Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana
Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana
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DOI：
10.1130/g46740.1
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发表时间：
2019-12-01
期刊：
影响因子：
5.8
通讯作者：
Yin, Qing-Zhu
中科院分区：
文献类型：
--
作者：
Griffis, Neil Patrick;Montanez, Isabel Patricia;Yin, Qing-Zhu
晚古生代冰期的消亡被假设为历时性的，首先发生在南美洲西部，然后向东穿过非洲，在澳大利亚达到顶峰，超过6000万年。这表明构造强迫机制的时间尺度为10（6）年或更长。我们测试西南部和中南部冈瓦纳新的单晶U-Pb锆石化学磨蚀热电离质谱法（CA-TIMS）年龄火山沉积在巴拉那（巴西）和卡鲁（南非）盆地，跨越终端冰消期，通过早期冰后期，这一穿时消退假说。新的高分辨率放射性同位素年龄所允许的盆内地层相关性表明，整个S至东南巴拉那盆地的冰川消退是同步的，冰川作用局限于石炭纪。跨流域的相关性揭示了两个额外的冰川-冰消旋回在卡鲁盆地后，在巴拉那盆地的终端冰消。南非冰川是准同生的（在U-Pb年龄不确定性范围内），具有三级层序边界（即，推断基准面福尔斯）在巴拉那盆地。冈瓦纳大陆西南部至中南部早二叠世冰川-冰消事件与pCO（2）波动之间的同步性表明，CO2对冰阈值具有主要控制作用。在卡鲁盆地，在巴拉那盆地终末冰消期后，重新冰川作用的发生，反映了区域古地理，地形和水分来源的次生影响。
The demise of the Late Paleozoic Ice Age has been hypothesized as diachronous, occurring first in western South America and progressing eastward across Africa and culminating in Australia over an -60 m.y. period, suggesting tectonic forcing mechanisms that operate on time scales of 10(6) yr or longer. We test this diachronous deglaciation hypothesis for southwestern and south-central Gondwana with new single crystal U-Pb zircon chemical abrasion thermal ionizing mass spectrometry (CA-TIMS) ages from volcaniclastic deposits in the Parana (Brazil) and Karoo (South Africa) Basins that span the terminal deglaciation through the early postglacial period. Intrabasinal stratigraphic correlations permitted by the new high-resolution radioisotope ages indicate that deglaciation across the S to SE Parana Basin was synchronous, with glaciation constrained to the Carboniferous. Cross-basin correlation reveals two additional glacial-deglacial cycles in the Karoo Basin after the terminal deglaciation in the Parana Basin. South African glaciations were penecontemporaneous (within U-Pb age uncertainties) with third-order sequence boundaries (i.e., inferred base-level falls) in the Parana Basin. Synchroneity between early Permian glacial-deglacial events in southwestern to south-central Gondwana and pCO(2) fluctuations suggest a primary CO2 control on ice thresholds. The occurrence of renewed glaciation in the Karoo Basin, after terminal deglaciation in the Parana Basin, reflects the secondary influences of regional paleogeography, topography, and moisture sources.