Development of early calcareous nannoplankton in the late Triassic (Northern Calcareous Alps, Austria)
Development of early calcareous nannoplankton in the late Triassic (Northern Calcareous Alps, Austria)
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DOI：
10.1016/j.gloplacha.2020.103254
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发表时间：
2020-10-01
影响因子：
3.9
通讯作者：
Piller, Werner E.
中科院分区：
文献类型：
--
作者：
Demangel, Isaline;Kovacs, Zsofia;Piller, Werner E.
钙质超微化石被认为是最具生产力的钙化生物，但它们的出现对晚三叠世海洋化学的影响尚不清楚。由于世界范围内保存完好的露头稀缺，这种生物事件的进化细节缺失。目前的研究重点是在奥地利北方钙质阿尔卑斯山的Sommeraukogel和Steinbergkogel的中Norian到下Rhaetian的钙质超微化石组合。沉积物沉积在古纬度约20-30 ° N的深陆棚上的地形高点上。在出现的浮游钙化的步骤记录的扫描电子显微镜（SEM）的研究。颗石的首次出现（FO），没有确定在一个物种的水平，记录在中Norian（Alaunian 3）。最古老的Crucirhabdus minutus和Cruceozygodiscus koessenensis在Norian晚期（Sevatian）被观察到，其次是Crucirhabdus primulus的FO在Rhaetian早期。这些观察结果表明，第一颗石藻的进化相当缓慢，从祖先C。minutus到C. primulus之间的演化，以及新属A. koessenensis。沉积序列的成岩叠加影响了钙质超微化石的保存程度，但不影响其数量的趋势，在所研究的样品中，钙质沉积物的岩相学研究和微量元素的签名证明。这支持了我们的定量估计的碳酸钙体积和古通量由于出口生产力的钙质超微化石，Prinsiosphaera triassica。我们的研究结果表明，优势和丰富的Prinsiosphaera triassica略高于Norian/Rhaetian边界的增加。然而，钙质超微化石并没有达到岩石形成的丰度在这个时候，因此并没有显着影响地球化学组成的西特提斯洋。
Calcareous nannofossils are considered to be the most productive calcifying organisms, but the impact of their emergence on the chemistry of the ocean in the Late Triassic is not understood yet. Evolutionary details of this bio-event are missing due to the scarcity of well-preserved outcrops worldwide. The current study focuses on the calcareous nannofossil assemblage of the middle Norian to lower Rhaetian at Sommeraukogel and Steinbergkogel in the Northern Calcareous Alps (Austria). The sediments were deposited on a topographic high on a deeper shelf at a palaeolatitude around 20-30 degrees N. The steps in the emergence of pelagic calcifiers are documented by a scanning electron microscope (SEM) study. The First Occurrence (FO) of coccolith, not identified at a species level, was recorded in the middle Norian (Alaunian 3). The oldest Crucirhabdus minutus and Archaeozygodiscus koessenensis were observed in the late Norian (Sevatian) and were followed by the FO of Crucirhabdus primulus in the early Rhaetian. These observations suggest a rather slow temporal evolution of the first coccolithophorids, with millions of years from the ancestor C. minutus to C. primulus, and in between the evolution of the new genus A. koessenensis. Diagenetic overprinting of the sedimentary succession has affected the preservation degree of the calcareous nannofossils but not the trend of their quantity in the studied samples, as proven by petrographic studies and trace element signatures of the calcareous sediments. This supports our quantitative estimates of the CaCO3 volume- and palaeo-fluxes due to the export productivity of the calcareous nannofossils, Prinsiosphaera triassica. Our results show the dominance and the increase in abundance of Prinsiosphaera triassica slightly above the Norian/Rhaetian boundary. However, calcareous nannofossils did not reach rock-forming abundances at this time and thus did not significantly influence the geochemical composition of the Western Tethys Ocean.