ASGP (2021), vol. 91: 67–74

DISCOVERY OF PLYWOOD STRUCTURE IN SPHENOTHALLUS FROM GUROVO FORMATION (MISSISSIPPIAN), CENTRAL RUSSIA

Olev VINN (1*) & Aleksandr A. MIRONENKO (2)

1) Institute of Ecology and Earth Sciences, University of Tartu, Ravila 14A, 50411 Tartu, Estonia; e-mail: olev.vinn@ut.ee
2) Geological Institute of Russian Academy of Sciences, Pyzhevski Lane 7, Moscow 119017, Russia
* Corresponding author

Vinn, O. & Mironenko, A. A., 2021. Discovery of plywood structure in Sphenothallus from Gurovo Formation (Mississippian), Central Russia. Annales Societatis Geologorum Poloniae, 91: 67–74.

Abstract: Sphenothallus specimens are reported for the first time from the Mississippian of Central Russia. All Sphenothallus specimens have a phosphatic composition and a characteristic laminar structure, which is best observable in the thickened lateral parts of a tube. Most of the lamellae in the tube wall are straight, but some have a wavy morphology and a few are so wrinkled that they form hollow “ribs”. The wrinkled lamellae presumably had an originally higher organic content than the straight lamellae. There are borings on the surfaces of some lamellae that are similar in morphology to the bioerosional traces in various hard, biomineral substrates. Lamellae in the inner parts of the tube wall are composed of fibres. The fibres are parallel to the surface of the tube wall and in successive laminae they differ in orientation by irregularly varying angles. It is possible that the plywood microstructure in Sphenothallus was originally organic and was later phosphatized during fossilization. An alternative, but less likely explanation is that the plywood structure was originally mineralized and therefore is comparable to
the phosphatic lamello-fibrillar structures of vertebrates.

Manuscript received 11 September 2020, accepted 21 December 2020.