Acta Geologica Polonica, Vol. 66 (2016), No. 2, pp. 227–256 DOI: 10.1515/agp-2016-0010 Sulfur isotope patterns of iron sulfide and barite nodules in the Upper Cretaceous Chalk of England and their regional significance in the origin of coloured chalks CHRISTOPHER V. JEANS1, ALEXANDRA V. TURCHYN2 AND XU-FANG HU3 1Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN, UK E-mail
[email protected] 2Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK 3Editorial Office of Journal of Palaeogeography, China University of Petroleum (Beijing), 20 Xueyuan Road, P.O. Box 902, Beijing, 100083, China ABSTRACT : Jeans, C.V, Turchyn, A.V. and X-F. Hu 2016. Sulfur isotope patterns of iron sulfide and barite nodules in the Upper Cretaceous Chalk of England and their regional significance in the origin of coloured chalks. Acta Geologica Polonica, 66 (2), 227–256. Warszawa. The relationship between the development of iron sulfide and barite nodules in the Cenomanian Chalk of England and the presence of a red hematitic pigment has been investigated using sulfur isotopes. In southern England where red and pink chalks are absent, iron sulfide nodules are widespread. Two typical large iron sulfide nodules exhibit δ34S ranging from -48.6‰ at their core to -32.6‰ at their outer margins. In eastern England, where red and pink chalks occur in three main bands, there is an antipathetic relationship between the coloured chalks and the occur- rence of iron sulfide or barite nodules. Here iron sulfide, or its oxidised remnants, are restricted to two situations: (1) in association with hard grounds that developed originally in chalks that contained the hematite pigment or its postulated precursor FeOH3, or (2) in regional sulfidization zones that cut across the stratigraphy.