Stratigraphy of the Campanian-Maastrichtian boundary in ODP Hole 122-762C@en

An integrated framework of magnetostratigraphy, calcareous microfossil bio-events, cyclostratigraphy and d13C stratigraphy is established for the upper Campanian-Maastrichtian of ODP Hole 762C (Exmouth Plateau, Northwestern Australian margin). Bulk-carbonate d13C events and nannofossil bio-events have been recorded and plotted against magnetostratigraphy, and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the Maastrichtian. Thirteen carbon-isotope events and 40 nannofossil bio-events are recognized and calibrated with cyclostratigraphy, as well as 14 previously published foraminifer events, thus constituting a solid basis for large-scale correlations. Results show that this site is characterized by a nearly continuous sedimentation from the upper Campanian to the K-Pg boundary, except for a 500 kyr gap in magnetochron C31n. Correlation of the age-calibrated d13C profile of ODP Hole 762C to the d13C profile of the Tercis les Bains section, Global Stratotype Section and Point of the Campanian-Maastrichtian boundary (CMB), allowed a precise recognition and dating of this stage boundary at 72.15 ± 0.05 Ma. This accounts for a total duration of 6.15 ± 0.05 Ma for the Maastrichtian stage. Correlation of the boundary level with northwest Germany shows that the CMB as defined at the GSSP is ~800 kyr younger than the CMB as defined by Belemnite zonation in the Boreal realm. ODP Hole 762C is the first section to bear at the same time an excellent recovery of sediments throughout the upper Campanian-Maastrichtian, a precise and well-defined magnetostratigraphy, a high-resolution record of carbon isotope events and calcareous plankton biostratigraphy, and a cyclostratigraphic study tied to the La2010a astronomical solution. This section is thus proposed as an excellent reference for the upper Campanian-Maastrichtian in the Indian Ocean.

针对澳大利亚西北陆缘埃克斯茅斯高原的大洋钻探计划（Ocean Drilling Program, ODP）762C孔的坎潘期晚期-马斯特里赫特阶地层，建立了一套整合磁地层学、钙质微化石生物事件、旋回地层学与碳同位素地层学的综合研究框架。研究记录了块状碳酸盐碳同位素事件与超微化石生物事件，并将其与磁地层学结果对比，同时结合旋回地层学研究成果与近期马斯特里赫特阶天文校准结果，赋予其绝对年龄。共识别出13个碳同位素事件、40个超微化石生物事件，以及14个已发表的有孔虫事件，上述事件均通过旋回地层学完成校准，为大区域地层对比提供了坚实基础。研究结果显示，该孔位的沉积记录几乎连续覆盖坎潘期晚期至白垩-古近纪（K-Pg）界线，仅在磁极性时C31n中存在一段50万年的沉积间断。将ODP 762C孔经年龄校准的碳同位素剖面，与坎潘-马斯特里赫特界线（Campanian-Maastrichtian boundary, CMB）全球界线层型剖面和点位（Global Stratotype Section and Point, GSSP）所在的泰尔西莱班剖面的碳同位素剖面进行对比，精准识别并测定该阶界线的年龄为72.15 ± 0.05 Ma。据此确定马斯特里赫特阶的总持续时长为6.15 ± 0.05 Ma。将该界线层位与德国西北部的地层进行对比后发现，全球界线层型剖面和点位所定义的坎潘-马斯特里赫特界线，比北方域箭石带所界定的坎潘-马斯特里赫特界线年轻约80万年。ODP 762C孔是首个同时具备以下特征的剖面：坎潘期晚期至马斯特里赫特阶完整的沉积物取芯记录、精确且界定清晰的磁地层序列、高分辨率的碳同位素事件与钙质浮游生物生物地层记录，以及绑定La2010a天文解的旋回地层学研究。因此，该剖面被提议作为印度洋区域坎潘期晚期-马斯特里赫特阶的优质参考剖面。