Molybdenum isotope signatures of mid-Cretaceous black shales: Implications on the spatial dimension of anoxic events?

白垩纪中期黑色页岩的钼同位素特征：对缺氧事件空间维度的影响？

基本信息

批准号：
29979009
负责人：
Professor Dr. Stefan Weyer, Ph.D.
金额：
--
依托单位：
Institut für Geowissenschaften (IfG)
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2006
资助国家：
德国
起止时间：
2005-12-31 至 2010-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/29979009?language=en
关键词：
Molybdenum isotope signatures mid Cretaceous

项目摘要

To evaluate the potential of Mo isotope compositions for the identification of global versus regional anoxia we propose to investigate the fractionation of Mo isotopes in sediments from regionally to globally distributed mid-Cretaceous black shales. The underlying idea is that during times of global or near-global anoxia, black shales can be expected to have served as the primary sink for Mo - as was the case during much of the Proterozoic. In contrast, under the predominantly oxic oceanic conditions prevailing in modern oceans, Fe-Mn-oxides appear to be the major sink for Mo. Adsorption to Mn-oxides, as it occurs under oxic conditions, leads to a significant fractionation of Mo isotopes, resulting in ¿isotopically heavy¿ modern seawater. However, the removal of Mo into black-shale sediments under anoxic conditions (e.g. Black Sea) does not seem to result in Mo isotopic fractionation. Hence, differences in the oceanic Mo mass balance should lead to a significant shift in Mo isotope systematics, depending on whether they result from the prevalence of either anoxic or oxic conditions. In fact, available Mo data from mid-Proterozoic and recent marine sediments support this view. Here we propose to test this hypothesis by analyzing the Mo isotope composition of mid-Cretaceous black shales that formed under different spatial and temporal boundary conditions. As a representative sample for an exceptional, presumably global and long-lived Oceanic Anoxic Event (OAE), black shales from OAE 2 (duration: ¿400 ka) will be analysed. To gain insights into the Mo isotope fractionation during a supraregional, short-lived (~45 ka) black shale event, sediments from OAE 1b (restricted to the western Tethys and Central Atlantic) will be investigated. To evaluate the Mo isotope signal under regional anoxic conditions prevailing over long (>10 ma) time scales, black shale sediments under- and overlying OAE 2 at Demerara Rise (ODP Leg 207) will be studied. The outcome of the proposed study will be (1) the evaluation of a new, widely applicable geochemical proxy to identify signals of global versus regional anoxia; (2) the possibility to validate Mo isotope-based models on ocean redox evolution during the Proterozoic; and (3) a characterization of the geochemical environment during mid-Cretaceous black-shale formation using Mo and other redox-sensitive metals as well as sulfur isotopes.

为了鉴定全球缺氧的potope组成，我们提出了从区域到全球中间白色的黑色页岩的沉积物中的Mo同位素。对于现代海洋中的莫有毒性海洋状况，Fe-Mn-氧化物似乎是用于Mo.Adsospoting Mn-氧化物的主要水槽同位素重重现代海水。 ND近期的海洋沉积物都可以通过分析MO同位素组合在不同的空间和颞范围内形成的MO同位素组合来测试这一假设。缺氧事件（OAE），来自OAE 2的黑色页岩，以在较短暂的，短暂的D到西部和中央大西洋中获得MO同位素分数的见解。在长期（> 10 mA）的时间尺度上，在Demerara Rise（ODP Leve 207）上覆盖的黑色页岩页岩和上覆的OAE 2。确定在proterokoic期间的全球氧化还原与区域缺氧的信号；同位素。