Dynamic climate-driven controls on the deposition of the Kimmeridge Clay Formation in the Cleveland Basin, Yorkshire, UK

Abstract

Abstract. The Kimmeridge Clay Formation (KCF) is a laterally extensive, total-organic-carbon-rich succession deposited throughout northwest Europe during the Kimmeridgian–Tithonian (Late Jurassic). It has recently been postulated that an expanded Hadley cell, with an intensified but alternating hydrological cycle, heavily influenced sedimentation and total organic carbon (TOC) enrichment by promoting primary productivity and organic matter burial in the UK sectors of the Boreal Seaway. Consistent with such climate boundary conditions, petrographic observations, total organic carbon and carbonate contents, and major and trace element data presented here indicate that the KCF of the Cleveland Basin was deposited in the Laurasian Seaway under the influence of these conditions. Depositional conditions alternated between three states that produced a distinct cyclicity in the lithological and geochemical records: lower-variability mudstone intervals (LVMIs) which comprise clay-rich mudstone and higher-variability mudstone intervals (HVMIs) which comprise TOC-rich sedimentation and carbonate-rich sedimentation. The lower-variability mudstone intervals dominate the studied interval but are punctuated by three ∼ 2–4 m thick intervals of alternating TOC-rich and carbonate-rich sedimentation (HVMIs). During the lower-variability mudstone intervals, conditions were quiescent with oxic to suboxic bottom water conditions. During the higher-variability mudstone intervals, highly dynamic conditions resulted in repeated switching of the redox system in a way similar to the modern deep basins of the Baltic Sea. During carbonate-rich sedimentation, oxic conditions prevailed, most likely due to elevated depositional energies at the seafloor by current–wave action. During TOC-rich sedimentation, intermittent anoxic–euxinic conditions led to an enrichment of redox-sensitive and sulfide-forming trace metals at the seafloor and a preservation of organic matter, and an active Mn–Fe particulate shuttle delivered redox-sensitive and sulfide-forming trace metals to the seafloor. In addition, based on TOC–S–Fe relationships, organic matter sulfurization appears to have increased organic material preservation in about half of the analysed samples throughout the core, while the remaining samples were either dominated by excess Fe input into the system or experienced pyrite oxidation and sulfur loss during oxygenation events. New Hg∕TOC data do not provide evidence of increased volcanism during this time, consistent with previous work. Set in the context of recent climate modelling, our study provides a comprehensive example of the dynamic climate-driven depositional and redox conditions that can control TOC and metal accumulations in a shallow epicontinental sea, and it is therefore key to understanding the formation of similar deposits throughout Earth's history.

Sedimentation of the Kimmeridge Clay Formation in the Cleveland Basin (Yorkshire, UK)

“…Total organic carbon contents were measured by a standard LECO combustion procedure at Newcastle University (Newcastle, UK), wavelength-dispersive X-ray fluorescence (XRF) analyses were used to determine elemental concentrations at the Institute for Chemistry and Biology of the Marine Environment (ICBM, University of Oldenburg, Oldenburg, Germany), and stable carbon isotopes values were measured BGS stable isotope facility (part of the National Environmental Isotope Facility) and are calculated to the VPDB standard. Full details reported in Atar et al (2019a) [14].…”

“…At least episodic bottom water/seafloor oxygenation is evidenced by the presence of agglutinated foraminifera. Total organic carbon contents range between 1.98 to 20.01 wt % (Table 1) [14], suggesting sediment-pore waters were sufficiently oxygen-depleted to inhibit extensive oxidative degradation of OM. Trace element geochemical data suggest a suboxic sediment-water interface [14], thus supporting the petrographic evidence for oxygen depletion.…”

“…Total organic carbon contents range between 1.98 to 20.01 wt % (Table 1) [14], suggesting sediment-pore waters were sufficiently oxygen-depleted to inhibit extensive oxidative degradation of OM. Trace element geochemical data suggest a suboxic sediment-water interface [14], thus supporting the petrographic evidence for oxygen depletion. However, the presence of organo-mineral aggregates offers a plausible explanation for the delivery of algal maceral material to the seafloor.…”

“…As such, it has been the subject of great interest over the past century [1][2][3][4][5][6][7]. Geoscientists continue to study the KCF using techniques ranging from sedimentology [8][9][10], geochemistry [6,[11][12][13][14][15], to palaeontology [16][17][18][19], and climate modelling [20][21][22][23], in an effort to correlate deposits, elucidate depositional controls and reconstruct global climate conditions. Characterisation of the sediment facilitates the interpretation of ancient depositional environments, which provide a unique and important insight into global climate and carbon cycle dynamics [24].…”

“…However, lateral sediment transport and potentially multiple episodes of sediment remobilisation prior to deposition means that mudstones may record palaeoenvironment conditions from other areas of the ocean with little or no evidence of long-range transport; therefore, [36] reproduced with permission after Atar et al (2019b) [15]. (b) Geological map of the Cleveland Basin (Yorkshire, UK) after Powell (2010) [52], reproduced with permission after Atar et al (2019a) [14]. The Marton 87, Ebberston 87, Flixton 87, and Reighton 87 cores are marked by red dots on the map.…”