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GCR Display Cores

Section 143-866A-98R-1

Location

North rim of the summit of the Resolution Guyot in the western Mid-Pacific Mountains.

Lithology

77R-1 Massive Oolitic Grainstone.
110R-2 Algal laminates-alternating clay rich organic rich and carbonate mudstones. Rhytmic latering may be due to tidal cycles.
167R-3 Dolomatised Oncoidal Rudstone

Interpretation

The Western Pacific is strewn with chains and clusters of seamounts, many of which are now flat- topped guyots, with summit depths of about 1500 m, capped by shallow-water carbonate platform sediments overlying volcanic substrate. Guyot sediments can monitor subsidence rates and relative changes in sea level for times when upward carbonate-platform growth paced the tectonic subsidence of their foundations and the volcanic pedestals preserve clues to the nature of their parent mantle materials and the processes of melt extraction and differentiation. Studying the origin of these guyots contributes to the concepts of seafloor spreading, hot spots, thermal subsidence and crustal thinning, and superswells, and may determine why the platform, after constructing a massive carbonate cap, suddenly ceased to keep pace with subsidence and why the apparent ages of the underlying volcano and the shallow-water cap lack the coherent patterns predicted from hot-spot and subsidence theories. During Leg 143, six sites were drilled on Allison and Resolution guyots in the Mid-Pacific Mountains (MPM) (Site 865 to Site 868), on the sediment apron flanking the Wodejebato Guyot-Pikinni Atoll pair (Site 869), and within the lagoon of a modern Marshall Islands atoll (Site 870).