Towards an orbitally-tuned Maastrichtian stage

最近的白垩纪见证了全球碳循环的扰动，据推测这与气候变冷和潜在的短暂冰川有关。为了了解这些事件的强迫机制，它们的全球意义和区域响应，有必要改进我们现有的地层框架。马斯特里赫特天体年代学的最新进展允许调整碳循环变化的节拍器的405 kyr长偏心率周期。然而，所有研究的时间序列不包括Campanian-Maastrichtian过渡73和71 Ma之间，一个严重的气候变冷的关键间隔。法国西南部Tercis-les-班斯的循环石灰岩序列记录了碳同位素扰动，是马斯特里赫特阶基底的批准GSSP。然而，实际上碳同位素地层学的分辨率太低，无法评估地球外生碳循环的潜在轨道强迫机制。此外，生物地层事件的定义为第一次和最后一次出现的钙质超微化石和浮游有孔虫还没有得到精确的解决。在这里，我们建议开发一个天体年代学与高分辨率的碳同位素地层学在GSSP部分的Tercis-les-班斯使用散装碳酸盐来解决短寿命的同位素事件的轨道时间尺度之间的73和71马。建立这样一个综合地层框架对于全球大陆架和海洋剖面之间以及低纬度和高纬度之间的相互关系十分重要。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。该项目的成果将提供一个轨道时间尺度上的强有力的地层框架，这是认识碳循环、海洋化学变化、环流和海平面以及海洋生态系统反应之间的时间关系所必需的。

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.