甘肃华亭中侏罗世银杏类化石及其气孔参数对古大气CO2的响应

The Middle Jurassic ginkgophyte fossils from Huating, Gansu and their stomatal parameters responding to paleoatmospheric CO2

对甘肃华亭中侏罗统延安组银杏类6属17种化石的裂片大小与表皮气孔参数相关性进行了分析,结果表明,当化石裂片宽度<5 mm时,气孔参数与裂片宽度之间表现出一定的相关性,其中,气孔指数与裂片宽度呈显著负相关,气孔密度与化石裂片宽度相关性较小;当化石裂片宽度≥5mm时,气孔指数和气孔密度与裂片宽度关系不明显.利用气孔指数法进行古大气φ(CO2)重建时,选取裂片宽度≥5 mm的叶片结果更可靠.选取银杏属/似银杏属、拟刺葵属裂片宽度>5 mm的化石叶片,通过气孔比率法重建华亭中侏罗世大气φ(CO2).其中利用胡顿银杏和6种似银杏属植物所得的古大气φ(CO2)平均值为1228×10-6(±116×10-6),华丽拟刺葵和狭叶拟刺葵所得的结果为1243×10-6(±75×10-6),二者比较接近,表明这些植物均可作为古大气φ(CO2)重建的良好指标.获得的古大气φ(CO2)数据与地球化学模型部分拟合曲线相近,推测甘肃华亭中侏罗世属于温暖、较湿润气候.

Some fossils of ginkgophyte were collected from the Yan’an Formation of the Middle Jurassic,in Huating,Gansu Province.The correlation between the lobe width and stomatal parameters on the epidermis of 17 fossil species within 6 genera of Ginkgo were analyzed.When the lobe width<5 mm,there was a certain correlation between the stomatal parameters and the lobe width,especially the stomatal index was significantly affected by the lobe width with an obvious negative correlation,while no distinct correlation was found between stomatal density and lobe width.When the lobe width was greater than 5 mm,the correlation between lobe width and stomatal index or stomatal density was indistinctive.We concluded that the fossils with lobe width greater than 5 mm would give more accurate results when thepaleo-φ(CO2)was reconstructed based on the stomatal index.Some selected fossils of Ginkgo/Ginkgoites and Phoenicopsis with lobe width greater than 5 mm were used to reconstruct the paleo-φ(CO2)of the Middle Jurassic in Huating.Ginkgo huttonii and 6 species of Ginkgoites showed a mean paleo-φ(CO2)value of 1228×10-6(±116×10-6),while Phoenicopsis speciose and Phoenicopsis angustifolia gave mean paleo-φ(CO2)value of 1243×10-6(±75×10-6).The two results were similar,indicating that these genera could well be used to reconstruct paleo-φ(CO2).Our results were consistent with the most geochemical models.We concluded that the climate during the Middle Jurassic in Huating was warm and humid.