Girvanella Explained

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.^[3]

Girvanella was originally described as a foraminifera.^[4] It was later assigned to the now-obsolete family porostromata.^[5] In 2020, it was assigned to the order Oscillatoriales.^[6]

Girvanella is characterised by having flexing, tubular filaments with a uniform diameter usually between 10 and 30 microns (rarely up to 100 microns). The walls of these tubules are relatively thick and calcareous. These tubules are typically (but not always) twisted together into nodules, and often encrust other objects including foraminifera.

Fossils of Girvanella are found from the Cambrian through the Cretaceous.

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.

Notes and References

1. Caron . Jean-Bernard. Jackson . Donald A.. Taphonomy of the Greater Phyllopod Bed community, Burgess Shale . PALAIOS . 21 . 5 . 451–65. October 2006. 10.2110/palo.2003.P05-070R. 20173022. 2006Palai..21..451C . 53646959 .
2. R. . Girvanella and other algae as depth indicators . Lethaia . 8. 2. Riding . 173–179 . 1975 . 10.1111/j.1502-3931.1975.tb01310.x.
3. Florencia Moreno, Ana Mestre, Susana Heredia. May 2023. Lower Ordovician calcareous microfossils from the San Juan Formation, Argentina: A new type of calcitarch and its paleoenvironmental implications. Andean Geology. 50. 2. 302—317. 10.5027/andgeoV50n2-3469. en. 11336/223379. free.
4. Web site: Calcareous algae, Volume 4 - 1st Edition. 2020-09-28. www.elsevier.com.
5. Monty. C. L.. 1981. Monty. Claude. Spongiostromate vs. Porostromate Stromatolites and Oncolites. Phanerozoic Stromatolites. en. Berlin, Heidelberg. Springer. 1–4. 10.1007/978-3-642-67913-1_1. 978-3-642-67913-1.
6. Lijing Liu . Yasheng Wu . Hongping Bao . Hongxia Jiang . Lijing Zheng . Yanlong Chen . 2020 . Diversity and systematics of Middle-Late Ordovician calcified cyanobacteria and associated microfossils from Ordos Basin, North China . Journal of Paleontology . 95 . 1–23 . 10.1017/jpa.2020.82 . 226349226 .