本文關(guān)鍵詞： 晚白堊世 大洋缺氧事件 大洋紅層 Fe同位素 古海洋　出處：《中國地質(zhì)大學(xué)(北京)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：白堊紀(jì)是地質(zhì)歷史記錄中極端溫室氣候的典型的代表,研究白堊紀(jì)的古海洋和古氣候系統(tǒng)變化對于預(yù)測正在升溫的地球未來溫室效應(yīng)變化方面具有重要的意義。上白堊統(tǒng)的海相地層存在富有機(jī)質(zhì)黑色頁巖向貧有機(jī)質(zhì)的大洋紅層的轉(zhuǎn)變,可能記錄了發(fā)生在Cenomanian-Turonian界線附近的白堊紀(jì)極端大洋缺氧事件OAE 2之后全球大洋逐漸轉(zhuǎn)為富氧狀態(tài)。這個(gè)轉(zhuǎn)變涉及溫室氣候條件下全球海洋和氣候系統(tǒng)波動,以及碳-氧循環(huán)等重要科學(xué)問題,因此已成為國際白堊紀(jì)研究領(lǐng)域新的重要方向。本文選取了東特提斯西藏床得剖面、西特提斯意大利Contessa Quarry剖面和北大西洋ODP 103航次Site 641A站點(diǎn)這三個(gè)剖面上白堊統(tǒng)黑-紅轉(zhuǎn)變層位的樣品,開展了系統(tǒng)的沉積學(xué)、元素地球化學(xué)、有機(jī)碳、Fe組分和Fe同位素組成分析研究,試圖重建晚白堊世古海洋-古氣候變化。結(jié)果顯示,三個(gè)剖面的大洋紅層與下伏黑色頁巖的Fe同位素組成及其他地球化學(xué)指標(biāo)均顯示有系統(tǒng)變化。本文是國際上首次報(bào)道上白堊統(tǒng)大洋紅層的Fe同位素組成,其Fe同位素組成相對均一,但某些樣品存在一定的變化,δ56Fe的變化范圍為-0.400~0.505‰,說明在大氣和表層水氧化條件下,巖性和區(qū)域Fe循環(huán)對Fe同位素組成的影響。代表大洋缺氧事件的黑色頁巖的Fe同位素組成有相對較大的變化范圍,隨三個(gè)剖面不同的沉積位置和沉積環(huán)境的不同而不同。結(jié)合Fe同位素、Fe組分和元素地球化學(xué)特征,在OAE 2黑色頁巖沉積期間東特提斯床得剖面處于弱氧化沉積環(huán)境,西特提斯Contessa Quarry剖面處于缺氧/硫化環(huán)境,而北大西洋的Site641A為硫化環(huán)境。三個(gè)剖面黑-紅過渡層段的Fe同位素組成變化范圍大,可能反映了轉(zhuǎn)變過程中水體環(huán)境的波動。三個(gè)剖面沉積時(shí)的氧化還原環(huán)境和Fe循環(huán)模式的不同,指示了在全球氣候變化的背景下,區(qū)域古地理、構(gòu)造等作用對古海洋環(huán)境和地球化學(xué)循環(huán)的作用。北大西洋Site641A站點(diǎn)的大洋紅層的Fe指標(biāo)和古生物化石證據(jù)可能暗示了在Turonian(晚)期赤道大西洋初期打開,初期打開之后經(jīng)歷了約0.6 Ma才有穩(wěn)定的海水連通,使大西洋演化為通風(fēng)良好的開放大洋環(huán)境。相比較而言,在西特提斯洋(意大利)從OAE 2的硫化環(huán)境過渡到富氧、通風(fēng)大洋環(huán)境用了大約1.1 Myr,在東特提斯洋(西藏南部)需要更長時(shí)間(9Myr)。根據(jù)本文的數(shù)據(jù)分析,并結(jié)合全球古氣候古海洋學(xué)和古氣候?qū)W指標(biāo)表明,從上白堊統(tǒng)黑色頁巖到大洋紅層的沉積,可能是這可能是由氣候變冷和大洋海道打開共同驅(qū)動的。
[Abstract]:The Cretaceous is a typical representative of the extreme greenhouse climate in the geological history records. The study of the Cretaceous paleooceanic and paleoclimate systems is of great significance in predicting the future Greenhouse Effect changes of the warming earth. The marine strata of the Upper Cretaceous are rich in organic matter, black shale and poor in organic matter. The transformation of the red layer of the ocean, It may have been recorded that after the Cretaceous extreme oceanic anoxic event OAE _ 2, near the Cenomanian-Turonian boundary, the global ocean gradually became oxygen-rich. This transition involves fluctuations in the global ocean and climate system under greenhouse climate conditions. As well as important scientific issues such as the carbon-oxygen cycle and so on, it has become a new important direction in the international Cretaceous research field. In this paper, the East Tethys Tibetan bed profile has been selected. The samples of the Cretaceous black-red transition horizon in the three sections of the Contessa Quarry section of West Tethys Italy and the North Atlantic ODP 103 voyage Site 641A station have developed systematic sedimentology and elemental geochemistry. The study on the composition of organic carbon and Fe isotopes in order to reconstruct the paleo-ocean-paleoclimate change of late Cretaceous shows that, The Fe isotopic compositions and other geochemical indices of the oceanic red beds and underlying black shale in the three sections show systematic variation. This is the first time that the iron isotopic compositions of the upper Cretaceous oceanic red beds have been reported in the world. Its Fe isotopic composition is relatively uniform, but some samples have some changes. The range of 未 56Fe varies from -0.400 to 0.505 鈥，

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