During Late Pliensbachian and Early Toarcian times (Early Jurassic Epoch, c. 185 to 180 Ma) major environmental instabilities and perturbations affected the evolution of the carbon cycle, climate, sea level and biota. The temporal and causal relationships between these global-scale phenomena however remain poorly understood. This study starts by refining the accuracy of the ages of Lower Toarcian ammonite zones and subzones, and carbon-isotope excursions defined in the carbon-13 isotope (δ13C) reference curve of Ruebsam and Al-Husseini (2020). Based on an extensive review of stratigraphic data our study identified and calibrated by numerical age ammonite-dated transgressive-regressive (T-R) sequences, sequence boundaries (SB), maximum flooding intervals (MFI) and climate cycles. These calibrations placed in a common temporal framework the δ13C reference curve, T-R sequences, climate cycles and the Karoo-Ferrar Large Igneous Province (K-F LIP).

The temporal framework revealed four intervals that are either fragmented, or completely missing in numerous Upper Pliensbachian and Lower Toarican δ13C records (Stratigraphic Black Holes: SBH; Ruebsam and Al-Husseini, 2020). The identified SBHs closely correlated to erosional unconformities or sequence boundaries and global cooling. Unconformities occur in the spinatum zone (SBH 1), in the middle tenuicostatum zone (SBH 2) and in the middle serpentinum zone (SBHs 3 and 4). The older three SBHs further contain global sequence boundaries SBs JPl8, JTo1 and JTo2 of Haq (2018). The sea falls associated with the unconformities have amplitudes of many tens to possibly 75 m and exceed by more than an order of magnitude falls associated with thermo-eustasy or aquifer-eustasy (Davies et al., 2020). Sea level falls are therefore attributed to build-ups of polar ice caps and their ages and those of subsequent highstands were found to be consistent with the predictions of the Orbital Scale of glacio-eustasy (Matthews and Al-Husseini, 2010). We conclude tuning of insolation caused by eccentricity cycles with periods of c. 0.1, 0.405 and c. 2.4 myr drove sea-level fluctuations and also paced changes in the global carbon cycle and climate. Greenhouse gas emissions associated with volcanism in the Karoo-Ferrar Large Igneous Province affected the global carbon cycle and thereby amplified climate and sea level changes.