美国密歇根大学Katharine M. Loughney团队报道了美国加利福尼亚州巴斯托组中新世中期的火灾活动和C4植被扩张。这一研究成果发表在2023年6月2日出版的国际学术期刊《地质学》上。
研究人员分析了横跨巴斯托组地层的沉积物样品中微观烧焦颗粒的浓度和累积速率(CHAR)以研究火灾活动、林冠覆盖和C4植被存在的关系。整个地层中的浓度和累积速率都很低，然后在13.5 Ma急剧增加。来自土壤有机质和植物化石计数的 δ13C 富集值表明，此时存在C4草和季节性干旱的开放树冠栖息地。
浓度峰值显示，其与中新世气候最佳期后南加州的气候变冷、变干相一致。火灾活动的增加可能有助于栖息地从森林开放到林地，并促进C4植物的传播。这是北美西南部中新世中期火灾活动的首个碳记录。
据悉，C4草原生态系统在ca. 8和3Ma之间扩展到整个北美。对南加州中新世中期巴斯托组的有蹄动物釉质和环境指示物的研究表明，在晚中新世C4草原扩张之前就有C4植被存在。火促进了现代C4草原的生长，并可能有助于C4植被在中新世的扩张。
附：英文原文
Title: Middle Miocene fire activity and C4 vegetation expansion in the Barstow Formation, California, USA
Author: Katharine M. Loughney, Anna Harkness, Catherine Badgley
Issue&Volume: 2023-06-02
Abstract: C4 grassland ecosystems expanded across North America between ca. 8 and 3 Ma. Studies of ungulate enamel and environmental indicators from the middle Miocene Barstow Formation of southern California (USA) have demonstrated the presence of C4 vegetation prior to the late Miocene expansion of C4 grasslands. Fire promotes the growth of modern C4 grasslands and may have contributed to the Miocene expansion of C4 vegetation. We analyzed the concentration and accumulation rate (CHAR) of microscopic charred particles from sediment samples spanning the Barstow Formation in order to investigate the relationship between fire activity, canopy cover, and the presence of C4 vegetation. Concentration and CHAR were low throughout the formation then increased dramatically at 13.5 Ma. Enriched values of δ13C from soil organic matter and phytolith counts indicate the presence of C4 grasses and seasonally dry, open-canopy habitats at this time. The spike in concentration coincides with climatic cooling and drying in southern California after the Miocene Climatic Optimum. Increased fire activity may have contributed to habitat opening from forest to woodland and promoted the spread of C4 plants. This is the first charcoal record of fire activity from the middle Miocene of southwestern North America.
DOI: 10.1130/G50881.1