Abstract Cyclostratigraphic analyses of Upper Pliensbachian and Lower Toarcian carbon-13 isotope (δ13C) data, together with radiometric dating, are used to calibrate biozones and magnetic chrons in the Astronomical Time Scale (ATS). In turn, the ATS is used to date sea-level and climate cycles in relation to the Early Toarcian carbon-isotope excursion (T-CIE) and the Karoo-Ferrar Large Igneous Provinces. The resulting chronology however is insufficiently accurate to determine if these global-scale events are causally related. In particular, cyclostratigraphic analyses typically underestimate the durations of biozones by failing to account for hiatuses in depositional discontinuities. To account for hiatuses this paper constructs a δ13C reference curve consisting of correlative segments from several localities and dates them with ammonite zones and subzones. By comparing the reference curve to those from numerous localities, four major discontinuity-prone intervals were identified and named ‘stratigraphic black holes’ (SBH). SBH 1 occurs in the Late Pliensbachian P. spinatum Zone. Early Toarcian SBH 2 occurs in a δ13C maximum interval in middle D. tenuicostatum Zone. The T-CIE is characterized by a decreasing δ13C trend (c. 0.4 myr falling limb) in D. semicelatum Subzone, a minimum δ13C interval (c. 0.4 myr valley) and an increasing δ13C trend (c. 0.4 myr rising limb) in the E. elegantulum Subzone. SBH 3 occurs at base T-CIE rising limb and SBH 4 near its top or above it in a c. 0.4 myr, post-T-CIE plateau in upper E. elegantulum Subzone. Comparisons to published floating chronologies resulted in an Early Toarcian timescale with ~1.0 myr for the D. tenuicostatum Zone, and ~1.6 myr for the H. serpentinum Zone. Initial volcanism in the Karoo Province correlates with the Pliensbachian/Toarcian boundary at ~183.6 Ma, while its second phase was coeval with the T-CIE. Volcanism in the Ferrar Province correlates with the T-CIE.

中文翻译：

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用地层黑洞 (SBH) 校准早托阿尔世（早侏罗世）

摘要 上普连斯巴阶和下托阿尔克阶碳 13 同位素 (δ13C) 数据的旋回地层分析与辐射测年一起用于校准天文时标 (ATS) 中的生物区和磁年代数。反过来，ATS 用于确定与早期托阿尔世碳同位素偏移 (T-CIE) 和 Karoo-Ferrar 大型火成岩省有关的海平面和气候周期的年代。然而，由此产生的年表不够准确，无法确定这些全球规模的事件是否存在因果关系。特别是，旋回地层分析通常由于未能考虑沉积不连续性中的间断而低估了生物带的持续时间。为了解释间断，本文构建了一条 δ13C 参考曲线，该曲线由来自多个地点的相关段组成，并用菊石带和亚带对它们进行年代测定。通过将参考曲线与来自多个地点的曲线进行比较，确定了四个主要的不连续性区间，并将其命名为“地层黑洞”（SBH）。SBH 1 发生在晚 Pliensbachian P. spinatum 区。早期 Toarcian SBH 2 出现在 D. tenuicostatum 区中部的 δ13C 最大区间。T-CIE 的特征是 D. semicelatum 亚区中的 δ13C 趋势下降（c. 0.4 myr 下降边），最小 δ13C 间隔（c. 0.4 myr 谷）和 δ13C 趋势增加（c. 0.4 myr 上升边） E.优雅亚区。SBH 3 出现在底部 T-CIE 上升翼，SBH 4 出现在靠近其顶部或上方的 c。0.4 myr，上 E 的 T-CIE 后平台。优雅亚区。与已发表的浮动年表的比较导致早期 Toarcian 时间尺度，D. tenuicostatum 区约为 1.0 myr，H. serpentinum 区约为 1.6 myr。卡鲁省的初始火山活动与约 183.6 Ma 的 Pliensbachian/Toarcian 边界相关，而其第二阶段与 T-CIE 同期。费拉尔省的火山活动与 T-CIE 相关。