Mudrocks are the most common rock type at the Earth's surface, and they play a major role in informing current understanding of the palaeoenvironmental history of the planet. Their suitability for this purpose is at least partly underpinned by the assumed stratigraphic completeness of mudrock successions, and the ostensible fidelity with which they record temporal changes in palaeoenvironment. Mud does not necessarily accumulate, however, as a steady, near-continuous ‘rain’ under low energy conditions. Advective modes of mud transport and episodic, ephemeral accumulation have been shown to dominate in many ancient successions. This has implications for the completeness of these records and their suitability for high-resolution sampling and analysis. In this study, a numerical model of mud accumulation, parameterized with data from the Lower Jurassic of Yorkshire (United Kingdom) is presented to explore completeness and resolution constraints on ancient epicontinental mudrock successions. Using this model, stratigraphic completeness of the analysed Yorkshire succession is estimated to be ca 13% and ca 98% at centennial and millennial time scales, respectively. The findings indicate that sub-millennial scale processes and events are unlikely to be accurately resolved, despite the largely unbioturbated and well-laminated nature of the succession. Epicontinental mudrock successions are a crucial archive of ancient environmental changes, and the findings of this study help to define a plausible upper limit on the resolution achievable in these successions. Even with high-resolution sampling, sub-millennial scale records of palaeoenvironmental change may not be attainable in ancient epicontinental mudrocks.
Kemp, David B.Fraser, Wesley T.Izumi, Kentaro
Faculty of Humanities and Social Sciences\Department of Social Sciences
Year of publication: 2018Date of RADAR deposit: 2018-01-10