Tithonian and Lower Berriasian calpionellid against ammonite biostratigraphy of the Dvuyakornaya Formation in eastern Crimea

The Dvuyakornaya Formation in eastern Crimea of late Kimmeridgian to Berriasian age represents a thick flysch-like succession of clays, marls and less common limestones. The ammonite zonation includes incomplete record from the Beckeri Zone in the uppermost Kimmeridgian up to the Jacobi Zone in the Lower Berriasian. Two main sections have been micropalaeontologically studied – the Dvuyakornaya Buhta and the Cape Svyatogo Ili’i. Eighteen calpionellid species of the genera Longicollaria, Chitinoidella, Daciella, Dobeniella, Popiella, Praetintinnopsella, Tintinnopsella, Crassicollaria and Calpionella have been found. The calpionellid zones Chitinoidella (with Dobeni and Boneti subzones), Crassicollaria and Calpionella (with Alpina and Elliptica subzones) are described and directly correlated to the existing ammonite biostratigraphy. The Dobeni Subzone corresponds to a part of the barren interval between the ammonite Hybonotum and Microcanthum zones, the Boneti Subzone – to the Microcanthum Zone, and the Crassicollaria Zone – to the Durangites Zone p.p. and Jacobi Subzone p.p. The boundary between the Crassicollaria and Calpionella zones is within the Jacobi Subzone. In the Berriasian, the Alpina Subzone has been correlated to the Jacobi and Grandis subzones, and the Elliptica Subzone – to upper part of the Grandis Subzone that was characterized in the Dvuyakornaya Formation by diverse ammonite faunas of the “Feodosiya Marlstones”. Chitinoidellids of the Dobeni Subzone for the first time determine late Early Tithonian age in the area. Calpionellid to ammonite correlation of the Dvuyakornaya Formation is discussed in the light of previous direct correlations between macro- and microfossil biostratigraphy of the Tithonian and the Lower Berriasian in the Tethyan Realm.