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2 Acta Geologica Polonica

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Calcite cements and the stratigraphical significance of the marine [delta^13]C carbonate reference curve for the Upper Cretaceous Chalk of England

Jeans C., Hu X., Mortimore R.

Acta Geologica Polonica

2012

Vol. 62, no. 2

173-196

The hypothesis of Jarvis et al. (2006) that a [delta^13]C (calcite) reference curve based upon bulk samples from the Upper Cretaceous Chalk of England can be used as a primary criterion for trans-continental correlation is reviewed in the light of new stable isotope data from the Upper Albian and Cenomanian chalks of eastern England and from the Cenomanian to Campanian chalks of southern England. Evidence demonstrates that in the coloured chalks of eastern England the cements invariably have positive [delta^13]C values (up to 3.5[per mil]) except where they have been affected by hardground development when the cements have negative [delta^13]C values down to -6.5[per mil]. in contrast, the White Chalk of southern England may have cements with [delta^13]C values as negative as -8[per mil]. Modelling indicates that the coloured chalks may preserve a truer record of the primary palaeo-oceanographic [delta^13]C signal than the white and grey chalks of southern England. it is suggested that (1) many of the 72 isotope events described from the [delta^13]C (calcite) reference curve and proposed for correlation may reflect the effects of variations in the type and extent of calcite cementation; and (2) until much more is known about the patterns of calcite cementation in the Upper Cretaceous Chalk the use of minor isotope events for trans-continental stratigraphic correlation can only be applied with the utmost caution.

New observations on the inoceramid biostratigraphy of the higher part of the Upper Turonian and the Turonian - Coniacian boundary transition in Poland, Germany and the UK

Wood C., Walaszczyk I., Mortimore R., Woods M.

Acta Geologica Polonica

2004

Vol. 54, no. 4

541-550

New studies of sections in southern England (Bridgewick Pit, Downley, Shoreham Cement Works Quarry), eastern England (Kiplingcotes Station Quarry, Arras Road Pit), Germany (Salzgitter-Salder Quarry, a potential candidate GSSP for the Coniacian Stage) and central Poland (Słupia Nadbrzeżna, another potential candidate GSSP) have enabled a re-evaluation and refinement of the inoceramid biostratigraphy of the higher part of the Upper Turonian and the Turonian-Coniacian boundary transition. The inoceramid record at Słupia Nadbrzeżna below the terminal Turonian entry of Cremnoceramus is shown to be more complete than at the standard Salzgitter-Salder Quarry section. A new inoceramid event (Inoceramus lusatiae Event) identified at Słupia Nadbrzeżna is inferred to be present at the Sonnenberg Quarry, Waltersdorf, the type locality of Inoceramus lusatiae, as well as of I. glatziae and Cremnoceramus waltersdorfensis,and it is possibly represented in the condensed Navigation Hardgrounds in southern England. The absence of this event at Salzgitter-Salder suggests a significant hiatus. An inoceramid assemblage characterised by a taxon of uncertain affinities that immediately precedes the flood occurrence of Cremnoceramus (waltersdorfensis I Event) at Salzgitter-Salder has been identified at a comparable biostratigraphic position in eastern England (Yorkshire) and, tentatively, also in southern England. Inoceramids from this assemblage in the UK had previously been incorrectly assigned to Cremnoceramus waltersdorfensis and the basal Coniacian marker taxon, C. deformis erectus. The position of the base of the Coniacian has accordingly been revised upwards in both the southern and eastern England successions.