Towards an orbitally-tuned Maastrichtian stage

最近的白垩纪见证了全球碳循环的扰动，这种扰动被认为与气候变冷和潜在的短暂冰期有关。为了了解强迫机制、它们的全球意义以及对这些事件的区域反应，有必要改进我们目前可用的地层框架。马斯特里赫特天文年代学的最新进展允许将碳循环变化调整为405 kyr长偏心周期的节拍器。然而，所有研究的时间序列都没有涵盖73 - 71 Ma之间的坎帕尼亚-马斯特里赫特过渡，这是一个严重气候变冷的关键时期。法国西南部tercies -les- bains的旋回灰岩演替记录了碳同位素的扰动，是马斯特里赫特基地的公认GSSP。然而，实际上碳同位素地层学的分辨率太低，无法评估地球外源碳循环的潜在轨道强迫机制。此外，将生物地层事件定义为钙质纳米化石和浮游有孔虫的首次和最后出现还没有精确解决。在这里，我们建议在tersis -les- bains的GSSP剖面上建立一个天体年代学和高分辨率碳同位素地层学，利用大块碳酸盐来解决73 - 71 Ma轨道时间尺度上的短寿命同位素事件。这种综合地层格架的发展对于大陆架和海洋剖面之间以及低纬度和高纬度之间的全球对比是重要的。它将进一步允许通过提供相对于地磁极性时间尺度的精确边界定义来重新评估GSSP。该项目的结果将在轨道时间尺度上提供一个强大的地层框架，以认识碳循环、海洋化学、环流和海平面变化以及海洋生态系统响应之间的时间关系。

The latest Cretaceous witnessed perturbations in the global carbon cycle assumed to have been associated to climatic cooling and potential ephemeral glaciations. In order to understand the forcing mechanisms, their global significance, and the regional response to these events it is necessary to improve our presently available stratigraphic framework. Recent advances in Maastrichtian astrochronology allowed for the tuning of carbon cycle variations to the metronome of the 405-kyr long eccentricity cycle. However, all studied time series do not cover the Campanian-Maastrichtian transition between 73 and 71 Ma, a critical interval of severe climatic cooling. The cyclic limestone succession at Tercis-les-Bains in SW France records carbon isotope perturbations and is the ratified GSSP for the base of the Maastrichtian. However, actually the resolution of carbon isotope stratigraphy is too low to assess potential orbital forcing mechanisms of the Earth’s exogenic carbon cycle. Further, the definition of biostratigraphic events as first and last occurrences of calcareous nannofossils and planktonic foraminifera is not precisely resolved yet. Here, we propose to develop an astrochronology together with a high-resolution carbon isotope stratigraphy at the GSSP section of Tercis-les-Bains using bulk-carbonates to resolve short-lived isotopic events on orbital timescales between 73 and 71 Ma. The development of such an integrated stratigraphic framework is important for global correlation between shelf and oceanic sections as well as between low and high-latitudes. It will further allow reassessing the GSSP by providing a precise boundary definition relative to the geomagnetic polarity time scale. Results of this project will provide a robust stratigraphic framework on orbital time scales necessary to recognize temporal relationships between the carbon cycle, changes in ocean chemistry, circulation and sea level, and the oceanic ecosystem response.