The Cretaceous–Tertiary boundary in southern low-latitude regions: preliminary study in Pernambuco, northeastern Brazil
The Cretaceous–Tertiary boundary in southern low-latitude regions: preliminary study in Pernambuco, northeastern Brazil
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南部低纬度地区的白垩纪-第三纪边界：巴西东北部伯南布哥州的初步研究
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发表时间：
1994
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影响因子：
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通讯作者：
P. Martins
中科院分区：
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作者：
G. Albertão;E. Koutsoukos;Marília S. P. Regali;M. Attrep;P. Martins
对巴西东北部伯南布哥的一个火山-第三纪（K/T）边界剖面进行的初步综合研究为最早期达尼安期的地外火流星撞击提供了证据。非分级、结节状碳酸盐泥岩/杂砂岩层被解释为崩塌或泥浆流存款，由海啸事件或海平面低位期间重力块体运动引起，前者可能由K/T边界尤卡坦影响产生。这一层覆盖着在上半深海环境中沉积的泥灰岩，标志着白垩纪的顶部。几乎所有已知的马斯特里赫特期最晚的浮游有孔虫都是在白垩纪地层中发现的。铱在K/T界线以上约75 cm的一薄层半远洋粘土岩中有一明显的峰，沉积于中深浅海环境。粘土岩上覆细粒石灰岩和泥灰岩交替层，以及50 cm厚的级配生物碎屑堆积岩，后者位于最低层达尼亚泥灰质石灰岩角砾岩之上。白垩纪后期有丰富的改造化石和罕见的最低层的丹尼期微体化石（如E. edita，E. eobulloides，E. fringa、毛果草G. irregularis，P. eugubina，P. cf. pseudobulloides，W. claytonensis和W. Hornerstownensis）已从这些地层中恢复。这些最低层的丹尼阶记录了大量的冲击变质石英颗粒的突然出现，有几套交叉变形纹层和微玻璃陨石状微球粒。这表明这些沉积物是由最早期的丹尼期的第二次撞击事件引起的额外海啸形成的，靠近或位于古新世P α和P1 a有孔虫带之间的边界。在白垩纪最上层地层中尚未发现撞击源物质。
A preliminary integrated study of a Cretaceous-Tertiary (K/T) boundary section in Pernambuco, northeastern Brazil, provides evidence for an extraterrestrial bolide impact in the earliest Danian. A non-graded, nodular carbonate mudstone/wackestone bed is interpreted as a slump or a mud Flow deposit, induced by a tsunami event or by a gravity mass movement during a sea-level lowstand, the former possibly generated by the K/T boundary Yucatan impact. This bed overlies marlstones deposited in an upper bathyal environment and marks the top of the Cretaceous. Nearly all known latest Maastrichtian planktonic foraminifera are recovered from the Cretaceous strata. Iridium shows a marked peak in a thin hemipelagic claystone layer, about 75 cm above the K/T boundary, deposited in a middle to deep neritic environment. The claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm-thick graded bioclastic packstone, which rests upon a marly limestone breccia of the lowermost Danian. Abundant reworked Cretaceous and rare lowermost Danian microfossils (e.g. E. edita, E. eobulloides, E. fringa, G. irregularis, P. eugubina, P. cf. pseudobulloides, W. claytonensis and W. hornerstownensis) have been recovered from these strata. These lowermost Danian beds record the sudden appearance of abundant shock-metamorphosed quartz grains, with several sets of intersecting deformation lamellae and microtektite-like microspherules. This suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest Danian, near or at the boundary between the Palaeocene P α and P 1a foraminiferal zones. Impact-derived material has not been found in the uppermost Cretaceous beds.