The expected duration of upward-shallowing peritidal carbonate cycles and their terminal hiatuses
The expected duration of upward-shallowing peritidal carbonate cycles and their terminal hiatuses
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向上变浅的潮间碳酸盐循环的预期持续时间及其终端中断
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发表时间：
1994
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通讯作者：
P. Sadler
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作者：
P. Sadler
米级的可容纳旋回，占主导地位的地层记录的潮缘碳酸盐岩的积累，可能会提供一个时间尺度的异常高的分辨率，但持续时间的间断盖所产生的旋回层是很难确定的。根据测量时间跨度的长短，将来自许多不同碳酸盐岩剖面的数千个潮缘堆积速率结合起来，以描述一个假设的平均剖面。由于所有部分都被间断中断，平均累积速率福尔斯随着时间跨度的增加而逐渐下降，并且在捕获最高比例的间断的时间跨度处最陡。将许多部门的费率合并的过程消除了间断分布的地方差异。只有在大多数章节中具有相似间距和持续时间的间隙才会在编译后突出。在累积速率与时间跨度的组合图中，一个明显的拐点的大小和位置确定了一个10万年的主导周期，其中终端间断占80%-90%。预期的旋回层厚度为10 m。由于潮周可容纳周期开始和结束与沉积物表面在海平面上，预期的周期可以估计通过找到的时间跨度，在该时间跨度的容纳和积累率的平衡。间断的最长持续时间是沉降率和海平面下降平衡的时间跨度。对许多经验测量的解释再次被用来确定时间跨度与沉降速率、海平面变化和净可容纳空间之间的关系。第二种方法证实了第一种方法的结果，并可加以修改，以预测在不同的气候，构造和沉积环境的预期旋回。由于第四纪数据占主导地位的短期利率，假设的平均部分最好地描述了一个被动的边缘，在冰室气候与强烈的冰川海平面升降波动。第二种方法经过极端温室气候条件的修正后，预测20,000年的可容纳周期将被优先记录，预计的旋回层厚度为2 m，约占周期的50%。沉降速率的增加，无论是在活动边缘，在被动边缘形成的初始阶段，或在一个平台的向海边缘，往往会延长循环持续时间的限制，增加旋回层厚度，并分区边界间断的时间更少。然而，沉降的增加增加了沉积物表面被淹没的风险。
Meter-scale accommodation cycles, which dominate the stratigraphic record of peritidal carbonate accumulation, might provide a time scale of unusually high resolution, but the duration of the hiatuses that cap the resulting cyclothems is difficult to determine. Thousands of rates of peritidal accumulation from many different carbonate sections have been combined, according to the length of the time span of measurement, to describe a hypothetical average section. Because all sections are interrupted by hiatuses, the average accumulation rate falls progressively with increasing time span and most steeply at the time spans that capture the highest proportion of hiatuses. The process of combining rates from many sections cancels local differences in the distribution of hiatuses. Only hiatuses that have similar spacing and duration in a majority of sections will stand out after compilation. The size and position of a pronounced inflection in the combined plot of accumulation rates against time span identifies a dominant cycle period of ∼100,000 yr, of which the terminal hiatus accounts for 80%-90%. The expected cyclothem is ∼10 m thick. Because peritidal accommodation cycles begin and end with the sediment surface at sea level, the expected cycle period can be estimated by finding the time span at which accommodation and accumulation rates balance. The maximum duration of the hiatus is the time span at which rates of subsidence and sea-level fall balance. Compilations of many empirical measurements were again employed to determine the relationship between time span and the rates of subsidence, sea- level change, and net accommodation. This second method confirms the results of the first and can be modified to predict the expected cyclothem in different climatic, tectonic, and depositional settings. Because Quaternary data dominate short-term rates, the hypothetical average section best describes a passive margin in an icehouse climate with strong glacio-eustatic fluctuations in sea level. After modification for an extreme greenhouse climate, devoid of ice caps, the second method predicts that 20,000-yr accommodation cycles will be preferentially recorded.The expected cyclothem is 2 m thick and accounts for about 50% of the cycle period. Increased subsidence rates, whether on active margins, in the initial phase of passive margin formation, or at the seaward edge of a platform, tend to extend the limit of cycle duration, increase cyclothem thickness, and partition less time to the bounding hiatus. Increased subsidence, however, raises the risk that the sediment surface will drown.