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Related to Oncoids: Peloid, Ooids


A spherical stromatolite that usually forms around a fragment of detritus such as a piece of shell or a grain of sand.

[Greek onkos, mass; see oncology + -lite.]

on′co·lit′ic (-lĭt′ĭk) adj.
References in periodicals archive ?
The one-meter tall stromatolites are marine in form, occur immediately adjacent to shore rather than in deeper water, are covered by a peat and soil with inter-head areas filled with a complex stratigraphy, are colonized by living freshwater mussels on their sides, appear to rim cenotes, and have oncoids in the sand flats surrounding the field.
Microherms in the Smackover consist of concentrically laminated (stromatolitic), clotted (thrombolitic), calcimicrobial, or structureless (leiolitic) carbonate, and texturally resemble associated oncoids (algal balls).
Matrix is dominated by peloids, but contains tuberoids, other intraclasts, oncoids, thin-shelled bivalves, benthic foraminifera, smooth-walled ost racodes, echinoid spines, and gastropods, in approximate order of decreasing abundance.
The oncoids, as large as 2 cm, typically have a bryozoan, stromatoporoid or brachiopod shell fragment as nucleus, encrusted with Girvanella and Rothpletzella.
Towards the eastern part of the section, it grades into 10 to 20 cm thick beds characterized by better sorting and a decreasing proportion of oncoids and micritic matrix (Fig.
These carbonate rocks formed during the maximum transgression of sea in Early Frasnian time and are rich in fauna (brachiopods, pelecypods, gastropods, cephalaspods, corals, stromatoporoids, stromatolites, oncoids and fishes; Sorokin 1978; Stinkulis 1998).