本文選題：龍門峽南剖面 + 早三疊世　； 參考：《中國科學(xué):地球科學(xué)》2017年01期

【摘要】：早三疊世作為二疊紀(jì)末集群滅絕后地球系統(tǒng)的生態(tài)恢復(fù)時期,與古海洋生態(tài)變化有關(guān)的各種地球化學(xué)記錄為地質(zhì)學(xué)家長期高度關(guān)注.在巖石學(xué)研究和樣品對海水代表性評估的基礎(chǔ)上,測試了四川盆地東部廣安龍門峽南剖面下三疊統(tǒng)(包括相鄰地層)350個碳酸鹽巖的碳氧同位素組成.研究表明:龍門峽南剖面下三疊統(tǒng)碳酸鹽巖對海水碳同位素組成具有良好的保存性,碳氧同位素組成之間缺乏相關(guān)性,二者間的確定系數(shù)只有0.0205,350個樣品中只有44個Mn/Sr2和/或δ~(18)O-6.5‰;根據(jù)306個Mn/Sr2和/或δ~(18)O-6.5‰的樣品建立了完整的下三疊統(tǒng)碳同位素曲線,曲線具有非常好的全球可對比性,二疊,三疊界線附近、嘉一段頂部和三段內(nèi)部的δ~(13)C極小值,夜郎組一段頂部、四段頂部和嘉陵江組二段底部、四段下部的δ~(13)C極大值,以及代表這些極大值的峰和代表這些極小值的谷所反映的都是全球信號;與全球其他地方年代地層框架內(nèi)同期碳同位素曲線的對比結(jié)果表明,剖面夜郎組一段可大致與Griesbachian亞階對應(yīng),夜郎組二,四段可大致與Dienerian亞階對應(yīng),嘉陵江組一段大致與Smithian亞階對應(yīng),嘉陵江組二-三段以及四段下部大致與Spathian亞階對應(yīng),嘉陵江組四段的中上部則應(yīng)歸于中三疊世的Aegean亞階;代表Smithian-Spathian亞階界線(SSB)的嘉一、嘉二段界線附近δ~(13)C從-0.911‰急劇上升至3.679‰,海水碳同位素如此劇烈的變化耗時可能小于36kyr,對沉積環(huán)境反映更為敏感的氧同位素在SSB附近先于碳同位素變化,反映海水在碳同位素急劇升高之前,鹽度已顯著增加,并導(dǎo)致了蒸發(fā)巖和白云巖的形成,該問題的更深入研究還需要考慮白云石-水和方解石-水系統(tǒng)、白云石-CO_2和方解石-CO_2系統(tǒng)白云石和方解石形成過程中同位素分餾效應(yīng)的差別.
[Abstract]:The early Triassic as the ecological restoration period of the Earth system after the late Permian mass extinction, various geochemical records related to the paleo-marine ecological changes have been highly concerned by geologists for a long time. On the basis of petrological study and representative evaluation of seawater samples, the carbon and oxygen isotopic compositions of 350 carbonate rocks of Lower Triassic (including adjacent strata) in the southern section of Longmen Gorge in Guang'an, eastern Sichuan Basin, were measured. The results show that the lower Triassic carbonate rocks are well preserved for the carbon isotopic composition of seawater in the south section of Longmen Gorge, and there is no correlation between the carbon and oxygen isotopic compositions. The coefficient of determination between them is only 0.0205350 samples with only 44 mn / Sr2 and / or 未 ~ (18) O ~ (-6.5) 鈥，

本文編號：2008868