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.本次研究利用锆石（Zircon）铀-铅（U-Pb）定年及金红石（rutile）微量元素数据，对北海中北部中北海高地北翼恩布拉（Embla）与弗洛拉（Flora）油田内晚泥盆世至早二叠世陆相砂岩开展物源分析。两件老红砂岩（Old Red Sandstone，ORS）样品（ORS 1）以1.2~0.9 Ga格伦维尔期锆石及低-中等变质级金红石为主，仅含少量寒武-奥陶纪加里东期锆石（占比2%~4%）与高变质级金红石（占比0%~5%），据此推断该类样品源自苏格兰加里东造山带的再旋回变沉积岩。另外两件老红砂岩样品（ORS 2）则含有高比例的加里东期（主要为志留纪）锆石（占比15%~19%）与高变质级金红石（占比15%~18%）；我们认为这些组分可追溯至东格陵兰的克鲁姆梅尔层序（Krummedal sequence）及相关沉积岩。综合数据表明，区域水系物源存在从西北向东北的时空演化，高变质级碎屑在法门期至早石炭世抵达中北海高地。一件晚石炭世与一件早二叠世砂岩的锆石与金红石特征，与苏格兰最南部以北的古生代沉积物再旋回特征相符，这可能反映了反转构造（inversion tectonics）作用。由此可见，中元古代至古生代沉积物的再旋回作用是本次研究的晚古生代砂岩的显著特征。