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Several thousand meters of Miocene-Pliocene sediments are predominantly fine to coarse-grained volcaniclastics deposited in shelf to deep marine environments, commonly as turbidites; coralgal reef limestones and fore-reef calcarenites formed locally. Original basins in both the Solomons and New Hebrides measured 375 to 435 mi (600 to 700 km) by 62 to 125 mi (100 to 200 km) but parts of their margins are strongly deformed, uplifted, and eroded. Cross-faulting and Holocene volcanism caused segmentation and further reduction of basinal areas. In both island arcs, the sediments are little deformed along a median structural basin which was downfaulted in Pleistocene to Recent time in the Solomons, and from Pliocene onward in the central New Hebrides; no downfaulting occurred i the northern New Hebrides.
Little is known of hydrocarbon source potential and degree of maturation. Back-reef or rapidly buried fore-reef environments may be the principal areas for source rock formation. Reefal limestones are the main potential reservoir rocks; they have, however, lost porosity locally because of recrystallization. Turbidite sandstones may form additional reservoirs, but volcanic derivation keeps permeability generally low. The main structural traps are fault-controlled near basin margins, but limited folding also occurs. The pre-Pliocene unconformity in the northern New Hebrides could generate stratigraphic traps. Water depth in the main prospective areas is several hundred to 5,000 ft (1,500 m) in the Solomons, and up to 10,000 ft (3,000 m) in the New Hebrides. Nearshore and onland prospect are extremely limited in both island arcs.
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