Cover Image Credits

The article by Tian and others titled “Early Cretaceous solar cycles recorded in lacustrine laminations in North China” (p. 1285–1307) provides a new record of annual laminated lacustrine sediments (varves) of the Early Cretaceous Yixian Formation—a Lagerstätte formation known for well-preserved feathered dinosaurs and the Jehol Biota in North China. Sub-millimeter scaled couplets of biofilm and siliciclastic rich lamina record the seasonal growth and withering of microbial mats during warm and cold season, respectively. Evolutionary spectral analyses of the varve thickness and gray scale data show strong periods of solar cycles. This new record is contextualized with a compilation of existing solar cycle records through geological time, to show that the 11-year Schwabe sunspot cycle and the 22-year Hale cycle have persisted over the last 1 billion years or longer. The stable phases of solar cycles support the presumption that solar variability will continue to influence Earth's climate in future.

Explanation of cover figure: This figure shows the depositional processes of the ‘striped shale’. Varve couplets were formed by deposition of organic-rich sublamina in warm seasons and siliciclastic-rich sublimina in cold seasons, as a result of seasonal growth of microbial mats. Strong inflow could cause temporary interruption of mat growth and lead to ‘striped shale’ with alternating varve couplets and event layers.