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

早中生代的放射性和生物地层时间尺度间标还没有很好地建立。部分三叠纪和侏罗纪的阶段边界的绝对年龄分配的不确定性可能超过30 Ma。本研究旨在为新西兰Murihiku超群保存完好的化石地层中玻璃凝灰岩层的高精度锆石U-Pb年龄定年提供支持。这一厚厚的碎屑序列主要由海相火山岩组成，跨越了三叠纪和侏罗纪的大部分时间，并可以根据几乎世界性的菊石和翼类双壳类在关键点上与国际柱相对应。Murihiku超群中-上三叠统段13个凝灰岩层的初步锆石年龄为232 ~ 204 Ma。根据逐步溶解实验的高精度Pb/Pb年龄，Monotis的FAD和LAD限制在226 ~ 218 Ma范围内。建议对Murihiku超群的中、上三叠统剖面进行详细、全面的研究，并将采样范围扩大到下三叠统和侏罗系部分。这项工作，连同该剖面砾岩类花岗岩碎屑的高精度定年，将提供关于沉积速率和物质在深部-隆升-侵蚀-搬运-沉积之间循环速率的信息，并将对理解盆地演化动力学作出重大贡献。

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.