CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY AND ASSEMBLAGES OF THE CENOMANIAN-TURONIAN BOUNDARY INTERVAL: IMPLICATIONS FOR THE ORIGIN AND TIMING OF OCEANIC ANOXIA
CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY AND ASSEMBLAGES OF THE CENOMANIAN-TURONIAN BOUNDARY INTERVAL: IMPLICATIONS FOR THE ORIGIN AND TIMING OF OCEANIC ANOXIA
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DOI：
10.1029/pa003i003p00275
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发表时间：
1988-06-01
期刊：
影响因子：
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通讯作者：
Bralower, Timothy J.
中科院分区：
文献类型：
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作者：
Bralower, Timothy J.
一个详细的超微化石分带已被推导出的Cenomanian-Turonian边界间隔组成的三个区，两个亚区，和九个额外的bioforms。这种生物地层学是在对欧洲、北美和非洲的许多剖面进行调查的基础上进行的，它使陆架和深海环境剖面的相互关系更加精确。分辨率的提高有助于解决这一时期的一些相关的古海洋学和沉积学问题。由于多种原因，该区间的相模式是可变的。一个广泛的间断发生在最新的森诺曼和最早的Turonian在欧洲西北部的大部分地区，可能是一个间接的结果，海洋海侵高峰。在特提斯深部的部分地区，碳酸盐的溶解作用发生在欠饱和的底层沃茨中或早期成岩作用期间。只有少数边界部分，主要是在美国西部内陆，以连续的碳酸盐沉积为特征。在许多部分，偏导数C-13偏移（与大量海洋有机质的埋藏有关）与相变、颗石碳酸盐与泥晶灰岩的比例较低以及超微化石保存较差相一致。因此，成岩作用可能强烈地叠加了这种偏移。大量的超微化石事件表明，碳漂移是轻微的穿时序列之间的西部内陆，并在该地区发生的转变明显晚于西北德国。所获得的数据并没有使Cenomanian-Turonian海洋缺氧事件的概念无效，但显示了局部构造，气候和海洋学扰动如何掩盖了全球情况。特别是，他们指出，碳的变化可能是盆地，并不总是海洋现象，这一结论可以合理化与整体缓慢的中白垩纪循环。在几乎所有的序列中观察到的超微化石组合包含特别高丰度的两个溶解抗性类群在特定的样品：Eprolithus floralis和Broinsonia sp.。然而，组合的整体组成并没有显着变化，在边界间隔，相反的宏体化石和有孔虫，遭受广泛的排斥。
A detailed nannofossil zonation has been derived for the Cenomanian-Turonian boundary interval consisting of three zones, two subzones, and nine additional biohorizons. This biostratigraphy, based on the investigation of numerous sections from Europe, North America, and Africa, allows accurate correlation of sections from shelf and deep-sea environments. The increased resolution helps solve several pertinent paleoceanographic and sedimentologic problems in this time period. Facies patterns are variable in this interval for numerous reasons. A widespread hiatus occurred in the latest Cenomanian and earliest Turonian in much of northwest Europe and may have been an indirect result of peak marine transgression. In parts of the deep Tethys, dissolution of carbonate took place in undersaturated bottom waters or during early diagenesis. Only a few boundary sections, mostly within the Western Interior, United States, are characterized by continuous carbonate deposition. In many sections a partial derivative C-13 excursion (which has been associated with the burial of large amounts of marine organic matter) coincides with a facies change, lower ratios of coccolith carbonate to micrite, and poorer nannofossil preservation. This excursion therefore may be strongly overprinted by diagenesis. Numerous nannofossil events indicate that the carbon excursion is slightly diachronous between sequences of the Western Interior, and that the shift occurred distinctly later in this region than in northwest Germany. The data obtained do not invalidate the concept of a Cenomanian-Turonian ocean-wide anoxic event but show how local tectonic, climatic, and oceanographic perturbations have masked the global scenario. In particular, they indicate that carbon shifts may be basinal and not always oceanic phenomena, a conclusion which can be rationalized with overall sluggish middle Cretaceous circulation. Nannofossil assemblages in almost all sequences observed contain exceptionally high abundances of two dissolution-resistant taxa in particular samples: Eprolithus floralis and Broinsonia sp.. However, the overall composition of assemblages does not change dramatically in the boundary interval, in contrast to the macrofossils and foraminifera, which suffered widespread extinctions.