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Supplementary figure showing MTM analyses of Rb-record (0-65m)

Supplementary figure showing MTM analyses of the Ti/AI record (0-65m)

Supplementary Figure S1. This figure summarizes most of the geochemical, sedimentary and biotic data available for the Mochras core. Comparisons are made with data from the Peniche section (grey curves). On the right side, ammonite biostratigraphy (Copestake and Johnson 2014). Calcareous nannofossil biostratigraphy based on Bown (1987), Mattioli and Erba (1999), and Ferreira et al. (2019). δ13Corg for the lower Toarcian (black dots) after Xu et al. (2018a) and for the upper Pliensbachian (grey dots) after Storm et al. (2020). (a) Envelope curve of δ180 (‰VPDB) values measured on brachiopod calcite from the Peniche section and interpreted as indicative of temperature changes (Suan et al. 2008a; Müller et al. 2020). (b) Peaks in low pH as deduced from δ11B (‰NIST951) measured on brachiopod calcite from the Peniche section (Müller et al. 2020). (c) Hg concentrations likely translating magmatic pulses of LIP (Large Igneous Province) volcanism in the Karro-Ferrar-Chon Aike provinces (Percival et al. 2015). (d) Osmium isotope trend (187Os/188Os) showing period of enhanced weathering rates (Percival et al. 2016). (e) Kaolinite/illite ratio percentage, whose peaks indicate the development of a more humid climate (Xu et al. 2018a). (f) High pyrite concentrations in the interval of the T-OAE negative CIE suggest transient photic-zone euxinia and episodic anoxia at the seafloor (Xu et al. 2018a). (g) Trends in calcium carbonate content for the lower Toarcian are after Xu et al. (2018b), and for the upper Pliensbachian are after Storm et al. (2020). (h) Trends in calcareous nannofossil flux as recorded in this paper. (j) Size variations of Schizosphaerella spp. valves as recorded in this paper. (k) Thickness of Schizosphaerella spp. valves as recorded in this paper. (l) Trends of meso-eutrophic taxa, mainly belonging to the Biscutaceae. (m) A prominent peak in Calyculaceae is recorded in the core of the T-OAE negative CIE, concomitant with the peak in pyrite. (n) The deep-dweller abundance trend (mainly Crepidolithus crassus) attest for the recovery of the deep-photic zone environments. (o) A peak in prasinophytes (green algae), and (p) a marked decrease of dinoflagellates in also documented at Mochras during the T-OAE by van de Schootbrugge et al. (2005). (q) Approximate ages of emplacement of Karoo and Ferrar LIPs (after Müller et al. 2020).

The late Early Jurassic Toarcian Stage represents the warmest interval of the Jurassic Period, with an abrupt rise in global temperatures of up to ~7°C in mid-latitudes at the onset of the early Toarcian Oceanic Anoxic Event (T-OAE; ~183Ma). The T-OAE, which has been extensively studied in marine and continental successions from both hemispheres, was marked by the widespread expansion of anoxic and euxinic waters, geographically extensive deposition of organic-rich black shales, and climatic and environmental perturbations. Climatic and environmental processes following the T-OAE are, however, poorly constrained, largely due to a lack of study of stratigraphically well-constrained and complete sedimentary archives. Here, we present integrated geochemical and physical proxy data (high-resolution carbonisotope data (δ13 C), bulk and molecular organic geochemistry, inorganic petrology, mineral characterization, and major- and trace-element concentrations) from the biostratigraphically complete and expanded entire Toarcian succession in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales, UK. With these data, we (1) construct the first high-resolution biostratigraphically calibrated chemostratigraphic reference record for the complete Toarcian Stage, (2) establish palaeoceanographic and depositional conditions in the Cardigan Bay Basin, (3) show that the T-OAE in the hemipelagic Cardigan Bay Basin was marked by the occurrence of gravity-flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine (shelf) basins, and (4) explore how early Toarcian (tenuicostatum and serpentinum zones) siderite formation in the Cardigan Bay Basin was linked to low global oceanic sulphate concentrations and elevated supply of iron (Fe) from the hinterland, in response to climatically induced changes in hydrological cycling, global weathering rates and large-scale sulphide and evaporite deposition.

Dip direction of the Early Jurassic succession — evidence from palaeomagnetic data