Petrological and geochemical investigations of deep sea turbidite sands in the Pandora and Moresby Troughs: Source to Sink Papua New Guinea Focus Area

Abstract

The Moresby and Pandora Troughs of the northern Coral Sea are components of the deep-sea depositional system that is the ultimate sink for the Source to Sink Papua New Guinea (PNG) Focus Area. Cores collected from the R/V Melville during March-April 2004 reveal marine volcaniclastic and terrigenous turbidites deposited in these troughs during the Quaternary. Constraining the spatial, temporal, and provenance characteristics for these terrigenous sands through mineralogical, chemical, and textural analysis is the primary focus of this study. All cores contain thinly-bedded sandy turbidite packages interlayered with hemipelagic marls and typical centimeter-to-meter-thick turbidite sequences. The Moresby Trough core JPC22 appears to be generally finer-grained then the Pandora trough core JPC 66. Typical QFL percentages from JPC22 are 13:65:23, respectively, and plagioclase/ total feldspar ratios are near 0.90. These basal turbidite sands contain well-preserved rhyolitic pumice fragments and glass shards, with phenocrysts of amphibole, plagioclase, biotite, pyroxene and oxides. Typical QFL percentages from Pandora Trough core JPC66 are 69:14:17, and plagioclase / total feldspar ratios are near 0.47. These basal turbidite sands are predominantly quartzofeldspathic with a significant amount of heavy minerals (zircon, amphibole and oxides). The contrast in submarine sand mineralogy and mineral chemistry between 66JPC and 22JPC reflects distinct sedimentary sources composed of both fluvial and volcaniclastic material. The Moresby Trough has received secondary monomagmatic volcaniclastic turbidite sands derived mostly from volcanic/collision margin highlands of SE PNG, and the Pandora Trough has received quartzo-feldspathic sands from the Fly/Strickland system, more akin to a trailing-edge margin. Mineral textures and chemistry suggests minimal associations between sand bodies, and may represent isolated basins controlled by complex sea-floor bathymetry and episodic turbidity flows from diverse sources. The signature of the adjacent submarine fan deposits may aid the interpretation of continental margin growth as a function of sediment flux, sediment source, and dispersal pathways. These deposits may also give insight into the evolution of volcanic island arcs on longer time scales. This investigation concludes that the Pandora and Moresby trough turbidite sand bodies record varying sediment sources and somewhat isolated volcanic events contributing to the evolution of the southern PNG continental margin.