ARCO Exploration and Production Technology Company, Plano, TX, United States

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. Due to a greater sampling density per unit of time, stable isotopes in this core reveal more defined trends than have previously been reported from DSDP/ODP (Deep Sea Drilling Project/Ocean Drilling Project) records and from more landward sections that have undergone intense subaerial alteration or erosion. The delta (super 18) O signature records eustatic sea level. delta (super 18) O becomes heavier as eustatic sea level falls and lighter as eustatic sea level rises. delta (super 18) O records a secular shift to heavy from the early Eocene to Oligocene of 3.0per mil. The delta (super 13) C signature records relative sea-level change (paleobathymetry). delta (super 13) C generally becomes heavier in shallower water deposits and lighter in deeper water deposits. However, in planktonic oozes, delta (super 13) C may shift to heavy. delta (super 13) C also records a secular shift to heavy from the early Eocene to the Oligocene of 3.5per mil. Although minor diagenetic perturbations in the stable isotopes are present, the depositional signal dominates the isotopic signal. Spar cements generally result in lighter delta (super 18) O and delta (super 13) C. If the dolomite is >20%, dolomitization results in heavier delta (super 18) O and delta (super 13) C.