In situpreserved equisetophyte stems in the Upper Bajocian Parkinsoni Zone (Middle Jurassic) of the Northern Caucasus (Russia)

Abstract

Abstract This paper focuses on the first record of equisetophyte stems preserved in situ in the dark siltstones of the Djangura Formation of the Late Bajocian (Middle Jurassic) age in the Bolshoi Zelenchuk River Basin (Zelenchuk district of the Karachaevo-Cherkessk Republic, Northern Caucasus, Russia). The stems are long and narrow, with long internodes, vertically orientated in growth upright position. The outer surface of the stems bears thin, prolonged ribs. There are well-formed diaphragms at the stem nodes. The diaphragms are covered with fine radial striations. The stems possess a central internal cavity of subcylindrical shape. The sedimentary conditions of forming the layer with equisetophyte stems can be interpreted as tidal plain or littoral.