A critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for Late Cretaceous global correlation
A critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for Late Cretaceous global correlation
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DOI：
10.1016/j.earscirev.2013.08.003
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发表时间：
2013-11
影响因子：
12.1
通讯作者：
I. Wendler
中科院分区：
文献类型：
--
作者：
I. Wendler
气候变化是由全球尺度过程的复杂相互作用驱动的，我们对它们的理解取决于地质记录的足够的时间分辨率及其精确的区域间相关性，在大多数情况下，仅靠生物地层学方法无法获得。基于大量沉积物碳同位素的化学地层对比越来越多地用于促进大距离高分辨率对比，但复杂性来自生物，成岩和物理化学因素对个体δ 13 C记录的局部差异的多种可能影响，这些影响可能掩盖全球信号。为了更好地评估δ 13 C记录中全球和局部贡献，有必要在全球范围内比较众多同位素记录。为了实现这一目标，本文回顾了晚白垩世大量沉积物的δ 13 C记录，以确定长期δ 13 C趋势的差异和相似性，从而帮助建立这一时期的全球参考δ 13 C记录。该研究提供了一个全球范围内的20个δ 13 C记录的比较，这些记录来自两个半球的不同古纬度和来自北方、特提斯、西部内陆、印度洋和太平洋的不同海洋环境，以及各种成岩叠加。同位素模式与生物地层学和古地磁数据的独立定年的基础上，揭示了良好的协议，尽管偏移的绝对δ 13 C值和振幅的网站之间的变化的主要同位素事件。这些差异反映了沉积环境、底层水年龄和成岩历史等不同的局部影响，而δ 13 C变化的一致模式可能代表全球海水溶解无机碳的δ 13 C波动。后者是调制的有机质埋藏相对于再矿化的变化，在全球范围内形成的自生碳酸盐，并在有机碳和碳酸盐汇之间的碳分配。这些变化主要受气候和植被变化的控制。此外，自生碳酸盐对沉积物贡献的平行变化可能导致δ 13 C碳记录的整体全球同步变化。这些水泥的形成通过生物介导的早期成岩过程与氧气和有机物质的可用性有关，因此，可以通过euclidum，大气和海洋氧气水平或大规模海洋环流的波动在全球范围内同步。由于早期成岩胶结物对δ 13 C碳信号的影响可以（但不一定）同步，因此化学地层学不应被用作跨大陆对比的独立方法，尤其是对微小的同位素变化必须极其谨慎地进行解释。尽管如此，所观察到的δ 13 C相关性的一致性证实了晚白垩世整体沉积物δ 13 C化学地层学的全球适用性，包括经历了岩化和埋藏成岩作用的沉积物，如喜马拉雅和阿尔卑斯剖面的沉积物。局限性来自以下方面：（1）碳酸盐含量非常低的沉积物中的不确定性增加，（2）非常浅的海洋环境中沉积物中δ 13 C变异较大，（3）未被识别的间断或沉积速率的强烈变化，以及（4）化学地层学、生物地层学和磁性地层学的结合，提高了区域间的精确度和时间分辨率
Climate variability is driven by a complex interplay of global-scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter-regional correlation, which in most cases cannot be obtained with biostratigraphic methods alone. Chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high-resolution correlation over large distances, but complications arise from a multitude of possible influences from local differences in biological, diagenetic and physico-chemical factors on individual δ13C records that can mask the global signal. To better assess the global versus local contribution in a δ13C record it is necessary to compare numerous isotopic records on a global scale. As a contribution to this objective, this paper reviews bulk sediment δ13Ccarbrecords from the Late Cretaceous in order to identify differences and similarities in secular δ13C trends that help establish a global reference δ13C record for this period. The study presents a global-scale comparison of twenty δ13C records from sections representing various palaeo-latitudes in both hemispheres and different oceanic settings from the Boreal, Tethys, Western Interior, Indian Ocean and Pacific Ocean, and with various diagenetic overprinting. The isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute δ13C values and variation in amplitude between the sites. These differences reflect the varying local influences e.g. from depositional settings, bottom water age and diagenetic history, whereas the concordant patterns in δ13C shifts might represent δ13C fluctuations in the global seawater dissolved inorganic carbon. The latter is modulated by variations in organic matter burial relative to re-mineralization, in the global-scale formation of authigenic carbonate, and in partitioning of carbon between organic carbon and carbonate sinks. These variations are mainly controlled by changes in climate and eustasy. Additionally, some globally synchronous shifts in the bulk δ13Ccarbrecords could result from parallel variation in the contribution of authigenic carbonate to the sediment. Formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and, thus, can be globally synchronized by fluctuations in eustasy, atmospheric and oceanic oxygen levels or in large-scale oceanic circulation. Because the influence of early diagenetic cements on the bulk δ13Ccarbsignal can, but need not be synchronized, chemostratigraphy should not be used as a stand-alone method for trans-continental correlation, and especially minor isotopic shifts have to be interpreted with utmost care. Nevertheless, the observed consistency of the δ13C correlations confirms global scale applicability of bulk sediment δ13C chemostratigraphy for the Late Cretaceous, including sediments that underwent lithification and burial diagenesis such as the sediments from the Himalayan and Alpine sections. Limitations arise from increased uncertainties (1) in sediments with very low carbonate content, (2) from larger δ13C variability in sediments from very shallow marine environments, (3) from unrecognized hiatuses or strong changes in sedimentation rates, and (4) in sections with short stratigraphic coverage or with few biostratigraphic marker horizons.The combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter-regional …