Southern Region Chalk Group Lithostratigraphy: Bristow et al. (1997) - Spurious Chalk Rock

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The Spurious Chalk Rock, named by Rowe (1908), occurs in the Isle of Wight and parts of Dorset. The name derives from the fact that although the bed was originally identified as correlative with the Chalk Rock of the Chilterns (Strahan, 1898), and thus assigned to the S. plana Zone, subsequent work (Rowe, 1901) showed that in the Isle of Wight and parts of Dorset, this bed is stratigraphically lower, and belongs to the T. lata Zone. The strongly indurated chalk that comprises the Spurious Chalk Rock equates with the Ogbourne and Pewsey hardgrounds that form the bottom hardground suite of Bromley & Gale's (1982) Chalk Rock 'Formation'. It formed as a condensed succession on a shallow marine wave -scoured platform at a time of reduced sea-level, and equates with an interval from the middle New Pit Chalk Member to the basal Lewes Chalk Member of the more expanded (i.e. deeper water) succession that formed over most of the Southern Region at this time (Gale, 1996). In Wiltshire and the Marlborough Downs the Ogbourne and Pewsey hardgrounds are closely associated with other, younger, hardgrounds, that condense strata of the upper T. lata Zone and lower S. plana Zone, forming a single indurated bed (the traditional Chalk Rock) that appeared to belong wholly to the S. plana Zone. However, following the formation of the Ogbourne and Pewsey hardgrounds in south Dorset and the Isle of Wight, there was a northward shift of the palaeogeographical region of hardground formation away from these areas, and this region developed a thin basinal type succession (Gale, 1996); none of the younger hardgrounds that elsewhere comprise the Chalk Rock were formed.

Macrofossil Biozonation: upper T. lata Zone

Correlation: see Correlation with other Southern Region successions

see Correlation with other UK successions

References[edit]

BROMLEY, R G & GALE, A S. 1982. The lithostratigraphy of the English Chalk Rock. Cretaceous Research, Vol. 3, 273 - 306.

GALE, A S. 1996. Turonian correlation and sequence stratigraphy of the Chalk in southern England. In HESSELBO, S P & PARKINSON, D N (eds), Sequence Stratigraphy in British Geology, Geological Society Special Publication, No. 103, pp. 177-195.

ROWE, A W. 1900-1908. Zones of the White Chalk of the English Coast. Proceedings of the Geologists' Association, Vol 16 (1900), 289-368; Vol. 17 (1902), 1-76; Vol. 18 (1903), 1-51, (1904), 193-296; Vol. 20 (1908), 209-352.

See: Chalk Rock (Chilterns and adjacent areas), New Pit Chalk Member, Lewes Nodular Chalk Member