Sedimentary record of Upper Triassic impact in the Lagonegro Basin, southern Italy: Insights from highly siderophile elements and Re Os isotope stratigraphy across the Norian/Rhaetian boundary
Sedimentary record of Upper Triassic impact in the Lagonegro Basin, southern Italy: Insights from highly siderophile elements and Re Os isotope stratigraphy across the Norian/Rhaetian boundary
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DOI：
10.1016/j.chemgeo.2021.120506
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发表时间：
2021-08
期刊：
影响因子：
3.9
通讯作者：
Honami Sato;A. Ishikawa;T. Onoue;Y. Tomimatsu;M. Rigo
中科院分区：
文献类型：
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作者：
Honami Sato;A. Ishikawa;T. Onoue;Y. Tomimatsu;M. Rigo
诺里安和雷氏过渡(晚三叠世)以主要远洋类群的动物群更替为特征，如放射虫、牙形刺和菊石。尽管已经提出了诸如大型火成岩省的侵位和/或外星撞击等灾难性事件可以解释这种生物更替，但仍然缺乏基于沉积序列地球化学的确凿证据。为了评估跨越Norian/Rhaetian边界(NRB)的环境变化，我们报道了意大利南部拉格格罗盆地Sasso di Castalda剖面全岩主要、微量和高度亲铁元素丰度的高分辨率地层变化，以及Re-Os同位素比值。该剖面由一个连续出露的上诺里安(Sevatian)至下Rhaetian的深盆沉积序列组成。我们的数据表明，上诺里安剖面以地层上升的顺序记录了重要的事件：(1)沉积环境移动到碳酸盐补偿深度以下，导致碳酸盐-生物硅转变，伴随着重矿物中有益元素的轻微亏损，(2)铂族元素异常检测到的罗氏冲击组分的输入，以及(3)氧化还原状态向低氧(缺氧到亚氧)状态的瞬时变化，其标志是V、U和Re的增加。这一系列事件表明，罗切肖特事件的影响早于导致NRB动物周转的主要环境变化。尽管考虑到冲击器的小尺寸以及影响范围和NRB之间的间隔，它们之间的直接因果关系非常值得怀疑，但不能排除引发随后的环境和生物坍塌的可能性。这项研究首次在海相地层中识别了罗切肖特影响层位，这可能是进一步研究拉格罗盆地和其他地区同时代剖面的重要事件标志。
The Norian and Rhaetian transition (Late Triassic) is characterized by a faunal turnover in major pelagic groups, such as radiolarians, conodonts, and ammonoids. Although catastrophic events such as emplacements of large igneous provinces and/or extraterrestrial impacts have been suggested to account for this biotic turnover, firm evidence based on geochemistry of sedimentary successions is still lacking. In order to assess environmental changes across the Norian/Rhaetian boundary (NRB), we report high–resolution stratigraphic variations for whole-rock major, trace, and highly siderophile element abundances, together with Re–Os isotope ratios for the Sasso di Castalda section in Lagonegro Basin, southern Italy. The section consists of a continuously exposed sequence of upper Norian (Sevatian) through the lower Rhaetian of a deep basinal deposits. Our data demonstrated that the upper Norian section records important events in stratigraphically ascending order: (1) a depositional environment moved below the Carbonate Compensation Depth, leading to the carbonate-biosilica transition associated with a slight depletion of elements favored in heavy minerals such as Zr, Hf, and Ti, (2) an input of Rochechouart impact components detected by platinum-group element anomaly, and (3) a transient change of redox state into low oxygen (dysoxic to suboxic) conditions marked by increases of V, U, and Re. This sequence of events suggests that the Rochechouart impact predates the major environmental changes resulting in faunal turnover at the NRB. Although their direct causal relationships are highly questionable given the small size of impactor and the interval between the impact horizon and the NRB, the possibility of triggering subsequent environmental and biotic collapses cannot be ruled out. This study provides the first identification of Rochechouart impact horizon in marine strata, which could be an important event marker for further studies on contemporaneous sections in the Lagonegro Basin and other localities.