Collaborative Research: Calibration of the Late Triassic-Early Jurassic Timescale Using U-Pb Dating of the High-Resolution Magnetostratigraphy of the Newark Supergroup

这笔资金将用于确定纽瓦克超群内沉积岩和火成岩的年代，以试图完善晚三叠世和早侏罗世的时间尺度，并测试在超群中观察到的旋回受米兰科维奇轨道强迫控制的有充分根据的假设。这笔拨款将为碳酸盐岩的铀铅定年提供一个非常重要的测试，澄清三叠纪/侏罗纪边界的陆地与海洋灭绝的时间，并提供关于边界实际日期和进展的更精确的数据。纽瓦克超群记录了三叠纪-侏罗纪灭绝，并在生物、旋回和岩浆地层学方面得到了深入的研究。虽然周期静止记录经常被引用作为轨道强迫的记录，但这种高分辨率记录缺乏绝对的年龄限制。在该层序中唯一确定年代的层位是一系列玄武岩流和侵入岩，其年代为201 +/- 1 Ma。麻省理工学院的一项新研究表明，从玄武岩的花岗岩层中测定锆石的年代，精度将达到0.2 Ma或更高。这些玄武岩支架单元含有沉积碳酸盐，似乎具有很大的U-Pb定年潜力。年龄的比较将测试沉积材料U-Pb定年的潜力，以获得准确的年龄。测试碳酸盐U-Pb定年的潜力是了解不含火山灰的厚层岩石序列中时间分布的关键领域。地球年代学数据是解决有关地球过程的基本问题所必需的，其中许多涉及到速率或相关性的问题。虽然磁地层学和旋回地层学可以用来细分岩石记录中的时间，但如果没有精确的校准，就不可能对时间的详细分布进行假设。尽管碳酸盐U-Pb年龄的精度似乎受到地质复杂性的限制（例如，Pb同位素的初始不均匀性；早期成岩作用期间U及其子元素的流动性），但其精度很可能等于所述年龄的不确定性。如果是这样的话，将碳酸盐的年代确定为1%（2西格玛）的不确定性的可能性，将为整个显生宙的序列提供一个急需的地球时计，因为这些序列无法识别空气落下的灰烬。纽约州立大学石溪分校、麻省理工学院和哥伦比亚大学的研究生将参与这项研究。由于我们的机构彼此接近，以及纽瓦克序列中一些研究最好的部分，我们期待一个非常有活力的合作，将为学生提供大量机会使用这三所机构的设施，并享受丰富的实地体验。

This grant will date sedimentary and igneous rocks from within the Newark Supergroup in an attempt to both refine the Late Triassic and Early Jurassic timescale and to test the well-grounded hypothesis that the cycles observed in the supergroup are controlled by Milankovitch orbital forcing. This grant will provide a very important test of Uranium-Lead dating in carbonates, clarify the timing of terrestrial vs. marine extinctions at the Triassic/Jurassic boundary, and provide much more precise data on the actual dates and progression of the boundary.The Newark Supergroup records the Triassic-Jurassic extinction and has been intensively studied in terms of bio-, cyclo-, and magentostratigraphy. Although the cyclostatigraphic record is often cited as recording orbital forcing, absolute age constraints on this high-resolution record are lacking. The only horizon that has been dated in this sequence is a series of basaltic flows and intrusions that were dated at 201 +/- 1 Ma. New work at MIT suggests it will be possible to date zircons from granophyric layers in basalts to a precision of 0.2 Ma or better. These basalts bracket units containing sedimentary carbonates that appear to have great potential for U-Pb dating. Comparison of the ages will test the potential for U-Pb dating of sedimentary materials for yielding accurate ages.Testing the potential of U-Pb dating of carbonates is a key area for understanding the distribution of time in thick sequences of rocks that do not contain volcanic ashes. Geochronological data are needed to address fundamental questions about Earth processes, many of which involve questions about rates or correlations. Although magnetostratigraphy and cyclostratigraphy can be used to subdivide time in the rock record, assumptions about the detailed distribution of time are impossible without precise calibration. Although the precision of U-Pb ages of carbonates appears to be limited by geologic complexity (e.g., slight initial heterogeneity in the Pb isotopes; mobility of U and daughters during early diagenesis) the accuracy may well be equal to the stated uncertainty in the age. If so, the possibility of dating carbonates to 1% (2-sigma) uncertainty will provide a much-needed geochronometer for sequences throughout the Phanerozoic for which no air-fall ashes can be identified. Graduate students at SUNY Stony Brook, MIT and Columbia University will be involved in this research. Due to the proximity of our institutions to each other as well as to some of the best studied parts of the Newark sequence we anticipate a very dynamic collaboration that will provide students with vast opportunities to use facilities at all three institutions and to enjoy a rich field experience.