Invited comment on Wray & Gale's 'The palaeoenvironment and stratigraphy of the Late Cretaceous chalks'

Despite the context of this reply we would wish to echo the tributes to Jake Hancock expressed elsewhere in this volume. His contribution in papers over many years (e.g. 1961, 1972, 1975, 1991, 2000) is considerable and, in many cases, still relevant. We would also like to thank Wray and Gale for demonstrating the breadth of research into the understanding of the Chalk and its environment of deposition. Our major concern is with the inaccuracy, incorrect assumptions and misrepresentations implied and stated by Wray & Gale (2006) in their discussion of the modern Chalk lithostratigraphical framework applied to British Geological Survey (BGS) maps and demonstrated in many published documents. This reply gives the BGS an opportunity to restate in brief the lithostratigraphical framework for the Chalk Group of England and to deal with specific points raised by Wray and Gale. Our reply is prompted in part by the implications in Wray & Gale that the geological mapping of the Chalk Group in England is carried out in a haphazard and uncontrolled manner without scientific rigour and is of ‘little value’. This implication is refuted absolutely. In fact, it is a test of the robustness of the framework that a large number of field geologists can apply the scheme across southern England and provide such a powerful predictive tool for the practical benefit of the nation. A further verification of the framework’s pertinence, over and above its application to pure scientific endeavours, is its widespread use in applied geological studies. For example, the framework provides the foundation for investigations into the structure of the Chalk, its engineering characteristics and hazards and, perhaps most importantly of all, provides the key and new impetus to studies, including predictive modelling, of the hydrogeology of the UK’s largest and most important aquifer. As stated by Wray & Gale, the development of the regional Chalk lithostratigraphies in the late 1970s to the mid-1980s (Wood & Smith 1978; Mortimore 1983, 1986; Jarvis & Woodroof 1984; Robinson 1986) made it apparent that the traditional tripartite scheme embodied by Jukes-Browne & Hill (1903, 1904) did not delineate fully the lithological variation in the Chalk. This inadequacy led to the development of a more detailed and broadly applicable framework by BGS. The modern lithostratigraphical framework builds upon the expertise of a large number of field geologists. It was presented in a model (Bristow et al. 1997) that was modified at a workshop of the UK’s Chalk experts in 1999. It belongs to all those who contributed and signed up to it, and is the ‘agreed lithostratigraphical framework’ (Rawson et al. 2001). The outline framework with minor additions at member level is given in Figure 1. The full framework report for the Chalk Group of the UK, approved by the Geological Society of London’s Stratigraphy Commission (GSLSC), appears in Hopson (2005) and is available (in pdf format) as a free download from the BGS website (http:// www.bgs.ac.uk) as a joint BGS/GSLSC publication.