Integrated astrochronology, sequence stratigraphy, and chronostratigraphy of a shallow marine sandy mudstone (Lower Jurassic, Redcar Mudstone Formation, Cleveland Basin, UK)

Abstract

Cyclostratigraphy and sequence stratigraphy are cornerstone disciplines of modern sedimentary geology but are not commonly applied to the same study sections. Here, we apply both concepts to the argillaceous, shallow marine, Early Jurassic (Sinemurian–Pliensbachian) Redcar Mudstone Formation exposed at Robin Hood’s Bay, Yorkshire. Hand-held X-Ray Fluorescence (HH-XRF) high-resolution elemental data and bulk organic matter carbon-isotope (δ13Corg) data are presented to elucidate the context and pace of climatic change in the Early Jurassic, focussing on the Sinemurian–Pliensbachian boundary interval. The carbon-isotope stratigraphy demonstrates a 4.5 ‰ negative carbon-isotope excursion in bulk organic matter, representing the Sinemurian–Pliensbachian Boundary Event (SPBE). Elemental ratios (Si/Al and Zr/Rb), which are effective grain-size proxies, reveal coarsening upward cycles at a scale of 1.2–1.6 m, and are interpreted as parasequences. Parasequence stacking patterns allow the identification of depositional sequences, signifying five cycles of relative sea level change, with a major 2nd order relative sea-level rise and transgression associated with the Sinemurian–Pliensbachian boundary event. Missing or condensed retrogradational parasequences are associated with flooding and indicative of hiatuses at sub-biostratigraphic resolution – particularly in the Oxynotum Subzone of the Oxynotum Zone, and the Macdonnelli Subzone of the Raricostatum Zone. Maxima of redox-sensitive elements (Mo, V) and TOC in the Jamesoni Zone indicate dysoxic palaeoredox conditions in an otherwise oxic succession at the start of the Pliensbachian. Spectral analysis indicates regular cyclicity for parasequences through the succession, which are interpreted as being forced by short orbital eccentricity, and abrupt transitions in evolutive harmonic analysis support the hypothesis of short-duration hiatuses identified using sequence stratigraphy. The estimation of missing time is constrained using the differences in durations from models tuned to interpreted 100 kyr and 405 kyr orbital eccentricity cycles. The tuned age model gives estimates of the duration of the Oxynotum (0.90–1.00 Myr) and Raricostatum (1.35–1.45 Myr) zones. This further suggests a duration of 1.1 Myr for the early phase of the Sinemurian–Pliensbachian boundary event and 200 kyr for the Sinemurian age Liasidium Event, both regarded as possible hyperthermal episodes. Integrated sequence stratigraphy and astrochronology help to refine the timescale for the Early Jurassic and provide a framework for understanding the precise timing of the development of sequence stratigraphic surfaces.

Keywords

• Milankovitch
• Early Jurassic
• Organic carbon isotopes
• Elemental abundance
• Total organic carbon content
• Sequence stratigraphy