Distribution of ammonites, foraminifera and dinoflagellate cysts in the Lower Cretaceous reference sections of the Khatanga Basin, and Boreal Valanginian biogeography

Abstract

The ammonite, foraminifera and dinoflagellate cyst succession in the Boreal Berriasian and Valanginian of the Paksa and Boyarka reference sections in the Khatanga Basin, northern Central Siberia are calibrated with each other. The lowermost Boreal Berriasian Chetaites sibiricus ammonite Zone is difficult to distinguish from the two uppermost Volgian ammonite zones on the basis of foraminifera. Kutsevella pseudogoodlandensis Bulynnikova, Gaudryina gerkei Vasilenko and Haplophragmoides mutabilis (Bulynnikova) appear in the overlying Hectoroceras kochi ammonite Zone and occur together with abundant Lenticulina sosipatrovae (Gerke & Ivanova). Upper Berriasian foraminiferal assemblages are characterized by Ammobaculites gerkei Sharovskaya and Lenticulina gudinae E. Ivanova in the Paksa section in contrast to Lenticulina pseudoarctica E. Ivanova and Lenticulina rostriformis E. Ivanova in the Boyarka section.Big and long representatives of a variety of the dinoflagellate cyst Tubotuberella apatela (Cookson & Eisenack) together with Valensiella ovula (Deflandre) characterize the uppermost Volgian C. chetae and the lowermost Boreal Berriasian C. sibiricus ammonite Zones. V. ovula may also occur in high numbers in the overlying H. kochi Zone, but is less common above this. Prolixosphaeridium spissum (McIntyre & Brideaux) is rare, but may be restricted to early Betriasian and older beds. Systematophora palmula Davey is another rare species in these sections. It has been observed in the uppermost part of the H. kochi Zone. Gochteodinia villosa (Vozzhennikova) seems to appear close to the lower/upper Boreal Berriasian boundary in the area. Pareodinia borealis Brideaux & Fisher is consistently present in the Berriasian in contrast to the Valanginian in which it is rare and may occur only as a result of reworking.The lower Valanginian Neotellia klimovskiensis and Temnoptychites syzranicus ammonite Zones contain a foraminiferal assemblage with Reinholdella tatarica (Romanova) and Ammodiscus micrus Rylkova. Globulina praelacrima Mjatliuk appears in the upper part of the T. syzranicus Zone and characterizes the uppermost lower Valanginian Polyptychites michalskii ammonite Zone. The dinoflagellate cyst Gongylodinium acmeum Århus appears in the lower Valanginian and in some samples occurs together with common representatives of Cyclonephelium cuculliforme (Davies). Muderongia simplex Alberti, Heslertonia heslertonensis (Neale & Sarjeant) and Spiniferites sp. have been found from the P. michalskii Zone upwards, and Oligosphaeridium complex (White) appears close to the lower/upper Valanginian boundary.As in the Upper Jurassic the faunal distribution in the Valanginian allows a Boreal Realm to be distinguished which comprises three subrealms: Arctic, Boreal-Atlantic and Boreal-Pacific. The Arctic Subrealm may be divided into three provinces based on the distribution of ammonites: North Siberia, Urals Greenland Pechora and Chukotka-Western Canada. The foraminiferal fauna and dinocyst flora give little supporting evidence for distinction between these provinces. The Boreal-Atlantic Subrealm comprises a west and east European ammonite province whereas the Boreal-Pacific Subrealm is not subdivided.