Carbonate Recrystallization on the Campbell Plateau: Preliminary Results from IODP Site 378-U1553

Abstract:

The sulfur isotope composition of carbonate associated sulfate (CAS) can be utilized as a tracer of the marine sulfur cycle provided the impact of diagenesis is limited. Previous studies suggest early diagenesis can alter the sulfur isotopic composition of CAS if the pore water value deviates significantly from the seawater composition when the carbonates precipitated. This alteration is tied to 1) rapid recrystallization rates in young carbonate sediments and 2) significant deviations between the CAS and pore water sulfur isotope values. This study analyzes the sulfur and oxygen isotope composition of coeval carbonate sediment and pore water samples recently recovered during International Ocean Discovery Program (IODP) Expedition 378 at IODP Site 378-U1553 on the Campbell Plateau to evaluate the extent of carbonate diagenesis at the Site and the potential for a long-term CAS sulfur isotope record of the Paleogene. Including both bulk carbonate sediment and pore waters provides insight into the changes in the water and sediment chemistry as well as their interactions. IODP Site 378-U1553 differs from previous CAS study areas due to the presence of an approximately 26-million-year unconformity at approximately five meters below the seafloor. This places these sediments above the preliminary estimate of the modern redox front approximately 20 mbsf. The position of these sediments within the redox zone suggests carbonate recrystallization or redox reactions could drive alteration in the CAS or other carbonate-based proxy records. This study represents a preliminary dataset which will be incorporated into a comprehensive study of carbonate diagenesis at IODP Site 378-U1553.