Abstracts for Carbonates and Evaporites
v. 15, no. 1, 2000, June

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U/TH ISOTOPIC STUDY OF SPELEOTHEMS FROM THE WADI SANNUR CAVERN,
EASTERN DESERT OF EGYPT

Adel A. Dabous and J. K. Osmond
Department of Geological Sciences, Florida State University, Tallahassee, Florida 32306

ABSTRACT: The Wadi Sannur Cavern was discovered in 1991 beneath an "Egyptian alabaster" (travertine) quarry, active since pharaonic times. It is the only extensively speleothem-decorated cavern that has been described in Egypt. Nine small stalagmites, 5-10 cm in diameter, were sectioned and sampled according to coloration bands a few cm thick. Of 32 individual samples several exhibited ²³⁰Th/²³⁴U activity ratios greater than unity, indicative of open-system leaching of uranium, and several others had anomalous ²³⁴U/²³⁸U activity ratios. The modal apparent age of the 17 "dateable" samples is close to 200,000 years, but because of leaching indications must be considered only a maximum age for the time of deposition of secondary carbonates in the cave. Both the initial formation of speleothems and subsequent leaching are consistent with what is known about pluvial climates in the Eastern Desert of Egypt.

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GEOCHEMISTRY OF GOLD-BEARING CARBONATES, BEACONSFIELD GOLD MINE,
TASMANIA, AUSTRALIA

¹C. Prasada Rao and ²Mohammad H. Adabi
¹School of Earth Sciences, University of Tasmania, GPO Box 252-79, Hobart, Tasmania, Australia 7001
²School of Earth Sciences, Shahid Beheshti University, Tehran, Iran

ABSTRACT: The major carbonates minerals in the Beaconsfield gold mine are calcite, dolomite and magnesian ankerite. Gold occurs in magnesian ankerite. Ankerite has high Ca, moderate Fe, Mg and Mn and low Na and Sr. The values of Ca and Mg and total amounts of Mg, Fe and Mn, and values of Fe, Mn and Sr are strongly correlated. This is due to the two layered structure of magnesian ankerite comprised of Mg, Fe and Mn carbonites and Ca carbonites. The elemental and isotopic compositions of magnesian ankerite are related to ordering, substitution of elements, salinity, redox potential, dissolution and reprecipitation, temperature, composition of fluids, environmental setting and gold mineralization.

Ca, Sr and Na are derived from dissolution of Ordovician limestone. Mg is derived from leaching of ultramafics. Fe and Mn are leached from both ultramafics and clay minerals. Meteoric water was high in Ca, Fe, Mg and Mn concentrations and formed magnesian ankerite in a reducing burial environment. The heat source was possibly deep burial depth, tectonic hot spots and a few granite intrusions east of Beaconsfield.

Gold and ankerite were precipitated in alkaline conditions. Gold and magnesium in ankerite are derived from the leaching of Cambrian ultramafic rocks during the Devonian by the passage of meteoric fluids through tectonically affected Ordovician carbonates.

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EVIDENCE OF MICROBIOLOGIC ACTIVITY IN MODERN TRAVERTINES: SICAKCERMIK GEOTHERMAL FIELD, CENTRAL TURKEY

Erdogan Tekin, Kamil Kayabali, Turhan Ayyidiz and Ozden Ileri
University of Ankara, Department of Geological Engineering, Ankara, 06100, Turkey;
[email protected]

ABSTRACT: Modern travertine deposits are observed in the Sicakçermik hot springs located northwest of Sivas, central Anatolia. They are the carbonate deposits of crustal (spongy) and/or alabaster-textured formations controlled by both organic and inorganic processes. The structures formed under the influence of inorganic processes include the accumulations on the fissure and joint ridges. These structures are adjacent to the hot water emergence spots representing the points of rapid hot water flow and sudden release of CO₂. The structures developed under the influence of organic processes form in areas at relatively farther distances from the hot water emergence points. These structures were described to be "waterfall or cascade deposits"; "terrace-mound travertines"; and "shallow lake fans" by different researchers. They are recognized in the field by special identifying trails such as manganous-ferrous travertine shrubs resembling ivy, siliceous stromatolites, and ferrous pisoids, 3 to 12 mm in diameter.

All the modern travertine samples examined are dominantly formed by subidiomorphic prismatic-tabular calcite crystals. Scanning Electron Microscopy revealed that calcite crystals forming the pisoids are characterized by zonal growth. Stromatolitic formations, on the other hand, bear regular joints developed as a consequence of sudden cooling and some special structures indicative of bacterial activity (in the form of nodule, spheroid, ellipsoid, column, filament and honeycomb or grape bunch structures). In addition, secondary dissolution vugs and pores giving way to the release of CO₂ are associated structures with the stromatolitic formations. The data collected from all the utilized techniques suggest that the microbiological formations observed in the travertines of Sicakçermik hot spring were produced by the sulfate-reducing, boring-budding bacteria such as Coccoids, Pedomicrobium, Beggiatoa sp., Thiobacillus sp., as well as blue-green algae (Cyanobacteria).

The travertine occurrences produced by both organic and inorganic processes have an annual average of 3-5 cm deposition in thickness. The hot water emergence points and their flowpaths manifest seldom-found natural features. These natural monuments are irresponsibly destroyed for several reasons. The authors argue that these formations, significant from the point of view of their occurrence mechanism as well as their final products, must be preserved. If accomplished, a modern natural monument similar to that in Pamukkale (Turkey) and Yellowstone National Park (Wyoming, USA) could develop within a reasonable length of time.

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SILURIAN PALEOCLIMATE DATA FROM FLUID INCLUSIONS IN THE SALINA GROUP HALITE, MICHIGAN BASIN

*Arthur B. Losey and Kathleen Counter Benison
Department of Geology, Central Michigan University, Mt. Pleasant, MI 48858;
* Current address: Department of Geology, 114 Shideler Hall, Miami University, Oxford, OH 45056

ABSTRACT: The Silurian Salina Group of the Michigan Basin consists of halite, carbonates, and shales. The halite was probably deposited when seawater became restricted over what is now southern Michigan. The halite consists of: (1) beds containing only chevrons, and (2) beds composed of chevron and cumulate crystals. This indicates shallow depositional waters. The primary fluid inclusions along growth bands in these crystals are well preserved and unaltered. These cubic, all-liquid inclusions, ranging in size from >1 to 150 µm, represent Silurian surface waters.

These all-liquid inclusions were cooled in order to nucleate a vapor bubble. After cooling, inclusions were warmed slowly and the homogenization of the vapor bubbles to liquid was observed. The homogenization temperatures ranged from 19.8°C to 59.0°C, with the majority of the measurements falling below 40.0°C. Validity of this temperature data is strongly suggested by: (1) reproducibility of homogenization temperatures within 1°C; and (2) similar homogenization temperatures within individual growth bands ranging between 4 - 10°C. Therefore, these homogenization temperatures represent Silurian shallow water temperatures.

In modern shallow evaporative settings, the water temperatures and the air temperatures are very similar. Since petrography of the halite beds indicates shallow water deposition, these homogenization temperatures may be good proxies for Silurian air temperatures.

This may be among the first quantitative Silurian climate data. Paleoclimate data such as these may give new insights into modern climate and future climate trends.

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LATE CAMBRIAN CABBAGE-HEAD STROMATOLITES FROM SARATOGA SPRINGS, NEW YORK, USA

Gerald M. Friedman
Department of Geology, Brooklyn College and Graduate Center of the City University of New York, Brooklyn, NY, and Northeastern Science Foundation affiliated with Brooklyn College, Rensselaer Center of Applied Geology, 15 Third Street, P.O. Box 746, Troy, NY 12181, USA; [email protected]

ABSTRACT: Saratoga Springs, New York, is the site of one of the finest examples of domed stromatolites to be seen anywhere in ancient rocks and is significant in the history of geology as the area where stromatolites were first described and interpreted. These cabbage-head structures, which are part of the Hoyt Limestone of Late Cambrian (Late Franconian to Early Trempeleauan) age, were described by James Hall as early as 1847. Glaciated surfaces expose horizontal sections of the cabbage-shaped heads composed of vertically stacked, hemispherical stromatolites. The microbial heads are discrete domal structures built of hemispheroidal and bulbous stromatolites expanding upward from a base. The heads, many of them compound, are circular in horizontal section, and range in diameter from a few centimeters to a meter. Between the heads are ooids, skeletal fragments of trilobites, brachiopods, pelecypods, and quartz-sand particles.

The earliest reference to stromatolites in this area was that of Steele (1825) whose description included the first reported oolitic limestone in North America among which the stromatolites occur. The depositional environment was that of a peritidal setting involving oolite shoals, lagoons, and intertidal flats.

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SUBSURFACE ARBUCKLE GROUP (CAMBRO-ORDOVICIAN) IN THE BOWMAN #4 WELL OF THE WILBURTON FIELD IN THE ARKOMA BASIN, OKLAHOMA: DEPOSITIONAL FACIES, DIAGENETIC SIGNATURES, PETROPHYSICAL ASPECTS, AND ECONOMIC POTENTIAL

Blanca Y. Ching and Gerald M. Friedman
Brooklyn College and Graduate School of the City University of New York, Brooklyn, NY, USA and Northeastern Science Foundation, Inc. affiliated with Brooklyn College, Rensselaer Center of Applied Geology, 15 Third St., Troy, NY, USA; [email protected]

ABSTRACT: Detailed petrographic and petrophysical analyses were performed on a core section of the Nicor #4 Bowman Well, Arkoma Basin, Oklahoma. The studied interval represents the Cambro-Ordovician Arbuckle Group. Petrographic analyses of core samples distinguish six lithofacies. They are as follows from the bottom to the top of the studied core: (1) Quartzose dolostone, (2) conglomeritic dolostone, (3) brecciated dolostone, (3a) crackle breccia, (3b) dissolution-collapse breccia, (4) oolitic dolostone, (5) stylolitic dolostone, and (6) stromatolitic dolostone. Diagenetic evolution has affected the petrophysical properties of these different lithofacies. The diagenetic history of the selected section records early to late dolomitization, stylolitization, dedolomitization (calcification), and silicification. Petrophysical analyses employing mercury porosimetric techniques determine three distinct petrofacies. These petrofacies are as follow: (1) low porosity and high recovery efficiency, (2) low porosity and low recovery efficiency, and (3) high porosity and high recovery efficiency. Based on petrophysical analyses, the best reservoir candidate is the crackle breccia petrofacies because it has intermediate porosity and high recovery efficiency values, plus this lithofacies is bounded by strata with low porosity and recovery efficiency values (impermeable layer).

The Arbuckle Group carbonates were uplifted and subaerially exposed, which, led to the development of an unconformity surface. Consequently, karstification developed and modified various petrophysical properties of the core.

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