Is the Devonian Chattanooga Shale
Really a Volcanic Ash-Fall Deposit?
A Review of a Creation Research Society Quarterly Paper
Copyright © 1997 by James L. Moore
[Last Update: October 3, 1997]
This document may be reproduced without royalty for non-profit, non-commercial use.
s a geologist whose hobby is the creation/evolution debate, I occasionally read articles of professional interest that appear in the "Creation Research Society Quarterly" (CRSQ) in order to keep abreast of current creationist thought in the field of geology.
In the December 1996 issue, an article by Carl Froede Jr., entitled "A theory for the volcanic origin of radioactive shales and clays: examples from the Southeastern United States," contended that the Devonian Chattanooga Shale of Middle America and the Tertiary Hawthorn Group of Florida were altered volcanic ash that was laid down during the Biblical flood. Froede also argued that the source of the uranium found in these formations is a primary deposit of this ash.
As his arguments were of a falsifiable nature, I wrote two private letters to Mr. Froede explaining the problems with his contentions. He challenged me to present these arguments to the CRSQ so that readers of that publication might be given an opportunity to compare the two viewpoints.
This paper was submitted to the CRSQ for publication as a "Comments" paper. The editor requested that the paper be shortened to between 1/3 and 1/4 of its present length. Had the paper been reduced as requested, much of its impact would have been lost. Therefore, I have allowed this paper to be posted to the Internet so that my entire critique can be presented to the public.
As the CRSQ is not a peer-reviewed, refereed journal, it is only by subjecting its articles to public scrutiny that their quality can be assessed. Therefore, I call upon educators and scientists in all fields to join with me in submitting critiques of their papers.
Appraisal of the Paper
My attention was recently drawn to an article, A theory for the volcanic origin of radioactive shales and clays: examples from the Southeastern United States by Carl R. Froede, Jr., that appeared in the December, 1996, edition of the Creation Research Society Quarterly. Mr. Froede's contention was that the Devonian Chattanooga Shale and the Tertiary Hawthorn Group of Florida, were deposited as volcanic ash. Being a geologist from Tennessee, I was surprised not only by Mr. Froede's contention, which goes strongly against conventional interpretation, but also by the fact that he had not presented any original field evidence to support his argument. The paper was solely a reinterpretation along creationist guidelines of mainstream journal articles. If Mr. Froede is to present an entirely new hypothesis that offers an interpretation counter to mainstream geologic thought, it is incumbent upon him to present a large amount of original research with evidence that supports his hypothesis.
The purpose of publishing papers in journals is to report new data gleaned from original research and, if warranted, to advance a new hypothesis to explain that data. Although Mr. Froede has presented no original data, he claims in the title that his contention is a "theory." Scientific theories are hypotheses that have much supporting evidence. They not only explain data, but they also predict new findings. Germ theory and gravitational theory immediately come to mind as examples of tried and tested scientific theories. Mr. Froede has only advanced his argument to the initial level of scientific explanation: the hypothesis.
I will restrict my comments to the Chattanooga Shale since I am more familiar with it. While examining Mr. Froede's paper, I tried to keep an eye toward whether there is evidence for his hypothesis in the Chattanooga Shale. After studying it, however, it appears that there are several evidences present in the Chattanooga Shale that speak against his hypothesis.
Do volcanoes supply sufficient radioactive elements to equal what is seen in rocks?
Mr. Froede's entire thesis is that volcanic rocks contain sufficient primary uranium to account for the amount observed in the Chattanooga Shale. He states:
Many volcanic ash deposits have been identified as containing significant levels of radioactive elements. Daniels (1954, p. 193-194) cites the collection of many volcanic ash deposits which were found to contain both uranium and thorium.However when reading Daniels, we find:
Lava and ashes, both acidic and basic, from many different volcanoes contain less than 1 ppm up to 11 ppm of uranium. In most cases the alpha counts are high enough to show that thorium is present also. The amount of radioactive materials given off by volcanoes is small, and it varies greatly with the location of the volcano and with the stage of eruption.Daniels' data is substantiated by Zielinski (1982, p. 200), who reports uranium concentrations of 8 ppm in fresh, glassy, rhyolitic ash from the Troublesome Formation of Colorado. However, analyses of the Chattanooga Shale (Hickman and Lynch, 1957, p. 20) show that the average concentration of uranium in the Chattanooga Shale is .006 percent or 60 ppm. From the cited references, it would appear that volcanoes are incapable of supplying even this low concentration of uranium, at least as a primary deposit.
A short distance later Mr. Froede says:
...reports the leaching and precipitation of uranium and thorium, from radioactive element containing sources, via the groundwater. Volcanic ash is now identified as the source for many uranium ore deposits in the western United States (Nations and Stump, 1981, p. 202-203; Sharp and Kyle, 1988, p. 470; Wood and Fernandez, 1988, p. 363).
Froede's thesis is that the source of uranium content in volcanic ash is primary. That is, the uranium was present when the material was erupted. But the references he quotes do not support his position. Wood and Fernandez (p. 363) acknowledge that "the high uranium contents of felsic, relative to basic, volcanic rocks makes them the most attractive sources." (Here, Wood and Fernandez use the word "sources" to refer to ore deposits, which is stated in the first sentence of this section in their paper.) But the next sentence states that "the concentration of uranium in volcanic rocks occurs by direct precipitation from magmatic fluids, precipitation from hydrothermal fluids, and remobilization of secondary uranium by low temperature ground water."
Mr. Froede has misidentified a secondary enrichment of uranium as a primary deposit, which it is not.
As an aside, his reference to Sharp and Kyle (1988, p. 470) lends credence to the mainstream interpretation that uranium is concentrated in organic matter. They say:
Uranium is readily transported as a complexed carbonate, sulfate, or phosphate uranyl ion in oxygen-rich ground water. When the oxygen-rich water encounters a chemically reducing environment, the uranium is reduced to the tetravalent state and precipitated. Reducing conditions par excellence are often associated with the presence of organic matter in porous media where sulfur-reducing anaerobes decompose organics.
This is precisely the environment of deposition of the Chattanooga Shale with its 10-20% organic content.
Close examination of Mr. Froede's references provides no support for his contention that volcanoes supply primary uranium in amounts comparable to what is found in the Chattanooga Shale.
What is the source of the organic matter?
The Chattanooga Shale has a very high organic content. Without providing a source, Mr. Froede argues that the presence of organic matter is due to debris:
I suggest that the Chattanooga Shale, as found in Tennessee, originated as a volcaniclastic deposit which mixed with organic debris.
Conant and Swanson (1957, p. 19) identify the organic constituents as marine algae and coalified driftwood of a species known to exist in Devonian time. They say:
Many plant and animal fossils are present in the shale... Plant remains are much the most abundant and are responsible for the dark color of the shale, but most of them are so degraded and in such minute fragments that they are best referred to simply as carbonaceous matter. Larger plant fossils are occasionally seen on freshly exposed bedding planes and are unmistakable. J. M. Schopf of the U.S. Geological Survey identified some of them as Callixylon, which came to the sea as driftwood from land areas. In cross section the large plant remains appear as thin shiny black layers, commonly only 1 to 2 mm thick but in places as much as 10 to 20 mm thick. Schopf (written communication, 1953) identified, in samples from various outcrops, parts of the free-floating marine algae Foerstia and Protosalvinia, both of which are known only from rocks of Devonian age. He also recognized parts of the algoid plant Prototaxites and several varieties of spores or sporelike objects which he assigned to the land-plant genus Tasmanites [Tasmanites is now known as the cyst of a planktonic, marine, prasinophyte algae].
The source of the organic matter in the Chattanooga has long been known. Swanson (1960, p. 12) relates:
Worthy of special note with regard to the high oil yield of the Foerstia sample, however, is that White and Stadnichenko (1923) long ago recognized this algae in Devonian black shales as one of the main "mother plants" of the oil that can be derived from these shales; the abundant spore cases, with their similar "waxy-resinous" protective coatings were also noted as source substances for the extractable oil.
Therefore, the only logical conclusion is that the organic matter was deposited along with the mineral constituents of the Chattanooga.
Do the organics really matter?
Mr. Froede did not address the differential concentrations of both organic matter and its associated uranium found in vertical sections of the Chattanooga. Had the plant life in the sea been killed at the time of Mr. Froede's hypothesized ash-fall, one would expect to see a single zone of carbonaceous material. This is not what is observed. As stated earlier, the Chattanooga has an exceptionally high organic content. Upwelling areas, with their high biologic activity, accumulate large amounts of organic materials, which become traps for dissolved uranium. This affinity of dissolved uranium for organic matter explains the correlation between organics and uranium (Swanson, 1960, figs. 6 and 7). Other units within the Chattanooga (see below), without concentrated organic material do not show this enrichment of uranium.
Mr. Froede remarks:
A syngenetic origin would also fit for radioactive elements derived from a blanket of volcanic ash. The only difference would be one of time.
Work performed by Milici and Roen (1981, p. 2) has shown the Chattanooga Shale can be divided into four units based on color, which in turn is a function of organic content. However their study did not report the levels of radioactivity found in each interval.
Milici and Roen's paper addressed an area in East Tennessee. In Central Tennessee, the Chattanooga is divided into five stratigraphic units (Swanson, 1960, p. 8). The lower two are the Lower and Upper Dowelltown Members, while the top three are the Lower, Middle, and Upper Gassaway Members. The organic matter and uranium are concentrated in the Lower Dowelltown and the Lower and Upper Gassaway. The Upper Dowelltown and Middle Gassaway have relatively lower concentrations of organic matter and uranium. In research for "Isopach and Structure Map of the Chattanooga Shale in Tennessee" (in progress), this variation in uranium concentration has been noted from the signatures of neutron and gamma-ray logs made of numerous oil and gas test wells.
The variation of organic matter in vertical sections of the Chattanooga would have provided Mr. Froede with important information had he only recognized it. Not only does organic matter appear throughout the section, but its concentration also varies vertically. If all the material had fallen together as he contends, we should observe a negative correlation between uranium and organic content, because increased concentrations of organic matter dilute a zone's uranium content. Unfortunately for Mr. Froede's hypothesis, Swanson has shown conclusively that uranium content correlates positively, not negatively, with organic content.
Is the Chattanooga Shale an ash-fall deposit?
Mr. Froede makes the following assertion:
Additionally, as previously cited, many of the radioactive shale and clay layers are found as laterally continuous units which extend over thousands of square miles [three references], and this clearly fits within a description of a volcanic ash fall.
Mr. Froede makes a valid statement that the units are very widespread but then makes an unfounded assertion that this is evidence for an ash fall. One way to determine if the Chattanooga Shale is an ash fall deposit would be to compare the isopachs (maps connecting points of equal thickness) of the Chattanooga Shale and its correlatives with isopachs of known volcanic ash falls. The isopach for the major eruption of Mt. St. Helens on May 18, 1980, is shown in Figure 1 (Sarna-Wojcicki, et al., 1981, fig. 336). A map for the much larger eruption of Mt. Pinatubo in the Philippines is shown in Figure 2 (Wiesner, et al., 1995, fig. 1). Note that the thicknesses are expressed in millimeters for Figure 1 and centimeters for Figure 2. Note also that the shapes of both isopachs are dictated by the prevailing wind direction.
|Figure 1. Isopach map of air-fall ejecta of May 18, 1980, eruption of Mt. St. Helens. Lines represent uncompacted thickness, in millimeters. (Reproduced with permission from Sarna-Wojcecki, et al., Fig. 336.)|
|Figure 2. Isopach, in centimeters, of tephra from the 1991 eruption of Mt. Pinatubo determined from sea bottom cores. Shaded area indicates extent of fallout tephra. (Reproduced with permission from Wiesner, et al., Fig. 1.)|
In their description of the enormous Ordovician eruptions, Huff et al. (1992, p. 876) state that these eruptions "have mushroom-shaped dispersal patterns that may override prevailing wind directions." Neither of the two maps, or the mushroom-shaped isopach suggested by Huff, shares any similarities with the isopach map of the Chattanooga Shale and correlatives in the eastern United States (Matthews, 1993, fig. 3) shown in Figure 3. Note that the thicknesses in this map are expressed in hundreds and, to the east, thousands of feet. Additionally, the shapes of the contours bear no resemblance to those in Figures 1 and 2.
|Figure 3. Preserved thickness of the Devonian-Mississippian shale in the Eastern United States. (Reproduced with permission from Matthews, 1983, Fig. 3.)|
Also, please note from Figure 4 the area of deposition of the Chattanooga Shale and equivalents. The great size and shape of the area of distribution speaks against Mr. Froede's hypothesis.
|Figure 4. Approximate extent of Chattanooga Sea (Reproduced with permission from Weil, et al., Fig. 1.)|
What do the rocks say?
The Chattanooga and its correlatives are known for their almost unvarying lithology. The quartz that makes up a large percentage of the Chattanooga is uniformly fine- to very fine-grained over its entire area of preservation. There is very little size grading. Conant and Swanson (1961, p. 43-45) describe the quartz in the Chattanooga as follows:
The following generalities are drawn from study of thin sections of rocks in the Chattanooga shale: (a) The chief detrital mineral grains of the massive black shale are silt-size quartz and somewhat smaller amounts of clay and mica, and these grains are well sorted...One of the most striking microscopic characteristics of the seemingly nearly massive black shale is a wellmarked lamination that results from a high degree of sorting of the grains...Volcanic ash fall deposits on the other hand, decrease in size logarithmically away from the source (Blatt, 1972, p. 388, Sarna-Wojcicki, et al., 1981, p. 586). In the Mt. St. Helens eruptions of May 25, June 12, and July 22, 1980, Waitt, et. al., (1981, p. 620-623), report that the size distribution of the ash fall deposits ranges from gravel near the volcano down through decreasing sizes of sand and culminating in very fine sand and silt as one moves away from the volcano. Another very important fact of tephra deposition is that larger materials with detectable crystals of quartz, feldspar, etc., are found near the base of the deposit, while the finer materials are found near the top. The sand grains in volcanic ash are euhedral (displaying crystal faces) to angular, reflecting a very short history with little or no abrasion during transport. None of this can be thought to be in any way descriptive of the very well-sorted, silt-sized, rounded quartz in the Chattanooga Shale.
Extremely fine-grained quartz is the major constituent of the black shale beds of the Chattanooga and probably makes up about 20 to 25 percent of the rock. Partings of quartz silt are visible throughout the formation, and petrographic examination shows even thinner partings to be especially characteristic of what appears on the outcrop to be the most massive part of the formation (pl. 11b). Within the densest black shale are microscopic layers, commonly less than 0.1 mm thick, composed of quartz grains ranging from 0.02 to 0.06 mm and averaging about 0.03 mm in greatest diameter. Still finer quartz ranging in diameter from about 0.004 to 0.012 mm and averaging 0.008 mm is disseminated fairly uniformly throughout the massive shale. . . In general, the quartz grains are typical sand grains that show various degrees of roundness but few other characteristics indicative of their history.
Are there volcanic rock fragments in the Chattanooga?
Mr. Froede presented no evidence for any volcanic rock type in the Chattanooga. Had he found samples of andesitic tuff or angular phenocrysts, his hypothesis possibly would have had at least some support. However, there is no mention of any such rock type present either in a fresh or weathered state.
Could real volcanic ash supply enough material?
Bentonites are recognized by mainstream geology as being formed by volcanic eruption. Indeed, the T-3 and T-4 bentonites in the Middle Ordovician Carters Limestone of Middle Tennessee (Wilson, 1949, p. 62) are interpreted as altered rhyolite ash. The bentonites contain biotite, a common igneous mineral. Other well-preserved bentonites contain volcanic glass shards, and pumice and bubble fragments (Rose and Chesner, 1987, p. 914). The T-3 and T-4 (Dieke and Millbrig, respectively) bentonites were laid down during an eruption described by Huff et al. (1992, p. 875) and revised and updated in Huff et al. (1996, p. 285-301). The minimum dense-rock equivalents (DRE) of the eruptions that formed these two bentonites was 2,481 km3. To give a perspective of the magnitude of this eruption relative to other, modern eruptions, the following table is reproduced with permission from Huff (1992, table 2).
|Eruption||Ref.||Magnitude (km3 DRE)|
|Millbrig-Big Bentonite||1||1,140 (Revised to 2,481)|
|Mt. St. Helens||9||0.2|
|Table 1. Airfall magnitude of some Plinian eruptions|
As great as these two eruptions were, the thicknesses of the T-bentonites in the Middle Tennessee area are on the order of 6 inches (15 cm). This is in no way comparable to the thickness of the Chattanooga Shale. It has been found to have an average thickness in Tennessee between 84 and 85 30' W. Longitude of 33.7 feet (10.3 m) (Moore, in progress) based on thicknesses from over 800 oil and gas test wells.
What do the clay minerals in the Chattanooga say?
Volcanic ash weathers into the clay mineral smectite (montmorillonite) (Berry and Mason, 1959, p. 509). Later alteration to a mixed layer illite-smectite composition occurs because of progressive burial, contact metamorphism, and hydrothermal alteration, among other mechanisms (Elliot, et al., 1991, p. 436). Bates and Strahl (1957, p. 1308) report an analysis of the clay mineralogy of a sample of the Chattanooga as mostly illite with some kaolinite present. No smectite was found. The clay mineralogy of the Chattanooga does not, therefore, lend support to Mr. Froede's contention.
Is the Chattanooga Shale really an ore?
Though there are several others, the last erroneous statement of Mr. Froede I will address is the following:
Levels of uranium found within the shale are sufficiently high to qualify the shale as a uranium ore (Upham, 1992, p. 47).
The Glossary of Geology defines ore as "the naturally occurring material from which a mineral, or minerals, of economic value can be extracted." The profit qualifier in the definition is very important. Unless one can expect monetary gain from an operation, which costs millions of dollars to finance, there is no point in developing it unless losing money is one's aim.
The pertinent part of Upham's remarks about economic feasibility follows. One will readily see that Upham said something quite different from what Mr. Froede alleges, and present economic conditions do not support the contention that the Chattanooga Shale is an ore for uranium.
Uranium occurs in several different mineralogical settings in Tennessee even though discrete, identifiable uranium minerals are very rare here. Concentrations ranging from 0.001 to 0.03 percent have been reported. None of these has proved economically significant, most being below ore grade by a factor of 10 or more ... The most promising source of uranium in Tennessee is the black, carbonaceous Chattanooga Shale, which contains from 0.001 to 0.03 percent disseminated uranium. (Emphasis added.)
Aside from the lack of any new information, data or evidence, the problems with Mr. Froede's ash-fall hypothesis are, in summary:
While Mr. Froede has admirably referenced mainstream explanations for the origin of radioactive shales, he has, in the end, dismissed the role that organic material plays in trapping radioactive elements and has focused only on their source. His hypothesis for the primary origin of radioactive shales from volcanic ash may appear viable to some, but it does not stand up to rigorous examination or to comparison with the evidence.
I would like to express my deep appreciation to several talk.origins regulars who critically read and made very useful suggestions to the preparation of this paper.
Bates, T. F., and E. O. Strahl, 1957, Mineralogy, petrography, and radioactivity of representative samples of Chattanooga Shale: Geological Society of America Bulletin, v. 68, p. 1305-1314.
Berry, L. G., and Brian Mason, 1959, Mineralogy: W. H. Freeman and Co., San Francisco.
Blatt, Middleton, and Murray, 1972, Origin of Sedimentary Rocks: Prentice-Hall, NJ, p. 388.
Conant, L. C., and V. E. Swanson, 1961, Chattanooga shale and related rocks of Central Tennessee and nearby areas: United States Geological Survey Professional Paper 357.
Elliot, W. C., Aronson, J. L., Matisoff, G., and Gautier, D. L., 1991, Kinetics of the smectite to illite transformation in the Denver Basin: clay mineral, K-Ar data, and mathematical model results: American Association of Petroleum Geologists Bulletin, v. 75, p. 436-462.
Glossary of Geology, 1972, Margaret Gary, Robert McAfee, Jr., and Carol L. Wolf, (eds.), American Geological Institute, Washington.
Hickman, R. C., and V. J. Lynch, 1957, Chattanooga Shale Investigations: United States Bureau of Mines Report of Investigations 6932.
Huff, Warren D., et al., 1992, Gigantic Ordovician volcanic ash fall in North America and Europe, biological tectonomagmatic, and event-stratigraphic significance: Geology, v. 20, p. 875.
______, 1996, Large-magnitude Middle Ordovician volcanic ash falls in North America and Europe: dimensions, emplacement and post-emplacement characteristics: Journal of Volcanology and Geothermal Research, v. 73, p. 285-301.
Matthews, David R., 1993, Review and revision of the Devonian-Mississippian stratigraphy in the Michigan Basin: p. D4 in Petroleum geology of the Devonian and Mississippian black shale of Eastern North America: Roen, John B., and Roy C. Kepferle, (eds.), United States Geological Survey Bulletin 1909.
Milici, Robert C., and John B. Roen, 1981, Stratigraphy of the Chattanooga Shale in the Newman Ridge and Clinch Mountain areas, Tennessee: Tennessee Division of Geology Report of Investigations 40.
Moore, James L., (in progress), Isopach and structure map of the Chattanooga Shale in Tennessee: Tennessee Division of Geology Report of Investigations.
Rose, W. L., and C. A. Chesner, 1987, Dispersal of ash in the great Toba eruption, 75Ka: Geology, v. 15, p. 913-917.
Sarna-Wojcicki, et al., 1981, Areal distribution, thickness, mass, volume, and grain size of air fall ash from the six major eruptions of 1980: p. 583, in The 1980 eruptions of Mount St. Helens: Lipman, Peter W., and Donal R. Mullineaux (eds.), United States Geological Survey Professional Paper 1250.
Sharp, J. M., Jr., and J. K. Kyle., 1988, Ground-water processes in formation of ore deposits: in Back, W., J. S. Rosenshein, P. R. Seaber (eds.). Hydrology: Geological Society of America, The Geology of North America Volume O-2. pp. 461-483.
Shrock, Robert R., and W. H. Twenhofel, 1953, Principles of Invertebrate Paleontology: McGraw-Hill Book Company, New York.
Swanson, Vernon E., 1960, Oil yield and uranium content of black shales: United States Geological Survey Professional Paper 356A.
Upham, G. A., 1992, Uranium In Upham, G. A. (Coordinator). Tennessee minerals annual: Tennessee Division of Geology Bulletin 83. Nashville. p. 47.
Waitt, Richard B., et al., 1981, Proximal air-fall deposits of eruptions between May 24 and August 7, 1980— stratigraphy and field sedimentology: in The 1980 eruptions of Mount St. Helens: Lipman, Peter W., and Donal R. Mullineaux (eds.), United States Geological Survey Professional Paper 1250.
Weil, S. A., H. L. Feldkircher, D. V. Punwani, and J. C. Janka, 1979, The IGT HytortTM process for hydrogen retorting of Devonian oil shales: Fig. 1, p. 5, in National Uranium Resource Evaluation: Chattanooga Shale Conference, U.S. Dept. of Energy.
White, David, and T. M. Stadnichenko, 1923, Some mother plants of petroleum in the Devonian black shales: Economic Geology, v. 18, no. 3, p. 238-252.
Wiesner, Martin G., Y. Wang, and L. Zheng, 1995, Fallout of volcanic ash to the deep South China Sea induced by the 1991 eruption of Mount Pinatubo (Philippines): Geology, v. 23; no. 10; p. 885-888.
Wilson, Charles W., Jr., 1949, Pre-Chattanooga stratigraphy in Central Tennessee: Tennessee Division of Geology Bulletin 56, 407 p.
Zielinski, R. A., 1982, The mobility of uranium and other elements during alteration of rhyolitic ash to montmorillonite: a case study in the Troublesome Formation, Colorado: Chemical Geology, v. 35, p. 185-204.
James Moore has been a geologist with the Tennessee Division of Geology in Nashville for the past 25 years. His research interests include geologic mapping in faulted Pennsylvanian-age terrains, and he is currently doing research for a state-wide map of the thickness and structure of the Chattanooga Shale. Critiquing creationism is one of his hobbies.
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