Fine-grained sedimentary successions contain the most detailed record of past environmental conditions. High-resolution analyses of these successions yield important insights into sedimentary composition and depositional processes and are, therefore, required to contextualise and interpret geochemical data which are commonly used as palaeoclimate proxies. The Kimmeridge Clay Formation (KCF) is a 500 m-thick mudstone succession deposited throughout the North Sea in the Late Jurassic and records environmental conditions through this time. Here, we present petrographic analyses (on 36 thin sections) on a 50 m section of a KCF core from the Cleveland Basin (Yorkshire, UK) to investigate controls on sedimentation in this region during the Tithonian, Late Jurassic. Facies descriptions demonstrate that deposition took place in a hydrodynamically variable environment in which the sediment origins, sediment dispersal mechanisms, and redox conditions fluctuated on the scale of thousands of years. Petrographic analyses show that the sediment comprises marine (algal macerals, calcareous fossils), detrital (quartz, clay, feldspar), and diagenetic (dolomite and authigenic kaolinite) components and that several sediment dispersal mechanisms influenced deposition and facilitated both the supply and preservation of terrestrial and marine organic material. This work provides a framework for the interpretation of geochemical palaeoclimate proxies and reinforces the importance of looking at the rock when interpreting whole-rock geochemical data.
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