Clinothem Lobe Growth and Possible Ties to Downslope Processes in the Gulf of Papua

Abstract:

The Gulf of Papua is fed by the large-floodplain Fly River and small mountainous rivers to the north, thus creating an ideal environment where end-member cases of river systems and their deltas (e.g. the large-floodplain Brazos River and the narrow-shelved Eel River) can be studied. Input from five rivers into the gulf has constructed a three-dimensional mid-shelf clinothem composed of three depositional lobes, with a central lobe downlapped by two younger lobes to the north and south. This geometry suggests that the three lobes are not syndepositional but rather that clinoform depocenters have shifted 60 km, thus bypassing adjacent accommodation. Newly examined CHIRP (Compressed High Intensity Radar Pulse) seismic lines and XRF analysis of piston cores from the 2004 NSF MARGINS program reveal distinct lobes offshore that exhibit increased complexity moving shoreward. Evidence of shoreward complexity and lobe interfingering cause us to question the originally proposed mechanism for depocenter shift involving circulation changes. An alternative hypothesis that stems from distinct lobe architecture farther offshore suggests that channelized downslope processes and nearshore storage may play important roles in lobe growth.