Stable isotopic evidence for relative and eustatic sea-level changes in Eocene to Oligocene carbonates, Baldwin County, Alabama

Eocene to Oligocene marine carbonate shelf deposits in a continuous core in Baldwin County, Alabama, were evaluated within a sequence stratigraphic framework to determine characteristic stable isotopic responses to inferred fluctuations in sea level. The δ ¹⁸ O signature records eustatic sea level. δ ¹⁸ O becomes heavier as eustatic sea level falls and lighter as eustatic sea level rises. δ ¹⁸ O records a secular shift to heavy from the early Eocene to Oligocene of 3.0‰. The δ ¹³ C signature records relative sea-level change (paleobathymetry). δ ¹³ C generally becomes heavier in shallower water deposits and lighter in deeper water deposits. However, in planktonic oozes, δ ¹³ C may shift to heavy. δ ¹³ C also records a secular shift to heavy from the early Eocene to the Oligocene of 3.5‰. Although minor diagenetic perturbations in the stable isotopes are present, the depositional signal dominates the isotopic signal. -from Authors