Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by the growth of one or more species of microorganisms, [1] usually containing cyanobacteria. [2] Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. [3]

Mar 25, 2019 · An oncolite is a type of sedimentary structure that is composed of oncoids formed by cyanobacterial growth. Technically, only structures that have an oncoid volume greater than 50% should be referred to as an oncolite.

Jun 1, 2024 · Oncoids are defined as coated grains commonly larger than 2 mm in diameter (Tucker and Wright, 1990; Flügel, 2004). Their cortex is developed by irregular or concentric laminae around a nucleus, made of skeletal or non-skeletal grains (e.g., Zhang et al., 2015).

Pisolites form by the precipitation of calcium Carbonate around nuclei trapped in sediment within the vadose zone of soils or marine tidal flats (Figure 24). Oncoids form on the surface of intertidal and supratidal flats where Carbonate precipitates from salt water spray and marine flood waters.

Oncoids are a group of algally (red algae excepted), cyanobacterially and bacteri-ally coated grains which originate(d) in marine and freshwater phreatic zones, although some workers prefer to use the term oncoids for all coated grains which are not ooids.

Aug 30, 2019 · Oncoids are rounded, spherical to oblate, laminar growths of algae around a nucleus (shells, mud intraclasts, broken lumps of algal crust). Their dimensions are measured in centimetres. The algae usually associated with oncoids …

Feb 28, 2020 · The oncoids are divided into six types based on their morphology and internal structure. Microscopic and ultrastructural observations reveal typical microbial fossils (Girvanella) and microbially-related sediments (framboidal pyrite), indicating the biogenicity of the oncoids.

Aug 1, 2015 · Oncoids are coated grains larger than 2 mm in diameter that exhibit irregularly concentric laminae (i.e., coatings or cortex) surrounding a nucleus of detrital origin (Tucker and Wright, 1990, Flügel, 2010).

Oncoids are a group of algally (red algae excepted), cyanobacterially and bacteri­ ally coated grains which originate(d) in marine and freshwater phreatic zones, al­ though some workers prefer to use the term oncoids for all coated grains which are not ooids. Recent oncoids have been described from the lacustrine, fluvial and marine environments.

Oncoids comprise grains of suspected or inferred (non red-)algal, cyanobacterial and bacterial origin. There are two main groups of oncoids: spongiostromate oncoids and porostromate oncoids (Peryt 1981).