High-precision U–Pb zircon CA-ID-TIMS dates from western European late Viséan bentonites

Three new U–Pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry dates obtained from late Viséan Belgian bentonites are reported and are used to estimate the periodicity of early Warnantian shallowing-upwards carbonate parasequences that are interbedded with the dated bentonites. Early Warnantian parasequences exhibit mean cycle periodicity values that are consistent with the <em>c</em>. 100 ka Milankovitch cycle, which is the dominant Milankovitch frequency recognized from recent Pleistocene glacial records, and thus strengthen the arguments for (1) these sedimentary cycles being of glacio-eustatic origin and (2) the initiation of the main phase of late Palaeozoic glaciation before the start of or during earliest Warnantian times. The new dates also provide additional high-precision age constraints for the improved calibration of the Mississippian time scale. Using the new dates, the stratigraphical age of the Clyde Plateau Volcanic Formation, Midland Valley of Scotland, is revised from Holkerian to early Asbian.

本文报道了3组基于晚维宪期（Viséan）比利时斑脱岩的全新铀-铅（U–Pb）锆石化学侵蚀同位素稀释热电离质谱测年数据，并利用这些数据估算了与测年斑脱岩互层的早沃南期（Warnantian）向上变浅碳酸盐岩准层序的周期。早沃南期准层序的平均旋回周期值与约10万年的米兰科维奇（Milankovitch）旋回一致——该旋回是近年更新世冰期记录中识别出的主导米兰科维奇频率，因此这一结果强化了两项论证：(1) 此类沉积旋回起源于冰川海平面变化；(2) 晚古生代冰期的主幕启动于沃南期初期之前，或沃南期早期阶段。本次新测年数据还为优化密西西比纪地质年代标尺的校准提供了额外的高精度年龄约束。依托这些新数据，苏格兰中部谷地的克莱德高原火山岩组（Clyde Plateau Volcanic Formation）的地层年代已从霍尔科阶（Holkerian）修订为阿斯比阶早期（Asbian）。