Oceanographic currents, differential subsidence, and physiography control three-dimensional clinothem growth in the Gulf of Papua, Papua New Guinea

Abstract

A regional high-resolution CHIRP seismic survey in the Gulf of Papua (GoP) extends the geographic scope of previous studies by 125 km and reveals that the Holocene clinothem along-margin geometries, surfaces of lap, and steepness of foreset slopes appear less dependent on eustatic sea level changes and sediment supply than previously suggested. Clinothems imaged by CHIRP profiles and sampled by sediment cores include two older, relict clinothems and a younger Holocene clinothem divided into three units by two surfaces of lap. New radiocarbon ages from this study establish that depositional timing is more recent than previously proposed for the transgressive deposits, the Holocene clinothem units, and surfaces of lap. While previous ages suggested that observed stratal relationships could coincide with meltwater pulses or sea level stillstands, the younger ages from this study question these results and suggest the dominant control on Holocene clinothem architecture may be inherited physiography, SW-NE differential subsidence, along-margin currents, and seasonal variations in wave energy. Inherited physiography underlying the Holocene clinothem consists of valleys incised during relative lowstands of Marine Isotope Stages (MIS) 4 and 2. Valleys in the relict clinothem potentially served as across-margin conduits for an older Holocene clinothem unit. After the older Holocene unit filled valleys and accommodation, younger Holocene units preferentially grew along- rather than across-margin as bottom shear stresses increased. Relict clinothems have undergone differential subsidence since deposition due to foreland basin loading, which has engendered more accommodation in the northeast GoP that systematically decreases toward the southwest. Areas with less accommodation are more likely to experience toplap as they are exposed to increased shear stresses. Therefore, the surfaces of lap are caused by interactions between accommodation and oceanographic currents. Examining stratal relationships along the Holocene clinothem has broad implications for sequence stratigraphy, as many clinothems exhibit a three-dimensional stacking pattern. Measurements of seafloor slopes yield complicated results, illustrating that seafloor steepness within lobes is influenced by a complex interplay of accommodation, sediment supply, underlying physiography, and oceanographic currents. This suggests that clinothem architecture in the GoP cannot simply be interpreted as a rate-related problem between rates of sediment supply and relative sea level.