What is the Difference Between Stromatolites and Thrombolites

The main difference between stromatolites and thrombolites is that stromatolites are finely laminated whereas thrombolites are not laminated and possess a clotted internal structure with fenestrae.

Stromatolites and thrombolites are two distinct types of microbialites, rock-like underwater microbial structures that look like reefs but, are entirely millions of microbes.

Key Areas Covered

1. What are Stromatolites
– Definition, Structure, Function
2. What are Thrombolites
– Definition, Structure, Function
3. Similarities Between Stromatolites and Thrombolites
– Outline of Common Features
4. Difference Between Stromatolites and Thrombolites
– Comparison of Key Differences

Key Terms

Stromatolites, Thrombolites

What are Stromatolites

Stromatolites are layered sedimentary formations of microbialites. Generally, photosynthetic organisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota create stromatolites. Generally, the production of the adhesive materials by these microorganisms cemented the sand and other rocky materials to form mineral microbial mats. Over time, these layers grew gradually to form the layered microbialites. Moreover, the fossiled stromatolites provide records about ancient life on earth.

Figure 1: Stromatolites

Furthermore, the main characteristic feature of stromatolites is that they are layered microbialites. On the other hand, they trap materials through carbonate-precipitating activities. Therefore, stromatolites have layers, which are accretionary structures that are also biochemical. They occur through the binding and cementation of the sedimentary grains in biofilms. However, this occurs through the action of cyanobacteria. Moreover, these cyanobacteria form various structures and morphologies such as columnar, domal, stratiform, conical, and branching types.

What are Thrombolites

Thrombolites are clotted accretionary structures formed in shallow water. They occur due to the sedimentation and cementation of grains by the biofilms of microorganisms, especially cyanobacteria. However, the most significant feature of thrombolites is that they are clotted structures but not layered structures like stromatolites. In addition, the other significant feature of thrombolites is that they form by calcification through microbial clots. Furthermore, each clot in the thrombolites is a microbial colony. In general, the size of the colony can range from millimeters to centimeters.

Figure 2: Thrombolites

Moreover, larger clots can make up more than 40% of the thrombolite’s volume. The internal structure of the clot is complex. In addition, there are two main types of thrombolites: calcified microbe thrombolites and coarse agglutinated thrombolites. Here, calcified thrombolites contain calcified microbial clots while coarse agglutinated thrombolites contain fine-grained sediments.

Similarities Between Stromatolites and Thrombolites

• Stromatolites and thrombolites are two types of microbial structures consisting of millions of microbes.
• They are microbialites, rock-like underwater microbial structures that look like reefs.
• They are fossils that are 3.45 billion years old.
• Moreover, cyanobacteria form both structures.

Difference Between Stromatolites and Thrombolites

Definition

Stromatolites refer to layered deposits, mainly of limestone, formed by the growth of blue-green algae, while thrombolites refer to a clotted structure without the laminae of stromatolite.

Structure

Generally, stromatolites are layered deposits, mainly of limestone, formed by the growth of blue-green algae, while thrombolites are clotted structures without the laminae of stromatolites.

Growth Forms

Individual lamina form by episodic sediment trapping and carbonate precipitating activities of mat-like microbial communities in stromatolites, while in thrombolites, individual mesoscopic clots form from discrete colonies of calcified, coccoid-dominated microbial communities.  

Conclusion

In brief, Stromatolites are deposits of limestones that occur due to the growth of blue-green algae. Usually, individual lamina of the stromatolites forms by the episodic sediment of the carbonate precipitating activities. In contrast, thrombolites are structures with no laminae. Moreover, individual mesoscopic clots form by discrete colonies of calcified microbial communities. Both stromatolites and thrombolites are 3.45 billion years old. Therefore, the main difference between stromatolites and thrombolites is their structure and formation.    

References:

1. “Stromatolite.” Wikipedia, Wikimedia Foundation, 3 Oct. 2022.
2. “Thrombolite.” Wikipedia, Wikimedia Foundation, 3 Feb. 2022

Image Courtesy:

1. “Stromatolites in Sharkbay” By Paul Harrison – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Lake Clifton SMC 2008” By SeanMack – Own Work (CC BY 3.0) via Commons Wikimedia