The Massignano Eocene-Oligocene golden spike section revisited
The Massignano Eocene-Oligocene golden spike section revisited
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重温马西尼亚诺始新世-渐新世黄金穗部分
作者：
C. V. Mourik;H. Brinkhuis
在实践中，始新世/渐新世(E/O)界线与OI-1 d18O海底同位素事件有关，反映了南极主要冰川作用的最古老阶段，并与磁亚时相C13n进行了校准。然而，IUGS批准的、目前位于意大利中部远洋马萨卡诺采石场部分的E/O全球地层学剖面和点(GSSP)，发生在较老的磁亚时C13r内。为了将Massignano的记录进一步延伸到渐新世早期，为了包括地表剖面中缺失的关键C13n事件，在采石场剖面的直接附近钻取了一个岩芯。首先，最近提出了岩芯和采石场区段之间的关联。在这篇论文中，我们使用高分辨率的有机管壁甲藻包囊分析来显著提高两个切片之间的相关性。此外，我们在早期研究的基础上，证明了目前的E/O GSSP标准是基于热带浮游有孔虫属Hantkenina的局部灭绝，它代表了一个孤立的事件，不适合全球关联。相反，我们认为OI-1事件的选择是确定E/O界面的主要标准，这为全球对比提供了更好的基础，此外，OI-1还与TA4.3/4.4三级层序界面和最后一次出现的双壳类Areosphaeridium diktyoplokum有关。选择这一略年轻的标准将把经典普里亚博阶段的上界推回到最新世，而鲁珀利阶段的底界放在最早的渐新世。由于提议的相关OI-1事件级别没有出现在地表(采石场)段，而只存在于马萨塔诺的取心段，因此应选择一个新的GSSP选址，例如在跨越C13n的其他意大利中部段之一。
In common practice, the Eocene/Oligocene (E/O) boundary is linked to the Oi-1 d18O benthic isotope event, reflecting the oldest phase of major Antarctic glaciation, calibrated against magnetosubchron C13n. Yet, the IUGS-ratified, current E/O Global Stratigraphic Section and Point (GSSP) at the pelagic Massignano quarry section, central Italy, occurs within the older magnetosubchron C13r. To extend the Massignano record further into the early Oligocene, to include the critical C13n episode missing in the surface section, a core was drilled in the direct vicinity of the quarry section. First correlations between the core and the quarry section have recently been proposed. In this paper, we use high-resolution organic-walled dinoflagellate cyst (dinocyst) analysis to significantly improve correlation between the two sections. In addition, we build on earlier studies, and demonstrate that the current E/O GSSP criterion, which is based on the local extinction of the tropical planktonic foraminifera genus Hantkenina represents an isolated event that is not suitable for global correlation. Instead, we argue that selection of the Oi-1 event be the main criterion for the determinating the E/O boundary, and that this provides a much better basis for global correlation, Moreover, the Oi-1 is also related to the TA4.3/4.4 third order sequence boundary and the last occurrence of the dinocyst Areosphaeridium diktyoplokum. Selection of this slightly younger criterion would place the upper boundary of the classic Priabonian Stage back in the latest Eocene, and the base of the Rupelian Stage in the earliest Oligocene. Since the proposed correlative Oi-1 event level is not represented in the surface (quarry) section, but only resides in the cored section at Massignano, a new GSSP site should be selected, for example in one of the other central Italian sections that does span C13n.