Nicholsonia Korde, 1973 Girvanella is a fossil thought to represent the calcified sheath of a filamentous cyanobacterium known from the Burgess Shale[1] and other Cambrian fossil deposits.

[2] Specimens are also known from the Early Ordovician San Juan Formation, Argentina.

These tubules are typically (but not always) twisted together into nodules, and often encrust other objects including foraminifera.

[4] Girvanella fossils are found in a wide range of environmental conditions, most commonly shallow-shelf carbonate facies, but also in nonmarine limestones.

Recent caliche deposits in Barbados may be referable to Girvanella.