泰国湾第四纪准层序建造及气候控制的旋回性

Climatically-driven cyclicity in the Quaternary of the Gulf of Thailand

泰国湾第四系显示出很好的旋回性。通过高分辨率二维地震(布玛)剖面图及工程钻井资料,共识别出8个准层序。在典型准层序中,沉积物自下而上,从海相泥沉积逐渐过渡为泛滥平原沉积。在每个准层序顶部都发育下切河体系及古土壤层,说明在每个准层序形成之后,都曾暴露过地表并遭受到侵蚀。每个准层序都代表一个海进和海退的过程。这些准层序的厚度为6～22m不等,平均厚度13m左右。通过与第四纪氧同位素曲线对比得出,这8个旋回的形成年代可追溯到距今730～10ka,平均91ka为一个循环周期,表明这些旋回应该是由气候因素所驱使的海平面升降导致的。该频率的气候变化周期相当于Milankovitch旋回中地球围绕太阳运动椭球体偏心率的变化周期,因此,在更早的地质历史时期中,类似的旋回也应该存在,并具有全球可对比性。

The Quaternary in the Gulf of Thailand shows well-developed cyclicity. Eight parasequences have been identified by using high resolution 2D seismic （Boomer） profiles and engineering boreholes. Sediments change from marine mud to floodplain deposits from the bottom to the top of a typical parasequence. Incised fluvial systems and soil crust developed on top of each parasequence, which may indicate a significant subaerial exposure period after construction of each parasequence. Each parasequence represents a cycle of marine transgression and regression. The thickness of these parasequences varies from 6 to 22 m, with an average about 13 m. By correlating to the Quaternary oxygen isotope curve, the eight cycles are dated 730 to 10 ka, with an average 91 ka of periodicity, which suggests that these cycles should be caused by climate driven sea level oscillations controlled by eccentricity cycles discovered by Milankovitch. These kinds of cycles should exist in earlier geological history and should have global impact.