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

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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.