Small- and Large-Scale Sedimentological Processes in the Early Jurassic Mud- Dominated Successions, Cleveland Basin, UK

UoM administered thesis: Phd

  • Authors:
  • Neveen Elsayed

Abstract

Early Jurassic mudstones of the Cleveland Basin, Yorkshire, NE England, exhibit complex heterogeneity in terms of their sedimentology and diagenesis. In this study, an outcrop and thin section approach was used to develop an understanding of the depositional and early diagenetic processes operating during the mudstone sedimentation. This study demonstrates that finegrained sediments, which seem homogeneous at the larger scale, at smaller scales exhibit high levels of textural variability at smaller scales. Macro- to micro-scale (outcrops, core, and petrographic) analysis has enabled the identification of variation in composition, texture, and sedimentary features of two mudstone successions ( the Whitby Mudstone and the Redcar Mudstone Formations) in the study area. A total of ten microfacies were identified from the analysis of 110 samples: 1) Laminated, argillaceous mudstones (M.F.1), Homogeneous, argillaceous mudstones (M.F.2), Finely-laminated to graded-bedded, organic carbon-rich, calcareous, argillaceous mudstone (M.F.3a), 4) Homogeneous, calcareous mudstone (M.F.4a), Finely-laminated to graded-bedded, carbonaceous mudstone (M.F.5a), Intraclast-bearing, homogeneous, argillaceous, mudstones (M.F.6a), Carbonate-bearing, thin-laminated, graded-bedding, argillaceous, mudstones (M.F.7a), Finely laminated to graded-bedding, siliceous, argillaceous mudstones (M.F.3b), Burrow-mottled, biogenic detritus- dominated, argillaceous mudstones (M.F.4b), and Glauconite pellets -bearing, argillaceous mudstones (M.F.5b). These heterogeneous mudstones reflect (1) various modes of sedimentation that have been revealed by the preserved microtextures (e.g. sharp bases, ripple laminae, normal graded bedding, triplet fabrics); (2)Lateral variation in the input of silt and clay grains across the basin, and (3) variation in the level of bottom water oxygen (dysoxic to oxic). Individually, the samples are highly heterogeneous (in terms of micro-texture and composition) and contain variable proportions of materials derived from inputs to the basin, primary production within the basin, and the effects of diagenesis. The presence of parallel lamination that shows low-angle down lap relationships throughout this succession reflects bedload transport of flocculated muds by currents. Whereas, triplet fabrics (e.g. tempestites) indicate sediment dispersal by a combination of storm set-up and wave action. The occurrence of intraclasts within ungraded mudstones indicates rapid en-mass deposition. The variability in the amount of organic carbon content ( 0.10 to 9.18 wt. % TOC) throughout the succession indicates the role of bottom water dysoxia in enhancing the organic carbon preservation in the sediments. Constituent authigenic minerals have been identified throughout the succession and include calcite, siderite, dolomite, quartz, kaolinite, illite, pyrite, and chlorite. The diagenetic processes interpreted and conclude coupled dissolution-precipitation reactions, sulphate reduction, clay mineral transformations, organic matter certification, and compaction. Overall, these Early Jurassic mudstones exhibit variability vertically and laterally in their sedimentology and organic-carbon content. This observed heterogeneity suggests that mudstone deposition is much more dynamic in this basin than previous researchers have previously assumed.

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Original languageEnglish
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Award date1 Aug 2021