Distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in Microbial Mats From Holocene and Miocene Sabkha Sediments
Distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in Microbial Mats From Holocene and Miocene Sabkha Sediments
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DOI：
10.3389/feart.2019.00310
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发表时间：
2019-12
影响因子：
2.9
通讯作者：
B. Petrick;L. Reuning;A. Martínez-García
中科院分区：
文献类型：
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作者：
B. Petrick;L. Reuning;A. Martínez-García
萨布卡是了解早期地球生物环境的重要环境，与之相关的藻席被认为是潜在的生烃源岩。本研究比较了阿布扎比现代和中全新世萨布哈沉积物中分支和类异戊二烯甘油二烷基甘油四醚(GDGTS)的沉积相和分布，以及最近在澳大利亚北部海岸外IODP站U1464发现的保存完好的中新世(12-13 Ma)萨布哈沉积物。结果表明，中新世沉积相与全新世和现代萨布卡非常相似。此外，我们还发现在现代萨布哈存在明显的类异戊二烯GDGT分布模式，这些模式在埋藏的全新世和中新世藻席中都得到了很好的保存。所分析的萨布哈沉积物具有高%GDGT-0和甲烷指数，分支GDGTS占优势(BIT指数高)，异戊二烯GDGTs1-3的异常分布，以及古醇的低丰度。分支GDGT在现代和中新世萨布卡沉积中的分布不同，而在中新世萨布哈和非萨布哈沉积中的分布相似，表明它们在区分古萨布哈沉积方面的作用有限。总体而言，类异戊二烯GDGT分布似乎不同于现代土壤、湖泊和海洋沉积物中的分布，也不同于萨布哈以下中新世浅水沉积中的分布，因此可以结合相分析来识别沉积层序中的古萨布哈环境。
Sabkhas are important settings for understanding early earth biological environments, and the algal mats associated with them are thought to be potential source rocks for hydrocarbon production. In this study we compare the sedimentological facies and distribution of branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) in modern and mid-Holocene sabkha sediments from Abu Dhabi with well-preserved Miocene (12-13 Ma) sabkha sediments recently recovered at IODP site U1464 off the north coast of Australia. We show that the facies of the Miocene sediments is very similar to Holocene and modern sabkhas. Furthermore, we show that there are distinct patterns of isoprenoid GDGT distributions in the modern sabkha and that these patterns are well preserved in both the buried Holocene and the Miocene algal mats. The sabkha sediments analyzed are characterized by high %GDGT-0 and methane index, dominance of branched GDGTs over crenarchaeol (high BIT index), an unusual distribution of isoprenoid GDGTs 1-3, and also low abundance of archaeol. The distribution of branched GDGT differs between modern and Miocene sabkhas and is similar in Miocene sabkha and non-sabkha sediments suggesting that they may be of limited use to distinguish paleo-sabkha sediments. Overall, isoprenoid GDGT distributions appear to be different from those found in modern soils, lakes and marine sediments, as well as from those found in Miocene shallow water sediments right below the sabkha, therefore they could be used in combination with facies analysis to identify paleo-sabkha environments in sedimentary sequences.