华南纳庆剖面早二叠世沉积记录对米兰科维奇旋回的响应

早二叠世晚期发生了显生宙以来规模最大的冰川消退事件, 地球气候经历了由冰室向温室的转变。然而, 低纬度地区对此次气候变化的响应细节仍存较多疑问。华南板块在早二叠世位于古特提斯洋中, 发育连续的海相碳酸盐岩沉积序列对气候变化响应敏感。本研究利用高分辨率Fe元素含量作为古气候替代指标, 对贵州省罗甸县纳庆剖面392.3 m至487.9 m的下二叠统亚丁斯克阶-空谷阶四大寨组进行旋回地层学研究。频谱分析显示研究段具有显著的7.46~10.46 m、2.01~3.15 m、0.46~0.68 m、0.27~0.39 m谱峰, 其比例约为26.7:7.8:1.7:1, 与利用La2004模型推算的早二叠世天文轨道周期比例(23.9:7.4:1.9:1)基本一致。利用405 ka偏心率校准的Fe元素序列存在405 ka、117 ka、90 ka、30.1~35.8 ka、15.6~22.9 ka周期信号, 表明沉积记录受到米兰科维奇旋回控制。估算出研究段的平均沉积速率为2.15 cm/ka, 构建了288.1 Ma至282.9 Ma, 持续时间约为5.16 Ma的高分辨率天文年代标尺。研究证实周期约为1.36 Ma的超长斜率旋回控制了海平面的升降, 但其控制机制在冰室和温室两种气候状态下并不相同。超长斜率旋回在冰室状态下通过控制高纬度冰川消长影响海平面变化; 在温室状态下, 斜率旋回或通过影响大陆含水层控制海平面升降。

Response of Early Permian sedimentary records in the Naqing section of South China to the Milankovitch cycle

The termination of the Late Paleozoic ice age in the Early Permian, was the largest deglaciation event during the Phanerozoic, when the Earth's climate undergone a transition from an icehouse to a greenhouse condition. However, the response of this climate transition at low latitudes is still unclear. South China block was located in the Paleo-Tethys Ocean in the Early Permian. The continuous marine carbonate sequences in South China block were sensitive to climate change. In this paper, we use high resolution Fe element content from the Sidazhai Formation at Naqing section(25°01' 39″ N, 106°29' 58″ E), Luodian County, Guizhou Province to conduct cyclostratigraphic analysis. The spectral analysis shows spectral peaks of 7.46~10.46 m, 2.01~3.15 m, 0.46~0.68 m, and 0.27~0.39 m, with the ratio of 26.7:7.8:1.7:1, which is consistent with the ratio of the periods of early Permian astronomical orbital cycles(23.9:7.4:1.9:1)calculated by La2004 model. 405-ka-calibrated Fe element shows periods of 405 ka, 117 ka, 30.1~35.8 ka, 15.6~22.9 ka, indicating that the sedimentary records are controlled by the Milankovitch cycles. The sedimentation accumulation rate of the study section is estimated to be 2.15 cm/ ka. A 5.16 Ma astrochronologic time scale was constructed from 288.1 Ma to 282.9 Ma. Our study indicates that the 1.36 Ma long-term obliquity cycle controlled the sea-level variations, but the control mechanism differentiated in icehouse and greenhouse conditions. In the icehouse condition, the long-term obliquity cycle controlled the sea level change by affecting the waning and waxing of glaciation, but in the greenhouse condition, the long-term obliquity cycle controlled the sea level change through the rise and fall of continental aquifers.