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首页> 外文期刊>The Journal of Geology: a semi-quarterly magazine of geology and related sciences >Distinguishing Milankovitch-Driven Processes in the Rock Record from Stochasticity Using Computer-Simulated Stratigraphy
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Distinguishing Milankovitch-Driven Processes in the Rock Record from Stochasticity Using Computer-Simulated Stratigraphy

机译：使用计算机模拟地层学将岩石记录中的米兰科维奇驱动过程与随机性区分开来

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Repetitive patterns of facies recurrence are frequently reported from the shallow-water sedimentary rock record and are postulated to have been driven by orbital forcing on eustatic sea level. Consequently, multiple statistical techniques have been developed to evaluate whether patterns of stratigraphic succession are more consistent with a periodic sea level signal or are stochastic. Previous studies focused on development and/or application of such methods to test empirical geological records. However, the character of such records cannot be known a priori, as deposition, erosion, and preservation influence the resultant composition, nor can those records be readily manipulated to explore the sensitivity, robustness, and overall validity of statistical methods. Here we simulate carbonate layers using computermodeled successions generated by periodic sea level changes. The resulting stratigraphic records were then evaluated statistically. Thickness distributions of simulated lithofacies were compared to distributions predicted for Poisson processes, which by definition are not driven by cyclical sea level changes. Our results suggest that periodic processes produce stratigraphic thickness frequencies that are difficult to distinguish from random frequencies except under high-magnitude sea level fluctuations. Similarly, autocorrelation fails to correctly recognize cyclic patterns in such simulated records. Models with high-magnitude sea level fluctuations (icehouse conditions) had thickness frequencies that are suggestive of orbital forcing, whereas low-magnitude sea level fluctuations (greenhouse conditions) appeared independent even though they were modeled using Milankovitch orbital forcing. The increasing evidence based on spectral data from real rock successions suggests that Milankovitch drivers are common in both icehouse and greenhouse periods. Because statistical approaches are unsuccessful in recognizing the cyclic driver of these simulated records, we infer that it is difficult to disprove independence from real stratigraphy even when orbital forcing is controlling the rock composition. Even in the necessarily simplified world of computer simulations, the numerous factors involved in depositing stratigraphic successions work to complicate or mask any periodic signal, thus generating the appearance of stochasticity in some successions.
机译：从浅水沉积岩石记录中经常报告相重复出现的重复模式，并假定是由恒海平面上的轨道强迫驱动的。因此，已经开发了多种统计技术来评估地层演替模式是否与周期性海平面信号更一致或是随机的。先前的研究集中于开发和/或应用这种方法来测试经验地质记录。但是，这类记录的特性无法事先确定，因为沉积，侵蚀和保存会影响所得的组成，也不能轻易地操纵这些记录以探索统计方法的敏感性，鲁棒性和整体有效性。在这里，我们使用周期性海平面变化产生的计算机模拟演替来模拟碳酸盐层。然后对得到的地层记录进行统计评估。将模拟岩相的厚度分布与针对泊松过程预测的分布进行了比较，根据定义，泊松过程不受周期性海平面变化的驱动。我们的结果表明，周期性过程产生的地层厚度频率很难与随机频率区分开，除非在高强度海平面波动下。同样，自相关无法正确识别此类模拟记录中的循环模式。具有高强度海平面涨落（冰室条件）的模型具有暗示轨道强迫的厚度频率，而低强度海平面涨落（温室条件）似乎是独立的，即使它们是使用Milankovitch轨道强迫建模的。基于来自真实岩石演替的光谱数据的越来越多的证据表明，Milankovitch驱动器在冰室和温室时期都很常见。由于统计方法无法识别这些模拟记录的周期性驱动因素，因此我们推断，即使在轨道强迫控制着岩石成分的情况下，也很难证明其与真实地层的独立性。即使在必须简化的计算机模拟世界中，沉积地层序列所涉及的众多因素也会使任何周期信号复杂化或掩盖，从而在某些序列中产生随机性。

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