Extreme aridity prior to lake expansion deciphered from facies evolution in the Miocene Ili Basin, south‐east Kazakhstan
Extreme aridity prior to lake expansion deciphered from facies evolution in the Miocene Ili Basin, south‐east Kazakhstan
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DOI：
10.1111/sed.12556
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发表时间：
2019-03
期刊：
影响因子：
3.5
通讯作者：
Konstantin Frisch;S. Voigt;T. Voigt;Alexandra Hellwig;V. Verestek;Y. Weber
中科院分区：
文献类型：
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作者：
Konstantin Frisch;S. Voigt;T. Voigt;Alexandra Hellwig;V. Verestek;Y. Weber
中亚在中新世经历了逐渐干旱，通常与山脉抬升、副特提斯海退缩和全球气候变冷有关。然而，中亚中新世湖泊的形成似乎与干旱条件相反，这表明干旱化的精确时间、程度和强迫仍然没有得到很好的限制。本研究提出了伊犁盆地中新世中晚期冲积湖相部分的相模型，该模型是从两个层序中获得的。该模型能够对区域水位和盐度进行半定量评估，并表征水位对蒸发岩形成和成岩作用的控制。近端的 Kendyrlisai 序列和远端的 Aktau 序列都显示出从干燥泥滩沉积到具有过渡普拉亚阶段的湖泊沉积的可用水量总体增加。不断增加的蒸发速度超过了供水速度，导致地下水盐化。随后的湖泊扩张与全流域的海水淡化同时发生，需要转向正水预算。由于突然的盐化和较小的构造影响，推断出气候对水文演化的控制。长期积水可能与中中新世早期（15·3Ma）盆地水文闭合有关。从14·3 Ma开始，逐步盐化与中新世气候转变的全球变冷同时发生。中新世气候转变导致伊犁盆地极度干旱，盆地中心早期成岩作用的硬石膏的形成凸显了这一点。中新世气候转变后伊犁盆地气温降低导致蒸发率降低，可能促进了淡水湖的扩张（12·7 Ma至11·5 Ma）。伊犁盆地的极端干旱被解释为与中部副提斯海巴登期盐度危机的大陆对应物。这强调了中中新世期间大气强迫对欧亚大陆蒸发沉积的作用。
Central Asia witnessed progressive aridification during the Miocene, commonly related to mountain uplift, the Paratethys retreat and global climate cooling. However, the formation of Miocene lakes in Central Asia seems to oppose drier conditions, suggesting that the precise timing, extent and forcing of the aridification is still not well constrained. This study presents a facies model for the alluvial–lacustrine part of the Middle to Late Miocene of the Ili Basin, obtained from two successions. The model enables the semi‐quantitative assessment of regional water level and salinity, and characterizes the control of water level on evaporite formation and diagenesis. Both the proximal Kendyrlisai and the distal Aktau successions show an overall increase in water availability from dry mudflat deposits to lacustrine sedimentation with a transitional playa phase. Increasing evaporation rates outpaced the water supply and caused groundwater salinization. Subsequent lake expansion coincided with a basin‐wide desalinization and required a shift to a positive water budget. A climatic control of the hydrological evolution is inferred due to abrupt salinization and a minor tectonic influence. The long‐term water accumulation is probably related to the hydrological closure of the basin in the early Middle Miocene (15·3 Ma). Starting at 14·3 Ma, the step‐wise salinization occurred simultaneously with the global cooling of the Miocene Climate Transition. The Miocene Climate Transition led to extreme aridity in the Ili Basin, highlighted by the early diagenetic formation of displacive anhydrite in the basin centre. The expansion of the freshwater lake (12·7 to 11·5 Ma) was possibly promoted by lower evaporation rates due to decreasing air temperatures in the Ili Basin after the Miocene Climate Transition. The extreme aridity in the Ili Basin is interpreted as a continental counterpart to the Badenian Salinity Crisis in the Central Paratethys. This emphasizes the role of atmospheric forcing on evaporite sedimentation across Eurasia during the Middle Miocene.