Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

Abstract

The study of past greenhouse climate intervals in Earth history, such as the Mesozoic, is an important, relevant and dynamic area of research for many sedimentary geologists, geochemists, palaeontologists and climate modellers. The Mesozoic sedimentary record provides key insights into the mechanics of how the Earth system works under warmer conditions, providing examples of natural climate change and perturbations to ocean chemistry, including anoxia, that are of societal relevance for understanding and contextualizing ongoing and future environmental problems. Furthermore, the deposition of widespread organic-carbon-rich sediments ('black shales') during the Mesozoic means that this is an era of considerable economic interest. In July 2015, an international group of geoscientists attended a workshop in Ascona, Switzerland, to discuss all aspects of the Mesozoic world and to celebrate the four-decade-long contributions made by Hugh Jenkyns (University of Oxford) and Helmut Weissert (ETH Zü rich) to our understanding of this fascinating era in Earth history. This volume of Sedimentology arose from that meeting and contains papers inspired by (and co-authored by!) Hugh and Helmi. Here, a brief introduction to the volume is provided that reviews aspects of Hugh and Helmi's major achievements; contextualizes the papers of the Thematic Issue; and discusses some of the outstanding questions and areas for future research.

Southern Hemisphere sea-surface temperatures during the Cenomanian–Turonian: Implications for the termination of Oceanic Anoxic Event 2

“…DR1). This observation contradicts the canonical model (e.g., Jenkyns, 2010;Robinson et al, 2017), which suggests that following an initial, transient increase in CO 2driven warming, burial of organic carbon would have lowered atmospheric pCO 2 and reversed greenhouse warming, leading to the cessation of conditions conducive to organic-carbon burial.…”

“…As less carbon was being sequestered, atmospheric CO 2 was able to remain high and maintain global warmth into the early Turonian. These factors that affected the relationship between carbon cycling, climate, and the termination of OAEs are not readily captured by the canonical model and provide further evidence that simple environmental reconstructions cannot be used universally to explain all features of all similar events in Earth history (e.g., Robinson et al, 2017;van der Ploeg et al, 2018).…”

“…Notwithstanding the PCE, existing temperature reconstructions (all from the Northern Hemisphere) suggest that temperatures remained high throughout OAE 2 and into the early Turonian (Jenkyns et al, 1994;Voigt et al, 2004;Forster et al, 2007;Sinninghe Damsté et al, 2010;van Helmond et al, 2014;O'Brien et al, 2017). The proxy evidence for relatively high and constant temperatures from the latter stages of OAE 2 and the immediate post-event phase seemingly contradicts the theory that increased organiccarbon burial led to a reversal of greenhouse climatic conditions and a subsequent return to normal, generally oxic, marine conditions (Jenkyns, 2010;Robinson, et al, 2017).…”

“…Oceanic Anoxic Event 2 (OAE 2) in the late Cenomanian was likely triggered by large-igneous-province volcanism (Turgeon and Creaser, 2008;Du Vivier et al, 2014;Holmden et al, 2016), which released CO 2 , and possibly biolimiting nutrients, into the ocean and atmosphere (see Jenkyns et al, 2017). Various proxies lend support to a canonical model that suggests that increased CO 2 led to a greenhouse climate, characterized by higher temperatures, increased wind-driven upwelling, an invigorated hydrological cycle, and enhanced weathering rates of silicate rocks, which, in turn, raised the supply of nutrients to the surface ocean and caused local salinity stratification (e.g., Arthur et al, 1988;Jenkyns, 2010;Robinson et al, 2017). These climatic and oceanographic factors would have promoted the production and preservation of organic carbon in a range of marine depositional settings.…”

Terrestrial expression of the Cretaceous greenhouse regime and its relationship withOAE1a: Evidence from the Jiaolai Basin, eastern China

“…Growing evidence shows that terrestrial ecosystems have also been strongly influenced by the greenhouse regimes and OAEs (Föllmi, 2012; Ge & Zhong, 2018; Hu, Zhao, Yilmaz, & Li, 2012; Mutterlose et al, 2014; Patruno et al, 2015; Robinson, Heimhofer, Hesselbo, & Petrizzo, 2017; Wang et al, 2013; Zhang, Li, Yan, Wang, & Geng, 2020). In China, our understanding of the Cretaceous greenhouse climate and associated OAEs is based mainly on the information revealed from the records of marine successions in the Tibet areas (Hu, Jansa, & Wang, 2008; Li, Wei, Li, & Zhang, 2016), and little has been published on the terrestrial records.…”