AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Source-to-Sink Sediment Delivery in the Gulf of Papua from SEM-MLA-aided Provenance and Textural Analysis of Turbidite Sands
(1) Earth Sciences, Memorial University of Newfoundland, St John's, NF, Canada.
(2) Geology and Geophysics, Louisiana State University, Baton Rouge, LA.
Provenance of Pleistocene-Holocene deepwater sediments in the Gulf of Papua (NSF Source to Sink Focus Area) has been studied to understand glacio-eustatic influences on sedimentary routing, and to develop a modern analog of dynamic processes controlling sediment sources and delivery. Turbidites were sampled in seven jumbo piston cores from the slope and basin floor, yielding 53 sand samples. A quantitative detrital compositional analysis was conducted using scanning electron microscopy (SEM) and mineral liberation analysis (MLA) of ~15,000 individual grains per sample, with a minimum grain diameter limit of 3.9 µm. Tests using the Gazzi-Dickinson ternary diagram show a lack of differentiation among samples. Although free from grain-size effects, use of this diagram is strongly affected by the detailed mineralogical classification that results from automated MLA. MLA allows identification of multiple mineral grains within larger particles, which, with felsic minerals, tends to increase the quantity of monocrystalline quartz over standard manual methods, shifting plots into more quartz and feldspar rich fields. MLA does allow sample differentiation using mafic/felsic ratios, and content of pumice and heavy minerals.
Time-sliced provenance based on our C-14 age model shows three major pathways: (1) long-distance NW-SE sediment transport of quartzo-feldspathic sand sourced from the Papuan Mainland, delivered from the Fly-Strickland fluvial system through Pandora shelf and slope (core MV-54), Pandora basin floor (cores MV-23, 33) and Moresby Channel (MV-25, 29); (2) short-distance transport of felsic-mafic volcanic sand apparently from the collision margin of the Papuan Peninsula, delivered via small rivers narrow shelf, and deep-sea canyons (MV-22); and (3) intermediate-distance delivery from the Fly-Strickland and Papuan Peninsula along coastal pathways to the Moresby Trough (MV-22). The vertical provenance pattern shows that the Pandora Trough samples (MV 23, 33, 54) were entirely pathway 1 during the time period 44-17 Ka, while Moresby Trough received sediment via pathway 1 (MV-25, 29) and pathway 2 (MV-22), gradually shifting to pathway 3 from late Pleistocene to the middle Holocene. We also suggest that the Gazzi Dickinson scheme be re-evaluated in light of powerful new automated MLA techniques, to allow better sample discrimination in fine-grained lithic and felsic sands typical of our study area, and many other deep-water depocenters.