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Journal of Creation 33(2):7–9, August 2019

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A case for rapid formation of calcareous concretions


Figure 1. Concretions in sandstone from near Winnett, Montana, USA (courtesy of Kevin Horton from the Institute for Biblical Authority)

A concretion is: “A hard, compact mass or aggregate of mineral matter, normally subspherical but commonly oblate, disk-shaped, or irregular with odd or fantastic outlines; formed by precipitation from aqueous solution about a nucleus or center, such as a leaf, shell, bone, or fossil, in the pores of a sedimentary or fragmental volcanic rock, and usually of a composition widely different from that of the rock in which it is found and from which it is rather sharply separated.”1 Sometimes, concretions have shrinkage cracks within that are filled with another chemical, such as calcite.2 Concretions are isolated in the sedimentary rocks and usually represent a minor constituent of the enclosing rock or cementing chemicals. They range in size from pellets to spheroidal bodies up to 3 m or more in diameter.

Concretions are considered to have formed during diagenesis and shortly after sediment deposition. Diagenesis refers to: “All the chemical, physical, and biological changes undergone by a sediment after its initial deposition, and during and after its lithification, exclusive of surficial alteration (weathering) and metamorphism.”3 The diagenesis involves the diffusion and rapid depositional reactions with organic molecules and other constituents of the pore water. However, there are still unanswered questions on the origin of concretions.4

Concretions are rather common in sedimentary rocks around the world, especially fine-grained marine rocks. Fossils are often found at their centres. People sometimes mistake them for dinosaur eggs, fossils, extraterrestrial objects, or human artefacts. Figure 1 shows several cannon-ball-shaped concretions in a sandstone from near Winnett, eastern Montana, USA. Figure 2 is a cross section through one of them showing the spheroidal deposition.

Since concretions are harder than the surrounding sedimentary rock, they can weather or erode out and accumulate on the ground. They are given such names as Moeraki boulders along the coast of South Island, New Zealand; Kouto boulders along the coast of North Island, New Zealand; Mokui Marbles that eroded out of the Navajo Sandstone in south-east Utah; and either coinstones or curling stones from the Lias Formation, Dorset, England.

Concretion formation not occurring today but considered slow

Figure 2. Cross section through one of the concretions found near Winnett, Montana, USA (courtesy of Kevin Horton)

Concretions are not forming in modern sediments, which, like many other phenomena, contradicts uniformitarianism:

“One of the great puzzles of early diagenesis is that although concretions are very common in rocks and are thought to be important products of early diagenesis, concretions similar to those in rocks have not been observed in modern sediments (Raiswell and Fisher, 2000). Indeed, Colman and Raiswell (1993) cite this discrepancy as a fundamental challenge to uniformitarianism.”5

The rate of formation of concretions is also not known, but like almost every aspect of geology, it has been considered a slow process. Such claimed ‘slow processes’ are a simple outgrowth from the belief in uniformitarianism and deep time. It has been believed to be caused by very slow advection of water during cementation,2,4 also considered a slow process. In concretions composed mostly of calcite, it has been difficult to account for the steep calcite chemical gradients across the margins of concretions, the nearly constant calcite concentration within the concretion, and the constant porosity within the concretion based on thin sections.6

Concretions form at least 1,000 to 10,000 times faster than previously thought

Yoshida et al. estimated the rate of calcareous concretions in fine-grained sedimentary rocks.6 They first noticed that at the edge of the concretions, there is a concentration gradient of CaCO3. They surmise that the concretion must have grown during early diagenesis soon after the sediment had accumulated. Based on the ubiquitous presence of decaying organic matter in the centre, HCO3 ions formed and diffused in all directions toward the margin of the concretion. The organic origin of the carbon in the HCO3 is supported by low carbon isotope ratios, indicative of organic matter. At the same time Ca from the environment diffused toward the organic matter forming a growing CaCO3 front that grew outward. The width of this front is proportional to the diameter of the growing concretion.

To find the rate of growth, the researchers used the diffusion coefficient in the Boom Clay of Western Europe which is about 10–6 cm2/sec. From this they determined the rate of growth to be greater than 3–4 orders of magnitude (1,000 to 10,000 times) as fast as originally thought. This resulted in a rate of growth of about 0.5 to 50 cm/yr.

Flood geology implications

However, the Boom Clay is semi-consolidated and diffusion would be faster when the sediments were unconsolidated. The diffusion coefficient of unconsolidated fine sediments is more like 10–5 cm2/s, about 10 times faster.6 Therefore, during early diagenesis before much compaction and cementation, the growth could be significantly faster. Based on figure 5 of Yoshida et al. growth could range from 5 to 500 cm/yr.7

Such numbers would fit nicely into a Flood scenario when sediments were rapidly accumulating during the Inundatory Stage of the Flood.8 There would be enough time to form concretions during the Inundatory and Recessive Stages of the Flood, and possibly a little after the Flood. Since concretions are of variable composition and internal structure, there may be other Flood mechanisms for their formation.

Ubiquitous calcareous concretions across the earth indicate that much dissolved calcite was in the floodwater sediments. Calcite is one of the major cementing agents for sedimentary rocks, and the formation of calcareous concretions indicates actively flowing calcite-rich water within the pores of the sediment. Thus, the sediments laid down during the Inundatory Stage would be easily and quickly cemented by calcite cement, though there are other possible cementing agents.

References and notes

  1. Neuendorf, K.K., Mehl, Jr., J.P., and Jackson, J.A., Glossary of Geology, 5th edn, American Geological Institute, Alexandria, VA, p. 134, 2005. Return to text.
  2. Seilacher, A., Concretion morphologies reflecting diagenetic and epigenetic pathways, Sedimentary Geology 143:41–57, 2001. Return to text.
  3. Neuendorf et al., ref. 1, p. 176 Return to text.
  4. Mozley, P. and Davis, J.M., Internal structure and mode of growth of elongate calcite concretions: evidence for small-scale, microbially induced, chemical heterogeneity in groundwater, GSA Bulletin 117:1400–1412, 2005. Return to text.
  5. Mozley and Davis, ref. 4, p. 1411. Return to text.
  6. Yoshida, H., Yamamoto, K., Minami, M., Katsuta, N., Sin-ichi, S., and Metcalfe, R., Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis, Scientific Reports 8(6308):1–10, 2018. Return to text.
  7. Yoshida et al., ref. 6, p. 7. Return to text.
  8. Oard, M.J. and Reed, J.K., How Noah’s Flood Shaped Our Earth, Creation Book Publishers, Powder Springs, GA, 2017. Return to text.

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Readers’ comments

Alexander M.
Amazing arcticle.
Thomas D.
What are often referred to as "shrinkage cracks" in clay-based concretions are due to their penultimate expansion by bloating, rather than the presumed contraction of a desiccating process. Careful observation of the sharp but congruent interfaces sidling the pure calcite veins strongly suggest a once coherent, stiffened pudding- or gel-like substance which has been torn apart by an internal buildup of gas pressure--which is often seen as having localized about kernels of decomposed organic matter at the axial center of the concretion. This gas cavity lastly fills with a hypertonic calcite solution.

(Some nodular surfaces exhibit evidence of an effervescent degassing.)

The body of such a concretion also appears to have originated as a coagulated nodule, perhaps as a semi-fluid mass captured by a gas cavity within the surrounding sediment. Liquefaction by gross soil movements (as those associated with quaking action) very typically results in the precipitation of fining or flocculating sediments about organic nuclei--e.g., pellets of animal excrement or aggregated plant debris.

At the time of the flood (we've come to recognize from the sedimentary evidence), great hydraulic processes extensively reworked all that could be ground down and entrained across the base surface of the globe. Sympathetic thermal and chemical processes, catastrophically provoked by the general agitation, conspired with the rest to capture, preserve and lithify a standing record of the flood judgement for all to witness for the remainder of history.
Michael B.
There is an outstanding paper done by Victoria Mcoy in which concluding she bemoans the fact that 50 year old concretions are indistinguishable from "ancient" concretions.
For those interested it is very much worth the reading. You can search on the title below and I also included the actual quote from her conclusion because it is quite telling.

"Patterns in Palaeontology: Exceptional Preservation of Fossils in Concretions"
Author: Victoria Mcoy

"As it turns out, some very young concretions are known. Concretions from West Haven, Connecticut (Fig. 11) have been carbon dated to a few thousand years old, and some concretions in the Norfolk marshes, UK, are estimated to be less than 50 years old. Unfortunately, they are all indistinguishable from more ancient concretions, so all they tell us about a possible transition from a calcium soap concretion to a carbonate concretion is that it happens in less than 50 years."
Richard G.
Julie's descriptive word cannonball is praiseworthy. And I absolutely enjoy Bro Oard whatever subject he takes up. It flatters me when schoolboy Latin and French and 3 months of self-taught Greek help me, but I despair of most people being able to understand much of what scholars write. How blessed we Bible-believers are, to have so many PhD's for those who require them but "unless you utter by the tongue speech easy to be understood, how shall it be known what is spoken, for you will be speaking into the air?" Remember those three clever pranksters who recently wrote utter rubbish and nonsense and yet got it published in a high-grade magazine and were even praised by an expert??" If you don't know about the case it proves another point, namely that the media don't report it (they hold down the truth in unrighteousness) when Bible Opposers are publicly exposed as frauds!! Those accretions make me recall God's omni-science. I pickabacked my Japanese brother to see the Moeraki Boulders. His wife married him to pickaback him so he could preach the gospel. (Our church might be the biggest north of Tokyo) God's science threatened mankind with hell but His omni-science (better His omni-love) paid the penalty for penitents. My big point is. Get CMI's message out widely and lovingly no matter how imperfectly but remember that your hearers are mostly very shallow and often only need your simple attempt at giving them the good news. Dawkins Hitchens Hawking are/were all shallow and sinful but some people ultimately listen when they hear your loving but clear witness to God's good news of a free entry to Heaven for anyone who is sorry they sinned and grateful that Jesus paid for them to be saved, and He proved it by coming back to life as he said He would do, 3 days later.
Julie M.
There are some great examples of this along the Great Ocean Walk in Victoria, Australia. Reddish coloured cannonballs in a cliff of grey mudstone.

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