Collaborative Research: A New Perspective on the Driving Forces of Controversial Middle Triassic Cyclostratigraphy: a Rock Magnetic Approach

合作研究：有争议的中三叠世旋回地层学驱动力的新视角：岩石磁学方法

• 批准号: 0823481
• 负责人: Linda Hinnov
• 金额: $ 7.1万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2012-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0823481&HistoricalAwards=false
• 关键词: Collaborative; Research; New; Perspective; Driving

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This collaborative project addresses an ongoing multidisciplinary debate concerning the cyclostratigraphy of the Middle Triassic Latemar platform Dolomites, Italy. The more than 600 meter-scale shallow-marine carbonate cycles of the Latemar were originally interpreted as the products of astronomically driven, 20,000 year sea-level oscillations. Radioisotope dating of ash-beds within the platform subsequently indicated that the individual cycles must have formed much faster, in 2,000 to 4,000 years, or even less. This inter-calibration discrepancy constitutes the so-called "Latemar controversy." With high-precision geochronology now available, the challenge is to find a reasonable explanation for the origin of the strongly cyclical Latemar facies. Prior research focused exclusively on facies analysis, and the role of sea level change in cycle formation. This project applies rock magnetic techniques to investigate a more comprehensive range of environmental factors (e.g., aeolian processes) that could have been involved in and/or influenced depositional cyclicity. A pilot study using magnetic measurements of magnetic susceptibility, anhysteretic remanent magnetism and saturation isothermal remanent magnetization of 200 samples from a 40-m transect of the Latemar succession reveals a coherent signal indicating magnetic mineral concentration variations in tune with the cycles. The project collects rock magnetic data at high resolution through the main exposure of the 500 m thick Latemar succession, for a new and objective characterization and thorough sampling of the succession's short and long term cyclicity. This work also expands an existing magnetic polarity stratigraphy database to a transect at a new location in the platform, to help resolve conflicting bio-magnetostratigraphies of the Middle Triassic Dolomites.Resolution of the Latemar controversy is important. The short radioisotope timescale implies accumulation rates of subaerial caliche and massive tepee-zone cementation that are orders of magnitude higher than known from Quaternary analogs.Addressing the Latemar controversy contributes to the International Commission on Stratigraphy global initiative to develop an Astronomical Time Scale (ATS) for the Mesozoic Era. The only major gap in coverage for the Triassic Period includes the stratigraphic interval occupied by the Latemar platform; it is important to confirm or reject the role of astronomical forcing in the formation of the Latemar cycles. This project brings together three universities, including one in Italy near the field area.

该奖项由 2009 年美国复苏和再投资法案（公法 111-5）资助。该合作项目旨在解决有关意大利多洛米蒂中三叠世晚海平台旋回地层学的持续多学科辩论。 Latemar 超过 600 米规模的浅海碳酸盐旋回最初被解释为天文驱动的 20,000 年海平面振荡的产物。随后对该平台内的灰床进行的放射性同位素测年表明，各个周期的形成速度一定要快得多，为 2,000 至 4,000 年，甚至更短。这种相互校准的差异构成了所谓的“Latemar 争议”。现在有了高精度地质年代学，面临的挑战是为强周期性晚海相的起源找到合理的解释。先前的研究仅集中于相分析以及海平面变化在旋回形成中的作用。该项目应用岩石磁性技术来研究可能参与和/或影响沉积循环的更全面的环境因素（例如风成过程）。一项初步研究使用磁化率、非滞回剩磁和饱和等温剩磁对来自 Latemar 序列 40 米横断面的 200 个样本进行磁测量，揭示了一个相干信号，表明磁性矿物浓度随周期变化。该项目通过对 500 m 厚的 Latemar 层序的主要暴露收集高分辨率岩石磁数据，以对层序的短期和长期循环性进行新的客观表征和彻底采样。这项工作还将现有的磁极性地层学数据库扩展到平台新位置的横断面，以帮助解决中三叠世白云岩生物磁地层学的冲突。解决 Latemar 争议非常重要。较短的放射性同位素时间尺度意味着地下钙质和大规模圆锥形帐篷区胶结作用的积累率比第四纪类似物高出几个数量级。解决拉特马尔争议有助于国际地层委员会制定天文时间尺度（ATS）的全球倡议为中生代。三叠纪时期唯一的主要覆盖范围包括拉特马尔台地所占据的地层区间；确认或否认天文强迫在拉特马尔旋回形成中的作用非常重要。该项目汇集了三所大学，其中一所位于意大利靠近现场区域的大学。