An integrated sequence stratigraphic analysis of the early Marsdenian substage of the Millstone Grit Group, Central Pennines, UK

Abstract

The early Marsdenian substage (Millstone Grit Group) of the Pennines comprises repeated deltaic cycles separated by ammonoid-bearing marine bands. This cyclicity, controlled by the combined forces of glacio-eustasy and modulations in sediment supply, provides an important outcrop area for the application of sequence stratigraphic principles. A new correlation framework is presented where two orders of sequence are identified: (1) a low-order sequence, within which marine bands (R 2a 1, R 2b 1, R 2b 2 and R 2b 3) represent a maximum flooding surface, and (2) high-order sequences nested within the low-order sequences. By integrating and correlating key exposures, historic well boreholes and field mapping, lateral changes in facies and facies association are observed, and palaeogeographic trends mapped. This allows the variation in sequence and systems tract stacking patterns to be interpreted. Three orders of Milankovitch cyclicity are inferred to control the sequence stacking patterns; long-duration ( c. 400 ka) eccentricity oscillation controlling maximum flooding events represented by the R 2a 1 and R 2b 2 marine bands, sub-100 ka obliquity oscillations (controlling the R 2b 1, R 2b 2 and R 2b 3 marine bands and intervening low-order sequence boundaries), and precessional frequencies ( c. 25 ka) which may control the periodicity of the high-order sequences. Supplementary material: Locality details, including lithostratigraphic units observed, gross and sand thicknesses within sequences, and palaeocurrent data measured are available at https://doi.org/10.6084/m9.figshare.c.6408203