Northern Province Chalk nomenclature - Burnham Chalk Formation

Name

The Burnham Chalk Formation was proposed by Wood and Smith (1978).

Type section

Burnham Lodge Quarry [TA 0685 1720] near Barrow upon Humber, Lincolnshire (Gaunt et al., 1992).

Reference Section

Coastal cliffs between north-west of Flamborough Head [TA 259 705 to c. TA 175 748] (this section has never been described in detail, but see e.g. Rowe, 1904; Neale, 1974; Rawson and Whitham, 1992, a, b).

Formal subdivision

None herein but there are many named marl and flint bands throughout the succession that are used to divide the formation. They are all of bed status.

Lithology

White, thinly bedded chalk with common tabular and discontinuous flint bands; sporadic marl seams.

Definition of upper boundary

Top of highest flint band within a flint-rich unit of chalk (i.e. Burnham Formation) succeeded by flint-free chalks (i.e. Flamborough Formation); at Flamborough Head, this is the High Stacks Flint, but elsewhere may be at a somewhat different horizon. Change particularly marked on borehole sonic velocity logs.

Definition of lower boundary

Marked change from massive, rubbly-weathering chalks below, to harder, thinly bedded or nodular chalk above. This horizon lies just below the Ravendale Flint, a tabular or semi-tabular flint up to 0.25 m thick that is the lowest such flint in the Chalk Group and base of the chalk unit in which such flint bands are common. The lowest few metres of the formation comprises hard chalks and thick, closely spaced, tabular flints; which produce a topographic feature by which the base of the formation can be mapped, and a characteristic geophysical log signature enabling its identification in boreholes.'

Thickness

The formation is about 130 m thick; equivalent beds in north Norfolk are approximately 100 m thick (based on Wood et al., 1994), suggesting thinning of the Burnham Formation in the south of the region. North of the Humber, the Burnham Formation is 140 m thick (Whitham, 1991) but thins to 85 to 100 m over the Market Weighton High. A complete section of the formation is exposed in the cliffs north of Flamborough Head, from Selwicks Bay to North Landing where Rowe (1904) recorded a thickness of 105 m. However, bed-by-bed measurements of the lower part of the formation indicate that it is thicker, perhaps 160 m for the whole formation. The difference in these figures suggests that the top of the formation in the Cleveland Basin (as defined by the presence of flints) lies at a lower horizon than in the south, perhaps just above the Middleton Marl (based on preliminary correlation of geophysical logs).

Distribution

Known throughout the Northern Province

Previous names

‘Chalk with Flints’ (upper part) of early Geological Survey maps

Upper Chalk (lower part).

Parent

Chalk Group.

Age and biostratigraphy

Upper Cretaceous, Turonian to Santonian (Sternotaxis plana (now Plesiocorys plana) to Micraster coranguinum zones).

References

Wood and Smith (1978; Gaunt et al. (1992); Whitham (1991).