Abstract Procedures used to define an international chronostratigraphic stage boundary and to locate and ratify a Global Boundary Stratotype Section and Point (GSSP) are outlined. A majority of current GSSPs use biostratigraphic data as primary markers with no reference to any physico-chemical markers, despite the International Subcommission on Stratigraphic Classification (ISSC) suggestion that such markers should be included if possible. It is argued that such definitions will not produce the high-precision Phanerozoic time scale necessary to understand such phenomena as pre-Pleistocene ice ages and global climate change. It is strongly recommended that all GSSPs should have physico-chemical markers as an integral part of their guiding criteria, and where such markers cannot be found, the GSSP should be relocated. The methods and approach embodied in oceanic stratigraphy – coring, logging, analysing and archiving of drill sites by numerous experts using a wide range of methods – could usefully serve as a scientific model for the analysis and archiving of GSSPs, all of which are on the present-day continents. The incorporation of many more stratigraphic sections into GSSP studies, the application of physico-chemical methods, and the replacement of old U–Pb dates by newer CA-TIMS U–Pb dates, together with the use of constrained optimization (CONOP) programs that produce a calendar of events from many sections, should lead to much more precise timescales for pre-Cenozoic time than are currently available.

Abstract Five Cenomanian successions, situated in contrasting positions within the Anglo-Paris Basin and on its margins, are described in detail, and their sequence stratigraphies analyzed and compared. The Cenomanian Stage was chosen specifically for this study because of the high biostratigraphical resolution (about 0.5 my/zone/subzone) achievable for this stage by the use of ammonites. The successions in Kent (south east England) and the Boulonnais (north east France) are the most basinward in position and comprise rhythmically bedded argillaceous micrites (chalks and marls) with few major hiatuses. The thinner succession of coarser carbonates in Normandy (north west France) contains larger gaps. The succession in Maine (north west France) was deposited in relatively shallow water near the basin margin and includes several sand bodies and well-developed hardgrounds. The highly condensed succession of sandy limestones, containing major hardground-bounded hiatuses in Devon (south west England) represents deposition closest to the basin margin. Systems tracts are characterized and defined by diverse criteria, including geometry of sediment bodies, basin margin onlap, discontinuity surfaces (omission surfaces and hardgrounds) and lithological characters, including variations in quartz sand content, clay: carbonate ratios and the presence of authigenic glauconite and phosphate. Detailed comparison of the successions enables us to demonstrate the existence of five basinwide sequences and the lower part of a sixth.