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What is Boundstone?

Angela Brady
Angela Brady

Boundstone is an indigenous deposit of limestone that was bound by algae, coral, or other unicellular organism when it was formed. Boundstone is found in areas surrounding coral reefs, and areas that were coral reefs 2.5-3 million years ago, but may be surrounded by dry land today. Depending upon the way the organic matter was arranged within the sediment when the stone was formed and what kind of organic matter it was, boundstone can be classified as either framestone, bindstone, or bafflestone.

Framestone is distinguished by a rigid framework of fossilized organic matter, usually deep-water sponges, that occur close together in a ”life position.” These sponges were bound by microbial crusts and hardened sand when living, and the spaces between gradually filled with sand, sediment, and calcite crystals. Over time, as the water receded and the structure was continuously exposed to air, the natural cementing action of the densely packed sediment preserved the remains of the organic matter as fossils. Framestone is named for the “framework” the organic matter provides, and can be found in massively large or small, dense deposits.

Boundstone often appears in areas surrounding coral reefs.
Boundstone often appears in areas surrounding coral reefs.

Bindstone is characterized by a more random dispersion of organic binding agents that may or may not be preserved. The most common binding agent in bindstone is algae, which holds together layers of mud and calcite with large “pores” caused by gas bubbles that became trapped in the sediment during formation. Stromatolites, which are fossilized mounds of layered algal mat and sediment, are the most common form of bindstone. Most bindstone deposits are oriented vertically as opposed to horizontally, due to the layering manner in which they form. The base of the stone is formed as an algal mat forms laterally, then is built upon by mud and other algae both vertically and laterally, changing with environmental conditions. Bindstone is the most commonly found type of boundstone.

Stromatolites, which are fossilized mounds of layered algal mat and sediment, are the most common form of bindstone.
Stromatolites, which are fossilized mounds of layered algal mat and sediment, are the most common form of bindstone.

Bafflestone is bound by thick-walled, parallel columns of coral, which permit only finer-grained sediment to pass through. As a result, the composition of bafflestone, other than fossilized coral, is mostly naturally-cemented sand and silt. The sand is composed of homogenous calcite and the silt consists of a mixed residue left behind after carbonate mud was filtered out. The unique structure of bafflestone means that it can only form on and around colonies of vertically-growing coral, and are therefore limited to small individual or clustered deposits. Bafflestone is named for the “baffling” action exhibited by the coral columns during the formation of the stone.

Frequently Asked Questions

What exactly is boundstone?

Boundstone is a type of sedimentary rock that is characterized by the binding of grains or particles by a mineral matrix. This matrix, often composed of calcium carbonate, cements the components together, forming a rigid structure. Boundstone is typically associated with organic reefs or carbonate platforms where organisms like corals and algae contribute to the binding process.

How does boundstone form?

Boundstone forms in marine environments where organisms such as corals, algae, and mollusks produce calcium carbonate as part of their biological processes. Over time, these organisms build up layers of skeletal material that, upon their death, become cemented together by the precipitation of minerals from seawater, creating a solid rock.

What organisms are most commonly involved in the creation of boundstone?

Corals and calcareous algae are the primary builders of boundstone. Corals construct their skeletons from calcium carbonate, while calcareous algae contribute to the cement that binds the structure. Other organisms like bryozoans, mollusks, and foraminifera can also play a role in boundstone formation.

Where can boundstone be typically found?

Boundstone is commonly found in ancient and modern reef environments. These can be present in tropical and subtropical marine waters where conditions are conducive to the growth of reef-building organisms. Boundstone formations are also found in fossilized reefs from past geological periods.

Why is boundstone important in the study of geology and paleontology?

Boundstone is crucial for understanding Earth's history as it provides insights into past marine environments and climate conditions. It helps paleontologists reconstruct ancient ecosystems and study the evolution of reef-building organisms. Geologically, boundstone formations can indicate the presence of oil and gas reservoirs, making them significant in the energy sector.

Can boundstone be used as a building material?

While boundstone itself is not commonly used as a modern building material due to its irregularity and the difficulty in quarrying it, limestone, which can be a type of boundstone, has been historically used in construction. Its durability and aesthetic appeal make it a choice material for architectural projects, according to the National Association of Home Builders.

Discussion Comments

cougars

@highlighter- Boundstone in itself is a fossil. I do not know much about boundstone, but I do remember from my physical geography of energy class, it has been found alongside oil and gas reserves in various places around the globe. One area in specific that I remember hearing about boundstone is in a region of Eastern Kazakhstan.

The place in particular is the Tenzgen field along the shores of the Caspian sea. I think this is the area where geologists and petroleum engineers are currently developing as gas fields. From what I remember, this area is very rich in natural gas reserves, many of which were discovered recently. As far as where in California you might find bounstone, I am not sure, but I would assume the state is rich in boundstone because it has a significant amount of oil resources and the state is along the coast. Maybe doing a photo search online will produce some results. I know people often post location data with photos of rock specimens.

highlighter

Where can I find natural geologic deposits of boundstone? I think it would be interesting to examine these stones. I would assume that they are loaded with fossils and the likes since they are sedimentary rocks that originated in areas rich in biodiversity. I live in California, are there any areas where I can find these types of sedimentary rocks?

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    • Boundstone often appears in areas surrounding coral reefs.
      By: LA Photographer
      Boundstone often appears in areas surrounding coral reefs.
    • Stromatolites, which are fossilized mounds of layered algal mat and sediment, are the most common form of bindstone.
      By: Ints
      Stromatolites, which are fossilized mounds of layered algal mat and sediment, are the most common form of bindstone.