Fossil Thrombolites at Lake Walyungup, April 2020 02

Thrombolites (from

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

θρόμβος ''thrómbos'' meaning " clot" and λῐ́θος ''líthos'' meaning "

stone In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...

") are clotted accretionary

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...

s formed in shallow water by the trapping, binding, and cementation of sedimentary grains by

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...

s of

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...

s, especially

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

Structures

Thrombolites have a clotted structure without the laminae of

stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...

s. Each clot within a thrombolite mound is a separate

colony In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state' ...

. The clots are on the scale of millimetres to centimetres and may be interspersed with

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

mud A MUD (; originally multi-user dungeon, with later variants multi-user dimension and multi-user domain) is a Multiplayer video game, multiplayer Time-keeping systems in games#Real-time, real-time virtual world, usually Text-based game, text-bas ...

or sparry carbonate. Clots that make up thrombolites are called thromboids to avoid confusion with other clotted textures. The larger clots make up more than 40% of a thrombolite's volume and each clot has a complex internal structure of

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

and rimmed lobes resulting primarily from

calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...

of the cyanobacterial colony. Very little sediment is found within the clots because the main growth method is calcification rather than sediment trapping. There is active debate about the size of thromboids, with some seeing thromboids as a macrostructural feature (domical hemispheroid) and others viewing thromboids as a mesostructural feature (random polylobate and subspherical mesoclots).

Types

There are two main types of thrombolites:

Calcified microbe thrombolites

This type of thrombolites contain clots that are dominantly composed of

calcified Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...

microfossil A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

components. These clots do not have a fixed form or size and can expand vertically. Furthermore,

burrow An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of sh ...

s and trilobite fragments can exist in these thrombolites.

Coarse agglutinated thrombolites

This type of thrombolites is composed of small openings that trap

fine-grained Granularity (also called graininess), the condition of existing in granules or grains, refers to the extent to which a material or system is composed of distinguishable pieces. It can either refer to the extent to which a larger entity is subd ...

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s. They are also known "thrombolitic-stromatolites" due to their close relation with the same composition of stromatolites. Because they trap sediment, their formation is linked to the rise of

algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

-cyanobacterial mats.

Differences from stromatolites

Thrombolites can be distinguished from

microbialite Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter < 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of

Stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

s are similar but consist of layered accretions. Thrombolites appear with random patterns that can be seen by the naked eye, while stromatolites has the texture of built up layers.

Ancient fossil record

Calcified microbe thrombolites occur in

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s from the shallow water

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

during the

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...

and early

Palaeozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and '' ...

Locations

Thrombolites are rare on modern Earth, but exist in areas of groundwater discharge with high concentration of nutrients and organic ions, such as shallow seawater, freshwater, and saltwater lakes, and streams. Thrombolites are now found in only a few places in the world, including: *

Laguna Negra, Catamarca Laguna Negra is a lake in the Catamarca Province of Argentina. It lies on the Altiplano, Puna high plateau next to two other lakes and Salt pan (geology), salt flats. The lake is less than deep and forms a rough rectangle with a surface of . ...

, Argentina * Basin Lakes and Blue Lake, Australia * Lake Clifton, Australia * Lake Richmond, Australia * Lake Thetis, Australia *

Flower's Cove Flower's Cove is a town in the Canadian province of Newfoundland and Labrador. The town had a population of 272 in the Canada 2021 Census. It is known for its thrombolite fossils. Geography ;Climate Flower's Cove has a subarctic climate (Koppe ...

, Canada * Manito Lake and

Pavilion Lake Pavilion Lake is a freshwater lake located in Marble Canyon, British Columbia, Canada home to colonies of freshwater microbialites. Location and Local Communities It is located between the towns of Lillooet and Cache Creek (29.44 kilometres WNW, ...

, Canada * Lakes Nuoertu and Huhejaran, China * Kiritimati Atoll, Kiribati *

Cuatro Ciénegas Cuatro Ciénegas () is a city in the northern Mexican state of Coahuila. It stands at , at an average elevation of above sea level. The city serves as the municipal seat for the surrounding municipality of the same name. It is located in the ...

and Lake Alchichica, Mexico * Ciocaia, Romania *

Lake Van Lake Van ( tr, Van Gölü; hy, Վանա լիճ, translit=Vana lič̣; ku, Gola Wanê) is the largest lake in Turkey. It lies in the far east of Turkey, in the provinces of Van and Bitlis in the Armenian highlands. It is a saline soda lake ...

and Salda Lake, Turkey * Green Lake, United States

References

{{Origin of life Trace fossils Cyanobacteria