An Atlas of Speleothem Microfabrics
L. Bruce Railsback, Department of Geology, University of Georgia.
Content of the Atlas
This Atlas of Speleothem Microfabrics is an attempt to systematically present images of all known microfabrics found in stalagmites, stalactites, flowstones, and other chemically precipitated cave deposits. "Microfabric" is a term for the appearance of rocks and minerals as viewed by a petrographic microscope or by an electron microscope. Variation in the mineralogy, shape, size, clarity, orientation, and layering of crystals in speleothems provides a vast array of microfabrics in speleothems.
The heart of the atlas is divided in nine parts. The first three present different primary minerals found in speleothems and the microfabrics in which they occur. "Primary" here refers to minerals that formed in-situ on the surface of the growing speleothem. Part 4 presents microcrystalline calcite fabrics that may be primary or may be detrital. Part 5 presents detrital minerals, the minerals that are present in speleothems but that previously formed elsewhere and were physically transported to the surface of the growing speleothem. Part 6 presents biogenic particles, which may either be detrital or have been deposited by the organism that formed them. Part 7 shows different kinds of layering of speleothems, which presumably result from changing conditions on the speleothem surface or from changes in the waters dripping onto the speleothem. Parts 8 and 9 show diagenetic fabrics, the fabrics that result from changes in speleothems after their formation.
Parts 1 through 9 contain 78 pages of photomicrographs of speleothems. Each of the images is accompanied by explanatory text and information regarding the source of the material. The images are all large format (roughly 600 x 350 pixels) JPEG color images. The images of thin sections were generated using a Leitz Laborlux 12 Pol S polarizing petrographic miscroscope, and the SEM images were generated using a LEO 982 Field emission scanning electron microscope.
In addition to those nine parts, two additional sections provide ancillary images.
shows non-spelean carbonate materials as a supplement for those readers who are not familiar with such materials but who may encounter them. Appendix B shows sections through entire speleothems. It is thus unlike the previous sections in not showing photomicrographs, but it provides contextual information for readers not familiar with the structure of speleothems.
The atlas also includes a glossary of terms used in the text and a bibliography of works cited and of other relevant literature. Those terms in the glossary range from the very basic, such as mineral names, to special terms used only to describe speleothem microfabrics. Some glossary entries evaluate past and recommended usage of terms critical to the petrography of speleothems.
Purpose of the Atlas
This atlas is intended primarily to serve the needs of researchers in speleology and in areas of study that use speleothems, such as paleoclimatology and paleohydrology. Speleothems, especially stalagmites, were increasingly used as records of past cave conditions in the late 1900s, and that use is expected to continue and increase as the demand for records of past climates increases and as techniques for study of speleothems improve. Such scholarly use of speleothems begins, or should begin, with petrographic examination of the speleothem. This atlas is intended as a reference collection against which to compare newly studied samples and as a standard for nomenclature in describing new samples.
A second purpose of this atlas is to provide an educational resource for classes in speleology, sedimentary petrology, and other earth sciences. Collection of speleothems is legally and ethically limited, with good reason, so that few educational institutions have teaching collections. This on-line collection of images provides illustrations to accompany academic instruction around the world.
Finally, the atlas is also intended to satisfy the curiosity of all persons interested in caves and cave deposits, whether they are scholars, active cavers, or cave enthusiasts. Speleothems provide a remarkably variety of petrographic fabrics that have great aesthetic appeal in addition to their scholarly application. The aesthetic satisfaction provided by speleothems and the sense history provided by their slow growth underground make speleothem microfabrics a source of fascination for all of us.
Growth of the Atlas
One reason for an on-line atlas, rather than a bound paper atlas, is that the on-line format allows growth of the atlas. The relative youth of this field of study means that examination of new samples will inevitably reveal new microfabrics worthy of illustration. New images will be added as study progresses, and researchers are encouraged to contribute images from their work. An accompanying web page discusses possible ways to contribute new images.
Review of the Atlas
This Atlas has not undergone the peer-preview process typical of documents printed on paper, because the Atlas exists only on the World-Wide Web. As a result, the author receives no credit for a contribution to scholarship. If you hold an academic position and would like to write a review of this Atlas, you are encouraged to do so. Please prepare two copies and send one to "Head, Department of Geology, University of Georgia, Athens, Georgia, 30602-2501 USA" and one to "Bruce Railsback, Department of Geology, University of Georgia, Athens, Georgia 30602-2501 USA". The copy to Railsback can be marked and mailed so as to preserve the anonymity of the reviewer.
My enthusiasm for the petrography of carbonate materials was seeded by Dr. Philip H. Heckel of the University of Iowa and nurtured by Dr. Phillip A. Sandberg of the University of Illinois. Dr. George A. Brook of the University of Georgia induced me to look at speleothems, leading to my present interest in them. Many of the specimens illustrated in this atlas were collected by him or in conjunction with his research. James Baldini, Jian Chen, Margaret Rafter, Shaw-Wen Sheen, James W. Webster, and Hong-lin Xiao have worked as students in my lab and contributed to our research on speleothems. Dr. John P. Shields of the University of Georgia Center for Advanced Ultrastructual Research has been immensely helpful in generating the SEM images in this Atlas. My research on speleothems at the University of Georgia has been funded by the National Oceanographic and Atmospheric Administration and by the National Science Foundation.
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