Applied palaeontology in the Chalk Group: quality control for geological mapping and modelling and revealing new understanding

摘要

The Chalk is a major aquifer, source of raw material for cement and agricultural lime, and a host geological unit for major civil engineering projects. Detailed understanding of its development and lateral variation is significant for our prosperity and for understanding the potential risks of pollution and groundwater flooding, and in this aspect palaeontology plays a central part. Historically, the distribution of macrofossils offered important refinement to the simple three-fold subdivision of the Chalk based on lithological criteria. In recent decades, the advent of a more sophisticated lithostratigraphy for the Chalk, more closely linked to variations in its physical properties, provided an impetus for the British Geological Survey to depict this on its geological maps. Tracing Chalk stratigraphical units away from the well-exposed successions on which the new stratigraphy is based requires subtle interpretation of landscape features, and raises the need for methods of ensuring that the interpretations are correct. New and archived palaeontological data from the vast BGS collections, interpreted as a component of a broad-based holostratigraphical scheme for the Chalk, and spatially analysed using modern Geographical Information Systems (GIS) and landscape visualisation technology, helps fulfil this need. The value of palaeontological data in the Chalk has been boosted by the work that underpins the new lithostratigraphy; it has revealed broad patterns of biofacies based on a range of taxa that is far more diverse than those traditionally used for biostratigraphy, and has provided a detailed reference framework of marker-beds so that fossil ranges can be better understood.ududIn the subsurface, biofacies data in conjunction with lithological and geophysical data, has been used to interpret and extrapolate the distribution of Chalk formations in boreholes across southern England, allowing development of sophisticated three-dimensional models of the Chalk; revealing the influence of ancient structures on Chalk depositional architecture, and pointing to palaeoenvironmental factors that locally affected productivity of Chalk in Late Cretaceous oceans.