High phosphate availability as a possible cause for massive cyanobacterial production of oxygen in the Paleoproterozoic atmosphere
High phosphate availability as a possible cause for massive cyanobacterial production of oxygen in the Paleoproterozoic atmosphere
复制标题
DOI：
10.1016/j.epsl.2012.11.050
复制
发表时间：
2013-01
影响因子：
5.3
通讯作者：
D. Papineau;R. Purohit;M. Fogel;G. Shields-Zhou
中科院分区：
文献类型：
--
作者：
D. Papineau;R. Purohit;M. Fogel;G. Shields-Zhou
主要的前寒武纪磷块岩的沉积仅限于元古代两端的全球变化和大气氧化时期。磷块岩是在古元古代Lomagundi-Jatuli事件和新元古代Cryogenian和Ediacaran时期沉积的碳酸盐中高度正的碳同位素漂移后形成的。元古代大气中氧气含量的逐步上升与碳循环的变化有关。然而，碳同位素事件，磷块岩和大气氧化之间的关系仍然无法解释。古元古代的Aravalli超群，印度的碳酸盐，保存蓝藻水华的证据，在世界上最古老的重要的沉积磷酸盐存款紧密堆积叠层石柱的形式。下阿拉瓦利群的局限盆地中，贾马科特拉、乌代布尔、贾布阿和萨洛帕特的叠层石磷块岩显示出接近零的δ 13 C碳值和介于−33.3‰和−10.1‰之间的大范围δ 13 C碳值，表明了一个复杂的碳循环。由于磷酸盐主要积累在含氧沉积物中，这些富营养化的微生物生态系统可能是在浅的含氧海洋领域的透光带中发展起来的。这与在大氧化事件（GOE）之后的越来越多的氧化条件期间的沉积一致。在Ghasiar、Karouli、Negadia、Umra和Babarmal等没有磷酸盐沉积的近似同生盆地中，δ 13 C碳偏移呈现一系列正值，有些值高达+11.2‰，表明有机碳埋藏率较高，而另一些δ 13 C碳值在+6‰或+3‰左右，表明碳循环扰动较小。所有这些岩石的δ 15 N值在−0.7‰和+3.4‰之间变化，与所有盆地类型中蓝藻水华期间的固氮优势一致。这种低氮同位素值被解释为是由于生物对高磷酸盐可用性的反应。我们的结论是，在古元古代Lomagundi-Jatuli事件期间和之后，磷酸盐的可用性增加可能导致蓝藻水华，是地球大气氧化的关键因素。约2.0Ga后，浅海海底氧合作用的增加有利于以自生磷灰石形式去除过量磷酸盐，从而抑制了风化作用对有机埋藏和海洋δ 13 C碳增加的影响。
The deposition of major Precambrian phosphorites was restricted to times of global change and atmospheric oxygenation at both ends of the Proterozoic. Phosphorites formed after highly positive carbon isotope excursions in carbonates deposited during the Paleoproterozoic Lomagundi-Jatuli event and the Neoproterozoic Cryogenian and Ediacaran periods. The correlative step-wise rise in atmospheric oxygen over the Proterozoic has been linked to changes in the carbon cycle. However, the postulated relations between carbon isotope events, phosphorites, and atmospheric oxygenation remain unexplained. Paleoproterozoic carbonates of the Aravalli Supergroup, India, preserve evidence for cyanobacterial blooms in the form of tightly packed stromatolitic columns in the world's oldest significant sedimentary phosphate deposit. Restricted basins of the Lower Aravalli Group with stromatolitic phosphorites in Jhamarkotra, Udaipur, Jhabua, and Sallopat exhibit near-zero δ13Ccarbvalues and large ranges of δ13Corgvalues between −33.3‰ and −10.1‰, indicative of a complex carbon cycle. Because phosphate accumulates primarily in oxic sediments, these eutrophic microbial ecosystems likely developed within the photic zone of the shallow, oxygenated marine realm. This is consistent with deposition during the time of increasingly more oxidizing conditions, after the Great Oxidation Event (GOE). Approximately contemporaneous basins without phosphate deposits from Ghasiar, Karouli, Negadia, Umra, and Babarmal exhibit a range of positive δ13Ccarbexcursions, some with values up to +11.2‰, that suggest high rates of organic carbon burial, and others with moderately high δ13Ccarbvalues around +6‰ or +3‰, that suggest smaller carbon cycle perturbations. The δ15N values of all these rocks vary between −0.7‰ and +3.4‰, and are consistent with the predominance of nitrogen fixation during cyanobacterial blooms in all basin types. Such low nitrogen isotope values are interpreted to have arisen from the biological response to high phosphate availability. We conclude that increased phosphate availability during and after the Paleoproterozoic Lomagundi-Jatuli event likely caused cyanobacterial blooms and was a key factor in the oxygenation of Earth's atmosphere. Increasing oxygenation of the shallow ocean seafloor favored the removal of excess phosphate as authigenic apatite, thus dampening effects of weathering increases on organic burial and marine δ13Ccarbafter about 2.0Ga.