2-Methylhopanoids as indicators of paleoproductivity in paleooceans during times of black shale deposition

2-甲基藿烷类化合物是大量蓝藻物种的生物学标记物。该项目研究这些化石有机化合物是否是古海洋中涉及硝酸盐限制和随后的固氮的高初级生产力的指标。ODP Leg 198期间在太平洋中部Shatsky隆起钻探的白垩纪黑色页岩是本研究的测试案例。这些黑色页岩的2-甲基藿烷类物质剖面与上、下伏沉积岩的对比。此外，还研究了整个黑色页岩古生产力的稳定或振荡变化规律。一种新的方法是结合分析可提取沥青馏分中的游离2-甲基藿烷和不溶性大分子有机物中的结合类似物。为了进行比较，我们用同样的方法研究了来自地中海东部（ODP Leg 160）的沉积物，它们代表了一个明显更年轻的年代和不同的古海洋环境。来自北大西洋和南大西洋的白垩纪黑色页岩可能是进一步比较的目标。最后，研究了培养蓝藻中2-甲基藿烷类化合物的含量，以扩展化石有机质的解释基础。

2-Methylhopanoids are biological markers of a significant number of cyanobacteria species. This project investigates if these fossil organic compounds are indicators of high primary productivity in the paleoocean involving nitrate limitation and subsequent nitrogen fixation. Cretaceous black shales from Shatsky Rise in the central Pacific Ocean drilled during ODP Leg 198 are the test case for this study. 2-Methylhopanoid profiles across these black shales are contrasted to those in over- and underlying sedimentary rocks. In addition, the distribution patterns across the black shale are studied for steady or oscillating changes of paleoproductivity. A novel approach is the combined analysis of free 2-methylhopanoids in the extractable bitumen fraction and bound analogs in the insoluble macromolecular organic matter. For comparison, sapropels from the eastern Mediterranean Sea (ODP Leg 160) representing a significantly younger age and a different paleoceanographic setting are investigated in the same way. Cretaceous black shales from the North and South Atlantic Ocean are possible further targets for comparison. Finally, cultured cyanobacteria are investigated for their 2-methylhopanoid content to extend the basis for interpretation in fossil organic matter.