Multi-phases of Coral Reef Development in the Late Pliocene (3.6–2.6 Ma) Along the Gulf of Papua Shelf Edge: Potentially Excellent Reservoir for Oil and Gas Generated in the Underlying Upper Slope Prograding Organic-rich Lowstand Muddy Sequences.
Along low-latitude mixed siliciclastic/carbonate continental shelf edges, onset of rapid sea-level rise during early deglaciations, when siliciclastics were deposited along newly formed coasts at updip positions, provided opportune time windows for coralgal communities to establish themselves on top of maximum lowstand siliciclastic coastal deposits. The last transgression since the Last Glacial Maximum corresponds to the high-amplitude reflections observed on today's outer shelf and relict drowned coralgal reefs, 60 to 80 m in height, along the modern shelf edge itself. In spite of the huge siliciclastic influx into the Gulf of Papua (GoP) during the late Pliocene (3.6–2.6 Ma), short-lived reefal platforms and barriers were able to establish and grow along the GoP shelf edge during intervals of high-amplitude sea-level transgression. These early transgressive reefs, growing on the shelf edge or in the outer-shelf environments, therefore remained relatively short-lived carbonate systems, but excellent markers for sea level transgression and highstands, and potentially excellent reservoirs for oil and gas, generated in the underlying upper slope prograding organic-rich lowstand muddy sequences. Systematic progradation of siliciclastic sediments during the Pliocene is observed in particular in the southwestern part the GoP. In the “mid Pliocene”, an aggradation component was added to the progradation for each of the last five late Pliocene sedimentary sequences, marking an overall relative sea-level transgression during this particular interval of the late Pliocene (∼3.3–2.9 Mya). The rollovers or outer-shelf– shelf-edge environments of the late Pliocene prograding and aggrading sequences are characterized by high amplitude reflections and mounded seismic facies, especially in the three youngest sequences (“Mid Pliocene” ∼3.0 Mya). During this interval, the mound-like edifices were replaced by several-kilometer-wide positive flattop features of high relief, which were undoubtedly small, short-lived carbonate platforms or barrier reefs lining up shelf edge.
AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014