South-west England Chalk Group Lithostratigraphy: Jarvis & Woodroof (1984) & Jarvis & Tocher (1987) - St Margaret's Member
The St Margaret's Member takes its name from a lithostratigraphical unit named by Robinson (1986) in the North Downs. It comprises hard, nodular, flinty chalk with marl seams and hardgrounds, c. 28 m thick at Pinhay Cliffs (Jarvis & Tocher, 1987). Nodular flints are typical, but anastomosing sheet flints also occur, especially in the higher part of the succession, where intervals of less nodular chalk are locally developed (Jarvis & Tocher, 1987). The base of the member is the lowest occurrence of regualrly nodular chalk, and the top is a conspicuous hardground, named the Chapel Rock Hardground (Jarvis & Tocher, 1987). A large, laterally continuous nodular flint, just below the middle of the member, is a conspicuous marker in many sections, and is named the Annis' Knob Flint by Jarvis & Tocher (1987). Other marker beds are identified in by Jarvis & Tocher (1987); in the interval below the Anni's Knob Flint the Whitlands Marl is overlain by the Arratt's Hill Hardground, while above the Annis' Knob Flint there are (in ascending order) the Rock Orchard Flint, the South Down Marl and the Lynch Cottage Hardgrounds. Terebratulid brachiopods, inoceramid bivalves and echinoids (especially Micraster and Echinocorys) are important fossils in the succession (Woods, 1999).
Macrofossil Biozonation: T. lata Zone (pars), S. plana Zone & M. cortestudinarium Zone (Woods, 1999)
Correlation: see Correlation with other lithostratigraphical schemes for south-west England
see Correlation with other UK regions
References
JARVIS, I & TOCHER, B A. 1987. Field Meeting: the Cretaceous of SE Devon, 14 - 16th March, 1986. Proc. Geol. Ass., Vol. 98 (1), 51-66.
ROBINSON, N D.1986. Lithostratigraphy of the Chalk Group of the North Downs, southeast England. Proceedings of the Geologists' Association, Vol. 97, 141-170.
WOODS, M A.1999. Draft contribution to the sheet description of the Sidmouth district (Sheet 326): Cretaceous. British Geological Survey Technical Report, WH/99/28R.
See: St. Margaret's Member (Robinson, 1986), flint, marl, hardground