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Magnetostratigraphic constraints for Early Permian rocks of the southwestern Karoo Basin, South Africa
Gondwana Research ( IF 6.1 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.gr.2020.11.009
Abosede O. Abubakre , Michiel O. de Kock

Abstract We present results of rock and paleomagnetic magnetic analyses of a ~ 671 m-thick continuous vertical drill core (KZF-1) that intersect the lower Ecca Group (early-mid Permian) of the southwestern Karoo Basin, South Africa. Rock magnetic and optic microscopy experiments indicate monoclinic pyrrhotite and single-domain magnetite in the mudstones, shales, and siltstones as carriers of characteristic remanent magnetization (ChRM), which is likely a post-detrital remanent magnetization. Stepwise demagnetization and removal of low-coercivity and thermally less stable magnetizations reveal the preservation of a dual polarity ChRM in 90 samples. These are used to construct a magnetostratigraphic profile for the core that is dominantly reversed polarity with four short normal polarity subchrons. Correlation with published U Pb SHRIMP and CA TIMS ages and the proposed composite reference section for the Early Permian allows us to propose an Artinskian (281 Ma) to Kungurian (276 Ma) age for the lower Ecca Group rocks. Our magnetostratigraphic profile can be tied in with published profiles from the mid to Upper Ecca Group to produce the first composite profile that spans all of the Ecca Group in the southwestern region of the Karoo Basin.

中文翻译:

南非卡鲁盆地西南部早二叠世岩石的磁地层约束

摘要 我们展示了与南非卡鲁盆地西南部的下 Ecca 群(早中二叠世)相交的约 671 m 厚的连续垂直钻芯 (KZF-1) 的岩石和古地磁分析结果。岩石磁性和光学显微镜实验表明,泥岩、页岩和粉砂岩中的单斜磁黄铁矿和单畴磁铁矿作为特征剩磁 (ChRM) 的载体,这可能是碎屑后剩磁。逐步退磁和去除低矫顽力和热稳定性较差的磁化显示在 90 个样品中保留了双极性 ChRM。这些用于为具有四个短的正常极性子时间的主要反向极性的核心构建磁地层剖面。与已发表的 U Pb SHRIMP 和 CA TIMS 年龄的相关性以及建议的早二叠世复合参考剖面,使我们能够为下 Ecca 群岩石提出 Artinskian (281 Ma) 至 Kungurian (276 Ma) 年龄。我们的磁地层剖面可以与已发布的从中到上 Ecca 群的剖面相结合,以生成第一个跨越 Karoo 盆地西南部地区整个 Ecca 群的复合剖面。
更新日期:2021-02-01
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