The record of global change in mid-Cretaceous (Barremian-Albian) sections from the Sierra Madre, Northeastern Mexico
The record of global change in mid-Cretaceous (Barremian-Albian) sections from the Sierra Madre, Northeastern Mexico
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发表时间：
1999-10
影响因子：
1.1
通讯作者：
T. Bralower;E. Cobabe;B. Clement;W. Sliter;C. Osburn;J. F. Longoria
中科院分区：
文献类型：
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作者：
T. Bralower;E. Cobabe;B. Clement;W. Sliter;C. Osburn;J. F. Longoria
我们目前对白垩纪中期全球变化的认识主要是基于对南欧和深海钻探地点的远洋剖面的调查。来自其他大陆和大陆边缘沉积的半深海部分的信息要少得多。这项调查旨在通过关注墨西哥东北部大陆边缘沉积的半深海剖面的记录，拓宽我们对白垩纪中期全球变化的理解。主要目标是比较墨西哥和其他地区海洋缺氧事件的记录、时间和范围，并确定这些事件与使用碳同位素的全球有机物质埋藏之间的关系。我们对马德雷山脉东方的四个剖面进行了调查，综合了生物地层学、磁性地层学和碳同位素地层学。根据有机碳(C Org)组分测量的碳同位素显示，从巴雷米期到阿尔比亚下部、欧洲和太平洋深海剖面的地层变化相同。我们的研究结果为阿尔卑斯中晚期的碳同位素地层学提供了新的细节。C org含量的三个突变峰与OAE1a(早阿普提亚)、OAE1b(早阿尔卑斯)和晚阿普提安Globigerinelloids algerianus带的一次事件相关。所有这三个事件的特点都是短期内碳同位素值每毫升下降0.5-3次，然后是类似幅度的上升。这些减少可能反映了有机碳类型的变化、碳循环的性质或热液活动的增加。碳同位素值的增加反映了碳组织的广泛埋藏。墨西哥和其他地区碳同位素曲线的相似形状，以及碳同位素对OAEs的响应，表明阿普提亚晚期事件广泛，OAE1a和OAE1b是全球性的。这三起缺氧事件似乎与相对海平面上升有关。OAE1a也对应于纳米化石组合的重大变化；众所周知的“纳米锥体危机”可以很容易地在墨西哥部分识别出来。这一事件的特点是沉积物中超微化石和有孔虫的丰度增加，可能反映了相对海平面上升导致的稀释减少。
Our current understanding of mid-Cretaceous global change is largely based on investigations of pelagic sections from southern Europe and deep sea drilling sites. Much less information exists from other continents and from hemipelagic sections deposited on continental margins. This investigation seeks to broaden our understanding of mid-Cretaceous global change by focusing on the record from hemipelagic sections deposited along the continental margin of northeastern Mexico. The major goals are to compare the record, timing, and extent of the Oceanic Anoxic Events (OAEs) in Mexico and other areas, and to determine the relationship between these events and the global burial of organic material using carbon isotopes. We have investigated four sections from the Sierra Madre Oriental, integrating biostratigraphy, magnetostratigraphy and carbon isotope stratigraphy. Carbon isotopes, measured on the organic carbon (C org ) fraction, show identical stratigraphic changes to curves from Barremian to lower Albian European and Pacific deep-sea sections. Our results add new detail to the C-isotope stratigraphy of the middle and late Albian interval. Three abrupt peaks in C org content correlate with OAE1a (early Aptian), OAE1b (early Albian) and an event in the late Aptian Globigerinelloides algerianus Zone. All three events are marked by short-term, 0.5-3 per mil decreases in C-isotope values followed by increases of similar magnitude. The decreases may reflect changes in the type of C org , the nature of carbon cycling, or an increase in hydrothermal activity. The increases in C-isotope values reflect widespread burial of C org . The similar shape of the C-isotope curves in Mexico and other areas, and the response of C-isotopes to the OAEs, indicate that the late Aptian episode was extensive, and that OAE1a and OAE1b were global. The three anoxic events appear to correlate with rising relative sea level. OAE1a also corresponds to major changes in nannofossil assemblages; the well-known "nannoconid crisis" can be easily recognized in the Mexican sections. This event is characterized by an increase in abundance of nannofossils and foraminifera in sediments, possibly reflecting a decrease in dilution as a result of the rise in relative sea level.