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

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该合作项目解决了一个正在进行的多学科辩论有关中三叠世晚期平台白云岩，意大利。Latemar超过600米尺度的浅海碳酸盐循环最初被解释为天文驱动的20，000年海平面振荡的产物。随后对平台内的火山灰层进行的放射性同位素测年表明，各个旋回的形成速度肯定要快得多，在2,000至4,000年之间，甚至更短。这种相互校准的差异构成了所谓的“拉特马尔争议”。“随着高精度地质年代学的出现，挑战在于找到一个合理的解释，解释强周期性的Latemar相的起源。以前的研究主要集中在相分析和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调查更全面的环境因素（例如，风成过程），可能参与和/或影响沉积旋回性。一个试点研究使用的磁化率，无滞后剩磁和饱和等温剩磁的200个样品从一个40米的横断面的Latemar继承磁性测量揭示了一个连贯的信号，表明磁性矿物浓度的变化与周期的调整。该项目通过500米厚的Latemar序列的主要暴露区以高分辨率收集岩石磁性数据，以便对序列的短期和长期旋回性进行新的客观表征和全面采样。这项工作还扩大了现有的磁极性地层数据库，以横断面在一个新的位置在平台上，以帮助解决冲突的生物磁性地层学中三叠世白云岩。解决的Latemar争议是很重要的。短的放射性同位素时间尺度意味着积累率的陆上钙华和大规模的火山锥区胶结，是数量级高于已知的第四纪analog.Addressing Latemar争议有助于国际地层学委员会的全球倡议，制定一个天文时间尺度（ATS）的中生代。三叠纪时期覆盖范围的唯一主要空白包括Latemar平台所占据的地层间隔;确认或拒绝天文强迫在Latemar旋回形成中的作用很重要。该项目汇集了三所大学，其中一所在外地附近的意大利。

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.