Periodic variations in Earth’s orbital parameters force climate on local and global scales, with global responses particularly sensitive to the presence of ice sheets and their associated feedbacks. Therefore, determining whether orbital forcings influenced sedimentary records of the past, and if so, which had such an effect, can shed light on Earth’s climate sensitivity and global ice volume. To this end, we present a field- and drone-based cyclostratigraphy of the predominantly lacustrine El Molino Formation of the Late Cretaceous–Early Paleogene Potosí Basin in present day Bolivia, which contains carbonate mud parasequences that record fluctuating hydrological conditions, including ephemeral marine connections, from 73 Ma to 64 Ma. We introduce a novel methodology for incorporating drone imagery into a quantitative, three-dimensional stratigraphic model that generates an upward-younging quantity comparable to stratigraphic height, and we find that our model outperforms our own field measurements of stratigraphic height. We project drone imagery at two sites into the stratigraphic model to construct time series of outcrop color, which vary systematically with facies and track basin water depth. Spectral analysis of these time series reveals sedimentary periodicities corresponding to short eccentricity, precession, and semi-precession, which are corroborated with measurements of magnetic susceptibility from mudstones. We generate independent age models at both study areas from four new U-Pb chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA–ID–TIMS) ages, which are consistent with an orbital interpretation for observed sedimentary periodicities. Importantly, we observe the presence of obliquity-scale periodicity in sedimentation during a period of marine connection, suggesting that sea level oscillations were driven by obliquity. This observation is consistent with previous claims about the presence of a small, orbitally forced Antarctic ice sheet during the latest Cretaceous.

中文翻译：

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玻利维亚晚白垩世亚热带波托西盆地的天文学强迫水文学

地球轨道参数的周期性变化迫使气候在局部和全球范围内变化，全球响应对冰盖的存在及其相关反馈特别敏感。因此，确定轨道强迫是否影响了过去的沉积记录，以及是否如此影响了过去的沉积记录，可以揭示地球的气候敏感性和全球冰量。为此，我们介绍了玻利维亚现今白垩纪至古近纪波托西盆地晚白垩世-古近纪波托西盆地主要湖相El Molino地层的基于地层和无人机的旋回地层，其中包含碳酸盐泥副沉积物，记录了波动的水文条件，包括短暂的海洋联系，从73 Ma到64 Ma。我们介绍了一种新颖的方法，可将无人机图像整合到定量，三维地层模型，该模型产生的上升量可与地层高度相媲美，我们发现该模型优于我们自己的地层高度实测值。我们将两个地点的无人机图像投影到地层模型中，以构造露头颜色的时间序列，该时间序列随相和跟踪盆地水深而系统地变化。这些时间序列的频谱分析显示出与短偏心率，旋进和半旋进相对应的沉积周期，这与泥岩的磁化率测量结果相符。我们通过两个新的U-Pb化学磨损-同位素稀释-热电离质谱（CA–ID–TIMS）年龄，在两个研究区域生成独立的年龄模型，与观察到的沉积周期的轨道解释一致。重要的是，我们观察到海洋连接期间在沉积过程中存在倾斜尺度周期性，这表明海平面振荡是由倾斜引起的。这一观察结果与先前关于在最近的白垩纪存在小的，轨道强迫的南极冰盖的主张是一致的。