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

这项资助将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，并测试有充分根据的假设，即超群中观察到的周期受米兰科维奇轨道强迫控制。这项资助将为碳酸盐岩铀铅测年提供一个非常重要的测试，澄清三叠纪/侏罗纪界线的陆地与海洋沉积的时间，并提供关于界线的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，并已在生物地层学、旋回地层学和岩浆地层学方面进行了深入研究。虽然循环静力学记录经常被引用为记录轨道强迫，但对这种高分辨率记录缺乏绝对的年龄限制。在这个序列中，唯一被测年的层位是一系列玄武岩流和侵入体，测年为201 +/- 1 Ma。麻省理工学院的新工作表明，将有可能从玄武岩中的花岗斑岩层中确定锆石的年代，精确到0.2 Ma或更高。这些玄武岩含有沉积碳酸盐，似乎有很大的潜力U-Pb测年的托架单位。年龄的比较将测试沉积物U-Pb测年的潜力，以获得准确的年龄。测试碳酸盐U-Pb测年的潜力是了解不含火山灰的厚层岩石序列的时间分布的关键领域。需要地质年代学数据来解决有关地球过程的基本问题，其中许多问题涉及速率或相关性。虽然磁性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，就不可能假设时间的详细分布。尽管碳酸盐岩U-Pb年龄的精确性似乎受到地质复杂性的限制（例如，铅同位素的初始不均匀性轻微;早期成岩作用期间U和子体的活动性），准确性可能与所述年龄的不确定性相当。如果是这样的话，碳酸盐定年的可能性，以1%（2-西格玛）的不确定性将提供一个急需的地质年代计的序列在整个中生代，没有空气降落灰可以确定。纽约州立大学斯托尼布鲁克、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，以及纽瓦克序列的一些最好的研究部分，我们预计将有一个非常活跃的合作，将为学生提供巨大的机会，使用所有三个机构的设施，并享受丰富的实地经验。

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.