Reduced sediment accumulation rate enhances early marine diagenesis of periplatform sediments

Abstract Early marine diagenesis can alter the δ 13 C values of carbonate sediments in the marine environment, hindering interpretations of changes in global carbon cycling through geological time. In this study, the influence of sediment accumulation rate on the localisation and intensity of diagenetic alteration in the marine burial environment is documented. New measurements of δ 18 O and δ 13 C values of bulk carbonate sediments as well as siliciclastic and total organic carbon content were conducted on Holocene–Pleistocene aged sediments collected by Ocean Drilling Program Leg 133 on a proximal–distal transect on the slope adjacent to the Great Barrier Reef. Significantly lower bulk carbonate δ 13 C values and total organic carbon content were found to occur during periods of reduced sediment accumulation, but sediments in these intervals lack obvious sedimentological evidence of alteration, like the development of hardgrounds. New findings suggest that changes in sediment accumulation rate may explain large, asynchronous changes towards lower stable carbon isotope values of marine carbonates deposited in oxygenated slope settings in the geological record. Based on these results, periods of reduced sediment accumulation rate are proposed to enhance diagenetic reactions by providing continued access to oxidants. Alteration during periods of low sediment accumulation rate is likely to be exacerbated in settings containing mixed siliciclastic‐carbonate sediments. Finally, while this new observation indicates that subtle early marine burial diagenesis can obscure records of the global carbon cycle preserved in periplatform sediments, new insights may prove useful in constraining the dynamic nature of sedimentation patterns in slope environments through Earth history.