南海北部陆缘早侏罗世海平面变化的古盐度记录

Paleosalinity Records to Sea Level Change of the Northern Margin of the South China Sea in Early Jurassic

早侏罗世南海北部陆缘粤东地区发生大规模海侵。古盐度的变化记录了海平面的变化。反映古盐度变化的Sr/Ba和B/Ga比值与海平面升降有关,前者为正相关,后者为负相关。本区m曲线(m=MgO/Al2O3×100)与B/Ga曲线相似,但在幅度方面有差异。结合沉积充填序列、沉积环境、沉积相演变,确定了本区海平面变化经历了两次海侵和一次海退。早侏罗世南海北部陆缘构造背景相对活动,前陆再旋回造山带或前陆隆起成为物源区,海丰地区具有周缘前陆盆地的性质。古盐度记录揭示的海平面变化可能受古特堤斯闭合的影响。

A large-scale transgression occured in early Jurassic in the eastern Guangdong Province, the continental margin of South China Sea. The sea level change is recorded by the variation of paleosalinity. The ratios of Sr/Ba and B/Ga reflecting the paleosalinity changes are coincident with the sea level changes, the former is a positive correlation and the latter is a negative correlation. In this area, the curves of m （m = MgO/ Al2O3 100）values and B/Ga are similar but different in ranges. According to variation of paleosalinity together with the filling succession, evolution of sedimentary environments and facies, two transgressions and one regression for sea level change are recognized in this area. The tectonic setting of the northern margin of the South China Sea in early Jurassic was active relatively. The recycled foreland orogenic belt or the foreland uplift became the source provenance, and the basin developed in this region including Haifeng area had some characteristics of the peripheral foreland basin. The sea level change of early Jurassic revealed by the records of paleosalinity variation may be affected by the paleotethys closure.