COLLABORATIVE RESEARCH: Geochemical and Isotopic Constraints on Mesproterozoic Ocean Chemistry Working Toward a Global Perspective

合作研究：中元古代海洋化学的地球化学和同位素约束面向全球视角

• 批准号: 9725397
• 负责人: Tracy Frank
• 金额: $ 2.61万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-01-15 至 1999-06-09
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9725397&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Geochemical; Isotopic; Constraints

9725397 Frank The Mesoproterozoic Eon (1600-1000 Ma) represents a critical period in Earth history from the standpoint of eukaryotic diversification (Knoll, 1991), fundamental transitions in the oxidation state of the Earth's atmosphere and oceans (Des Marais et al., 1992; Canfield and Teske, 1996), and global tectonic reorganization (Dalziel, 1991). Yet despite this obvious significance, the Mesoproterozoic remains one of the most poorly understood and poorly documented intervals in Earth history. For example, in reference to an apparent stability in the Mesoproterozoic marine carbon isotopic record, the era between 1600 Ma and 1000 Ma has been reported as 'the dullest time in Earth's history' (Buick et al., 1995). However, a large positive shift (3-4%) in marine carbonate (13C values has recently been recognized in late Mesoproterozoic (1300 Ma) successions from Siberia, Arctic Canada, Greenland, and the United States. Rather than a short-lived excursion, this shift appears to represent a prolonged and fundamental change that may represent a significant transition in the Earth's global carbon cycle. The timing of this observed transition, between ~1300 and ~1150 Ma, is particularly intriguing in that it occurs in conjunction with the early assembly of the Rodinian supercontinent and a purported rise in the concentration of atmospheric oxygen. The goal of the proposed research is to generate carbon, sulfur and strontium isotopic data for this interval and, thereby, document and begin to address mechanistically the most fundamental (first-order) shifts in the chemistry of the Mesoproterozoic ocean. These objectives will be achieved through a multidisciplinary study that integrates depositional, diagenetic, and geochemical information into a single comprehensive framework. Although no single stratigraphic succession adequately encompasses the interval surrounding the observed carbon isotopic shift, two distinct successions (Society Cliffs Formation, northern Baffin Island; Dismal L akes Group, Coppermine homocline, Northwest Territories) can be effectively spliced to provide coverage across the interval of the observed transition. Each of these successions has been chosen on the basis of accessibility and exposure of stratigraphic units, the presence of a wide variety of facies and lithologies suitable for geochemical analysis, and the abundance of a variety of allochems and marine cements from different depositional environments. Combined, these prerequisites assure recognition of depositional and diagenetic trends that would otherwise hamper the interpretation of geochemical and isotopic data. Such an integrated approach will provide the clearest path toward understanding the complex evolution of the Proterozoic biosphere.

9725397弗兰克 从真核生物多样化的角度来看，中元古代的Eon（1600-1000 Ma）代表了地球历史上的一个关键时期（Knoll，1991），地球大气和海洋氧化态的根本转变（Des Marais et al.，1992年;坎菲尔德和Teske，1996年），以及全球构造重组（Dalfeld，1991年）。 然而，尽管有着明显的意义，中元古代仍然是地球历史上最缺乏了解和记录的时期之一。 例如，关于中元古代海洋碳同位素记录的明显稳定性，1600 Ma和1000 Ma之间的时代被报道为“地球历史上最无聊的时期”（Buick等人，1995年）。 然而，最近在西伯利亚、加拿大北极、格陵兰和美国的中元古代晚期（1300 Ma）的地层序列中，海洋碳酸盐（13 C）值出现了较大的正向变化（3-4%）。 这一转变不是短暂的，而是一种长期的根本性变化，可能代表着地球全球碳循环的重大转变。 这一观测到的过渡的时间，约1300和1150马之间，是特别有趣的，因为它发生在与早期组装的Rodinian超大陆和一个所谓的上升，在大气中的氧气浓度。 拟议研究的目标是生成这一时间段的碳、硫和锶同位素数据，从而记录并开始从机械上解决中元古代海洋化学中最基本的（一阶）变化。 这些目标将通过多学科研究实现，该研究将沉积、成岩和地球化学信息整合到一个综合框架中。 虽然没有一个单一的地层序列充分涵盖周围的间隔观察到的碳同位素变化，两个不同的继承（社会悬崖形成，北方巴芬岛;迪斯马尔拉克斯组，铜矿同斜，西北地区）可以有效地拼接，以提供覆盖整个间隔观察到的过渡。 这些序列中的每一个都是根据地层单位的可及性和暴露、适合地球化学分析的各种相和岩性的存在以及来自不同沉积环境的各种变质物和海相胶结物的丰度来选择的。 结合起来，这些先决条件确保了沉积和成岩趋势的识别，否则会妨碍地球化学和同位素数据的解释。 这样一种综合的方法将为理解元古宙生物圈的复杂演化提供最清晰的途径。