Quantitative Test for Eustatic Events of 2 - 6 M.Y. Durationin Early Paleozoic Strata of North America

我们已经完成了开发一种新的定量方法的第一阶段，用于分析从北美寒武纪地层开始的复杂的旋回记录。到目前为止，我们已经发现了两个周期，一个周期由一个波长约为7000万年的长期周期组成。另一个是由2到6百万年波长的重复短期周期组成。已发现的模式旋回性发生一致的古代被动边缘的北美。这种复杂信号的形式非常类似于有争议的中生代和第三纪海平面变化曲线的形式，该曲线是沿着大陆的淹没边缘使用地震地层学方法构建的。海平面升降机制也是寒武纪旋回性的一个可行解释，如果正确的话，它证明了海平面的短期振荡是地球历史上大部分（如果不是全部）地层记录演变的主导因素。然而，不能排除构造机制。除了周期的起源问题之外，我们的研究结果还提出了周期不是随机的可能性，但由于缺乏可靠的时间尺度，对这个问题的进一步研究受到阻碍。最后，由于我们的分析一直局限于主要沉积在碳酸盐岩台地的地层，我们不能评估我们的新程序对地层记录的普遍适用性的程度。我们将进行一项为期两年的研究计划，以解决我们以前的工作结果所提出的问题。我们将在北美克拉通内的关键地点测量部分，在那里应该可以测试海平面与构造起源的周期，并评估我们的方法在不同沉积环境中的有效性。

We have completed the first phase of developing a new, quantitative method for analyzing a complex record of cyclicity beginning with the Cambrian strata of North America. So far we have found two orders of cycles, one consisting of a single long- term cycle with a wave length of about 70 m.y. and the other consisting of repeating short-term cycles with wavelengths of 2 to 6 m.y. The pattern cyclicity has been found to occur consistently within the ancient passive margins of North America. The form of this complex signal strongly resembles the form of the controversial eustatic sea level curve for the Mesozoic and Tertiary that has been constructed using seismic stratigraphic methods along the submerged margins of the continents. A eustatic mechanism is also a viable explanation for the Cambrian cyclicity, and, if correct, is evidence that short-term oscillations of sea level have been a dominant factor in the evolution of the stratigraphic record for much, if not all, of the earth's history. A tectonic mechanism cannot be ruled out, however. In addition to the question of the origin of the cycles, the results of our research have raised the possibility that the period of the cycles is not random, but further investigation of this problem is hampered by the lack of a reliable time scale. Finally, since our analyses have been confined to strata that were deposited mainly within a carbonate platform, we cannot evaluate the degree to which our new procedures have general applicability to the stratigraphic record. We will conduct a two-year program of research to address the questions that have been raised by the results of our previous work. We will to measure sections in key localities within the North American craton where it should be possible to both test the eustatic versus tectonic origin of the cycles and to assess the validity of our methodology in different depositional environments.