An integrated sequence stratigraphic analysis of the early Marsdenian Substage of the Millstone Grit Group, central Pennines, UK

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 (sub 2a) 1, R (sub 2b) 1, R (sub 2b) 2 and R (sub 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 ( approximately 400ka) eccentricity oscillation controlling maximum flooding events represented by the R (sub 2a) 1 and R (sub 2b) 2 marine bands, sub-100ka obliquity oscillations (controlling the R (sub 2b) 1, R (sub 2b) 2 and R (sub 2b) 3 marine bands and intervening low-order sequence boundaries), and precessional frequencies ( approximately 25ka) which may control the periodicity of the high-order sequences. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6408203