EARLY DIAGENETIC EVALUATION OF STABLE STRONTIUM ISOTOPES IN SHALLOW CARBONATE SEDIMENTS

The stable strontium isotope composition of carbonate has emerged as a promising proxy for carbon cycling in both modern and ancient oceans. However, the behavior of the Sr isotope system during diagenetic processes remains under-constrained, hampering broader application of this proxy system. In this contribution, we present stable Sr isotope (δ88Sr) and other geochemical data for carbonate sediments from two Bahamian shallow cores. The two cores represent different carbonate compositions and depositional settings—one was collected from a lagoonal environment and is composed of coarse-grained allochthonous limestone (from rudstone to floatstone), whereas the other was collected from the Great Bahamas Bank platform and is composed of oolitic grainstone. Sediments from different depths as well as associated porewaters were analyzed. We found that the mean value of δ88Sr in the carbonate sediments are 0.2‰ lower than that of the porewater. Although porewater δ88Sr values increase and then decrease with depth, sediment δ88Sr values appear to be decoupled from porewater variation. Moreover, the sediments from different cores yield distinct mean δ88Sr values, likely reflecting different sediment compositions associated with the two depositional environments.