海相碳酸盐的碳同位素组成记录了地球发展与演化过程中的若干重大事件,作为古生代—中新生代转折时期的石炭纪—三叠纪初具有非常高的 ¹³C值,以此作为主线,综合研究了相应时间段的氧、锶同位素组成与变化、碳酸盐沉积盆地面积与变化,以此探讨海相碳酸盐碳同位素组成与海平面变化、有机碳库和碳酸盐碳库碳存量的变化、大气和海洋系统中CO ₂含量的变化,以及地球生态系统的长周期变化之间的联系。研究表明：①显生宙的碳同位素演化趋势中, ¹³C值大于3‰的时间基本上都集中在石炭纪—三叠纪初,但三叠纪初表现为 ¹³C值的高频率大幅度波动,石炭纪—二叠纪则表现为长时间持续稳定的高 ¹³C值,显示该时间段有机碳库存量的大幅度增加,相应时间段较高的 ¹⁸O值显示有机碳高速埋藏时间间隔中地球系统经历了长时间的变冷和冰室气候条件,说明有机碳高速埋藏、气候变冷、大气 pCO ₂的降低和 pO ₂升高之间存在有机的联系;② ¹³C高值时间间隔中大气CO ₂被绿色植物过度消耗,海水被迫不断向大气输送CO ₂以达到平衡,但全球气候变冷导致海水数量减少和水柱压力降低又使得海水对CO ₂的溶解能力降低以及海相碳酸盐碳库碳存量的减少,从泥盆纪、石炭纪到二叠纪,碳酸盐沉积速度显著降低,全球碳酸盐沉积盆地面积显著减小,到中、晚二叠世,一些碳酸盐沉积被硅质沉积取代,甚至包括一些浅水台地,这可能会导致一些钙质无脊椎动物数量的减少,这也说明二叠纪广泛的硅质沉积是一种全球事件;③显生宙碳酸盐锶同位素演化趋势表明,晚二叠世海水 ⁸⁷Sr/ ⁸⁶Sr急剧降低,并在二叠纪—三叠纪界线附近达到极小值,显示晚古生代结束时幔源锶的迅速加入,并伴随深部CO ₂对大气和海洋系统的补充,但与该过程有关的广泛的火山活动和地球表面温度的升高进一步加速了二叠纪末的生物群体绝灭;④全球气候变冷及相应的大陆冰盖体积的增加,北非与劳伦大陆的拼合是石炭纪—二叠纪全球海平面降低的主要原因,但该时间间隔有机碳库存量大幅度增加所消耗的水可能也是海平面降低的重要原因之一,降低幅度可能达到数十米的范围;⑤二叠纪末全球生物群体绝灭是地球系统调整的一种必然,晚古生代有机碳长时间高速埋藏,全球海水数量减少,海水对CO ₂溶解量降低,钙质无脊椎动物难以生存,最终在古生代结束前通过广泛的岩浆事件从深部向海洋和大气中补充CO ₂以调整地球系统碳库存量的不平衡,但短时间的热事件和地球表面温度的升高加剧了生物的群体绝灭与更替。

Carbon isotopic composition of marine carbonates is a record for various important geological events in the process of earth development and evolution. The carbonates of Carboniferous, Permian and Triassic, as the transition from Paleozoic to Mesozoic-Cenozoic have very high ¹³C value. Taking this as the main point, and combined with the oxygen, strontium isotopic composition in carbonates, distribution of carbonate basin area through geologic time, the correlation of carbon isotopic composition of marine carbonates to sea level change, organic carbon burial flux, exchange of CO ₂ content in atmosphere and ocean, and long cycle evolution of the earth ecosystems were approached. The results are shown as follows: ①The interval of ¹³C >3‰ during Phanerozoic was concentrated in Carboniferous, Permian and the beginning of Triassic, but the beginning of Triassic was characterized by higher frequency and larger fluctuations in ¹³C value during a short time, whereas the Carboniferous-Permian presented a continuously stable high ¹³C value, indicating a larger amount of organic carbon accumulation in this time interval. Relatively high ¹⁸O values during this time was also observed, showing a long time of glaciations and cold climate, which suggest a connection among rapid organic carbon burial, cold climate, as well as pCO ₂ and pO ₂ states of atmosphere. ②The over consumption of atmosphere CO ₂ by green plants during the time with high ¹³C of seawater forced CO ₂ being transferred from ocean to atmosphere for the balance, but the decrease in the seawater amount and water column pressure caused by the global cooling could weaken dissolution capacity of CO ₂ in seawater and carbon storage of marine carbonates, and also reduce the carbonate sedimentary rate and decrease the carbonate basin area globally from Devonian to Carboniferous and Permian. During the middle-late Permian carbonate was widely replaced by siliceous sediments even though in shallow carbonate platform, which resulted in the decrease of marine invertebrates, suggesting the Permian chert event should be global. ③The Phanerozoic ⁸⁷Sr/ ⁸⁶Sr trend of seawater showed a sharp fall in Permian and drop to a minimum at the end of the Permian, indicting input of strontium from the submarine hydrothermal systems (mantle flux). Such process should accompany with a supplement of CO ₂ from deep earth to atmosphere and ocean system, but the process associated with widespread volcanism and rises of earth’s surface temperature pricked up the mass extinction during the time of end Permian. ④Cold climate and increase of continental icecap volume, the amalgamation of northern Africa and Laurentia continentals were the main reasons responsible for the sea level drop, but the water consumption result from the significantly increased accumulation of organic carbon should also be one of the reasons for the sea level drop on the order of tens of meters. ⑤The mass extinction at the end Permian was an inevitable event in the process of earth system adjustment. It was difficult for marine invertebrates to survive because of the continuously rapid burial of organic carbon, and of the decrease of sea water amount and its dissolution ability to CO ₂. At last, at the end of Paleozoic, the supplement of CO ₂ to atmosphere and ocean by widely magma activities resulted in a high temperature of earth surface and intensified mass extinction.