Abstract
AbstractMudrocks 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 (UK) 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 timescales, 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.
Highlights
Linking strata and time is a core challenge of stratigraphy
In mud-dominated successions deposited under low energy conditions, ostensible steadiness and continuity of sedimentation limits both the frequency and duration of hiatuses (Sadler, 1981; see Hilgen et al, 2014, and references therein), underpinning their suitability for highresolution sampling and analysis
Marine mudrocks play a major role in informing current understanding of the detailed palaeoenvironmental history of the Earth
Summary
Linking strata and time is a core challenge of stratigraphy This endeavour is complicated by the fact that sedimentation is an inherently discrete and unsteady process, and stratigraphic successions are replete with hiatuses at multiple temporal and spatial scales (Shaw, 1964; Ager, 1973; Sadler, 1981; Tipper, 1983). This incompleteness means that the stratigraphic record is an imperfect archive of Earth history. In the Mulgrave Shale Member of the Yorkshire succession there is a link between basal silt lags and the occurrence of marine snow aggregates (Ghadeer & Macquaker, 2012), suggestive of episodic delivery linked by an association between storm events and increased nutrient delivery from either stormrelated fluvial discharge increases, and/or storm-induced nutrient recycling from bottom waters layers back to surface layer (Ghadeer & Macquaker, 2012)
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