【摘要】：魚骨狀方解石是一種特殊的碳酸鹽沉積,由鋸齒狀亮暗交互的亞毫米級(jí)條帶組成,主要見于太古宙。以往認(rèn)為,魚骨狀方解石屬無機(jī)化學(xué)沉淀成因,形成于水體缺氧、碳酸鹽過飽和、富Fe~(2+)、Mn~(2+)等碳酸鹽沉淀抑制劑的環(huán)境條件;在地質(zhì)記錄中其豐度隨時(shí)間的減少反映了海洋的長(zhǎng)期氧化趨勢(shì)。文中首次在華北地臺(tái)中元古界高于莊組四段微生物礁內(nèi)發(fā)現(xiàn)了大量魚骨狀方解石。宏觀觀察表明,這些魚骨狀方解石主要以微生物礁孔洞充填物形式產(chǎn)出,明顯區(qū)別于太古宙以海底沉淀形式直接產(chǎn)出在海底的魚骨狀方解石。顯微研究發(fā)現(xiàn),魚骨狀方解石晶體纖維具有沿晶體生長(zhǎng)方向旋轉(zhuǎn)消光特征,證明其內(nèi)部亞晶的光學(xué)C軸從纖維底部的隨機(jī)排列逐步旋轉(zhuǎn)至上部垂直纖維生長(zhǎng)方向。這符合球狀晶體生長(zhǎng)模式,需要方解石沉淀抑制劑的參與。魚骨狀方解石產(chǎn)出具有豐度隨時(shí)間減少以及產(chǎn)出形式由海底沉淀向孔洞膠結(jié)物轉(zhuǎn)變的特征。這些特征與海洋氧化逐漸增強(qiáng)以及具氧化還原敏感屬性的碳酸鹽沉淀抑制劑逐漸從水體中移除相吻合。筆者認(rèn)為魚骨狀方解石的沉淀抑制劑為Fe~(2+)和Mn~(2+),這與微生物巖無明顯Ce異常和Fe~(2+)極強(qiáng)的抑制能力相一致。因此,魚骨狀方解石可用于指示缺氧環(huán)境條件。此外,顯微和超微研究也表明魚骨狀方解石晶體內(nèi)存在有大量與其生長(zhǎng)方向一致的菌絲體殘余和與之密切伴生的有機(jī)礦物,表明微生物為魚骨狀方解石成核和初始沉淀提供了重要墊板。
[Abstract]:Fishbone calcite is a special carbonate deposit consisting of zigzag bright and dark interacting submillimeter bands mainly found in Archean. In the past, it was considered that fishbone calcite belongs to inorganic chemical precipitation, which was formed under the environmental conditions of anoxia, supersaturation of carbonate, rich in Fe~ (2) mn ~ (2) and so on. The decrease of abundance over time in geological records reflects the long-term oxidation trend of the ocean. In this paper, a large number of fishbone calcite was first found in the microbe reef of the Proterozoic in Taizhong, North China. Macroscopic observation shows that these fish bone calcite are mainly produced in the form of microorganism reef pore filling, which is obviously different from Archean fish bone calcite produced directly in the form of submarine sedimentation. Microscopic study shows that the fishbone calcite crystal fiber has the characteristics of rotation and extinction along the crystal growth direction. It is proved that the optical C axis of the inner subcrystal rotates gradually from the random arrangement at the bottom of the fiber to the vertical fiber growth direction in the upper part. This is in line with the growth pattern of spheroid crystals and requires the participation of calcite precipitation inhibitors. The fish bone calcite production is characterized by the decrease of abundance over time and the transition from seabed sedimentation to pore cementation. These characteristics are consistent with the gradual enhancement of marine oxidation and the gradual removal of carbonate precipitation inhibitors with redox sensitivity from water. The authors consider that the depressants of fishbone calcite are Fe~ (2) and Mn~ (2), which are consistent with the fact that there is no obvious Ce abnormality in microbe rock and the strong inhibition ability of Fe~ (2). Therefore, fishbone calcite can be used to indicate anoxic environmental conditions. In addition, microscopic and ultrastructural studies also showed that there are a large number of mycelium residues and organic minerals closely associated with the fishbone calcite crystal. The results show that the microorganism provides an important cushion for the nucleation and initial precipitation of fish bone calcite.
【作者單位】： 中國(guó)地質(zhì)大學(xué)生物地質(zhì)與環(huán)境地質(zhì)國(guó)家重點(diǎn)實(shí)驗(yàn)室;中國(guó)地質(zhì)大學(xué)(北京)科學(xué)研究院;中國(guó)地質(zhì)大學(xué)(北京)地球科學(xué)與資源學(xué)院;中國(guó)地質(zhì)調(diào)查局油氣資源調(diào)查中心;
【基金】：國(guó)家自然科學(xué)基金項(xiàng)目(編號(hào):41402024,41272039) 中央高�；究蒲袠I(yè)務(wù)費(fèi)專項(xiàng)資金項(xiàng)目(編號(hào):2652014063)共同資助~~
【分類號(hào)】：P578.61

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