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

为了试图限制全球变暖的未来影响，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距今1.4亿至6500万年前的白垩纪。 最近对白垩纪气候的研究表明，这种快速的变化似乎发生在几千年或更短的时间里，这些变化对进化产生了巨大的影响。 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主要问题之一是，它们发生的时间比使用传统技术确定岩石年代的时间短一个数量级。 因此，我们无法确定重要过程（如演化）的速率，也无法限制储层之间的物质（如CO2）通量。 这个多学科合作项目涉及北卡罗来纳州大学查佩尔山分校、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间尺度的精确度和准确性：（1）根据化石记录编制时间尺度（生物地层学）海洋微生物（有孔虫和微型浮游生物）的分辨率比以前更高;（2）根据生物地层学、地球地磁极性的逆转，地球轨道的变化和波动都记录在岩石中，（3）提高生物地层学和最近获得的放射性年龄之间的相关性;（4）使用轨道时间尺度校准白垩纪时间尺度的大部分时间，以及（5）以逻辑的方式关联和缩放不同的地层要素。我们还建议以用户友好的格式发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标。 结合将在深海和陆地地区知名岩石暴露区进行的生物地层学工作，这些Excel文件将包括计算其深度样本年龄的宏。 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本的深度。 我们所有的数据也将在网上存档，为将来的修订提供一个现成的手段。 提出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，时标的通信模式将提高各种地质应用的准确性。

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.