Relationships Between Early Diagenetic Processes, Carbon Remineralization, and Sedimentary Dynamics in the Gulf of Papua Deltaic Complex

A range of diagenetic environments is found within the central Gulf of Papua clinoform, each characterized by different balances between sedimentary dynamics, net accumulation, physical and biogenic transport processes, and biogeochemical properties. Sediments are generally diagenetically reactive, with Σ CO₂ production and benthic O₂ fluxes typically ranging between 10 - 40 mmol / m² / d (upper 20 cm). Highest remineralization rates occur within mobile inner topset and channel muds (1-20 m depth) and in the high accumulation rate rollover region of the topset - foreset beds (40-50 m). Lowest rates are found inshore along sandy channels, middle topset, and the deeper foreset (75 m). Topset deposits are typically suboxic, nonsulfidic over the upper ∼0.2 - 1 m, due to various combinations of physical reworking and deep bioirrigation. Pore water sulfate can be measureably depleted at depths > 0.3 m, however dissolved sulfide remains below detection (upper ∼1-2 m). Sedimentary C / S ratios are ∼4 - 6 within the topset regions but decrease to < 3 in offshore foreset beds and inshore mud banks where sulfidic diagenesis dominates. Remineralization patterns are independent of relative abundance of terrestrial or marine sedimentary carbon, both are efficiently remineralized. C_org isotopic analyses (^13,14C) demonstrate that although terrestrial sources can be primary substrates at inshore sites, young marine C_org preferentially dominates pore water Σ CO₂ relative to bulk C_org in the upper foreset A small quantity of young, rapidly recycled marine organic material is often superimposed on a generally older, less reactive terrestrial background.