The Chalk revolution – the role of geological mapping for engineering and hazard assessment

Since the last Chalk symposium in 1989 in Brighton, our understanding of the UK Chalk has undergone a revolution, not just in terms of the stratigraphical and engineering properties of this enigmatic material, but also in its spatial distribution and variability in 2D and 3D space from geological mapping. The old tripartite Chalk stratigraphy has been replaced with a more detailed stratigraphical scheme with up to nine Formations. The increased stratigraphical precision this brings has revealed far more geological structure and facies variability across the outcrop than previously recognized. Most of the major basin boundary faults, including the Hog’s Back, Mere and Pewsey Faults are now known to cut the Chalk sequence. Geological mapping has also provided a wealth of information on associated superficial and mass movement deposits, karst features and hydrogeology. The role of the engineering geology community in providing data has been a key part of this revolution. High precision site-specific information from ground investigations including the identification of key stratigraphical marker beds in boreholes, quarry and coastal sections is critical in characterizing the Chalk succession. Such point-specific data combined with spatially extensive data derived from geological mapping data enables thickness and facies trends to be identified and allows the prediction of ground conditions over wide areas. This paper outlines how our understanding of the facies variability and structure of the Chalk can be improved using high resolution geological mapping, and how this can benefit the engineering community using specific examples. Advances in technology means that the Chalk is increasingly being visualized in three dimensions through the production of 3D geological models that can be updated dynamically as new site investigation data comes in. These models can be used as a geotechnical risk management tool, promoting a cycle of risk reduction. The accuracy and resolution of these models depends on the quantity, quality and spatial distribution of 3D data, particularly the availability of accessible, high quality, well described borehole logs identifying key stratigraphical markers

Examining the case for the use of the Tertiary as a formal period or informal unit

The ‘Tertiary’, omitted from IUGS-approved timescales since 1989, is still in common use. With the recent re-instatement of the Quaternary as a formal unit, the question arises as to whether the Tertiary too should be reinstated as a formal period, with the ‘Paleogene’ and ‘Neogene’ being downgraded to sub-periods. This paper presents arguments for and against this proposal, stemming from discussions by members of the Geological Society Stratigraphy Commission. It is intended to stimulate discussion of the topic in the wider community

Palaeosalinity variations in the Early Cretaceous of the Neuquen Basin, Argentina: evidence from oxygen isotopes and palaeoecological analysis

The Neuquén Basin is a stratigraphically- and economically-important Early Cretaceous depocentre located in west-central Argentina. The Early Valanginian to Early Barremian succession (upper Vaca Muerta, Mulichinco and Agrio Formations) contains a rich fossil record, with abundant bivalves and ammonoids. Palaeosalinities are determined systematically throughout the succession, based on an oxygen isotope analysis of unaltered oyster shells from two localities in Neuquén province. A total of 188 oyster samples from 52 stratigraphic levels were processed. A total of 52 mean values of δ18O isotope are used to calculate palaeosalinities, assuming an estimated water temperature of 25 °C. The observed range of palaeosalinities, between the maximum and the minimum, is 19, which is in conflict with published accounts of this being a fully marine succession. The isotopic data are combined with independent faunal evidence to evaluate palaeosalinity variation both laterally and temporally. Significant fluctuations in water salinity are indicated, with a clear tendency to increase from brachyhaline to euhaline and near hyperhaline conditions through time. The fluctuations were probably due to dilution from normal marine water, caused primarily by variations in rainfall and continental runoff. In addition, the presence of a volcanic island arc along the western margin of the basin may have at least partially isolated the basin from the marine waters of the Pacific Ocean. Also, a gulf-shaped basin may have inhibited hydrodynamic exchange with the ocean while enhancing retention of continental waters.Fil: Lazo, Dario Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Aguirre-Urreta, Maria Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Price, Gregory D.. University of Plymouth; Reino UnidoFil: Rawson, Peter F.. Colegio Universitario de Londres; Reino UnidoFil: Ruffell, Alastair H.. The Queens University of Belfast; IrlandaFil: Ogle, N.. The Queens University of Belfast; Irland

[Proceedings of the 4th International Workshop of the Lower Cretaceous Cephalopod Team (IGCP-Project 362) / Peter F. Rawson and Philip J. Hoedemaeker (editors)]: Report on the 4th international workshop of the Lower Cretaceous Cephalopod Team (IGCP-Project 362)

The Working Group proposes only one modification to its current zonation of the Mediterranean Region, the addition of a cristatum Subzone in the lower part of the inflatum Zone (upper Albian). But in the light of newly published research it highlights levels/areas where further work is required, especially to resolve conflicting zonal schemes. It also proposes a 'Tethyan Province' zonation for the middle Albian. Alternative correlations for the Boreal/Tethyan Valanginian to Barremian stages are tabulated, one based on ammonite evidence alone, the other with additional biostratigraphical data coupled with sequence stratigraphy and magnetostratigraphy

[Proceedings of the 4th International Workshop of the Lower Cretaceous Cephalopod Team (IGCP-Project 362) / Peter F. Rawson and Philip J. Hoedemaeker (editors)]: Report on the 4th international workshop of the Lower Cretaceous Cephalopod Team (IGCP-Project 362)

The Working Group proposes only one modification to its current zonation of the Mediterranean Region, the addition of a cristatum Subzone in the lower part of the inflatum Zone (upper Albian). But in the light of newly published research it highlights levels/areas where further work is required, especially to resolve conflicting zonal schemes. It also proposes a 'Tethyan Province' zonation for the middle Albian. Alternative correlations for the Boreal/Tethyan Valanginian to Barremian stages are tabulated, one based on ammonite evidence alone, the other with additional biostratigraphical data coupled with sequence stratigraphy and magnetostratigraphy