent coastal areas. Ooids are the major sedimentary constituents. These ooids are polymineralic and consist of three minerals, aragonite which comprises about 73.3% followed by calcite and Mg-calcite. Data of O¹⁸ and C¹³ on some selected ooids fall within the field of shallow marine carbonates. O¹⁸ ranges from 2.834‰ to 3.635‰. On the other hand C¹³ is ranging between -0.014‰ and 0.695‰. On the basis of the size of nucleus, the thickness of laminae, the type of the nucleus, as well as the situation in Ras Abu el-Darag sediments where those ooids were not associated with mud, the ooids found in Ras Abu el-Darag sediments are considered to be autochthonous ooids having intrabasinal origin.

*****GUESTIMATING RESERVES: A MATTER OF TECHNIQUES?

Julia Hubbard
Member of Editorial Board, The Geological Studies Group, Kings College London, The Strand, London, WC2R 2LS, England; [email protected]

ABSTRACT: Disparities in preparation techniques are fundamental to our interpretation of poroperm readings from long established tables. Given that analytical scanning electron microscope images are used to complement cathodoluminescence light microscope petrography, isotope chemistry and petrophysical methods etc as background information to the calculation of poroperm predictability in probability plots, it follows that the preparation of these images deserves careful scrutiny. To this end reef materials sampled from contrasting settings are used as the basis of demonstration. Non-standardized preparation techniques that are standards for other uses are used to calibrate results against each other. They clearly demonstrate the efficacy of freon as a dust remover but also as a remover of dried fines of bacterial proportions.

By or outsourcing or delegating analytical preparations to service units that are not dedicated to basic research the basic elemental counts that are derived from x-ray systems may be consistent while the visual imagery yields major discrepancies. This is central to the argument that we can be deluded into accepting the implied influences of microbial activity on scant evidence. Where comparative treatments were applied to agglutinating polychaete worm fabrics from the intertidal the resultant images could be presented as either the products of deep burial or shallow marine depending on the preparation technique used.

*****CALCITE CEMENT SUCCESSIONS IN MIDDLE DEVONIAN (GIVETIAN) CARBONATE MUD BUILDUPS OF THE SOUTHERN AHNET BASIN (ALGERIAN SAHARA)Bernd Kaufmann and Jobst Wendt
Geologisch-Paläontologisches Institut, Universität Tübingen, Sigwartstrasse 10, 72076 Tübingen, GermanyABSTRACT: In the Ahnet Basin of southern Algeria, carbonate mud buildups were established in a deeper subtidal environment during Givetian times. The primary cavity system (irregular cavities, stromatactis) of these buildups exhibits a calcite cement succession precipitated in marine-phreatic to deep-burial environments.

Cementation started in the marine environment. Cloudy, radiaxial-fibrous calcites (RFCs) of originally high Mg-calcite composition coat the walls of the cavities and occupy 50-80% of the pore space. The carbon- and oxygen-isotopic signature of these cements corresponds to that of co-occurring, nonluminescent brachiopod shells and to that of coeval RFCs from the Mader Basin of Morocco. Average values of ¹⁸O = -2.6 (± 0.4)‰ PDB and ¹³C = +2.6 (± 0.4)‰ PDB are assumed to represent the Givetian stable-isotopic seawater signature of the Northwest-African carbonate province. The exceptional high ¹⁸O values, compared to Middle Devonian data of North America, are interpreted to result from the mid-latitudinal (about 40°S), colder-water settings of the Northwest-African carbonate buildups. The ⁸⁷Sr/⁸⁶Sr ratios of RFCs (0.70802±17) and nonluminescent brachiopod shells (0.70780±3) fit well into established Sr-isotopic curves of Devonian seawater.

Cementation in the shallow-burial realm is characterized by a typical non-bright-dull cathodoluminescence sequence of nonluminescent scalenohedral cements (dog-tooth cements) with bright-luminescent outer margins overgrown by slight-ferroan, moderate-luminescent cements. Meteoric influence on this cement sequence can be excluded.

Deep-burial cementation following a rather long period of non-cementation is represented by strong-ferroan, dull-luminescent blocky cements. Alternatively to pressure solution, outgassing of CO₂ by decreasing pore-fluid pressure caused by Variscan fracturing can be considered as carbonate source for ferroan calcite precipitation in the remaining pore space. Strong ¹⁸O depletion (-10.6 to -14.8‰ PDB) of these cements point to the influence of hydrothermal fluids rather than to a pure depth-related temperature control. ¹³C values show a trend from a nearly marine signature to more negative values (up to -9.0‰ PDB) which suggests the input of methane by hydrocarbon migration during Variscan compression. More radiogenic ⁸⁷Sr/⁸⁶Sr ratios (0.70826 to 0.71684) with respect to the marine composition are probably caused by the input of radiogenic strontium from K-feldspar dissolution and/or clay recrystallization from adjacent siliciclastic units.

*****THE GEOLOGICAL HISTORY OF PLIOCENE-PLEISTOCENE EVAPORITES IN MOUNT SEDOM (ISRAEL) AND HOW STRONTIUM AND SULFUR ISOTOPES RELATE TO THEIR ORIGIN

¹M. Raab, ²G.M. Friedman, ³B. Spiro, ⁴A. Starinsky, and ⁴I. Zak
¹Geological Survey of Israel, 30, Malkhe Yisrael Street, Jerusalem, 95501, Israel
²Brooklyn College and Graduate School of the City University of New York, Brooklyn, NY and Northeastern Science Foundation affiliated with Brooklyn College of the City University of New York, Rensselaer Center of Applied Geology, 15 Third Street, P.O. Box 746, Troy, NY 12181, U.S.A; [email protected]
³British Natural Environment Research Council, Isotope Geosciences Laboratory, Keyworth, Nottingham K5GG, United Kingdom
⁴The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel

ABSTRACT: Evaporites, comprising of gypsum, anhydrite and halite are described from the Pliocene Sedom Formation, the Caprocks units and the Pleistocene 'Amora Formation in Mount Sedom, Southern Jordan Valley, Israel. Strontium and sulfur isotopic compositions of the evaporite minerals, and their Sr/Ca and Br/Cl ratios were used to interpret their environments of deposition and processes of formation and diagenesis. Some of the evaporites of the Sedom Formation were deposited from evaporated seawater. Others were deposited from a mixture of seawater and brines. The brines were composed of seawater which penetrated the carbonate rocks of the Rift margins, participated in dolomitization processes and, when hydrologic conditions allowed, seeped out into the Sedom basin and were mixed with evaporated seawater. These processes yielded non-homogeneous fluid masses of mixtures, as indicated by their wide range of 87Sr/86Sr ratios (0.70824 - 0.70905) as compared to the narrow Sr/Ca ratios of the derived evaporites. Their marine origin is indicated by their d34S values which are around 20 ‰. The evaporites of the 'Amora Formation were precipitated from Ca-chloride brines only, which were originally evaporated seawater trapped in the Rift walls in the "Sedom Formation times", returning to the Sedom basin after its disconnection from the sea. The high Sr content and Sr/Ca ratios indicate that the anhydrites existing today in the Sedom and 'Amora formations were originally deposited from the evaporated seawater as gypsum which was later recrystallized at depth, at high pressures and temperatures. The caprocks are residual rocks of marine origin, formed by the dissolution of the exposed rock-salt units in the Sedom Formation. They represent mainly the gypsum (or anhydrite) beds intercalated in the rock-salt units of the Sedom Formation in Mount Sedom rather than Ca-sulfates disseminated in the halites.

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STUDY OF THE SOURCES OF SALINITY IN THE GOMBAN KARST SPRING, SOUTHERN IRAN

¹E. Raeisi and ²M.H. Nejati
¹Geology Department, College of Science, Shiraz University, Shiraz, Iran
²Fars Regional Water Authority, Minstry of Energy, Iran

ABSTRACT: The Dalneshine anticline is composed of the calcareous karstified Ilam-Sarvak Formations. The Gomban springs with an average annual discharge of 1680 L/s emerge from the plunge of the Dalneshine anticline near the saline Tashk lake. The electrical conductivity, water temperature, pH and major ions of the water resources emerging from the Dalneshine anticline were measured. The electrical conductivity of the Gomban springs is about 5500 microsiemens/cm. The probable sources of the Gomban springs salinity are saltdome, halite solution, oil field and gas field brines, agricultural return flow, evapotranspiration and lake-water intrusion. The hydrogeology and hydrochemistry data reveal that lake-water intrusion is the main source of salinity.

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MICROFACIES AND DEPOSITIONAL ENVIRONMENTS OF THE ASMARI FORMATION, AT DEHDEZ AREA (A CORRELATION ACROSS CENTRAL ZAGROS BASIN)

Ali Seyrafian
Geology Department, Faculty of Sciences, University of Esfahan, Esfahan, Iran

ABSTRACT: The predominant microfacies of the Asmari Formation at Dehdez area are: (1) globigerinid bioclastic wackestone to packstone, (2) globigerinid laminated wackestone, (3) coral and coralline algal boundstone, (4) bioclastic-lithoclastic wackestone to packstone, (5) foraminifera bioclastic wackestone to packstone, (6) foraminifera grainstone, (7) peloid wackestone to packstone, and (8) peloid bioclastic grainstone.

Based on microfacial characteristics the Asmari Formation was deposited at the study area as a transgressive sequence from base to top from shoal to restricted and normal marine shelf to fore-slope to basin margin deposits. Deposition continued with a regressive cycle from basin margin to fore-slope and restricted shoal and finally to restricted platform sediments.

Microfacies analysis and facies interpretations across the central high Zagros suggests that the Asmari Formation was deposited mostly in a very shallow marine environment at the eastern margin of the basin. Deposition of a thick sequence of pelagic sediments indicates deeper marine conditions existed at the central parts of the basin during Burdigalian. Westward, the exposed Asmari Formation reflects an occurrence of very shallow marine condition prevailed during Oligo-Miocene. Finally deposition of the Asmari Formation took place under transition environment at farwest of central Zagros Basin.

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