Elemental abundance anomalies in the late Cenomanian extinction interval: a search for the source(s)
Elemental abundance anomalies in the late Cenomanian extinction interval: a search for the source(s)
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DOI：
10.1016/0012-821x(93)90126-t
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发表时间：
1993-05
影响因子：
5.3
通讯作者：
C. Orth;M. Attrep;L. R. Quintana;W. Elder;E. Kauffman;R. Diner;T. Villamil
中科院分区：
文献类型：
--
作者：
C. Orth;M. Attrep;L. R. Quintana;W. Elder;E. Kauffman;R. Diner;T. Villamil
在北美西部内陆盆地的16个地点和地球仪周围12个相距甚远的地点（包括6个ODP/DSDP地点）收集的样品中，用中子活化法测量了Cenomanian-Turonian（晚白垩世）灭绝间隔期的元素丰度。在大多数西部内陆盆地地点，哥伦比亚和西欧（较弱），两个间隔很近的元素丰度峰值出现在上塞诺曼阶（1.92亿年），横跨Sciponoceras gracile到Neocardioceras juddii的菊石带。具有异常高浓度的元素包括Sc、Ti、V、Cr、Mn、Co、Ni、Ir、Pt和Au。较低的峰值与有孔虫Rotalipora cushmani的消失（灭绝）相吻合。在北美地区。绿角化也在这个水平线上或略低于这个水平线消失，但在欧洲，它的消失要比R早得多。库什马尼一系列的软体动物灭绝和物种形成或迁移事件也开始于下部元素丰度峰值附近的地层水平，δ 13 C正偏移正好在沉积和元素异常之前开始，并一直持续到下土伦统，远高于上部异常。这种碳同位素偏移已被观察到在东欧部分，我们发现很少或根本没有证据的元素异常，这表明这两种现象可能不是紧密耦合。异常中的元素丰度比与大西洋中脊玄武岩或夏威夷熔岩（拉斑玄武岩）的丰度比非常相似，但与堪萨斯东南部年龄大致相似的C1球粒陨石、黑色页岩、平均地壳岩石或钾镁煌斑岩和金伯利岩的丰度比不同。过量的Ir和其他亲铁体暗示了可能的大天体撞击源。然而，我们还没有找到微球体（生物成因的calcispheres以外）或冲击矿物质颗粒在我们的任何样品。此外，Sc、Ti、V和Mn在分异的太阳系天体中并不富集，尽管彗星撞击产生的微弱地球化学信号可能被强烈的类地叠加所掩盖，但这些异常更可能是由于强烈的海底扩张活动或仅仅是由于深海环流的增加，富金属水与大的晚期Cenomanian通过早期Turonian海平面上升和深水开放的南大西洋。大陆水道和大陆边缘的泛滥也可能造成异常，因为它阻止了大量大陆碎屑稀释正常的海洋地球化学背景成分。
Elemental abundances have been measured by neutron activation methods across the Cenomanian-Turonian (late Cretaceous) extinction interval in samples collected from sixteen sites in the Western Interior Basin of North America and from twelve widely separated locations around the globe, including six ODP/DSDP sites. In most Western Interior Basin sites, in Colombia, and in western Europe (weaker), two closely spaced elemental abundance peaks occur in the upper Cenomanian (∼ 92 m.y.), spanning the ammonite zones ofSciponoceras gracilethroughNeocardioceras juddii. Elements with anomalously high concentrations include Sc, Ti, V, Cr, Mn, Co, Ni, Ir, Pt and Au. The lower peak coincides with the disappearance (extinction) of the foraminiferRotalipora cushmani. In North American sectionsR. greenhornensisalso disappears at or just below this horizon, but in Europe it disappears considerably earlier thanR. cushmani. A series of molluscan extinction and speciation or migration events also begins near the stratigraphic level of the lower elemental abundance peak.The well-documented positiveδ13Cexcursion begins just before the extinctions and the elemental anomalies, and continues into the lower Turonian, well above the upper anomaly. This carbon isotope excursion has been observed in East European sections where we find little or no evidence of the elemental anomalies, suggesting that the two phenomena may not be tightly coupled. Elemental abundance ratios in the anomalies closely resemble those of Mid-Atlantic Ridge basalt or Hawaiian lava (tholeiitic), but not those of C1 chondrite, black shale, average crustal rocks, or lamproite and kimberlite of roughly similar age in southeastern Kansas. The excess Ir and other siderophiles hint at possible large-body impact(s) for the source. However, we have not located microspherules (other than biogenic calcispheres) or shocked mineral grains in any of our samples. Furthermore, Sc, Ti, V and Mn are not enriched in differentiated Solar-System bodies.Although the weak geochemical signal from comet impact(s) could be masked by the strong terrestrial-like overprint, these anomalies more likely resulted either from intense seafloor spreading activity or merely from increased circulation of deep, metal-rich water associated with the large late Cenomanian through early Turonian eustatic rise and deep-water opening of the South Atlantic. The flooding of continental seaways and margins also could have contributed to the anomalies by preventing much continental detritus from diluting the normal background marine geochemical component.