重建南海27Ma以来高分辨率碳酸盐补偿深度

High-resolution reconstruction of carbonate compensation depth in the South China Sea since 27 Ma

新生代海洋碳酸盐补偿深度(CCD)的重建长期受到学术界的广泛关注。本研究以南海14个站位20个钻孔的综合大洋钻探计划(IODP)物质数据与年龄-深度模型,恢复了对应钻孔的古水深,计算了碳酸盐累积速率(CAR),基于线性回归的方法,重建了南海27 Ma以来CCD变化。研究结果显示:南海在海盆拉张形成期(27~18 Ma)出现了CCD超过2000 m大幅度的下降;在随后的中中新世气候适宜期(MMCO)期间,南海CCD出现800 m变浅。8 Ma以来南海CCD演化和赤道太平洋的演化呈现了不同的演化趋势:前者在3500~4000 m范围内波动,后者则从4000 m持续下降到4500 m左右。27 Ma之前,广泛的陆源输入和上升洋流发育导致南海出现浅的CCD。27~18 Ma时期的构造拉张导致的海盆加深,同时上升洋流减弱,被解释为该时期CCD下降的主要因素。MMCO期间气候驱动下的海平面波动导致了碳酸盐沉积核心区域的变化,是造成CCD波动的重要原因。8 Ma以来南海和太平洋CCD的差异演化是太平洋底水与南海底水的交换不畅的结果。

The reconstruction of carbonate compensation depth(CCD)in the Cenozoic Ocean has been a focus of attention from the academic community.In this paper,based on the IODP(Integrated Ocean Drilling Program)substances data and age-depth models from 20 boreholes at 14 sites in the South China Sea,the paleo-water depths in the boreholes were restored,the carbonate accumulation rate(CAR)was calculated,and CCD changes in the South China Sea since 27 Ma were reconstructed using linear regression method.Results showed that CCD in the South China Sea significantly decreased by more than 2000 m during the basin stretching period(2718 Ma),while during Middle Miocene Climate Optimum(MMCO)it became shallower by 800 m.Since 8 Ma,CCDs in the South China Sea and the equatorial Pacific Ocean exhibited different evolutionary trends,with the former fluctuating between 35004000 m and the latter continuing to decline from 4000 m to~4500 m.Prior to 27 Ma,extensive terrigenous input and development of upwelling led to shallow CCD in the South China Sea.The deepening of the sea basin and the weakening of the upwelling caused by tectonic tension during 2718 Ma were interpreted as the main factors contributing to the decline of CCD during this period.Climate-driven sea-level fluctuations during MMCO led to changes in the core region of carbonate deposition,which was an important reason for CCD fluctuations.The differential evolution of CCD in the South China Sea and the Pacific Ocean since 8 Ma was the result of poor bottom water exchange between the Pacific Ocean and the South China Sea.