Nav: Home

Cracking open the formation of fossil concretions

May 02, 2018

Nagoya, Japan - All over the world, spectacular fossils have frequently been found preserved inside solid, roughly spherical rocks called "concretions." From geologists to casual observers, many have wondered why these hardened masses of carbonate formed around dead organisms, with round shapes and sharp boundaries with the surrounding material, typically in marine mud and mudstone.

Several important questions regarding concretions have long puzzled scientists. What conditions cause them to form? How long do they take to grow? Why do they stop growing? Why are they so distinct from the surrounding rock or sediments?

Now, researchers led by Nagoya University have developed a method to analyze concretions using L-shaped "cross-plot diagrams" of diffusion and growth rate, reported in a new study published in Scientific Reports. With this method, they analyzed dozens of concretions from three sites across Japan and compared them with concretions from England and New Zealand.

The results of this new study dramatically impact understanding of the rate at which concretions form. "Until now, the formation of spherical carbonate concretions was thought to take hundreds of thousands to millions of years," co-author Koshi Yamamoto says. "However, our results show that concretions grow at a very fast rate over several months to several years." This rapid sealing mechanism could explain why some concretions contain well-preserved fossils of soft tissues that are rarely fossilized under other conditions.

Study first author Hidekazu Yoshida explains, "The concretions maintained their characteristics, with well-preserved fossils at their centers or textures indicative of the original presence of organic matter. Simple mass balance calculations also demonstrate that the carbon fixed in the carbonate concretions came predominantly from the organs of organisms inside the concretions."

All of the studied concretions were composed of calcite, with relatively consistent compositions throughout, distinct from the surrounding muddy matrix. Fine-grained, generally clay-rich sediments were found to be important to limit diffusion and permeability, and to slow the migration of solutes. Thus, bicarbonate concentrations would rise high enough at a reaction front to cause rapid precipitation of calcium carbonate, with sharp boundaries from the surrounding mud.

This new unified model for the creation of spherical concretions, which can be generalized by simple formulas, can be applied to interpret concretions from all over the world. In addition to advancing our knowledge of this important preservation mechanism in the fossil record, this improved understanding of the rapid precipitation of calcite due to the presence of organic material may have practical applications in the field of sealing technology.
-end-
The article, "Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis," was published in Scientific Reports at DOI: 10.1038/s41598-018-24205-5.

Nagoya University

Related Organic Matter Articles:

Let there be light: Synthesizing organic compounds
The appeal of developing improved drugs to promote helpful reactions or prevent harmful ones has driven organic chemists to better understand how to synthetically create these molecules and reactions in the laboratory.
Metal-organic framework nanoribbons
The nanostructure of metal-organic frameworks (MOFs) plays an important role in various applications since different nanostructures usually exhibit different properties and functions.
Next step in producing magnetic organic molecules
A team from the Ruhr Explores Solvation Cluster of Excellence at Ruhr-Universität Bochum has created new molecules with magnetic properties.
Researchers reveal mechanisms for regulating temperature sensitivity of soil organic matter decompos
Recently, a research team led by Prof. YANG Yuanhe from the Institute of Botany elucidated the mechanisms underlying vertical variations in Q10. Based on the natural gradient of soil profile in Tibetan alpine grasslands, the team collected soil samples at two soil depths and then conducted long-term incubation, SOM decomposition modeling and manipulative experiments.
Verifying 'organic' foods
Organic foods are increasingly popular -- and pricey. Organic fruits and vegetables are grown without synthetic pesticides, and because of that, they are often perceived to be more healthful than those grown with these substances.
Water creates traps in organic electronics
Poor-quality organic semiconductors can become high-quality semiconductors when manufactured in the correct way.
Organic semiconductors: One transistor for all purposes
In mobiles, fridges, planes - transistors are everywhere. But they often operate only within a restricted current range.
Breakthrough in organic electronics
Researchers from Chalmers University of Technology, Sweden, have discovered a simple new tweak that could double the efficiency of organic electronics.
Organic food worse for the climate
Organically farmed food has a bigger climate impact than conventionally farmed food, due to the greater areas of land required.
Organic ferromagnetism: Trapping spins in the glassy state of an organic network structure
A team of researchers, affiliated with South Korea's Ulsan National Institute of Science and Technology (UNIST) presents alternative approaches for versatile future applications of plastic magnets.
More Organic Matter News and Organic Matter Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.