Palynostratigraphy of the Lower-Middle Jurassic deposits, borehole section Vostok 4 (Southeast of West Siberia)

An Early Jurassic age for the Puchezh‐Katunki impact structure (Russia) based on40Ar/39Ar data and palynology

“…The restriction to the Pliensbachian is based on the co‐occurrence of P. asaccatus and Lycopodiumsporites subrotundus , with the latter seemingly having its first occurrence in the Pliensbachian (Goryacheva ; Ilyina ). The assemblage from core 17 also contains Lycopodiumsporites marginatus (first occurrence late Pliensbachian; Goryacheva ), which indicates a late Pliensbachian maximum and early Aalenian minimum age. However, one of the problems with Early Jurassic palynostratigraphy of Russia is the general lack of successions older than Pliensbachian.…”

“…The listed assemblages from the brecciated Neoproterozoic to Lower Triassic rocks on the northeastern slope of the central uplift, as well as from the allogenic breccias in core 17 (located in the northeastern part of the central depression) suggest a maximum–minimum age of early Pliensbachian–early Aalenian (approximately 191–170 Ma), but are most likely restricted to the Pliensbachian (approximately 191–183 Ma). This is based primarily on the obtained composite range for Paleoconiferus asaccatus , which has a common occurrence in Hettangian to early Pliensbachian strata, with only rare occurrences in late Pliensbachian to early Aalenian strata, and is absent from younger Jurassic assemblages (Goryacheva ; Ilyina , ; Jaroshenko ). The restriction to the Pliensbachian is based on the co‐occurrence of P. asaccatus and Lycopodiumsporites subrotundus , with the latter seemingly having its first occurrence in the Pliensbachian (Goryacheva ; Ilyina ).…”

“…). Therefore, the present re‐evaluation of the palynology of the Puchezh‐Katunki impact structure is based on an interpolation of stratigraphic ranges of selected spore‐pollen taxa from independently dated (ammonites and dinoflagellate cysts) palynozonations in western Siberia (Ilyina ; Goryacheva ) and northwestern Europe (Batten and Koppelhus ), as well as spore‐pollen floras from Caucasus (Jaroshenko ). A few Middle Jurassic assemblages from the Russian Platform (Dobrutskaja ; Rostovtseva , ) have also been taken into account.…”

“…This approach is in many respects fundamentally different from the standard form taxonomy normally used for Jurassic spores and pollen in Europe (e.g., Batten and Koppelhus ). For this reason, we carefully re‐evaluated the photographs and sketches of the specific taxa in the original publications by Bolkhovitina (, ), and the ones published in subsequent papers by other authors (e.g., Jaroshenko ; Ilyina , ; Goryacheva ).…”

“…Lower Jurassic to lower Middle Jurassic strata are generally missing on the Russian platform, with shallow marine, coastal, and terrestrial strata of Bajocian and Bathonian age commonly comprising the oldest Jurassic rocks in the region (Mitta et al 2012). Therefore, the present re-evaluation of the palynology of the Puchezh-Katunki impact structure is based on an interpolation of stratigraphic ranges of selected spore-pollen taxa from independently dated (ammonites and dinoflagellate cysts) palynozonations in western Siberia (Ilyina 1985;Goryacheva 2011) and northwestern Europe (Batten and Koppelhus 1996), as well as spore-pollen floras from Caucasus (Jaroshenko 1965). A few Middle Jurassic assemblages from the Russian Platform (Dobrutskaja 1968;Rostovtseva 2013Rostovtseva , 2014 have also been taken into account.…”