Collaborative Research: A New Generation, User-Friendly Time Scale for the Cretaceous Period

为了试图限制未来全球变暖的影响，地质学家越来越多地将研究重点放在岩石记录中的温暖气候时期。这种温暖的“温室”气候最具代表性的时期之一发生在白垩纪，比现在早140到6500万年。最近对白垩纪气候的研究表明，似乎发生在数千年或更短时间内的快速波动。这些变化对进化产生了戏剧性的影响。地质学家在限制这些变暖事件的确切环境影响方面面临的一个主要问题是，它们发生的时间比用传统方法测定岩石年龄所能解决的时间短了一个数量级。因此，我们无法确定进化等重要过程的速率，也无法限制二氧化碳等物质在储集层之间的流动。这个合作的多学科项目涉及北卡罗来纳大学教堂山分校、布朗大学和其他大学的咨询科学家，旨在通过以下方式提高白垩纪时标的精确度和准确度：(1)根据微小海洋生物(有孔虫和微型浮游生物)的化石记录(生物地层学)编制时标，分辨率高于以前；(2)完善基于生物地层学的时标之间的校准，地球地磁极性的反转和地球轨道的波动都记录在岩石中，(3)改善生物地层学和最近获得的辐射年龄数据之间的相关性；(4)利用轨道时标将白垩纪的大部分时间刻度为流逝时间；(5)以合理的方式对不同的地层元素进行对比和标度。我们还建议以用户友好的格式公布这一时间尺度和相关数据，以便所有地质学家能够以最小的误差估计样品的年龄。为此，我们将在万维网上以可下载的Excel文件的形式向地质界提供时间刻度。结合将在深海和陆地地区众所周知的岩石暴露中进行的生物地层学工作，这些Excel文件将包括从深度计算样品年龄的宏。因此，例如，地球化学家绘制数据所需做的就是下载文件并输入样品的深度。我们的所有数据也将在网上存档，为未来的修订提供了一种现成的手段。建议的新一代时间尺度将提供更高的精度和分辨率，使地质学家能够研究白垩纪地球的突然变化。此外，时间尺度的通信方式将提高在各种地质应用中的精度。

To attempt to constrain the future effects of global warming, geologists are increasingly focussing studies on periods of warm climate in the rock record. One of most representative intervals of such warm, "greenhouse" climate occurred in the Cretaceous Period from 140 to 65 million years before present. Recent investigations of Cretaceous climate have shown rapid swings that seem to have occurred over millennia or less. These changes had dramatic effects on evolution. One of the major problems facing geologists in constraining the exact environmental effects of these warming events is that they took place over periods an order of magnitude shorter than that resolvable using traditional techniques to date rocks. Thus we cannot determine the rates of important processes such as evolution nor can we constrain the fluxes of materials such as CO2 between reservoirs. This collaborative, multidisciplinary project involving the University of North Carolina at Chapel Hill, Brown University and consulting scientists at other universities seeks to improve the precision and accuracy of the Cretaceous time scale by: (1) compiling time scales based on the fossil record (biostratigraphy) of microscopic marine organisms (foraminifera and nannoplankton) with higher resolution than previously attainable; (2) refining the calibration between time scales based on biostratigraphy, reversals in the Earth's geomagnetic polarity, and fluctuations in the Earth's orbit that are all recorded in rocks, (3) improving the correlation between biostratigraphy and recently acquired radiometric age dates; (4) calibrating large portions of the Cretaceous time scale to elapsed time using the orbital time scale, and (5) correlating and scaling the different stratigraphic elements in a logical fashion. We also propose to publish this time scale and associated data in a user-friendly format so that all geologists can estimate ages of samples with the minimum of error. To do this we will make the time scale available to the geologic community on the world wide web as downloadable Excel files. Combined with the biostratigraphic work that will be conducted in well-known rock exposures from the deep sea and land areas, these Excel files will include macros that calculate the ages of samples from their depths. Thus all a geochemist, for example, needs to do to plot data is to download the file and input the depth of samples. All of our data will also be archived on the web providing a ready means of future revision. The new generation time scale proposed will provide improved precision and resolution that will enable geologists to study abrupt changes in the Cretaceous Earth. Moreover, the mode of communication of the time scale will improve accuracy in diverse geologic applications.