A Boreal Toarcian Biochronological Zonation Based on Bivalve Mollusks of the Genus Meleagrinella Whitfield, 1885

A First Record of Lower Jurassic (Toarcian) Coleoid Jaws in Siberia

“…One of smaller concretions from the level 1 m above the Pliensbachian/Toarcian boundary in exposure 4d was found to contain numerous micro-onychites. Although the lowermost part of black shales throughout the Vilyui River basin lacks ammonites, the age of the studied unit can be deducted through bivalve occurrences, as Kedonella mytileformis collected from the jaw-bearing level is restricted to two lowermost lower Toarcian ammonite zones [22]. Our observations on the belemnite distribution across the succession confirm Repin's statement [12] on the first occurrence of belemnites within the 'Pliensbachian'.…”

“…Although the lowermost part of black shales throughout the Vilyui River basin lacks ammonites, the age of the studied unit can be deducted through bivalve occurrences, as Kedonella mytileformis collected from the jaw-bearing level is restricted to two lowermost lower Toarcian ammonite zones [23]. Our observations on the belemnite distribution across the succession confirm Repin's statement [22] on the first occurrence of belemnites within the 'Pliensbachian'. Near the top of the Tyung Formation, there is a level with poorly preserved belemnite rostra of the genus?…”