peloidal

Peloidal refers to a texture in carbonate rocks characterized by small, rounded to ellipsoidal grains called peloids. Peloids are typically submillimeter in size (generally less than 1 millimeter in diameter) and consist of microcrystalline calcite or micrite. They have smooth, featureless exteriors and usually lack internal structure, distinguishing them from coarser recognizable bioclasts or ooids.

The origin of peloids is diverse and complex. Many peloids are believed to form by micritization or recrystallization of fecal pellets, algae, or other organic matter within a carbonate mud. They can also arise from direct precipitation of micritic carbonate around organic remnants or in microbial-rich environments. Post-depositional processes such as cementation and abrasion can modify their appearance, but they typically retain their diminutive, rounded shape.

In carbonate petrography, peloids are a key grain type and are used in texture-based classifications such as the Folk framework. They occur in peloidal limestones and are common in wackestones and packstones, often alongside other allochems like fine bioclasts and micrite. Peloids contrast with ooids, which possess a recognizable concentric cortex surrounding a nucleus.

Peloidal textures are commonly associated with low-energy, shallow-memi-brackish to normal-marine settings where abundant carbonate mud and microbial activity promote micritic precipitation and pellet formation. Their presence informs interpretations of depositional environments, diagenetic history, and sedimentologic processes in carbonate successions.