西沙群岛埋藏较浅的新近系白云岩主要发育在风化壳之下,沉积时处于海平面下降旋回,白云石化作用受海平面变化的控制.白云石化层段对应较低的温度和较高的盐度,冰期导致海平面下降并致海水浓缩,由此引起白云石化作用.冰期/间冰期的交替引起海平面变化并导致海水的性质周期性改变,最终引起白云石化作用也周期性地发生,从而导致白云岩与石灰岩周期性叠置.将新近系白云岩与古老层系白云岩的成因对比分析认为:通常认为的大面积分布的古老层系埋藏成因白云岩可能是准同生期因海水浓缩而形成的,只是遭受了埋藏流体改造而显示出埋藏白云石化特征.研究发现,西沙群岛新近系风化壳之上的石灰岩与风化壳之下的白云岩,孔隙类型及孔隙度几乎完全一样.

Dolostones in palaeostrata suffered complex diagenesis, so the origin of dolomization has been a multiple solution problem. Core samples of the shallow-buried Neogene dolostones from drilled wells in the Xisha Islands, South China Sea, is chosen for studying the origin of dolomization to presume upon some revelation for the dolomization in palaeostrata. It is shown that the dolostones develop under the weathering crust, which means they were in the cycles of sea level decline during deposition, and it is proved that dolomization is controlled by periodic global eustasy. The fact that the beds with dolomitization correspond to relatively low palaeotemperature and relatively high palaeosalinity of seawater reveals that glacial periods lead to sea level declines and lead to seawater condensation, which brings about the dolomization. The alternating glacial/interglacial periods bring in sea level changes which lead to periodical changes of seawater nature and accordingly periodical dolomization to take place. That is the reason why there are the situations of periodical dolostone/ limestone superposition in the Xisha Islands. By correlating the origin of dolostones in Neogene strata with that of dolostones in palaeostrata, it is enlightened that the so-called burial dolostone distributed extensively in palaeostrata should be derive from penecontemporaneous dolostone that has suffered burial fluid reformation due to seawater condensation so that they exhibit the characteristics of burial dolostone. It is discovered also that the limestones above weathering crusts are of almost same pore type and porosity with the dolostones under weathering crusts in the Xisha Islands.