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DISCUSSION AND REPLY |
1 Northeastern Science Foundation, 15 Third Street, P.O. Box 746, Troy, New York 12181; gmfriedman@thesciencefoundation.com
| The first 20% of the full text of this article appears below. |
THOUGHTS ABOUT THE TERM "HYDROTHERMAL DOLOMITE"
One of the issues of the AAPG Bulletin (v. 90, no. 11) was concerned with "hydrothermal dolomite reservoirs," specifically "hydrothermal dolomite fields" (Davies and Smith, 2006). The term "hydrothermal dolomite" is confusing and meaningless (Machel and Lonnee, 2002). To study the origin of dolomite and its hydrothermal depositional setting, I examined modern settings, including the Mediterranean Sea (Friedman, 1991) (Figure 1). The shallow-water facies in this modern setting consists of dolomite and gypsum. The rocks range from almost pure gypsum to pure tough dolostone so thoroughly cemented that sampling required hammer and chisel. X-ray diffraction analysis indicates the presence of minor anhydrite. Sporadic aragonitic gastropods occur, but fossils are otherwise absent. Under the microscope, it is a peloidal micrite (dolomicrite). The
13CPDB of the dolostone is –39.3 to –31.2
. These strongly negative
13C values suggest that carbon of the dolomite came from methane. Methane forms when all sulfate has been reduced. Bacterial reaction was responsible for dolomite formation through the methane pathway. This syngenetic dolomite is like most dolomites of hydrothermal origin, but my students and I avoid this confusing bandwagon term.
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The term
This article has been cited by other articles:
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G. R. Davies and L. B. Smith Jr. Structurally controlled hydrothermal dolomite reservoir facies: An overview: Reply AAPG Bulletin, September 1, 2007; 91(9): 1342 - 1344. [Full Text] [PDF] |
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