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：岩石磁性方法

• 批准号: 0823477
• 负责人: Kenneth Kodama
• 金额: $ 4.85万
• 依托单位: Lehigh 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=0823477&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.

该奖项是根据2009年的《美国复苏与再投资法》（公法111-5）资助的。该协作项目介绍了关于意大利中三叠纪三叠纪latemar平台白云岩的循环地层学的持续的多学科辩论。 Latemar的600米级浅海洋碳酸盐周期最初被解释为天文驱动的20,000年海平面振荡的产物。平台内的灰床的放射性同位素年代随后表明，单个周期必须在2,000至4，000年内甚至更少的速度形成得更快。这种校准差异构成了所谓的“ Latemar争议”。借助高精度的年代学现已可用，挑战是为强烈的周期性纬度相的起源找到合理的解释。该项目应用岩石磁技术来研究可能参与和/或影响沉积循环性的更全面的环境因素（例如，风化过程）。一项使用磁化率的磁性测量，对磁敏感性的磁性测量，厌含的磁性和饱和的等热磁化，从40米的LATEMAR演替区带有200个样品，揭示了一个连贯的信号，表明与周期的磁性矿物质浓度变化。该项目通过500 m厚的Latemar演替的主要暴露以高分辨率收集岩石磁数据，以对继任的短期和长期循环性进行新的和客观的表征以及彻底的采样。这项工作还将现有的磁性极性地层数据库扩展到平台的新位置的样带，以帮助解决中间三叠纪白云岩的矛盾的生物 - 磁性地层图。分辨率的解决方案很重要。简短的放射性同位素时间尺度意味着，海鲜次钙和大型TEPEE-Zone胶结的累积速率比第四纪类似物中已知的数量级高。对LATEMAR争议进行了补习，这对国际地层全球倡议有助于制定天文时间尺度（ATS）的全球全球倡议，以实现Mesozozozozozozozozozozozozogien Era。三叠纪时期覆盖范围的唯一主要差距包括Latemar平台占据的地层间隔；重要的是要确认或拒绝天文强迫在纬度周期形成中的作用。该项目汇集了三所大学，其中包括在野外地区附近的意大利一所大学。