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北部湾周围各类岩石露头的时代是从寒武纪到近代。北部湾的基底杂岩,由石炭纪的碳酸盐岩和下古生代的变质岩所组成。北部湾及附近地区包括三个构造单元:(1)华南—北越加里东褶皱带;(2)东南沿海华力西褶皱带;(3)越南印支褶皱带。北部湾是在白垩纪以后沉陷的,北部湾中堆积了5公里以上的第三纪沉积物。北部湾中部有一明显的+10毫伽的布格重力异常。这必与该处莫霍面深度较浅有关。近来在北部湾发现的天然气和石油可以表明那里有较大的油气回。
Various types of rock outcrop around the Beibu Gulf were from Cambrian to modern times. The basement complex in the Beibu Gulf consists of carbonates from the Carboniferous and metamorphic rocks from the Lower Paleozoic. There are three tectonic units in the Beibu Gulf and its vicinity: (1) the South China-North Vietnam Gadong Fold Belt; (2) the southeastern Variscan Fold Belt; and (3) the Indo-China Fold Belt. The Beibu Gulf subsided after the Cretaceous, with more than 5 km of Tertiary sediments accumulated in the northern Gulf. There is a clear +10 milligram Bragg gravity anomaly in the central North Bay. This must be related to the shallow Moho depths there. The recent discovery of natural gas and oil in the Beibu Gulf can indicate a greater return of oil and gas there.