30 Nov 2022
30 Nov 2022
Status: this preprint is currently under review for the journal CP.

Environmental changes during the onset of the Late Pliensbachian Event (Early Jurassic) in the Mochras Borehole, Cardigan Bay Basin, NW Wales

Teuntje P. Hollaar1,2, Stephen P. Hesselbo2,3, Jean-François Deconinck4, Magret Damaschke5, Clemens V. Ullmann2,3, Mengjie Jiang2, and Claire M. Belcher1 Teuntje P. Hollaar et al.
  • 1WildFIRE Lab, Global Systems Institute, University of Exeter, Exeter, EX4 4PS, UK
  • 2Camborne School of Mines, Department of Earth and Environmental Science, University of Exeter, Penryn Campus, Penryn, TR10 9FE, UK
  • 3Environment and Sustainability Institute, University of Exeter, Penryn Campus, Penryn, TR10 9FE, UK
  • 4Biogéosciences, UMR 6282 CNRS, Université de Bourgogne/Franche-Comté, 21000 Dijon, France
  • 5Core Scanning Facility, British Geological Survey, Keyworth, NG12 5GG, UK

Abstract. The Late Pliensbachian Event (LPE), in the Early Jurassic, is associated with a perturbation in the global carbon cycle (positive carbon isotope excursion (CIE) of ~ 2 ‰), cooling of ~5 °C, and the deposition of widespread regressive facies. Cooling during the Late Pliensbachian has been linked to enhanced organic matter burial and/or disruption of thermohaline ocean circulation due to North Sea doming. Orbital forcing had a strong influence on the Pliensbachian environments and recent studies show that the terrestrial realm and the marine realm in and around the Cardigan Bay Basin were strongly influenced by orbital climate forcing. In the present study we build on the previously published data for long eccentricity cycle E459 ± 1 and extend the palaeoenvironmental record to include E458 ± 1. We explore the environmental and depositional changes on orbital time scales for the Mochras core during the onset of the LPE. Clay mineralogy, XRF elemental analysis, isotope ratio mass spectrometry, and palynology are combined to resolve systematic changes in erosion, weathering, fire, grain size and riverine influx. Our results indicate distinctively different environments before and after the onset of the LPE positive CIE, and show increased physical erosion relative to chemical weathering. We also identify 5 swings in the climate, in tandem with the 405 kyr eccentricity minima and maxima. Eccentricity maxima are linked to precessionally repeated occurrences of a semi-arid, monsoonal climate with high fire activity and relatively coarser fraction of terrestrial runoff. In contrast, 405 kyr minima in the Mochras core are linked to a more persistent, annually wet climate, low fire activity, and relatively finer grained deposits across multiple precession cycles. The onset of the LPE +ve CIE did not impact the expression of the 405 kyr in the proxy records, however, during the second pulse of lighter carbon (12C) enrichment, the clay minerals record a change from dominant chemical weathering to dominant physical erosion.

Teuntje P. Hollaar et al.

Status: open (until 20 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-87', Stephane Bodin, 21 Dec 2022 reply
  • RC2: 'Comment on cp-2022-87', Wolfgang Ruebsam, 08 Feb 2023 reply

Teuntje P. Hollaar et al.

Data sets

Terrestrial palaeo-environmental proxy data of the Upper Pliensbachian, Mochras Borehole sediments, deposited in the Cardigan Bay Basin, Wales Teuntje Hollaar

Llanbedr (Mochras Farm) Core Scanning Dataset Magret Damaschke, Simon Wylde, Mengjie Jiang, Teuntje Hollaar, Clemens Vinzenz Ullmann

Teuntje P. Hollaar et al.


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Short summary
Palaeoclimatological reconstructions aid our understanding of current and future climate change. In the Pliensbachian (Early Jurassic) a climatic cooling event occurred globally. We show that this cooling event has a significant impact on the depositional environment of the Cardigan Bay Basin, but that the 405 kyr eccentricity cycle remained the dominant control on terrestrial and marine depositional processes.