Analysis of available geological'and geophysical materials including the results of deep-water drillings shows that up to the Middle Jurassic all the northwestern part of the Pacific mega-basin had formed a shallow sea basin in which intensive fracture outpouring of basalts occurred similar to the trappean provinces on continents. In the Late Jurassic the southern part of the study region started sagging and in the Cretaceous the entire region downwarped. The most intensive subsidence began in the Miocene and has been proceeding until today. The factual evidence disproves the significant horizontal movement in this region as claimed by plate tectonics. Dredged xenoliths and geological analogy to the adjacent regions, in particular to Mussau Trough, suggest that the bottom section of the Earth's crust ("Third Layer") consists of metamorphic rocks (epidote-amphibolite facies) and serpentinized intrusive rocks with an ultrabasic structure (metaultrabasite complex). Although the age of this complex cannot be determined with certainty due to the unreliability of the absolute age determination caused by secondary alteration, the basement complex differs considerably from the overlying gabbro-dolerite-basalt complex in its higher degree metamorphism and traces of plastic deformation, an indication that it is more ancient than the former (Paleozoic, and probably Pre-Cambrian).