Stable carbon and oxygen isotope-based sclerochronology of bivalve mollusk shells from the Upper Cretaceous (upper Campanian) Coon Creek Formation in Tennessee, USA: Implications for paleoecology and paleoenvironment

Abstract

Stable carbon and oxygen isotope-based sclerochronology was carried out on well-preserved fossil shells of bivalve mollusks Crassatella vadosa and Cucullaea vulgaris from the Upper Cretaceous (upper Campanian) Coon Creek Formation in Tennessee, USA, to reconstruct their life-history traits and sedimentary settings on an intra-annual time scale. The δ13CShell values along with the shell growth showed the cyclic variation with downward convex to lower value, likely reflecting the seasonal cycle of ambient seawater dissolved inorganic carbon (DIC) or metabolism of the bivalve or both. The δ13CShell cycles were largely associated with the strong growth disturbance lines, supporting hypothesis that the growth lines were formed annually. We estimated the ages of the shells based on both δ13C cycle or the growth cessation line. The modeled relationship between age and shell growth showed that Cr. vadosa and Cu. vulgaris grew up to about 40 mm at 7 years old and about 65 mm at 10 years old, respectively. The paleotemperatures estimated from the δ18OShell profiles of the examined specimens ranged from 16.2 °C to 24.2 °C and from 18.8 °C to 27.0 °C when assuming the bottom seawater δ18O to be −1.00‰ and −0.46‰ (VSMOW), respectively, and showed no clear seasonal cycle. The bottom seawater temperatures reconstructed from the specimens of the two bivalve species were lower than the near-surface seawater temperatures (29.0–30.6 °C) estimated from the planktic foraminiferal δ18O. We inferred that the benthic bivalve habitat of the Coon Creek Formation was at least 10 m or deeper below the thermocline.