Magnetic susceptibility dataset from the Danian Contessa Highway section, Gubbio, Italy

We studied a high-resolution multiproxy data set, including magnetic susceptibility (MS), CaCO3 content, and stable isotopes (d18O and d13C), from the stratigraphic interval covering the uppermost Maastrichtian and the lower Danian, represented by the pelagic limestones of the Scaglia Rossa Formation continuously exposed in the classic sections of the Bottaccione Gorge and the Contessa Highway near Gubbio, Italy. Variations in all the proxy series are periodic and reflect astronomically forced climate changes (i.e., Milankovitch cycles). In particular, the MS proxy reflects variations in the terrigenous dust input in this pelagic, deep-marine environment. We speculate that the dust is mainly eolian in origin and that the availability and transport of dust are influenced by variations in the vegetation cover on the Maastrichtian-Paleocene African or Asian zone, which were respectively located at tropical to subtropical latitudes to the south or far to the east of the western Tethyan Umbria-Marche Basin, and were characterized by monsoonal circulation. The dynamics of monsoonal circulation are known to be strongly dependent on precession-driven and obliquity-driven changes in insolation. We propose that a threshold mechanism in the vegetation coverage may explain eccentricity-related periodicities in the terrigenous eolian dust input. Other mechanisms, both oceanic and terrestrial, that depend on the precession amplitude modulated by eccentricity, can be evoked together with the variation of dust influx in the western Tethys to explain the detected eccentricity periodicity in the d13C record. Our interpretations of the d18O and MS records suggest a warming event ~400 k.y. prior to the Cretaceous-Paleogene (K-Pg) boundary, and a period of climatic and environmental instability in the earliest Danian. Based on these multiproxy phase relationships, we propose an astronomical tuning for these sections; this leads us to an estimate of the timing and duration of several late Maastrichtian and Danian biostratigraphic and magnetostratigraphic events.

本研究针对覆盖最晚马斯特里赫特阶至丹尼阶早期的地层间隔展开分析，所用数据为一套高分辨率多代用指标数据集，涵盖磁化率（magnetic susceptibility, MS）、碳酸钙（CaCO₃）含量以及稳定同位素（δ¹⁸O与δ¹³C）；该地层间隔以斯卡利亚罗萨组（Scaglia Rossa Formation）的远洋灰岩为沉积主体，其连续出露于意大利古比奥附近的博塔乔内峡谷与孔泰萨公路经典剖面中。所有代用指标序列的变化均具有周期性，反映了受天文因素驱动的气候变化（即米兰科维奇旋回（Milankovitch cycles））。具体而言，磁化率代用指标可反映该远洋深海环境中陆源粉尘输入的变化。我们推测，该粉尘主要为风成成因，其可获得性与搬运过程受马斯特里赫特期-古新世非洲或亚洲区域植被覆盖变化的影响；上述区域分别位于西特提斯翁布里亚-马尔凯盆地以南的热带至亚热带纬度区，以及其东侧远缘区域，且以季风环流（monsoonal circulation）为主要特征。已知季风环流的动力学过程强烈依赖于由岁差（precession）与斜度（obliquity）驱动的日照量（insolation）变化。我们提出，植被覆盖的阈值机制可解释陆源风成粉尘输入序列中与偏心率（eccentricity）相关的周期性特征。此外，我们可结合西特提斯区域粉尘输入通量的变化，引入其他依赖于受偏心率调制的岁差振幅的海洋与陆地机制，以解释δ¹³C记录中观测到的偏心率周期性特征。我们对δ¹⁸O与磁化率记录的解译结果表明，在白垩纪-古近纪（K-Pg）界线之前约40万年存在一次升温事件，且在丹尼阶早期存在一段气候与环境不稳定时期。基于上述多代用指标的相位关系，我们对这些地层剖面提出了天文调谐方案；据此我们估算了晚马斯特里赫特期与丹尼阶的数项生物地层学与磁地层学事件的发生时间与持续时长。