Correlation of Radiometric and Biostratigraphic Timescales for the Triassic and Jurassic Murihiku Supergroup of New Zealand

早中生代放射性和生物地层学时间尺度的相互校准还没有很好地建立。三叠纪和侏罗纪部分地区阶段界线的绝对年龄分配的不确定性可能超过30 Ma。这项提议寻求对产于新西兰Murihiku超级群保存完好的化石地层中的玻璃凝灰岩层进行高精度的锆石U-Pb年龄测定。这一厚重的碎屑岩系主要由海相火山岩组成，这些火山岩跨越了三叠纪和侏罗纪的大部分时间，并可在关键位置与国际柱进行对比，其基础是几乎世界性的菊石和翼形双壳类。13个凝灰岩岩层的锆石初步年龄范围为232~204 Ma，这些凝灰岩岩层分布在村里古群中上三叠统段约6公里处。根据逐级溶解实验获得的高精度Pb/Pb值，确定斑腿藻类的FAD和LAD发生在226~218 Ma之间。建议完成对村里古超群中、上三叠统剖面的详细、全面的研究，并将采样范围扩大到包括层序的下三叠统和侏罗系部分。这项工作以及对该剖面砾岩中花岗岩类碎屑的高精度测年，将提供关于深成-抬升-侵蚀-运移-沉积之间的沉积速率和物质循环速率的信息，并将对了解盆地演化的动力学有重要意义。

Intercalibration of radiometric and biostratigraphic time scales for the early Mesozoic is not well established. Uncertainties in absolute age assignments to stage boundaries for parts of the Triassic and Jurassic may exceed 30 Ma. This proposal seeks support for high-precision zircon U-Pb age dating of vitric tuff beds that occur within well-preserved fossiliferous strata of the Murihiku Supergroup of New Zealand. This thick clastic succession comprises mainly marine volcanogenic rocks that span most of Triassic and Jurassic time and can be correlated to the international column at key points on the basis of virtually cosmopolitan ammonoids and pteroid bivalves. Preliminary zircon ages from 13 tuff beds spaced through ~6 km of section within the Middle to Upper Triassic portion of the Murihiku Supergroup range from 232 to 204 Ma. On the basis of high-precision Pb/Pb ages from step-wise dissolution experiments, the FAD and LAD for Monotis are constrained to occur within 226 Ma to 218 Ma. It is proposed to complete detailed, comprehensive study of the Middle and Upper Triassic sections of the Murihiku Supergroup, and extending the range of our sampling to include the Lower Triassic and Jurassic portions of the sequence. This work, along with high-precision dating of granitoid clasts from conglomerates in the section, will provide information on sedimentation rates and cycling rates of material between plutonism-uplift-erosion- transport-deposition, and will contribute significantly to understanding the dynamics of basin evolution.