lS 



MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 

 III. STRATIGRAPHY AND HISTORICAL BACKGROUND 



a. The Speeton Clay 



By W. A. S. SARJEANT 



The Speeton Clay is the lowest of the three horizons principally dealt with in 

 this work. Two boreholes were put down through the Speeton Clay during the 

 summer of i960 by Koninklijke Shell Exploratie en Produktie Laboratorium, 

 Rijswijk, The Netherlands. The first of these, Shell Speeton No. 1, was sited near 

 Speeton Beck (grid ref. TA.151753) and reached a depth of 135-25 metres (443 ft. 

 11 in.) ; the second, Shell West Heslerton No. 1, was put down at West Heslerton, 

 some 1-4 miles west of Speeton, reaching a depth of 117 metres (383 ft. 4 in.) without 

 bottoming the Lower Cretaceous. Through the courtesy of Shell Internationale 

 Research Maatschappij N.V., The Hague, Netherlands, specimens were made 

 available for micropalaeontological and palynological study to various specialists. 

 Results of study of the Speeton Clay ostracod faunas have been published by Neale 

 (1960a, 1962a), Neale & Kilenyi (1961) and Kaye (1963a, 19636, 1964a). These 

 authors also published accounts of the outcrop stratigraphy (Neale 19606, 19626 ; 

 Kaye 19646) ; their accounts of the stratigraphy and ostracod faunas of the bore- 

 holes are currently in press. 



The assemblages of fossil microplankton proved unexpectedly rich. They are 

 dominated by dinoflagellate cysts, acritarchs being relatively infrequent. Studies 

 have to date been concentrated on the assemblages from the West Heslerton bore- 

 hole, a brief account of some new species from a Hauterivian horizon having already 

 been published (Neale & Sarjeant 1962). The holotypes of the species described in 

 that paper, formerly in the collections of the Sedimentology Research Laboratory, 

 University of Reading, are now lodged in the British Museum (Natural History) 

 under the following numbers : 



Species 



Reading Nos. 



B.M.(N.H.) 



Heslertonia heslertonensis 







(formerly Gonyaulax) 



44Y/8/10 



V.51713W 



Gonyaulacysta cretacea 







(formerly Gonyaulax) 



44Y/4/21 



V.5i 7 n(2) 



Cribroperidinium sepimentum 



44Y/7/7 



V.51712 (1) 



Gardodinium albertii 



44Y/1/28 



¥.51709(2) 



Pseudoceratium (Eopseudoceratium) gochti 



44Y/I/36 



V.51709 (4) 



Muderongia cruris 



44Y/4/1 



¥.51711(1) 



Heliodinium patriciae 



44Y/3/3 



V. 5 i 7 io(i) 



Oligosphaeridium vasiformum 







(formerly Hystrichosphaeridium) 







Holotype 



44Y/I/34 



V.5i7°9(3) 



Paratype 



44Y/1/26 



V.5i7°9(i) 



Oligosphaeridium macrotubulum 







(formerly Hystrichosphaeridium) 



44Y/7/20 



V.5I 7 I2(2) 



Systematophora complicata 



44Y/4/22 



V.5*7 ll (3) 



