Palaeoecology and diagenesis of bored wood from the London Clay Formation of Sheppey, Kent

Abstract

Fossil wood from the London Clay (Eocene) of Sheppey, Kent, UK is commonly bored by shipworms (Mollusca, Teredinidae). The morphology of the borings and their calcite linings are described, and the life history shown to comprise a boring (protrusive) phase followed by a retrusive episode in which a prismatic alcite lining and septa were deposited. Valves, pallets and pseudofaeces are preserved in the borings. After burial, the bored wood acted as centres of carbonate concretion formation. Concretion and burrow cement compositions, mineral associations and ∂ 13 C and ∂ 18 O stable isotope data indicate that precipitation principally occurred in the sulphate reduction zone. The tube cements are zoned with the two most abundant zones generally having the same composition as the cement filling the 2 sets of micro-fractures. It is inferred that sudden variation and fluctuations in cement chemistry may be a cosequence of sudden release of fluid by dewatering events, with gradual shifts in chemistry being controlled by evolution, through the oxic, Fe, Mn and S reduction zones. All teredinid tubes and cements have recrystallized by a dissolution: reprecipitation process which has preserved the earlier cement chemistry.