Provenance of late Palaeozoic terrestrial sediments on the northern flank of the Mid North Sea High: detrital zircon geochronology and rutile geochemical constraints

Zircon U–Pb and rutile trace element data are used to investigate the provenance of late Devonian to early Permian terrestrial sandstones in the Embla and Flora oil fields on the north flank of the Mid North Sea High, central North Sea. Two Old Red Sandstone samples (ORS 1) are dominated by 1.2–0.9 Ga Grenvillian zircons and low- to medium-grade rutile, with sparse Cambro-Ordovician Caledonian zircons (2–4%) and high-grade rutiles (0–5%). The samples are interpreted as recycled metasediments from the Scottish Caledonides. Two other Old Red Sandstone samples (ORS 2) contain a high proportion of Caledonian, mainly Silurian zircons (15–19%) and high-grade rutiles (15–18%); we propose that these components are traceable to the Krummedal sequence on East Greenland (and related sediments). We interpret the data to reflect a temporal evolution of the regional drainage system from northwestern to northeastern sources, with high-grade detritus reaching the Mid North Sea High in the Famennian–early Carboniferous. A late Carboniferous and an early Permian sandstone yielded zircon and rutile signatures compatible with recycling of Palaeozoic sediments north of southernmost Scotland, probably reflecting inversion tectonics. Recycling of Mesoproterozoic to Palaeozoic sediments is thus a prominent feature of the studied late Palaeozoic sandstones.

本数据集采用锆石（Zircon）铀-铅（U-Pb）和金红石（rutile）微量元素数据，对北海南部中部中北海隆起北翼的恩布拉（Embla）与弗洛拉（Flora）油田内晚泥盆世至早二叠世陆相砂岩的物源开展研究。两件老红砂岩样品（ORS 1）以1.2~0.9 Ga的格伦维尔期锆石（Grenvillian zircons）及低-中等变质程度金红石为主，仅含少量寒武-奥陶纪加里东期锆石（占比2%~4%）与高变质程度金红石（占比0%~5%）。研究表明，该类样品源自苏格兰加里东造山带的再沉积变沉积岩。另外两件老红砂岩样品（ORS 2）含有高比例的加里东期（主要为志留纪）锆石（占比15%~19%）与高变质程度金红石（占比15%~18%）；我们提出这些组分可追溯至东格陵兰的克鲁姆迈尔层序（Krummedal sequence）及相关沉积地层。本次数据反映区域水系系统的物源供给方向从西北向东北发生演化，高变质碎屑物质于法门期至早石炭世抵达中北海隆起。一件晚石炭世与一件早二叠世砂岩的锆石及金红石特征，与苏格兰最南部以北的古生代沉积物再沉积特征相符，这可能反映了反转构造（inversion tectonics）的作用。由此可见，中元古代至古生代沉积物的再沉积作用是本次研究的晚古生代砂岩的显著特征。