Paleocene methane seep and wood-fall marine environments from Spitsbergen, Svalbard

•We describe Paleocene shallow water seep and wood-fall environments from Spitsbergen.•Both seep and wood-fall faunas are heavily dominated by thyasirid bivalve Conchocele.•The associated species are mostly shallow water background molluscs.•Paleocene seep and wood-fall environments from Spitsbergen spatially overlapped.•They are most comparable to Recent forest litter accumulations in New Zealand fiords.

Here we describe a Paleocene-aged methane seep locality and an associated layer of sunken wood, from Fossildalen on Spitsbergen, Svalbard, hosted in offshore to prodelta siltstones of the Basilika Formation, Van Mijenfjorden Group. The fossiliferous seep carbonates were first identified in museum collections from expeditions in the 1920s and 1970s, and subsequently sampled as ex-situ blocks in the field in 2015. The isotopically light composition (δ13C values approaching − 50‰ V-PDB), and characteristic petrographic textures of the carbonates combined with the isotopically light archaeal lipids are consistent with their formation at fossil hydrocarbon seep environment. The invertebrate fauna within the carbonates is of moderate diversity (17 species) and has a shallow water affinity. Wood specimens within the carbonates contain the borings and shells of wood-boring bivalves. The seep fauna is dominated by a species of the thyasirid genus Conchocele, common to other seeps of similar age. The data shed new light onto the history of methane seepage on Svalbard, and the evolution and ecology of seep and wood-fall faunas during the latest Cretaceous–earliest Paleogene time interval.