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旋回记录。到目前为止，我们已经发现了两种周期，一种是由一个波长约为70毫微米的单一长期周期组成的，另一种是由波长为2至6毫微米的重复短期周期组成的。这种周期模式已经发现在北美古代被动边缘持续发生。这种复杂信号的形式与有争议的中生代和第三纪海平面上升曲线的形式非常相似，该曲线是用地震地层学方法沿着大陆的淹没边缘构造的。海平面上升机制也是对寒武纪旋回的一种可行解释，如果正确的话，它将证明海平面的短期波动在地球历史的大部分时间（如果不是全部）地层记录的演变中是一个主导因素。然而，不能排除构造机制的影响。除了周期起源的问题外，我们的研究结果还提出了周期并非随机的可能性，但由于缺乏可靠的时间尺度，这一问题的进一步调查受到阻碍。最后，由于我们的分析仅限于主要沉积在碳酸盐岩台地内的地层，我们无法评价我们的新方法在多大程度上普遍适用于地层记录。我们将开展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的关键位置测量剖面，在那里应该可以测试旋回的升降与构造起源，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.