Stratigraphy of the Late Aptian Lower Greensand around Nutfield, Surrey

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A detailed study of Lower Greensand deposits exposed in the fuller's earth workings of Nutfield. Surrey, has yielded new information on their lithofacies and stratigraphy. Two informal lithostratigraphic units, representing contrasting depositional regimes, are proposed for the Sandgate Formation of the Nutfield area. These units are of member status but, pending a comprehensive review of Upper Aptian lithostratigraphic nomenclature, they are provisionally assigned the informal terms Nutfield Beds and Redhill Sands. The Nutfield Beds are characterized by muddy, bioturbated, calcareous sandstones, deposited in quiet-water environments; they include economically important beds of fuller's earth, deposited as reworked volcanic ash. The overlying Redhill Sands consist of poorly consolidated, glauconitic sandstones, characterized by large-scale foresets of tidal bar origin. The Nutfield Beds form a geographically restricted lens, up to 15 m thick, lying within a syndepositional basin referred to as the ‘Nutfield Basin’ in this study. The underlying cherty sandstones ( c . 1–2 m), which constitute the top of the Hythe Formation, show a similarly restricted distribution. The Redhill Sands are also thickest ( c . 15 m) in the middle of the basin, but extend beyond the limits of the Nutfield Beds to the west. Relatively rapid subsidence within the Nutfield Basin combined with high sea-level stand during deposition of the Nutfield Beds produced conditions favourable for the accumulation and subsequent preservation of volcanic ash (now fuller's earth) deposits. Five candidate sequence boundaries have been identified in this study. SB1 is placed at a level within the uppermost Hythe. SB la is placed at the base of a thin glauconitic, pebbly sandstone bed that underlies the top-Hythe cherty sandstones. The cherty sandstones and the Nutfield Beds are interpreted as transgressive and highstand deposits within the same sequence. SB2 is drawn at the base of the Redhill Sands, and SB2a at the base of a unit of pebbly, clay-rich sandstone within the upper part of the Redhill Sands. SB3 is taken at the base of the Folkestone Sands, and is marked by an erosional surface with a relief of up to 4.5 m. Biostratigraphic control is not sufficiently precise to allow correlation of the sequences with those identified in the coastal sections of Folkestone.