Early Jurassic Palaeoenvironmental Change – A North African Perspective

Saker-Clark, Matthew (2019). Early Jurassic Palaeoenvironmental Change – A North African Perspective. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000efb6

Abstract

Extreme palaeoclimate change events from Earth history can be used to further our understanding of the Earth’s potential responses to anthropogenic climate change. The geological record of the Toarcian Oceanic Anoxic Event (T-OAE; ~183 million years ago) provides an opportunity to study a period of extreme palaeoclimate change that was associated with global carbon release and global warming. This research presents: evidence for the effects of T-OAE climate change at tropical latitudes; a more efficient technique for high-resolution proxy dataset production, and an astronomical timescale for the T-OAE.

In this study, protocols for elemental analysis using portable X-ray fluorescence spectroscopy (pXRF) have been optimised for the production of high quality, high-resolution proxy data from sedimentary successions. The new protocols have been used to demonstrate that these data are suitable for cyclostratigraphic studies, and that they provide the opportunity to produce astronomical timescales more quickly, cheaply and more easily than commonly-used combustion analyses.

Three published and two previously unstudied successions of early Toarcian strata along a proximal to distal profile in the Middle Atlas Basin, Morocco were investigated and recorded. Sedimentological and geochemical analyses show widespread deposition of storm beds and increased sedimentation rates within the T-OAE, providing evidence for acceleration of the tropical hydrological cycle due to global warming associated with the T-OAE.

High-resolution sedimentological and geochemical records of a T-OAE succession reveal an -8‰ carbon isotope excursion over 66.6 m of strata coincident with evidence for enhanced storm activity. Cyclostratigraphic analysis of the sedimentological and geochemical data show that T-OAE enhanced storm activity lasted for >950 kyr and was modulated by 100 kyr and 21 kyr astronomical cycles in seasonality. Furthermore, it is demonstrated that intense tropical storm frequency increased in response to increasing temperature, and that the T-OAE carbon cycle perturbation lasted ~1.3 Myr.

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