Site surveys conducted in conjunction with Leg 130 on the Ontong Java Plateau reveal a strong seismic reflector at 0.8 to 1.0 s below the seafloor that drilling at Sites 803 and 807 confirmed is Cretaceous basalt. This reflector is generally smooth, except for the northeastern margin of the plateau, where it forms a series of small, irregularly shaped depressions. Correlatable reflectors present at the bottom of the depressions are also present on the adjacent highs, suggesting that these depressions are original volcanic topography. A strong sub-basalt reflector occurs on many seismic profiles on the northeastern portion of the plateau. This reflection may be caused by a density and velocity contrast between pillow lavas and flood basalt flows or it may result from interbedded sediment and thus may represent significant lulls in volcanic activity. The presence of sub-basalt reflectors near Site 803 may indicate that later volcanic episodes occurred there, in contrast to Site 807, where this reflector was not observed and where older basalt ages were obtained.
Center for Coastal and Ocean Mapping Affiliate
International Ocean Discovery Program
Proceedings of the Integrated Ocean Drilling Program
Hagen, R.A., Mayer, L.A., Mosher, D.C., Kroenke, L.W., Shipley, T.H., and Winterer, E.L., 1993. Basement structure of the northern Ontong Java Plateau. Proceedings of the Ocean Drilling Program: Scientific Results, vol. 130, pp. 23-31.