东西特提斯晚白垩世深水底栖有孔虫生物相和岩相

摘要

白垩纪深水古海洋学研究仍处于早期发展阶段,一方面是由于来自钙质底栖有孔虫的稳定同位素和地球化学数据的缺乏,其原因在于白垩纪高碳酸盐补偿深度;另一方面在于深水有机质胶结有孔虫示踪古海洋还没有充分发展起来.深海环境深水胶结有孔虫的分布主要取决于碳酸盐可利用状况、原始生产的输入通量、深水交换、环境波动(深海洋流、浊流和快速沉积事件)和底层沉积类型,因此对于重建深海环境具有非常巨大的潜力.东、西特提斯Campanian-Maastrichtian深水底栖有孔虫组合的统计分析揭示出6个生物相,代表着明显不同的沉积环境.包括:深海红色泥岩与矮小深海生物组合(生物相1);红色深海泥灰岩 ("Couches Rouges"相),含钙质胶结有孔虫组合(生物相3);深水远洋灰岩("Scaglia Rossa"相),含易碎的Rhizammina组合(生物相2);绿色-灰色半远洋泥灰岩,含适应高输出通量生物组合(生物相4);半远洋泥岩和粉砂岩,含Aschemocella-Nothia 组合(生物相5);陆源浊积层序,含"复理石型"Rhabdammina 组合(生物相6).Campanian-Maastrichtian红色氧化深水环境动物组合与现今深海类似,而白垩纪贫氧深海环境胶结组合在现今无法找到相类似物.随着古生态信息的增加和数据库的扩展,深水胶结有孔虫有望成为揭示古海洋条件的重要工具,尤其是对于非均变的白垩纪深海沉积的形成而言,比如深海黑色页岩和广泛分布的大洋红层.%Cretaceous deep-water paleoceanography is still in an early stage, since stable isotope analysis and geochemical data from calcitic benthic foraminifera are generally unavailable owing to an unusually high calcite compensation depth, and since the use of organically cemented deep-water agglutinated foraminifera as tracers is still insufficiently exploited. Distribution patterns of deep-water agglutinated foraminifera in the deep-sea are mainly dependent on carbonate availability, export fluxes from primary production, deep-water ventilation, environmental disturbance (deep-sea currents, turbidites and rapid sedimentation events) and substrate types and have thus significant potential to reconstruct the environments of the deep-sea. Statistical analysis of deep-water benthic foraminiferal assemblages from the Campanian-Maastrichtian of the Western Tethys reveals six biofacies, which occur in distinct depositional environments. Assemblages from Campanian-Maastrichtian red oxic deep oceanic settings exhibit remarkable similarities to modern deep-sea faunas, whereas agglutinated assemblages of Cretaceous dysaerobic deep-sea settings have no real modern analogue. With increasing paleoecological information and an expanded database, Late Cretaceous deep-water agglutinated foraminifers have the potential to become a powerful tool for understanding the palaeoceanographic conditions under which non-uniformitarian Cretaceous deep-sea sediments such as deep-sea "black shales" and the widely distributed oceanic red beds formed.