Deglacial Shelf Edge Coralgal Reef 19 ky Establishment, Successive 14.5 and 11.5 ky Partial Drowning and Back-stepping along the Papua New Guinea Peninsula Outer Shelf (Gulf of Papua)

Abstract:

During the last deglaciation, coralgal reefs established themselves on newly flooded continental shelf, accurately recording the stepwise character of the deglacial sea level rise (meltwater pulses). This study, conducted along the Papua New Guinea Peninsula outer shelf (Gulf of Papua), focuses on the analyses of a Calypso core, MD05-2945 (MD-45), and the interpretation of seismic lines obtained during the PECTEN (2005) and PANASH (2004) cruises aboard the R/V’s Marion Dufresne and Melville, respectively. Sediments and coralgal detritus were identified, analyzed, and dated with AMS radiocarbon and U/Th.

The seismic lines illustrate the establishment of reefal edifices directly on top of a lowstand shelf edge delta, shrinking through time towards the southeast by partial drowning and back-stepping. MD-45 sampled the reef that thrived during the 19 ky meltwater pulse. At its base, a 19.3 kyr BP-old coral colony (Faviid Goniastrea), part of a shallow/inter-tidal framework, was retrieved in living position at 111 mbsl. Then, a clear deepening/drowning pattern is observed; shallow Faviid Goniastrea framework coral is covered by debris from shallow/upper fore-reef corals (Faviids, Galaxeas, Acroporas), and lastly by encrusting/foliacious corals (Agariciids, Pectiniids, Montiporiids, Poritiids) and encrusting algae/digitate Microbialites. When the reef back-stepped 5 km to the SE where it continued to accreted to sea level, Sr/K (excellent proxy for reef derived detritus) drops dramatically and siliciclastics increase at 6 mbsf in MD-45. This coincides also with the end of the coralgal clasts within a well dated gasteropod-rich (Turritella cingulifera) interval (15-14.5 cal kyr BP), contemporaneously with the globally established MWP-1A. At 11.5 kyr, roughly synchronous with MWP-1B, a 3.5 m-thick 98% siliciclastic mud unit, interpreted as the onset of the Indo-Australian Monsoons, was abruptly deposited in MD-45, coinciding with an even more severe back-stepping of the reef towards the southeast.