A Dactylioceras – Meleagrinella (Clathrolima) assemblage from the Agardhbukta (eastern coast of Spitsbergen): a first in situ Toarcian molluscan occurrence from Svalbard providing interregional correlation

Diverse microfossil assemblages characterise the Lower Jurassic deposits on Svalbard, but until recently nearly all Lower Jurassic macrofossils from this region were known only from re-deposited phosphorite pebbles in the Brentskardhaugen Bed. Here, we briefly describe a unique in situ molluscan assemblage from the lower Toarcian part of the Agardhbukta section. This assemblage is dominated by ammonites (Dactylioceras only), while belemnites and bivalves are less common. Ammonites are typical for the Commune zone of the Arctic and belong to the new species Dactylioceras (D.) kopiki Rogov, sp. nov. and D. (Microdactylites) sp., and their findings are characteristic for a new kopiki biohorizon located in the top of this zone. Bivalves are dominated by Meleagrinella (Clathrolima) substriata providing additional evidence for the age of this assemblage. The pattern of ammonite and bivalve stratigraphical and geographical distributions in the Arctic suggest bilateral molluscan immigrations via the Greenland–Norwegian seaway during the latest early Toarcian: dactylioceratid ammonites migrated northwards, while oxytomid bivalves migrated southwards.