Reconstructing an early Albian (Cretaceous) marine food web by employing macrofossil δ 13 C carb data

Abstract

Abstract Stable isotope data (δ 13 C, δ 18 O, 87 Sr/ 86 Sr) from fossil carbonate shells are widely used throughout the Phanerozoic for stratigraphic dating and palaeoenvironmental reconstructions. The incorporation of δ 13 C carbonate (δ 13 C carb ) is controlled by various factors, making its interpretation ambiguous. The analysis of co-occurring pristine carbonate-shelled organisms, which occupied different ecological niches during their lifetimes, will help to better understand the effect of biological parameters (food sources, biofractionation) on the carbonate composition. We have studied the geochemistry (elements, δ 13 C carb , δ 18 O carb , 87 Sr/ 86 Sr) of eight well-preserved macrofossils (corals, oysters, gastropod, ammonite, belemnites) of earliest Albian age (112 Ma). The up to 5‰ variation in δ 13 C carb values from the aragonitic and calcitic skeletons of these organisms with different feeding strategies (primary, secondary, tertiary consumers) was used to reconstruct a food-chain. The exceptional low δ 13 C carb values of belemnites are explained by the incorporation of larger amounts of metabolic carbon into the skeletons of these active predators. The findings suggest that the δ 13 C carb signal of the different organisms is controlled by (1) their food source and (2) subsequent biofractionation. The here discussed approach to interpreting δ 13 C carb data may help in the future to reconstruct past food-webs.